Wednesday, June 5, 2013
Wednesday, February 23, 2011
NTPC PREVIOUS PAPERS
Technical Paper :
1. Given four unit-circle plots identify the one corresponding to a bandpass filter.
2. A 4 kHz signal is sampled at thrice the Nyquist rate and sent through a channel
with error ≤1%. Calc the bandwidth of the channel.
3. Given a two port network in the form of a T find o/p admittance in terms of y-
parameters.
4. Connect two 1Ω resistors in series, then connect two 1H inductors across one of the resistors such that the ckt looks like a 1Ω resistor in series with a Π-section of
a resistor and two inductors. With the series resistance on the i/p side, calc the
transfer function of this ckt
5. Inverse laplace transform of 1/s2[d/ds(e-3s/s)]
6. Lower useful input limit of a transducer is determined by…
7. Air-cored inductors are used for low frequency/high frequency/equal
frequency operations.
8. Given 4 pole-zero plots identify which one corresponds to the driving point
impedance of a series resonant ckt.
9. Expression for δ(n): u(n)-u(n-1)/ u(n-1)-u(n+1)/ u(n)+u(n+1)/...
10. The sequence (2,3,4,3) is circularly even/circularly odd/circularly zero/both
circularly even and odd.
11. Z-transform of 3n u(n).
12. Match the following with their characteristics: LED/LCD/nixie tube/optical
fibre.
13. Numerical on a photodiode: to calculate the responsivity/sensitivity when a
specified no of incident photons cause a specified no of electron generation.
14. Given an op-amp ckt obtain an expression for o/p voltage.
15. No. of encirclements made about the origin of the nyquist plot of the open
loop TF:1/[(s-1)(s+2)(s+3)].
16. For a radioactive sample which decays to 12.5% of its initial value in x days,
the half life is given by____
17. For a repeater in a PCM cable identify the correct sequence of actions amongst
threshold/equalization/etc.
18. O/P of a delta modulator when a ramp input is fed to it.
19. Steady state error with ramp i/p for a type-0 system.
20. Creeping occurs in energy meters bcoz….
21. Ultrasonic method of flow measurement cannot be used in liquids with air bubbles/has less attenuation in air compared to liquid-identify the false
statement (if any) among these.
22. Major cause of losses in a fibre optic cable: dispersion/total internal
refraction/presence of core and cladding/…
23. Which layer in the OSI model is concerned with printer buffering,etc:
network/session/transport/…
24. Given some function F(jω) calc its inverse CTFT.
25. Relation between laplace and z-transform: s=z/ s=ln z/ s=( ln z/T) /…
26. Maxm and minm probability error among ASK,PSK,FSK,DPSK etc
27. Which of the following is a non linear modulation scheme: PAM/QAM/PCM/
…
28. Match the following functions: e-t , e-t + et, sin(πt) with causal and stable
system, causal and unstable system, etc.
29. Given a ckt with a 50 Ω resistor in series between two voltage sources of 10 V
and 5 V magnitude calc power delivered by 5 V source.
30. Laplace transform of e-3tu(t)+e2tu(-t).
31. Which photodetector has output affected by own intrinsic noise:
PN/APD/PIN/all.
32. AC signal conditioning is used for inductive and
capacitive/resistive/piezoelectric transducers/all of the above.
33. When I mode is added to proportional control system stability increases/
decreases/ steady state performance deteriorates/damping increases.
34. Reset control is another name for integral/derivative/proportional/….
Control.
35. Time response of system having transfer function 625/(s2+25) will be of the
form…
36. Given some transfer function calc the peak response time.
37. The nyquist sampling rate of the function [sin(at)/t]2 will be…
38. The feedback topology that results in increased i/p and o/p impedance is
current series/voltage series/current shunt voltage shunt.
39. Numerical on cardiac output calculation given heart rate and volume per
beat.
40. In an ECG instrumentation amplifier the differential gain is provided by 1st
stage/2nd stage/mismatched resistors/output stage.
41. Repeat ques 40 above for the classic 3-op amp instrum amplifier.
42. EMG signals are of the order of mV/V/μV/…
43. Computer assisted tomography is used for…
44. Numerical on electrostatic instrument, to calculate deflection given spring
constant, torque etc.
45. To prevent loading of a ckt i/p impedance of a CRO should bee
high/low/inductive/capacitive.
46. Addition of a zero to a 2nd order underdamped system results in
increase/decrease of rise time and increase/decrease of peak overshoot.
47. For PI ctrl we obtain improved bandwidth/improved steady state
performance/ worsened steady state performance/…
48. SNR of normal AM system is comparable/3 dB lower/3 dB higher/6 dB lower
over DSB-SC and SSB system.
49. Which is an effective measure of the noise related performance of an
amplifier: SNR/noise ratio/thermal noise/shot noise.
50. Given baseband signal freq and carrier freq calc which of the freq given will
not be present for conventional AM.
51. Distinction between FM and PM at high frequencies.
52. Which of these has the least propagation delay RTL/ECL/I2L/CMOS.
53 Switching speed of CMOS is affected/unaffected by changes in supply voltage.
54. Which of these provides a measure of heart rate P/QRS complex/T/none of
these.
55. Given a ckt of a logarithmic amplifier you had to identify what ckt was it.
56. JFET can operate in depletion/enhancement/both/none of the above modes.57. When a BJT operates in saturation the junctions are fwd biased/reverse
biased/…
58. BIBO stability criterion implies that poles are within/outside/on the unit
circle.
59. For faithful amplification of low amplitude signals the cut-
off/active/saturation regions of a transistor is used.
60. Lissajous pattern of a signal rotates 36 times per minute. if the oscillator
frequency is 560 kHz then the unknown freq is…
61. % resolution of a 10 bit ADC.
62. To obtain 10 mV resolution on 5 V range how many bit DAC is to be used..
63. Why is LCD preferred to LED.
64. How will 0.6973 be displayed on 10 V range of a 4 ½ digit multimeter.
65. Which of the following cannot be used for an automatic feedback temp ctrl
system thermocouple/thermometer/thermistor/IC sensor.
66. Y(n)=X(-n+3) is an example of a linear/non linear and shift variant/invariant
system.
67. The falling body method is used to determine viscosity/humidity/….
68. Which of these methods of viscosity measurement gives greatest accuracy
falling body method/rotating cylinder method/both/…
69. Some question on gas chromatography
70. A device having a rotor with 3 Y-connected coils and a stator is likely to be a
synchro/RVDT/control transformer/…
71. In a twisted ring counter the initial count is 1000. after the 4th clock pulse its
state will be….
72. A 240 kHz signal is given into a 3 bit binary ripple counter. The lowest o/p
freq obtainable is….
73. For parity bit checking which of the following gates can be used
XOR/NAND/OR/XNOR.
74. Why is a BJT called so..75. Identify the expression for gauge factor of a strain gauge among the given
options.
76. In a semiconductor strain gauge as tensile strain is applied what changes take
place in the n and p areas..
77. How does a radioactive level gauging system work…
78. A capacitive transducer measuring level works on the principle of change in
distance between plates/change in dielectric strength/…
79. For maximum power transfer in an AC circuit the condition to be satisfied is
ZL+ZS=0/XL+XS=0/none of these/….where l and s refers to load and source
respectively.
80. Find the transfer function from a block diagram.
81. Synchronous ctrs are preferred to asynchronous ctrs bcoz they are
faster/glitches at the output can be avoided/both/none of these.
82. The lissajous figure formed on an oscilloscope looks like the English figure of
8. if the vertical channel input is 1 kHz the horizontal input freq is….
83. IE=IC for a transistor in saturation/cutoff/active/both saturation and active
regions.
84. Reproducibility of measurements is called accuracy/precision/linearity/none
of these.
85. Which of these is not strictly a static characteristic
accuracy/precision/tolerance/linearity.
86. The shunt coil in a Q meter has resistance of the order of mΩ/Ω/kΩ/..
87. For measuring inductance of high Q coils the bridge used is Maxwell-
wien/Schering/…
88. Which of these measures inductance in terms of capacitance Maxwell and
hay/Maxwell and Schering/hay and Schering/…
89. In a flip-flop with preset and clear inputs both are applied
simultaneously/clear is cleared when preset is applied/preset is cleared when
clear is applied/….
90. What happens when the RET instruction is encountered by 808591. A 1024*8 memory chip needs how many address lines…
92. What happens when the PUSH instruction is encountered by 8051.
93. In FM relation between no of sidebands w.r.t. modulating freq
94. Numerical on DPSK.
95. A multiplexer accepts input data and provides one output all the time/one
output at a time/many outputs at a time/many outputs all the time.
96. Pulse modulation is essentially a process of multiplexing/….
97. Wave shape is altered by clipper/clamper/voltage doubler/amplifier.
98. 4 signals of frequencies 100,100,200 and 400 Hz are sampled at nyquist rate
and sent through TDM on a channel.the bandwidth of the channel is…
99. Superposition can be applied to a ckt with initial conditions/non-linear ckt/…
100. Kelvin’s double bridge is used for the measurement of…
101. Which of these is not an active transducer thermocouple/solar
cell/RTD/none of these.
102. Oscillator using positive feedback has gain of 0/∞/undefined value/…
103. Wien bridge oscillator should initially have closed loop gain >3/<3/=3/…
104. Some question on gain margin and phase shift of a system.
105. Fourier series expansion of even function has sine terms only/cosine terms
only/no odd harmonics/…
106. Full wave rectifier gives clean dc o/p/dc o/p with small ripple/positive half
and inverted negative half of i/p as o/p.
107. Which of these values of ζ gives damped oscillations: 0/1/1.6/0.6
108. For a transformer of ratio 1:a and excited by a source V with impedances Z1
and Z2 on the primary and secondary side value of a for maxm power transfer
should be..
109. Fourier transform of cos(ω0t) is…
110. At t=0 the step response of a 1st order system is….111. 555 can be used as a monostable/astable/freq dividing ckt/all of these.
112. In a PT when the secondary is open ckted with the primary excited what will
happen.
113. If a system is marginally stable then the nature of oscillations will be…
114. Linear encoders mostly use straight binary/BCD/gray code.
115. For an accelerometer working in displacement mode the ratio of forcing freq
to natural freq should be…..
It may Contain questions with options like Both a) and b) . While solving this
type of Question we may get some difficulty, but practicing more we can
overcome this difficulty. All the best and do more Practice.
1. Given four unit-circle plots identify the one corresponding to a bandpass filter.
2. A 4 kHz signal is sampled at thrice the Nyquist rate and sent through a channel
with error ≤1%. Calc the bandwidth of the channel.
3. Given a two port network in the form of a T find o/p admittance in terms of y-
parameters.
4. Connect two 1Ω resistors in series, then connect two 1H inductors across one of the resistors such that the ckt looks like a 1Ω resistor in series with a Π-section of
a resistor and two inductors. With the series resistance on the i/p side, calc the
transfer function of this ckt
5. Inverse laplace transform of 1/s2[d/ds(e-3s/s)]
6. Lower useful input limit of a transducer is determined by…
7. Air-cored inductors are used for low frequency/high frequency/equal
frequency operations.
8. Given 4 pole-zero plots identify which one corresponds to the driving point
impedance of a series resonant ckt.
9. Expression for δ(n): u(n)-u(n-1)/ u(n-1)-u(n+1)/ u(n)+u(n+1)/...
10. The sequence (2,3,4,3) is circularly even/circularly odd/circularly zero/both
circularly even and odd.
11. Z-transform of 3n u(n).
12. Match the following with their characteristics: LED/LCD/nixie tube/optical
fibre.
13. Numerical on a photodiode: to calculate the responsivity/sensitivity when a
specified no of incident photons cause a specified no of electron generation.
14. Given an op-amp ckt obtain an expression for o/p voltage.
15. No. of encirclements made about the origin of the nyquist plot of the open
loop TF:1/[(s-1)(s+2)(s+3)].
16. For a radioactive sample which decays to 12.5% of its initial value in x days,
the half life is given by____
17. For a repeater in a PCM cable identify the correct sequence of actions amongst
threshold/equalization/etc.
18. O/P of a delta modulator when a ramp input is fed to it.
19. Steady state error with ramp i/p for a type-0 system.
20. Creeping occurs in energy meters bcoz….
21. Ultrasonic method of flow measurement cannot be used in liquids with air bubbles/has less attenuation in air compared to liquid-identify the false
statement (if any) among these.
22. Major cause of losses in a fibre optic cable: dispersion/total internal
refraction/presence of core and cladding/…
23. Which layer in the OSI model is concerned with printer buffering,etc:
network/session/transport/…
24. Given some function F(jω) calc its inverse CTFT.
25. Relation between laplace and z-transform: s=z/ s=ln z/ s=( ln z/T) /…
26. Maxm and minm probability error among ASK,PSK,FSK,DPSK etc
27. Which of the following is a non linear modulation scheme: PAM/QAM/PCM/
…
28. Match the following functions: e-t , e-t + et, sin(πt) with causal and stable
system, causal and unstable system, etc.
29. Given a ckt with a 50 Ω resistor in series between two voltage sources of 10 V
and 5 V magnitude calc power delivered by 5 V source.
30. Laplace transform of e-3tu(t)+e2tu(-t).
31. Which photodetector has output affected by own intrinsic noise:
PN/APD/PIN/all.
32. AC signal conditioning is used for inductive and
capacitive/resistive/piezoelectric transducers/all of the above.
33. When I mode is added to proportional control system stability increases/
decreases/ steady state performance deteriorates/damping increases.
34. Reset control is another name for integral/derivative/proportional/….
Control.
35. Time response of system having transfer function 625/(s2+25) will be of the
form…
36. Given some transfer function calc the peak response time.
37. The nyquist sampling rate of the function [sin(at)/t]2 will be…
38. The feedback topology that results in increased i/p and o/p impedance is
current series/voltage series/current shunt voltage shunt.
39. Numerical on cardiac output calculation given heart rate and volume per
beat.
40. In an ECG instrumentation amplifier the differential gain is provided by 1st
stage/2nd stage/mismatched resistors/output stage.
41. Repeat ques 40 above for the classic 3-op amp instrum amplifier.
42. EMG signals are of the order of mV/V/μV/…
43. Computer assisted tomography is used for…
44. Numerical on electrostatic instrument, to calculate deflection given spring
constant, torque etc.
45. To prevent loading of a ckt i/p impedance of a CRO should bee
high/low/inductive/capacitive.
46. Addition of a zero to a 2nd order underdamped system results in
increase/decrease of rise time and increase/decrease of peak overshoot.
47. For PI ctrl we obtain improved bandwidth/improved steady state
performance/ worsened steady state performance/…
48. SNR of normal AM system is comparable/3 dB lower/3 dB higher/6 dB lower
over DSB-SC and SSB system.
49. Which is an effective measure of the noise related performance of an
amplifier: SNR/noise ratio/thermal noise/shot noise.
50. Given baseband signal freq and carrier freq calc which of the freq given will
not be present for conventional AM.
51. Distinction between FM and PM at high frequencies.
52. Which of these has the least propagation delay RTL/ECL/I2L/CMOS.
53 Switching speed of CMOS is affected/unaffected by changes in supply voltage.
54. Which of these provides a measure of heart rate P/QRS complex/T/none of
these.
55. Given a ckt of a logarithmic amplifier you had to identify what ckt was it.
56. JFET can operate in depletion/enhancement/both/none of the above modes.57. When a BJT operates in saturation the junctions are fwd biased/reverse
biased/…
58. BIBO stability criterion implies that poles are within/outside/on the unit
circle.
59. For faithful amplification of low amplitude signals the cut-
off/active/saturation regions of a transistor is used.
60. Lissajous pattern of a signal rotates 36 times per minute. if the oscillator
frequency is 560 kHz then the unknown freq is…
61. % resolution of a 10 bit ADC.
62. To obtain 10 mV resolution on 5 V range how many bit DAC is to be used..
63. Why is LCD preferred to LED.
64. How will 0.6973 be displayed on 10 V range of a 4 ½ digit multimeter.
65. Which of the following cannot be used for an automatic feedback temp ctrl
system thermocouple/thermometer/thermistor/IC sensor.
66. Y(n)=X(-n+3) is an example of a linear/non linear and shift variant/invariant
system.
67. The falling body method is used to determine viscosity/humidity/….
68. Which of these methods of viscosity measurement gives greatest accuracy
falling body method/rotating cylinder method/both/…
69. Some question on gas chromatography
70. A device having a rotor with 3 Y-connected coils and a stator is likely to be a
synchro/RVDT/control transformer/…
71. In a twisted ring counter the initial count is 1000. after the 4th clock pulse its
state will be….
72. A 240 kHz signal is given into a 3 bit binary ripple counter. The lowest o/p
freq obtainable is….
73. For parity bit checking which of the following gates can be used
XOR/NAND/OR/XNOR.
74. Why is a BJT called so..75. Identify the expression for gauge factor of a strain gauge among the given
options.
76. In a semiconductor strain gauge as tensile strain is applied what changes take
place in the n and p areas..
77. How does a radioactive level gauging system work…
78. A capacitive transducer measuring level works on the principle of change in
distance between plates/change in dielectric strength/…
79. For maximum power transfer in an AC circuit the condition to be satisfied is
ZL+ZS=0/XL+XS=0/none of these/….where l and s refers to load and source
respectively.
80. Find the transfer function from a block diagram.
81. Synchronous ctrs are preferred to asynchronous ctrs bcoz they are
faster/glitches at the output can be avoided/both/none of these.
82. The lissajous figure formed on an oscilloscope looks like the English figure of
8. if the vertical channel input is 1 kHz the horizontal input freq is….
83. IE=IC for a transistor in saturation/cutoff/active/both saturation and active
regions.
84. Reproducibility of measurements is called accuracy/precision/linearity/none
of these.
85. Which of these is not strictly a static characteristic
accuracy/precision/tolerance/linearity.
86. The shunt coil in a Q meter has resistance of the order of mΩ/Ω/kΩ/..
87. For measuring inductance of high Q coils the bridge used is Maxwell-
wien/Schering/…
88. Which of these measures inductance in terms of capacitance Maxwell and
hay/Maxwell and Schering/hay and Schering/…
89. In a flip-flop with preset and clear inputs both are applied
simultaneously/clear is cleared when preset is applied/preset is cleared when
clear is applied/….
90. What happens when the RET instruction is encountered by 808591. A 1024*8 memory chip needs how many address lines…
92. What happens when the PUSH instruction is encountered by 8051.
93. In FM relation between no of sidebands w.r.t. modulating freq
94. Numerical on DPSK.
95. A multiplexer accepts input data and provides one output all the time/one
output at a time/many outputs at a time/many outputs all the time.
96. Pulse modulation is essentially a process of multiplexing/….
97. Wave shape is altered by clipper/clamper/voltage doubler/amplifier.
98. 4 signals of frequencies 100,100,200 and 400 Hz are sampled at nyquist rate
and sent through TDM on a channel.the bandwidth of the channel is…
99. Superposition can be applied to a ckt with initial conditions/non-linear ckt/…
100. Kelvin’s double bridge is used for the measurement of…
101. Which of these is not an active transducer thermocouple/solar
cell/RTD/none of these.
102. Oscillator using positive feedback has gain of 0/∞/undefined value/…
103. Wien bridge oscillator should initially have closed loop gain >3/<3/=3/…
104. Some question on gain margin and phase shift of a system.
105. Fourier series expansion of even function has sine terms only/cosine terms
only/no odd harmonics/…
106. Full wave rectifier gives clean dc o/p/dc o/p with small ripple/positive half
and inverted negative half of i/p as o/p.
107. Which of these values of ζ gives damped oscillations: 0/1/1.6/0.6
108. For a transformer of ratio 1:a and excited by a source V with impedances Z1
and Z2 on the primary and secondary side value of a for maxm power transfer
should be..
109. Fourier transform of cos(ω0t) is…
110. At t=0 the step response of a 1st order system is….111. 555 can be used as a monostable/astable/freq dividing ckt/all of these.
112. In a PT when the secondary is open ckted with the primary excited what will
happen.
113. If a system is marginally stable then the nature of oscillations will be…
114. Linear encoders mostly use straight binary/BCD/gray code.
115. For an accelerometer working in displacement mode the ratio of forcing freq
to natural freq should be…..
It may Contain questions with options like Both a) and b) . While solving this
type of Question we may get some difficulty, but practicing more we can
overcome this difficulty. All the best and do more Practice.
NTPC PAPER : 2007 AT NEW DELHI :
APTITUDE SECTION :
For this section no special attention is required only rs aggarwal is enough and it also has easy
level of English section.
TECHNICAL SECTION :
For this section u have to b good in the basics. No hard question were asked but u
should b careful about your time . It has also some part of very basic general
knowledge. The questions were from following topics
10-12 Questions about microprocessor(8085)
3 Questions about RS232 standard
7-10 Questions of GK
4-6 Questions on opamp
10-15 Questions on Digital Communications
2-5 Questions on microwaves
15-20 Questions on Analog Devices
20-23 Questions on Digital Electronics (flip flops,gates,mux,no system etc)
1 Questions on ISO OSI Model
5-8 Questions on Control System
10-12 Questions on Signals and their Processing
AND SOME QUESTIONS ON PASSAGES & LIKE
1. Passage
2. Word meaning based (antonym and synonyms) fetter, fester, lucid, anomaly, elucidate etc
3. Word analogy based
4. What is a tunnel diode
5. What is a Zener diode
6. Effect of + and – feedback on stability7. Composition of gobar gas
8. Function of differential in the vehicle
9. Function of stack register
10. Fun of instruction pointer
11. Fun of rst6.5,7.5
12. Wht is an interrupt
13. Output vtg calc on op amp
14. How a pulse train can b generated using registers
15. Conversion of oct to hex,hex to binary
16. Fun of quantizer in pcm
17. Why fm is less prone to noise
18. Fun of limiter in detection of FM
19. What is envelop detector
20. Phase shift of 1/s^2
21. Signal limited to 1000 hz sampled at nyquist rate. quantizer has 128 level .calculate the bit rate of the system.
22. 1.5 V battery supply same power to R1 and R2 separately(R1>R2).calc the internal
resistance of battery
23. A wire is cut in two halves. one half is again stretched to th twice of length .calc the resistance.
For this section no special attention is required only rs aggarwal is enough and it also has easy
level of English section.
TECHNICAL SECTION :
For this section u have to b good in the basics. No hard question were asked but u
should b careful about your time . It has also some part of very basic general
knowledge. The questions were from following topics
10-12 Questions about microprocessor(8085)
3 Questions about RS232 standard
7-10 Questions of GK
4-6 Questions on opamp
10-15 Questions on Digital Communications
2-5 Questions on microwaves
15-20 Questions on Analog Devices
20-23 Questions on Digital Electronics (flip flops,gates,mux,no system etc)
1 Questions on ISO OSI Model
5-8 Questions on Control System
10-12 Questions on Signals and their Processing
AND SOME QUESTIONS ON PASSAGES & LIKE
1. Passage
2. Word meaning based (antonym and synonyms) fetter, fester, lucid, anomaly, elucidate etc
3. Word analogy based
4. What is a tunnel diode
5. What is a Zener diode
6. Effect of + and – feedback on stability7. Composition of gobar gas
8. Function of differential in the vehicle
9. Function of stack register
10. Fun of instruction pointer
11. Fun of rst6.5,7.5
12. Wht is an interrupt
13. Output vtg calc on op amp
14. How a pulse train can b generated using registers
15. Conversion of oct to hex,hex to binary
16. Fun of quantizer in pcm
17. Why fm is less prone to noise
18. Fun of limiter in detection of FM
19. What is envelop detector
20. Phase shift of 1/s^2
21. Signal limited to 1000 hz sampled at nyquist rate. quantizer has 128 level .calculate the bit rate of the system.
22. 1.5 V battery supply same power to R1 and R2 separately(R1>R2).calc the internal
resistance of battery
23. A wire is cut in two halves. one half is again stretched to th twice of length .calc the resistance.
Ntpc sylaabus for E&Tc
Syllabus for Control & Instrumentation
1. Basics of Circuits and Measurement Systems:
Kirchoff's laws, mesh and nodal Analysis. Circuit theorems. One-port and two-port Network Functions. Static and dynamic characteristics of Measurement Systems. Error and uncertainty analysis. Statistical analysis of data and curve fitting.
2. Transducers, Mechanical Measurement and Industrial Instrumentation:
Resistive, Capacitive, Inductive and piezoelectric transducers and their signal conditioning. Measurement of displacement, velocity and acceleration (translational and rotational), force, vibration and shock. Measurement of pressure, flow, temperature and liquid level. Measurement of pH, conductivity, humidity, hydrazine, silica, dissolved O2. Units and standards of measurement.
3. Analog Electronics:
Characteristics of diode, BJT, JFET and MOSFET. Diode circuits. Transistors at low and high frequencies, Amplifiers, single and multi-stage. Feedback amplifiers. Operational amplifiers, characteristics and circuit configurations. Instrumentation amplifier. Precision rectifier. V-to-I and I-to-V converter. Op-Amp based active filters. Oscillators and signal generators. Voltage stabiliser and regulator circuits. Inverter and converter circuits.
4. Digital Electronics:
Combinational logic circuits, minimization of Boolean functions. IC families, TTL, MOS and CMOS. Arithmetic circuits. Comparators, Schmitt trigger, timers and mono-stable multi-vibrator. Sequential circuits, flip-flops, counters, shift registers. Multiplexer, S/H circuit. Analog-to-Digital and Digital-to-Analog converters. Basics of number system. Microprocessor applications, memory and input-output interfacing. Microcontrollers.
5. Electrical and Electronic Measurements:
Bridges and potentiometers, measurement of R,L and C. Measurements of voltage, current, power, power factor and energy. A.C & D.C current probes. Extension of instrument ranges. Q-meter and waveform analyzer. Digital voltmeter and multi-meter. Time, phase and frequency measurements. Cathode ray oscilloscope. Instrument Transformer.
6. Control Systems and Process Control:
Feedback principles. Signal flow graphs. Transient Response, steady-state-errors. Routh and Nyquist criteria. Bode plot, root loci. Time delay systems. Phase and gain margin. State space representation of systems. Mechanical, hydraulic and pneumatic system components. Synchro pair, servo and step motors. On-off, cascade, P, P-I, P-I-D, feed forward and derivative controller, Fuzzy controllers. Multi-state variable and Adaptative controls. System modeling, Digital controls, Distributed digital controls, control loops based on computers.
7. Analytical, Optical and Biomedical Instrumentation:
Mass spectrometry. UV, visible and IR spectrometry. X-ray and nuclear radiation measurements. Optical sources and detectors, LED, laser, Photo-diode, photo-resistor and their characteristics. Interferometers, applications in metrology.
8. Signals and Systems:
Definitions and properties of Laplace transform, continuous-time and discrete-time Fourier series, continuous-time and discrete-time Fourier Transform, DFT and FFT, z-transform. Sampling theorem. Linear Time-Invariant (LTI) Systems: definitions and properties; causality, stability, impulse response, convolution, poles and zeros, parallel and cascade structure, frequency response, group delay, phase delay. Signal transmission through LTI systems.
9. Communications:
Random signals and noise: probability, random variables, probability density function, autocorrelation, power spectral density. Analog communication systems: amplitude and angle modulation and demodulation systems, spectral analysis of these operations, superheterodyne receivers; elements of hardware, realizations of analog communication systems; signal-to-noise ratio (SNR) calculations for amplitude modulation (AM) and frequency modulation (FM) for low noise conditions. Fundamentals of information theory and channel capacity theorem. Digital communication systems: pulse code modulation (PCM), differential pulse code modulation (DPCM), digital modulation schemes: amplitude, phase and frequency shift keying schemes (ASK, PSK, FSK), matched filter receivers, bandwidth consideration and probability of error calculations for these schemes. Basics of TDMA, FDMA and CDMA and GSM. Basic Network topology and Net work hard wares. LAN / WAN configurations. UTP and OFC Links and components. Serial and parallel communication, Shielding and grounding. IEEE standards and broadband.
1. Basics of Circuits and Measurement Systems:
Kirchoff's laws, mesh and nodal Analysis. Circuit theorems. One-port and two-port Network Functions. Static and dynamic characteristics of Measurement Systems. Error and uncertainty analysis. Statistical analysis of data and curve fitting.
2. Transducers, Mechanical Measurement and Industrial Instrumentation:
Resistive, Capacitive, Inductive and piezoelectric transducers and their signal conditioning. Measurement of displacement, velocity and acceleration (translational and rotational), force, vibration and shock. Measurement of pressure, flow, temperature and liquid level. Measurement of pH, conductivity, humidity, hydrazine, silica, dissolved O2. Units and standards of measurement.
3. Analog Electronics:
Characteristics of diode, BJT, JFET and MOSFET. Diode circuits. Transistors at low and high frequencies, Amplifiers, single and multi-stage. Feedback amplifiers. Operational amplifiers, characteristics and circuit configurations. Instrumentation amplifier. Precision rectifier. V-to-I and I-to-V converter. Op-Amp based active filters. Oscillators and signal generators. Voltage stabiliser and regulator circuits. Inverter and converter circuits.
4. Digital Electronics:
Combinational logic circuits, minimization of Boolean functions. IC families, TTL, MOS and CMOS. Arithmetic circuits. Comparators, Schmitt trigger, timers and mono-stable multi-vibrator. Sequential circuits, flip-flops, counters, shift registers. Multiplexer, S/H circuit. Analog-to-Digital and Digital-to-Analog converters. Basics of number system. Microprocessor applications, memory and input-output interfacing. Microcontrollers.
5. Electrical and Electronic Measurements:
Bridges and potentiometers, measurement of R,L and C. Measurements of voltage, current, power, power factor and energy. A.C & D.C current probes. Extension of instrument ranges. Q-meter and waveform analyzer. Digital voltmeter and multi-meter. Time, phase and frequency measurements. Cathode ray oscilloscope. Instrument Transformer.
6. Control Systems and Process Control:
Feedback principles. Signal flow graphs. Transient Response, steady-state-errors. Routh and Nyquist criteria. Bode plot, root loci. Time delay systems. Phase and gain margin. State space representation of systems. Mechanical, hydraulic and pneumatic system components. Synchro pair, servo and step motors. On-off, cascade, P, P-I, P-I-D, feed forward and derivative controller, Fuzzy controllers. Multi-state variable and Adaptative controls. System modeling, Digital controls, Distributed digital controls, control loops based on computers.
7. Analytical, Optical and Biomedical Instrumentation:
Mass spectrometry. UV, visible and IR spectrometry. X-ray and nuclear radiation measurements. Optical sources and detectors, LED, laser, Photo-diode, photo-resistor and their characteristics. Interferometers, applications in metrology.
8. Signals and Systems:
Definitions and properties of Laplace transform, continuous-time and discrete-time Fourier series, continuous-time and discrete-time Fourier Transform, DFT and FFT, z-transform. Sampling theorem. Linear Time-Invariant (LTI) Systems: definitions and properties; causality, stability, impulse response, convolution, poles and zeros, parallel and cascade structure, frequency response, group delay, phase delay. Signal transmission through LTI systems.
9. Communications:
Random signals and noise: probability, random variables, probability density function, autocorrelation, power spectral density. Analog communication systems: amplitude and angle modulation and demodulation systems, spectral analysis of these operations, superheterodyne receivers; elements of hardware, realizations of analog communication systems; signal-to-noise ratio (SNR) calculations for amplitude modulation (AM) and frequency modulation (FM) for low noise conditions. Fundamentals of information theory and channel capacity theorem. Digital communication systems: pulse code modulation (PCM), differential pulse code modulation (DPCM), digital modulation schemes: amplitude, phase and frequency shift keying schemes (ASK, PSK, FSK), matched filter receivers, bandwidth consideration and probability of error calculations for these schemes. Basics of TDMA, FDMA and CDMA and GSM. Basic Network topology and Net work hard wares. LAN / WAN configurations. UTP and OFC Links and components. Serial and parallel communication, Shielding and grounding. IEEE standards and broadband.
Tuesday, September 7, 2010
INTERVIEW QUESTIONS
Why does a zener diode work in reverse bias?
A zener diode is designed to allow a current to flow through it in a direction that is reverse to the normal flow of current that would occur if it were used as a rectifier. Current can flow through a zener diode in both directions. In the forward direction, current will flow at a low voltage, usually about 1 volt. In the reverse direction, no current will flow until the voltage impressed across it is equal to the zener voltage. At this point, a current will flow and an extremely small increase in voltage will cause a large increase in current. Most importantly, it should be noted that the current flow through the zener diode is in the reverse direction to that of a normal rectifier.
With the application of sufficient reverse voltage, a p-n junction will experience a rapid avalanche breakdown and conduct current in the reverse direction. Valence electrons which break free under the influence of the applied electric field can be accelerated enough that they can knock loose other electrons and the subsequent collisions quickly become an avalanche. When this process is taking place, very small changes in voltage can cause very large changes in current. The breakdown process depends upon the applied electric field, so by changing the thickness of the layer to which the voltage is applied, zener diodes can be formed which break down at voltages from about 4 volts to several hundred volts.
Difference between FM and AM, which is preferred & its advantages.
AM and FM are methods of delivering signals embedded in a carrier frequency. There are many applications for them but they are best known for radio applications
AM means amplitude modulation. In this technique, the amplitude or height of the carrier signal increases and decreases as the base signal changes. AM radio signals will travel great distances so a single transmitter can cover large areas.
FM means Frequency Modulation where the frequency of the carrier signal increases and decreases to represent the change in voltage of the base signal. FM signals tend to offer better signal quality than AM but the range is far less, demanding multiple transmitters to cover the same area as one AM transmitter.
AM means amplitude modulation. In this technique, the amplitude or height of the carrier signal increases and decreases as the base signal changes. AM radio signals will travel great distances so a single transmitter can cover large areas.
FM means Frequency Modulation where the frequency of the carrier signal increases and decreases to represent the change in voltage of the base signal. FM signals tend to offer better signal quality than AM but the range is far less, demanding multiple transmitters to cover the same area as one AM transmitter.
To what does RS-232 refer?
It refers to the 25-pin or 9-pin male serial port on the back of a PC.
"A serial port conforms to the interface standard called RS-232c (Reference Standard 232 revision c), which is why a serial port is sometimes called the RS-232 port. The maximum cable length for a serial cable according to RS-232 standards is 50 feet. This interface standard originally called for 25 pins, but because microcomputers use only nine of those pins, manufacturers often installed a modified 9-pin port."
"A serial port conforms to the interface standard called RS-232c (Reference Standard 232 revision c), which is why a serial port is sometimes called the RS-232 port. The maximum cable length for a serial cable according to RS-232 standards is 50 feet. This interface standard originally called for 25 pins, but because microcomputers use only nine of those pins, manufacturers often installed a modified 9-pin port."
What is Lenz law ?
A law of electromagnetism which states that, whenever there is an induced electromotive force (emf) in a conductor, it is always in such a direction that the current it would produce would oppose the change which causes the induced emf. If the change is the motion of a conductor through a magnetic field, the induced current must be in such a direction as to produce a force opposing the motion. If the change causing the emf is a change of flux threading a coil, the induced current must produce a flux in such a direction as to oppose the change.
Lenz's law is a form of the law of conservation of energy, since it states that a change cannot propagate itself.
What is Transmission Frequency of Bluetooth, Wi-Fi and Wi-MAX ?
Wi-Fi is transmitted at different rates according to IEEE 802.11
There are also different letters that specify speed (example: 802.11n)
There are also different letters that specify speed (example: 802.11n)
This varies on what wireless device you use.
A typical wi-fi home router using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. The new IEEE 802.11n however, can apperently exceed that range by more than double (nearly 200m)
A typical wi-fi home router using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. The new IEEE 802.11n however, can apperently exceed that range by more than double (nearly 200m)
What is difference between Piconet and Scatternet ?
Meaning "tiny" network, a piconet is a Bluetooth network composed of two or more Bluetooth devices that operate in close proximity on the same channel and frequency hopping sequence. Piconets operate in both ad hoc (peer-to-peer) and infrastructure (central base station) modes of operation.
Masters, Slaves and Scatternets
In a piconet, one device is the master, which establishes the frequency hopping scheme, and there can be up to seven active and 255 inactive slave devices. However, a slave in one piconet can be a master in another, creating a chain of piconets called a "scatternet" that extends the distance between all devices. See Bluetooth.
What is Moore's Law ?
(computer science) The prediction by Gordon Moore (cofounder of the Intel Corporation) that the number of transistors on a microprocessor would double periodically (approximately every 18 months).
"The number of transistors and resistors on a chip doubles every 18 months." By Intel co-founder Gordon Moore regarding the pace of semiconductor technology. He made this famous comment in 1965 when there were approximately 60 devices on a chip. Proving Moore's law to be rather accurate, four decades later, Intel placed 1.7 billion transistors on its Itanium chip.
"The number of transistors and resistors on a chip doubles every 18 months." By Intel co-founder Gordon Moore regarding the pace of semiconductor technology. He made this famous comment in 1965 when there were approximately 60 devices on a chip. Proving Moore's law to be rather accurate, four decades later, Intel placed 1.7 billion transistors on its Itanium chip.
In 1975, Moore extended the 18 months to 24 months. More recently, he said that the cost of a semiconductor manufacturing plant doubles with each generation of microprocessor.
How many satellites comprise the GPS and expand it ?
There are at least 24 GPS satellites in operation at any given time with a number of on-orbit spares in case one fails. Each one is in a 12 hour orbit (meaning it takes 12 hours to orbit the earth). They are in a variety of six different orbits and are not just locked into a geosynchronous orbit (meaning they stay over roughly the same place on earth at all times, like your satellite TV and communications satellites) like some satellites.
All GPS satellites are owned and operated by the US Air Force and are controlled specifically by the 2d Space Operations Squadron at Schriever AFB in Colorado Springs, CO. There is not an easy way to deny the GPS capability to our enemies without also denying our own capability, so it is a free system open to anyone that has the technology to utilize it.
GPS satellites carry not only positional data but also extremely precise timing signals, which help the GPS receivers on the ground to triangulate their position and are even used to validate and secure financial transactions, etc. When the system was first created, artificial timing errors were put into the signal to try to reduce the effectiveness of the system for non-military users, but it was removed in 2000.
The GPS satellites also have NUDET (Nuclear Detonation) sensors on them to detect nuclear detonations almost anywhere on earth.
To use GPS you need to be in clear view of at the very least 3 satellites but you should be in view of 6 satellites at any given time unless some are blocked by objects, mountains, etc. So, GPS usually doesn't work well in-doors or even in a forrest or valley at times.
What is ZigBee and its specifications ?
ZigBee is a standard (rules, specifications, etc.) of a wireless network. This network aims specifically for home devices and appliances by making each 'node' 'speaks' with another, and benefit from each other.
What is FPGA ?
(Field Programmable Gate Array) A type of gate array that is programmed in the field rather than in a semiconductor fab. Containing up to hundreds of thousands of gates, there are a variety of FPGA architectures on the market. Some are very sophisticated, including not only programmable logic elements, but programmable interconnects and switches between the elements. The interconnects take up a lot of FPGA real estate, resulting in a chip with very low gate density compared to ASICs. In 2008, Altera introduced its Stratix IV FPGA with 2.5 billion transistors and 680K logic elements.
The vast majority of FPGAs are SRAM-based, although there are some flash and antifuse versions. The antifuse varieties are of interest to aerospace designers because they are more radiation hardened (rad hard). See PLD and adaptive computing.
What is MIMO ?
(Multiple Input/Multiple Output) Pronounced "my-mo," it is the use of multiple transmitters and receivers (multiple antennas) on wireless devices for improved performance. When two transmitters and two or more receivers are used, two simultaneous data streams can be sent, which double the data rate. Multiple receivers alone allow greater distances between devices. For example, the IEEE 802.11n (Wi-Fi) wireless standard uses MIMO to increase speed to 100 Mbps and beyond, doubling at minimum the 802.11a and 11g rates. MIMO antennas are also used in WiMAX and LTE.
MIMO, MISO and SIMO
The M, S, I and O relate to the air, not the device. For example, multiple inputs (MI) means multiple transmitters send multiple data streams "into" the air. Multiple outputs (MO) means multiple receivers acquire multiple data streams "out of" the air (see illustration below). See 802.11n, antenna diversity, beamforming and HSPA.
ARCHITECTURE AND ADVANTAGES OF
MULTIPLE ANTENNA TECHNOLOGIES
Compared to
Single Antenna (SISO)
Technologies
Transmit Receive Data
Type Antennas Antennas Rate Distance
MIMO Multiple Multiple Greater Greater range
MISO Multiple Single Same Same range but
More Reliable
SIMO Single Multiple Same Greater range
M = Multiple S = Single
I = Input O = Output
MIMO Wireless Router |
This "Pre-N" wireless router from Belkin uses two transmitters and three receivers to provide 108 Mbps between its access point and Belkin Pre-N cards in laptops. Introduced in 2004, this was the first "Preliminary-802.11n" system on the market (see 802.11n). (Image courtesy of Belkin Corporation, www.belkin.com)
What is VOIP ?
(Voice Over IP) A digital telephone service that uses the public Internet and private backbones for call transport. Support for the public switched telephone network (PSTN) is also provided so that VoIP calls can originate and terminate from regular telephones. Many companies, including Vonage, 8x8 and AT&T (CallVantage), typically offer calling within the country for a fixed fee and a low per-minute charge for international. Customers are required to have broadband Internet access (cable or DSL).
Handset Based
Regular phones can be used with many VoIP services by plugging them into an analog telephone adapter (ATA) provided by the VoIP provider or purchased from a third party. The ATA converts the phone to IP packets. IP phones can also be used that have built-in IP packet support.
Softphone Based
VoIP providers may be entirely softphone based, which requires a computer, phone software and microphone and speakers (or headset) to make and receive calls. Usually free of cost if both sides are on the same service, softphones let users call any phone in the world from their laptops and an Internet connection. Per-minute charges apply to call a regular phone number, but calls from a regular phone may not be possible. In 1995, VocalTec Communications introduced the first VoIP service in the U.S., and it was softphone based (see Internet Phone).
VoIP Features
Voicemail, caller ID, call forwarding and a softphone option (if not a softphone-only service) are typically part of a VoIP package. Phone numbers with area codes outside of one's own home area may also be an option (see virtual phone number). See IP telephony for more details and history of
On what principle do Transformers work ?
The transformer is based on two principles: firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnitude of the applied magnetic field. The changing magnetic flux extends to the secondary coil where a voltage is induced across its ends.
A transformer is a device which is use to convert high alternatic voltage to a low alternatic voltage and vice versa.
A transformer is a device which is use to convert high alternatic voltage to a low alternatic voltage and vice versa.
WORKING PRINCIPLE
Transformer works on the principle of mutual induction of two coils. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.
CONSTRUCTION
A transformer consists of a rectangular core of soft iron in the form of sheets insulated from one another. Two separate coils of insulated wires, a primary coil and a secondary coil are wound on the core. These coils are well insulated from one another and from the core. The coil on the input side is called Primary coil and the coil on the output side is called Secondary coil
What is EDFA ?
(Erbium-Doped Fiber Amplifier) A device that boosts the signal in an optical fiber. Introduced in the late 1980s, the EDFA was the first successful optical amplifier. It was a major factor in the rapid development of fiber-optic networks in the 1990s, because it extended the distance between costly regenerators. In addition, an EDFA amplifies all the channels in a WDM signal simultaneously, whereas regenerators require optical to electrical conversion for each channel.
A Laser Without Mirrors
Functioning like a laser without mirrors, the EDFA uses a semiconductor pump laser to introduce a powerful beam at a shorter wavelength into a section of erbium-doped fiber several meters long. The pump light excites the erbium atoms to higher orbits, and the input signal stimulates them to release excess energy as photons in phase and at the same wavelength. EDFAs boost wavelengths in the 1550 nm range, and the pump light is typically 1480 nm or 980 nm. See EDWA, WDM, Raman amplifier and optical amplifier.
EDFAs boost the input regardless of the number of wavelengths. In several meters of doped fiber, the pump laser excites the doped atoms to higher orbits, and the input signal stimulates them to release excess energy as photons in phase and at the same wavelength. (Illustration courtesy of Jeff Hecht.)What are different types of antennas ?
There are different types of antennas,they can mainly devided into directional & undirectional
a simply type of directional antennas: helical antenna
a simple type of undirectional antennas:yagi & loop antennas
What is Yagi-Uda antenna ?
(electromagnetism) An end-fire antenna array having maximum radiation in the direction of the array line; it has one dipole connected to the transmission line and a number of equally spaced unconnected dipoles mounted parallel to the first in the same horizontal plane to serve as directors and reflectors. Also known as Uda antenna; Yagi antenna.
What is latest satellite from ISRO?
PSLV-C15
What is meant by D-FF?
(D-flip flop stands for Delay flip-flop, it delays input by one clock pulse)
What is the basic difference between Latches and Flip flops?
(Latches are monostable and flip-flops are bistable)
What is a multiplexer?
(It is used to multiplex data from different sources normally used in TDM)
How can you convert an SR Flip-flop to a JK Flip-flop?
How can you convert an JK Flip-flop to a D Flip-flop?
( Connect J to D and K to not(D))
What is Race-around problem? How can you rectify it?
( Race around condition occurs in a JK flip-flop when both the inputs are set to '1', it can be rectified using edge-triggered flip-flop or using master-slave flip-flops)
Which semiconductor device is used as a voltage regulator and why?
What do you mean by an ideal voltage source?
What do you mean by zener breakdown and avalanche breakdown?
( zener breakdown takes place when very high voltage is applied to the diode this results in very high reverse current, as voltage is further increased minority carriers gain further momentum and strike atoms releases more carriers, which results in further increase in temp. It becomes vicious cycle and leads to avalanche breakdown or on other words "thermal runaway".
What are the different types of filters?
( analog filters n digital filters not sure wht u meant)
What is the need of filtering ideal response of filters and actual response of filters?
What is sampling theorem?
( sampling frequency should be atleast twice the maximum freq present in the signal)
What is impulse response?
( response given by a digital system when impulse signal is applied to it. Used to find out stability of system)
Explain the advantages and disadvantages of FIR filters compared to IIR counterparts.
What is CMRR? Explain briefly.
( Common mode rejection ratio)
What do you mean by half-duplex and full-duplex communication? Explain briefly.
( half-duplex: either sender or receiver can use the channel at one time eg walky-talky and full-duplex: sender or receiver or both can use the channel at one time eg telephone)
Which range of signals are used for terrestrial transmission?
What is the need for modulation?
Which type of modulation is used in TV transmission?
( video signal: vestigial side band modulation and audio signal: FM)
Why we use vestigial side band (VSB-C3F) transmission for picture?
( why not DSBSC: large bandwidth req.why not SSBSC: To over come distortion by filters used at receivers thus demodulation becomes complex hence costly)
When transmitting digital signals is it necessary to transmit some harmonics in addition to fundamental frequency?
( yup but not sure why)
For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?
( for asyn tx it is necessary to use start and stop bits as no common clock is there)
BPFSK is more efficient than BFSK in presence of noise. Why?
What is meant by pre-emphasis and de-emphasis?
( used in TV Tx for voice signal not sure why)
What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB? What do you mean by ASCII, EBCDIC?
1.What are the flags in 8086?
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2.What are the various interrupts in 8086??
Maskable interrupts, Non-Maskable interrupts
3.What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4.Which interrupts are generally used for critical events??
Non-Maskable interrupts are used in critical events Such as Power failure, Emergency, Shut off etc.
5.What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
6.What are the various segment registers in 8086?
Code, Data, Stack, Extra
7.Which Stack is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
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1.What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .
2.What is Stack Pointer
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack
3.What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
4.Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
5.What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
6.What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
7.Give an example of one address microprocessor?
8085 is a one address microprocessor.
8.In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
9.examples of Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
10.EXAMPLES of Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR.
11.Which interrupt has the highest priority?
TRAP has the highest priority.
12.Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes.
13.How many interrupts are there in 8085?
There are 12 interrupts in 8085.
14.What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
15.In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
16.Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn't drift with aging. Crystal is used as a clock source most of the times.
17.What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
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1.what is the differnce between SCR and diode rectifier?
ans: diode is a 2 terminal device, in scr gate controls the rectifing.SCR is used in High frequency applications but diode is low freuency devices, SCR can be in high temparatures but not diode.
2.whatis intersymbol interference
ans:In telecommunication, intersymbol interference (ISI) means a form of distortion of a signal that causes the previously transmitted symbols to have an effect on the currently received symbol. This is usually an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by echoes or non-linear frequency response of the channel. Ways to fight against intersymbol interference include adaptive equalization or error correcting codes (especially soft-decoding with Viterbi algorithm).
3.Distinguish between Angle modulation and Amplitude modulation.
ans: In amplitude Modulation as the amplitude of given signal varies, the amplitude of carrier signal also varies in the same way.
In angle modulation, the frequency or phase may vary according to the amplitude of given signal
4.What is Biasing?
ans: biasing is a process of connecting dc voltage to a device by which we can select the operating point of the device. by biasing actually we select the operating point of the device.
5.What do you mean by ASCII, EBCDIC?
ans:ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet.
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
6.What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
ans:3db implies 70%(o.7o7) of the power,i'e we r interested to consider the bandwidth range from peak to 70% b'coz uptp 70% its reliable.hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
7.What is meant by pre-emphasis and de-emphasis?
ans:Pre-emphasis
" Improving the signal to noise ratio by increasing the magnitude of higher frequency signals with respect to lower frequency signals"
De-emphasis
" Improving the signal to noise ratio by decreasing the magnitude of higher frequency signals with respect to lower frequency signals"
8.What is sampling theorem?
ans:It is defined as the sampling frequency should be greater than or equal to twice the sampling frequency then we can generate the original signal if the condition does not satisfy we get the signal in the distorted mannerit is given as ( fs >/ 2 fs)
9.What is Race-around problem? How can you rectify it?
ans: A condition in logic network in which the difference in propagation times through two or more signal paths in the network can produce an erroneous output.in jk flip flop race around problem will occur when both the inputs are high. it can be prevented by using master slave jk flip flop
10.What is the basic difference between Latches and Flip flops?
ans:latch works without clock signal,but works with a control signal and it is level triggered device.whereas flip flop is a 1 bit storage element and works with a clock signal.its a edge triggered device. normally latches are avoided and flip flops are preferred.
11. what is Barkhausen Criterion?
ans:
1./AB/=1,i.e. the magnitude of loop gain must be unity
2.the total prase shift around the closed loop is zero or 360 degrees.
12.what are active and Passive Components?
ans:ACTIVE COMPONENTS The components which produce the energy in the form of current or voltage are called as active components.Example:transistors etc,.
PASSIVE COMPONENTS
The components which stores the energy in the form of current or voltage are called as passive components.example:inductors,resistors,capacitors etc
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2.What are the various interrupts in 8086??
Maskable interrupts, Non-Maskable interrupts
3.What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4.Which interrupts are generally used for critical events??
Non-Maskable interrupts are used in critical events Such as Power failure, Emergency, Shut off etc.
5.What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
6.What are the various segment registers in 8086?
Code, Data, Stack, Extra
7.Which Stack is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
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1.What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .
2.What is Stack Pointer
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack
3.What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
4.Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
5.What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
6.What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
7.Give an example of one address microprocessor?
8085 is a one address microprocessor.
8.In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
9.examples of Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
10.EXAMPLES of Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR.
11.Which interrupt has the highest priority?
TRAP has the highest priority.
12.Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes.
13.How many interrupts are there in 8085?
There are 12 interrupts in 8085.
14.What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
15.In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
16.Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn't drift with aging. Crystal is used as a clock source most of the times.
17.What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.what is the differnce between SCR and diode rectifier?
ans: diode is a 2 terminal device, in scr gate controls the rectifing.SCR is used in High frequency applications but diode is low freuency devices, SCR can be in high temparatures but not diode.
2.whatis intersymbol interference
ans:In telecommunication, intersymbol interference (ISI) means a form of distortion of a signal that causes the previously transmitted symbols to have an effect on the currently received symbol. This is usually an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by echoes or non-linear frequency response of the channel. Ways to fight against intersymbol interference include adaptive equalization or error correcting codes (especially soft-decoding with Viterbi algorithm).
3.Distinguish between Angle modulation and Amplitude modulation.
ans: In amplitude Modulation as the amplitude of given signal varies, the amplitude of carrier signal also varies in the same way.
In angle modulation, the frequency or phase may vary according to the amplitude of given signal
4.What is Biasing?
ans: biasing is a process of connecting dc voltage to a device by which we can select the operating point of the device. by biasing actually we select the operating point of the device.
5.What do you mean by ASCII, EBCDIC?
ans:ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet.
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
6.What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
ans:3db implies 70%(o.7o7) of the power,i'e we r interested to consider the bandwidth range from peak to 70% b'coz uptp 70% its reliable.hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
7.What is meant by pre-emphasis and de-emphasis?
ans:Pre-emphasis
" Improving the signal to noise ratio by increasing the magnitude of higher frequency signals with respect to lower frequency signals"
De-emphasis
" Improving the signal to noise ratio by decreasing the magnitude of higher frequency signals with respect to lower frequency signals"
8.What is sampling theorem?
ans:It is defined as the sampling frequency should be greater than or equal to twice the sampling frequency then we can generate the original signal if the condition does not satisfy we get the signal in the distorted mannerit is given as ( fs >/ 2 fs)
9.What is Race-around problem? How can you rectify it?
ans: A condition in logic network in which the difference in propagation times through two or more signal paths in the network can produce an erroneous output.in jk flip flop race around problem will occur when both the inputs are high. it can be prevented by using master slave jk flip flop
10.What is the basic difference between Latches and Flip flops?
ans:latch works without clock signal,but works with a control signal and it is level triggered device.whereas flip flop is a 1 bit storage element and works with a clock signal.its a edge triggered device. normally latches are avoided and flip flops are preferred.
11. what is Barkhausen Criterion?
ans:
1./AB/=1,i.e. the magnitude of loop gain must be unity
2.the total prase shift around the closed loop is zero or 360 degrees.
12.what are active and Passive Components?
ans:ACTIVE COMPONENTS The components which produce the energy in the form of current or voltage are called as active components.Example:transistors etc,.
PASSIVE COMPONENTS
The components which stores the energy in the form of current or voltage are called as passive components.example:inductors,resistors,capacitors etc
Monday, September 6, 2010
Electronics and communication engineering core interview questions
1: What is difference between Microprocessor and Microcontroller ?
2: Why is Zener Diode always used in Reverse Bias condition ?
3: Difference between FM and AM, which is preferred & its advantages.
4: Questions on different coding techniques ?
5: Questions on signal processing techniques ?
6: What is RS in RS-232 ?
7: What is Lenz law ?
8: What is Transmission Frequency of Bluetooth, Wi-Fi and Wi-MAX ?
9: What is difference between Piconet and Scatternet ?
10: What is Moore's Law ?
11: How many satellites comprise the GPS and expand it ?
12: What is ZigBee and its specifications ?
13: What is FPGA ?
14: What is MIMO ?
15: What is VOIP ?
16: On what principle do Transformers work ?
17: What is EDFA ?
18: What are different types of antennas ?
19: What is Yagi-Uda antenna ?
20: What is latest satellite from ISOR ?
..............................
2: Why is Zener Diode always used in Reverse Bias condition ?
3: Difference between FM and AM, which is preferred & its advantages.
4: Questions on different coding techniques ?
5: Questions on signal processing techniques ?
6: What is RS in RS-232 ?
7: What is Lenz law ?
8: What is Transmission Frequency of Bluetooth, Wi-Fi and Wi-MAX ?
9: What is difference between Piconet and Scatternet ?
10: What is Moore's Law ?
11: How many satellites comprise the GPS and expand it ?
12: What is ZigBee and its specifications ?
13: What is FPGA ?
14: What is MIMO ?
15: What is VOIP ?
16: On what principle do Transformers work ?
17: What is EDFA ?
18: What are different types of antennas ?
19: What is Yagi-Uda antenna ?
20: What is latest satellite from ISOR ?
..............................
......................................................................................................................................................................
why the input resistance of an op-amp is high whereas it's output resistance is low?
A.Loading at the input point and to pass the maximum output to the load is the requirement of Op-Amp which is a current exchange device from input side to output side.
Q.what do you understand by microwaves? why these are called micro
A.micro waves are those waves whose wavelength is less than a foot(30 cms) or freq ranging from 1 GHz to 1000 GHz.Because of there tinyness these are called micro.
Q. how do microwave oven works??
A. Heart of microwave oven is magnatron which generates frequency of appox. 2.4 GHz.explain working of magnatron.
Q.What is CMRR? Explain briefly.
A. CMRR stands for common mode rejection ratio. It is a measure of the ability of a test instrument to reject
interference that is common to both of its measurement input terminals. It is expressed in decibels and it is the ratio of the actual or common signal level appearing on the
two input terminals together to the measured level.
----------------------------------------------------------------------------------------------------------------------------------------------------
-----------------------------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------------------------------------------------------
Hello puys,
I am posting some of the imp questions subject wise:
Following r some imp topics:
Semiconductor devices and circuits:
Resistance, inductance(dc short, ac open), capacitance (ac short , dc open)
Diodes:
types& definitions: p-n, zener(zener breakdown, voltage regulator),tunnel (tunneling effect),varactor,
Impatt,Trapatt, gunn, pin;
Transistors:
two types 1. Based on minority carrier(BJT:npn,pnp) 2. based on FET principle(IGFET,JFET,MOSFET,MESFET);
Amplifiers:
types:LNA,Power amp,feedback,balanced,distributed amp
Active state (for CE conf):Base if FB and collector is RB:
Saturation:Both bas and collector are FB
Cut-off:Both bas and collector are RB
Untuned Amp:Class A,B,AB,C
Oscillator:total phase shift at input is 0 or multiples of 2pi.
MPMC:
MP are memoryless.General purpose processors
MC have inbuilt memory and IO ports
to interface MP with ports 825 is used
MP types: 8085 (8-data, 16 address);8086(16data,16 address); 80186(16 data, 20 adddress); 80286(16 data, 24 address);80386(16 data, 32 address);80486 (32 data, 32 address); pentium (64 data, 32 address,Pipelining,More segmentations&memory banks);Pentium Pro(64 data,36 address)
MC: 4K rom, 128 bytes ram,2 timers,4 io ports,1 serial port, 8 bit cpu, 16 address lines, 40 pins
Control systems:
Definitions:
System:A no of elements are connected in a sequence to perform a specific function is called a system.
Control system: system in which o/p is controlled by i/p.
Open loop system(o/p does not change automatically)& closed loop system (output changes automatically)
Stability:BIBO condition :i/p=0 then o/p tends to 0.
Limtedly stable,absolutely stable and conditionally stable:
Three ways to check stability: Routh-herwitz criteria, nyquist criteria, root locus method
PS: Will be posting topics of other subjects soon.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.What are the flags in 8086?
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2.What are the various interrupts in 8086??
Maskable interrupts, Non-Maskable interrupts
3.What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4.Which interrupts are generally used for critical events??
Non-Maskable interrupts are used in critical events Such as Power failure, Emergency, Shut off etc.
5.What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
6.What are the various segment registers in 8086?
Code, Data, Stack, Extra
7.Which Stack is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .
2.What is Stack Pointer
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack
3.What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
4.Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
5.What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
6.What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
7.Give an example of one address microprocessor?
8085 is a one address microprocessor.
8.In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
9.examples of Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
10.EXAMPLES of Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR.
11.Which interrupt has the highest priority?
TRAP has the highest priority.
12.Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes.
13.How many interrupts are there in 8085?
There are 12 interrupts in 8085.
14.What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
15.In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
16.Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn't drift with aging. Crystal is used as a clock source most of the times.
17.What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.what is the differnce between SCR and diode rectifier?
ans: diode is a 2 terminal device, in scr gate controls the rectifing.SCR is used in High frequency applications but diode is low freuency devices, SCR can be in high temparatures but not diode.
2.whatis intersymbol interference
ans:In telecommunication, intersymbol interference (ISI) means a form of distortion of a signal that causes the previously transmitted symbols to have an effect on the currently received symbol. This is usually an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by echoes or non-linear frequency response of the channel. Ways to fight against intersymbol interference include adaptive equalization or error correcting codes (especially soft-decoding with Viterbi algorithm).
3.Distinguish between Angle modulation and Amplitude modulation.
ans: In amplitude Modulation as the amplitude of given signal varies, the amplitude of carrier signal also varies in the same way.
In angle modulation, the frequency or phase may vary according to the amplitude of given signal
4.What is Biasing?
ans: biasing is a process of connecting dc voltage to a device by which we can select the operating point of the device. by biasing actually we select the operating point of the device.
5.What do you mean by ASCII, EBCDIC?
ans:ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet.
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
6.What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
ans:3db implies 70%(o.7o7) of the power,i'e we r interested to consider the bandwidth range from peak to 70% b'coz uptp 70% its reliable.hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
7.What is meant by pre-emphasis and de-emphasis?
ans:Pre-emphasis
" Improving the signal to noise ratio by increasing the magnitude of higher frequency signals with respect to lower frequency signals"
De-emphasis
" Improving the signal to noise ratio by decreasing the magnitude of higher frequency signals with respect to lower frequency signals"
8.What is sampling theorem?
ans:It is defined as the sampling frequency should be greater than or equal to twice the sampling frequency then we can generate the original signal if the condition does not satisfy we get the signal in the distorted mannerit is given as ( fs >/ 2 fs)
9.What is Race-around problem? How can you rectify it?
ans: A condition in logic network in which the difference in propagation times through two or more signal paths in the network can produce an erroneous output.in jk flip flop race around problem will occur when both the inputs are high. it can be prevented by using master slave jk flip flop
10.What is the basic difference between Latches and Flip flops?
ans:latch works without clock signal,but works with a control signal and it is level triggered device.whereas flip flop is a 1 bit storage element and works with a clock signal.its a edge triggered device. normally latches are avoided and flip flops are preferred.
11. what is Barkhausen Criterion?
ans:
1./AB/=1,i.e. the magnitude of loop gain must be unity
2.the total prase shift around the closed loop is zero or 360 degrees.
12.what are active and Passive Components?
ans:ACTIVE COMPONENTS The components which produce the energy in the form of current or voltage are called as active components.Example:transistors etc,.
PASSIVE COMPONENTS
The components which stores the energy in the form of current or voltage are called as passive components.example:inductors,resistors,capacitors etc
why the input resistance of an op-amp is high whereas it's output resistance is low?
A.Loading at the input point and to pass the maximum output to the load is the requirement of Op-Amp which is a current exchange device from input side to output side.
Q.what do you understand by microwaves? why these are called micro
A.micro waves are those waves whose wavelength is less than a foot(30 cms) or freq ranging from 1 GHz to 1000 GHz.Because of there tinyness these are called micro.
Q. how do microwave oven works??
A. Heart of microwave oven is magnatron which generates frequency of appox. 2.4 GHz.explain working of magnatron.
Q.What is CMRR? Explain briefly.
A. CMRR stands for common mode rejection ratio. It is a measure of the ability of a test instrument to reject
interference that is common to both of its measurement input terminals. It is expressed in decibels and it is the ratio of the actual or common signal level appearing on the
two input terminals together to the measured level.
----------------------------------------------------------------------------------------------------------------------------------------------------
- What is meant by D-FF? D Flip Flop (or did you mean to ask its working?)
- What is the basic difference between Latches and Flip flops? (Latches do not store information, here, a bit)
- What is a multiplexer?
- How can you convert an SR Flip-flop to a JK Flip-flop?
- How can you convert an JK Flip-flop to a D Flip-flop?
- What is Race-around problem? How can you rectify it?
- Which semiconductor device is used as a voltage regulator and why? (zener diode in reverse bias, why because it allows for a large variation in current for a negligible variation in voltage)
- What do you mean by an ideal voltage source? (Sources infinite current to any load without any change in o/p voltage)
- What do you mean by zener breakdown and avalanche breakdown?
- What are the different types of filters? (low pass, high pass, band pass, band stop, resonant)
- What is the need of filtering ideal response of filters and actual response of filters?
- What is sampling theorem? (minium 2 samples per time period? not too sure of this)
- What is impulse response?
- Explain the advantages and disadvantages of FIR filters compared to IIR counterparts.
- What is CMRR? Explain briefly. (explained by someone a few posts above)
- What do you mean by half-duplex and full-duplex communication? Explain briefly. (half duplex - both sender & receiver can communicate with each other, but not simultaneously...full duplex - same but simultaneous communication possible)
- Which range of signals are used for terrestrial transmission?
- What is the need for modulation? (transmitting over a distance, encryption?)
- Which type of modulation is used in TV transmission?
- Why we use vestigial side band (VSB-C3F) transmission for picture?
- When transmitting digital signals is it necessary to transmit some harmonics in addition to fundamental frequency?
- For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?
- BPFSK is more efficient than BFSK in presence of noise. Why?
- What is meant by pre-emphasis and de-emphasis?
- What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB? (3dB is the half power value)
- What do you mean by ASCII, EBCDIC?
- What is meant by D-FF?(D-flip flop stands for Delay flip-flop, it delays input by one clock pulse)
- What is the basic difference between Latches and Flip flops?(Latches are monostable and flip-flops are bistable)
- What is a multiplexer?(It is used to multiplex data from different sources normally used in TDM)
- How can you convert an SR Flip-flop to a JK Flip-flop?
- How can you convert an JK Flip-flop to a D Flip-flop?( Connect J to D and K to not(D))
- What is Race-around problem? How can you rectify it?( Race around condition occurs in a JK flip-flop when both the inputs are set to '1', it can be rectified using edge-triggered flip-flop or using master-slave flip-flops)
- Which semiconductor device is used as a voltage regulator and why?
- What do you mean by an ideal voltage source?
- What do you mean by zener breakdown and avalanche breakdown?( zener breakdown takes place when very high voltage is applied to the diode this results in very high reverse current, as voltage is further increased minority carriers gain further momentum and strike atoms releases more carriers, which results in further increase in temp. It becomes vicious cycle and leads to avalanche breakdown or on other words "thermal runaway".
- What are the different types of filters?( analog filters n digital filters not sure wht u meant)
- What is the need of filtering ideal response of filters and actual response of filters?
- What is sampling theorem?( sampling frequency should be atleast twice the maximum freq present in the signal)
- What is impulse response?( response given by a digital system when impulse signal is applied to it. Used to find out stability of system)
- Explain the advantages and disadvantages of FIR filters compared to IIR counterparts.
- What is CMRR? Explain briefly.( Common mode rejection ratio)
- What do you mean by half-duplex and full-duplex communication? Explain briefly.( half-duplex: either sender or receiver can use the channel at one time eg walky-talky and full-duplex: sender or receiver or both can use the channel at one time eg telephone)
- Which range of signals are used for terrestrial transmission?
- What is the need for modulation?
- Which type of modulation is used in TV transmission?( video signal: vestigial side band modulation and audio signal: FM)
- Why we use vestigial side band (VSB-C3F) transmission for picture?( why not DSBSC: large bandwidth req.why not SSBSC: To over come distortion by filters used at receivers thus demodulation becomes complex hence costly)
- When transmitting digital signals is it necessary to transmit some harmonics in addition to fundamental frequency?( yup but not sure why)
- For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?( for asyn tx it is necessary to use start and stop bits as no common clock is there)
- BPFSK is more efficient than BFSK in presence of noise. Why?
- What is meant by pre-emphasis and de-emphasis?( used in TV Tx for voice signal not sure why)
- What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
- What do you mean by ASCII, EBCDIC?
Hello puys,
I am posting some of the imp questions subject wise:
Following r some imp topics:
Semiconductor devices and circuits:
Resistance, inductance(dc short, ac open), capacitance (ac short , dc open)
Diodes:
types& definitions: p-n, zener(zener breakdown, voltage regulator),tunnel (tunneling effect),varactor,
Impatt,Trapatt, gunn, pin;
Transistors:
two types 1. Based on minority carrier(BJT:npn,pnp) 2. based on FET principle(IGFET,JFET,MOSFET,MESFET);
Amplifiers:
types:LNA,Power amp,feedback,balanced,distributed amp
Active state (for CE conf):Base if FB and collector is RB:
Saturation:Both bas and collector are FB
Cut-off:Both bas and collector are RB
Untuned Amp:Class A,B,AB,C
Oscillator:total phase shift at input is 0 or multiples of 2pi.
MPMC:
MP are memoryless.General purpose processors
MC have inbuilt memory and IO ports
to interface MP with ports 825 is used
MP types: 8085 (8-data, 16 address);8086(16data,16 address); 80186(16 data, 20 adddress); 80286(16 data, 24 address);80386(16 data, 32 address);80486 (32 data, 32 address); pentium (64 data, 32 address,Pipelining,More segmentations&memory banks);Pentium Pro(64 data,36 address)
MC: 4K rom, 128 bytes ram,2 timers,4 io ports,1 serial port, 8 bit cpu, 16 address lines, 40 pins
Control systems:
Definitions:
System:A no of elements are connected in a sequence to perform a specific function is called a system.
Control system: system in which o/p is controlled by i/p.
Open loop system(o/p does not change automatically)& closed loop system (output changes automatically)
Stability:BIBO condition :i/p=0 then o/p tends to 0.
Limtedly stable,absolutely stable and conditionally stable:
Three ways to check stability: Routh-herwitz criteria, nyquist criteria, root locus method
PS: Will be posting topics of other subjects soon.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.What are the flags in 8086?
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2.What are the various interrupts in 8086??
Maskable interrupts, Non-Maskable interrupts
3.What is meant by Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4.Which interrupts are generally used for critical events??
Non-Maskable interrupts are used in critical events Such as Power failure, Emergency, Shut off etc.
5.What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock frequency in 8086.
6.What are the various segment registers in 8086?
Code, Data, Stack, Extra
7.Which Stack is used in 8086?
FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.What are the various registers in 8085?
Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .
2.What is Stack Pointer
Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack
3.What is Program counter?
Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
4.Which Stack is used in 8085?
LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
5.What is meant by a bus?
A bus is a group of conducting lines that carriers data, address, & control signals.
6.What is Tri-state logic?
Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
7.Give an example of one address microprocessor?
8085 is a one address microprocessor.
8.In what way interrupts are classified in 8085?
In 8085 the interrupts are classified as Hardware and Software interrupts.
9.examples of Software interrupts?
RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
10.EXAMPLES of Hardware interrupts?
TRAP, RST7.5, RST6.5, RST5.5, INTR.
11.Which interrupt has the highest priority?
TRAP has the highest priority.
12.Name 5 different addressing modes?
Immediate, Direct, Register, Register indirect, Implied addressing modes.
13.How many interrupts are there in 8085?
There are 12 interrupts in 8085.
14.What is clock frequency for 8085?
3 MHz is the maximum clock frequency for 8085.
15.In 8085 which is called as High order / Low order Register?
Flag is called as Low order register & Accumulator is called as High order Register.
16.Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn't drift with aging. Crystal is used as a clock source most of the times.
17.What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.what is the differnce between SCR and diode rectifier?
ans: diode is a 2 terminal device, in scr gate controls the rectifing.SCR is used in High frequency applications but diode is low freuency devices, SCR can be in high temparatures but not diode.
2.whatis intersymbol interference
ans:In telecommunication, intersymbol interference (ISI) means a form of distortion of a signal that causes the previously transmitted symbols to have an effect on the currently received symbol. This is usually an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by echoes or non-linear frequency response of the channel. Ways to fight against intersymbol interference include adaptive equalization or error correcting codes (especially soft-decoding with Viterbi algorithm).
3.Distinguish between Angle modulation and Amplitude modulation.
ans: In amplitude Modulation as the amplitude of given signal varies, the amplitude of carrier signal also varies in the same way.
In angle modulation, the frequency or phase may vary according to the amplitude of given signal
4.What is Biasing?
ans: biasing is a process of connecting dc voltage to a device by which we can select the operating point of the device. by biasing actually we select the operating point of the device.
5.What do you mean by ASCII, EBCDIC?
ans:ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet.
EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
6.What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
ans:3db implies 70%(o.7o7) of the power,i'e we r interested to consider the bandwidth range from peak to 70% b'coz uptp 70% its reliable.hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
7.What is meant by pre-emphasis and de-emphasis?
ans:Pre-emphasis
" Improving the signal to noise ratio by increasing the magnitude of higher frequency signals with respect to lower frequency signals"
De-emphasis
" Improving the signal to noise ratio by decreasing the magnitude of higher frequency signals with respect to lower frequency signals"
8.What is sampling theorem?
ans:It is defined as the sampling frequency should be greater than or equal to twice the sampling frequency then we can generate the original signal if the condition does not satisfy we get the signal in the distorted mannerit is given as ( fs >/ 2 fs)
9.What is Race-around problem? How can you rectify it?
ans: A condition in logic network in which the difference in propagation times through two or more signal paths in the network can produce an erroneous output.in jk flip flop race around problem will occur when both the inputs are high. it can be prevented by using master slave jk flip flop
10.What is the basic difference between Latches and Flip flops?
ans:latch works without clock signal,but works with a control signal and it is level triggered device.whereas flip flop is a 1 bit storage element and works with a clock signal.its a edge triggered device. normally latches are avoided and flip flops are preferred.
11. what is Barkhausen Criterion?
ans:
1./AB/=1,i.e. the magnitude of loop gain must be unity
2.the total prase shift around the closed loop is zero or 360 degrees.
12.what are active and Passive Components?
ans:ACTIVE COMPONENTS The components which produce the energy in the form of current or voltage are called as active components.Example:transistors etc,.
PASSIVE COMPONENTS
The components which stores the energy in the form of current or voltage are called as passive components.example:inductors,resistors,capacitors etc
Sunday, September 5, 2010
Digital Design Interview Questions - All in 1
1. How do you convert a XOR gate into a buffer and a inverter (Use only one XOR gate for each)?
Answer
2. Implement an 2-input AND gate using a 2x1 mux.
Answer
3. What is a multiplexer?
Answer
A multiplexer is a combinational circuit which selects one of many input signals and directs to the only output.
4. What is a ring counter?
Answer
A ring counter is a type of counter composed of a circular shift register. The output of the last shift register is fed to the input of the first register. For example, in a 4-register counter, with initial register values of 1100, the repeating pattern is: 1100, 0110, 0011, 1001, 1100, so on.
5. Compare and Contrast Synchronous and Asynchronous reset.
Answer
Synchronous reset logic will synthesize to smaller flip-flops, particularly if the reset is gated with the logic generating the d-input. But in such a case, the combinational logic gate count grows, so the overall gate count savings may not be that significant. The clock works as a filter for small reset glitches; however, if these glitches occur near the active clock edge, the Flip-flop could go metastable. In some designs, the reset must be generated by a set of internal conditions. A synchronous reset is recommended for these types of designs because it will filter the logic equation glitches between clock.
Problem with synchronous resets is that the synthesis tool cannot easily distinguish the reset signal from any other data signal. Synchronous resets may need a pulse stretcher to guarantee a reset pulse width wide enough to ensure reset is present during an active edge of the clock, if you have a gated clock to save power, the clock may be disabled coincident with the assertion of reset. Only an asynchronous reset will work in this situation, as the reset might be removed prior to the resumption of the clock. Designs that are pushing the limit for data path timing, can not afford to have added gates and additional net delays in the data path due to logic inserted to handle synchronous resets.
Asynchronous reset: The major problem with asynchronous resets is the reset release, also called reset removal. Using an asynchronous reset, the designer is guaranteed not to have the reset added to the data path. Another advantage favoring asynchronous resets is that the circuit can be reset with or without a clock present. Ensure that the release of the reset can occur within one clock period else if the release of the reset occurred on or near a clock edge then flip-flops may go into metastable state.
6. What is a Johnson counter?
Answer
Johnson counter connects the complement of the output of the last shift register to its input and circulates a stream of ones followed by zeros around the ring. For example, in a 4-register counter, the repeating pattern is: 0000, 1000, 1100, 1110, 1111, 0111, 0011, 0001, so on.
7. An assembly line has 3 fail safe sensors and one emergency shutdown switch.The line should keep moving unless any of the following conditions arise:
(1) If the emergency switch is pressed
(2) If the senor1 and sensor2 are activated at the same time.
(3) If sensor 2 and sensor3 are activated at the same time.
(4) If all the sensors are activated at the same time
Suppose a combinational circuit for above case is to be implemented only with NAND Gates. How many minimum number of 2 input NAND gates are required?
Answer
Solve it out!
8. In a 4-bit Johnson counter How many unused states are present?
Answer
4-bit Johnson counter: 0000, 1000, 1100, 1110, 1111, 0111, 0011, 0001, 0000.
8 unused states are present.
9. Design a 3 input NAND gate using minimum number of 2 input NAND gates.
Answer
10. How can you convert a JK flip-flop to a D flip-flop?
Answer
Connect the inverted J input to K input.
11. What are the differences between a flip-flop and a latch?
Answer
Flip-flops are edge-sensitive devices where as latches are level sensitive devices.
Flip-flops are immune to glitches where are latches are sensitive to glitches.
Latches require less number of gates (and hence less power) than flip-flops.
Latches are faster than flip-flops.
12. What is the difference between Mealy and Moore FSM?
Answer
Mealy FSM uses only input actions, i.e. output depends on input and state. The use of a Mealy FSM leads often to a reduction of the number of states.
Moore FSM uses only entry actions, i.e. output depends only on the state. The advantage of the Moore model is a simplification of the behavior.
13. What are various types of state encoding techniques? Explain them.
Answer
One-Hot encoding: Each state is represented by a bit flip-flop). If there are four states then it requires four bits (four flip-flops) to represent the current state. The valid state values are 1000, 0100, 0010, and 0001. If the value is 0100, then it means second state is the current state.
One-Cold encoding: Same as one-hot encoding except that '0' is the valid value. If there are four states then it requires four bits (four flip-flops) to represent the current state. The valid state values are 0111, 1011, 1101, and 1110.
Binary encoding: Each state is represented by a binary code. A FSM having '2 power N' states requires only N flip-flops.
Gray encoding: Each state is represented by a Gray code. A FSM having '2 power N' states requires only N flip-flops.
14. Define Clock Skew , Negative Clock Skew, Positive Clock Skew.
Answer
Clock skew is a phenomenon in synchronous circuits in which the clock signal (sent from the clock circuit) arrives at different components at different times. This can be caused by many different things, such as wire-interconnect length, temperature variations, variation in intermediate devices, capacitive coupling, material imperfections, and differences in input capacitance on the clock inputs of devices using the clock.
There are two types of clock skew: negative skew and positive skew. Positive skew occurs when the clock reaches the receiving register later than it reaches the register sending data to the receiving register. Negative skew is the opposite: the receiving register gets the clock earlier than the sending register.
15. Give the transistor level circuit of a CMOS NAND gate.
Answer
16. Design a 4-bit comparator circuit.
Answer
17. Design a Transmission Gate based XOR. Now, how do you convert it to XNOR (without inverting the output)?
Answer
18. Define Metastability.
Answer
If there are setup and hold time violations in any sequential circuit, it enters a state where its output is unpredictable, this state is known as metastable state or quasi stable state, at the end of metastable state, the flip-flop settles down to either logic high or logic low. This whole process is known as metastability.
19. Compare and contrast between 1's complement and 2's complement notation.
Answer
20. Give the transistor level circuit of CMOS, nMOS, pMOS, and TTL inverter gate.
Answer
21. What are set up time and hold time constraints?
Answer
Set up time is the amount of time before the clock edge that the input signal needs to be stable to guarantee it is accepted properly on the clock edge.
Hold time is the amount of time after the clock edge that same input signal has to be held before changing it to make sure it is sensed properly at the clock edge.
Whenever there are setup and hold time violations in any flip-flop, it enters a state where its output is unpredictable, which is known as as metastable state or quasi stable state. At the end of metastable state, the flip-flop settles down to either logic high or logic low. This whole process is known as metastability.
22. Give a circuit to divide frequency of clock cycle by two.
Answer
23. Design a divide-by-3 sequential circuit with 50% duty circle.
Answer
24. Explain different types of adder circuits.
Answer
25. Give two ways of converting a two input NAND gate to an inverter.
Answer
26. Draw a Transmission Gate-based D-Latch.
Answer
27. Design a FSM which detects the sequence 10101 from a serial line without overlapping.
Answer
28. Design a FSM which detects the sequence 10101 from a serial line with overlapping.
Answer
29. Give the design of 8x1 multiplexer using 2x1 multiplexers.
Answer
30. Design a counter which counts from 1 to 10 ( Resets to 1, after 10 ).
Answer
31. Design 2 input AND, OR, and EXOR gates using 2 input NAND gate.
Answer
32. Design a circuit which doubles the frequency of a given input clock signal.
Answer
33. Implement a D-latch using 2x1 multiplexer(s).
Answer
34. Give the excitation table of a JK flip-flop.
Answer
35. Give the Binary, Hexadecimal, BCD, and Excess-3 code for decimal 14.
Answer
14:
Binary: 1110
Hexadecimal: E
BCD: 0001 0100
Excess-3: 10001
36. What is race condition?
Answer
37. Give 1's and 2's complement of 19.
Answer
19: 10011
1's complement: 01100
2's complement: 01101
38. Design a 3:6 decoder.
Answer
39. If A*B=C and C*A=B then, what is the Boolean operator * ?
Answer
* is Exclusive-OR.
40. Design a 3 bit Gray Counter.
Answer
41. Expand the following: PLA, PAL, CPLD, FPGA.
Answer
PLA - Programmable Logic Array
PAL - Programmable Array Logic
CPLD - Complex Programmable Logic Device
FPGA - Field-Programmable Gate Array
42. Implement the functions: X = A'BC + ABC + A'B'C' and Y = ABC + AB'C using a PLA.
Answer
43. What are PLA and PAL? Give the differences between them.
Answer
Programmable Logic Array is a programmable device used to implement combinational logic circuits. The PLA has a set of programmable AND planes, which link to a set of programmable OR planes, which can then be conditionally complemented to produce an output.
PAL is programmable array logic, like PLA, it also has a wide, programmable AND plane. Unlike a PLA, the OR plane is fixed, limiting the number of terms that can be ORed together.
Due to fixed OR plane PAL allows extra space, which is used for other basic logic devices, such as multiplexers, exclusive-ORs, and latches. Most importantly, clocked elements, typically flip-flops, could be included in PALs. PALs are also extremely fast.
44. What is LUT?
Answer
LUT - Look-Up Table. An n-bit look-up table can be implemented with a multiplexer whose select lines are the inputs of the LUT and whose inputs are constants. An n-bit LUT can encode any n-input Boolean function by modeling such functions as truth tables. This is an efficient way of encoding Boolean logic functions, and LUTs with 4-6 bits of input are in fact the key component of modern FPGAs.
45. What is the significance of FPGAs in modern day electronics? (Applications
of FPGA.)
Answer
46. What are the differences between CPLD and FPGA.
Answer
47. Compare and contrast FPGA and ASIC digital designing.
Answer
48. Give True or False.
(a) CPLD consumes less power per gate when compared to FPGA.
(b) CPLD has more complexity than FPGA
(c) FPGA design is slower than corresponding ASIC design.
(d) FPGA can be used to verify the design before making a ASIC.
(e) PALs have programmable OR plane.
(f) FPGA designs are cheaper than corresponding ASIC, irrespective of design
complexity.
Answer
(a) False
(b) False
(c) True
(d) True
(e) False
(f) False
49. Arrange the following in the increasing order of their complexity: FPGA,PLA,CPLD,PAL.
Answer
Increasing order of complexity: PLA, PAL, CPLD, FPGA.
50. Give the FPGA digital design cycle.
Answer
51. What is DeMorgan's theorem?
Answer
For N variables, DeMorgan’s theorems are expressed in the following formulas:
(ABC..N)' = A' + B' + C' + ... + N' -- The complement of the product is equivalent to the sum of the complements.
(A + B + C + ... + N)' = A'B'C'...N' -- The complement of the sum is equivalent to the product of the complements.
This relationship so induced is called DeMorgan's duality.
52. F'(A, B, C, D) = C'D + ABC' + ABCD + D. Express F in Product of Sum form.
Answer
Complementing both sides and applying DeMorgan's Theorem:
F(A, B, C, D) = (C + D')(A' + B' + C)(A' + B' + C' + D')(D')
53. How many squares/cells will be present in the k-map of F(A, B, C)?
Answer
F(A, B, C) has three variables/inputs.
Therefore, number of squares/cells in k-map of F = 2(Number of variables) = 23 = 8.
54. Simplify F(A, B, C, D) = S ( 0, 1, 4, 5, 7, 8, 9, 12, 13)
Answer
The four variable k-map of the given expression is:
The grouping is also shown in the diagram. Hence we get,
F(A, B, C, D) = C' + A'BD
55. Simplify F(A, B, C) = S (0, 2, 4, 5, 6) into Product of Sums.
Answer
The three variable k-map of the given expression is:
The 0's are grouped to get the F'.
F' = A'C + BC
Complementing both sides and using DeMorgan's theorem we get F,
F = (A + C')(B' + C')
56. The simplified expression obtained by using k-map method is unique. True or False. Explain your answer.
Answer
False. The simplest form obtained is not necessarily unique as grouping can be made in different ways.
57. Give the characteristic tables of RS, JK, D and T flip-flops.
Answer
RS flip-flop.
JK flip-flop
D flip-flop
T flip-flop
58. Give excitation tables of RS, JK, D and T flip-flops.
Answer
RS flip-flop.
JK flip-flop
D flip-flop
T flip-flop
59. Design a BCD counter with JK flip-flops
Answer
60. Design a counter with the following binary sequence 0, 1, 9, 3, 2, 8, 4 and repeat. Use T flip-flops.
Answer
Answer
2. Implement an 2-input AND gate using a 2x1 mux.
Answer
3. What is a multiplexer?
Answer
A multiplexer is a combinational circuit which selects one of many input signals and directs to the only output.
4. What is a ring counter?
Answer
A ring counter is a type of counter composed of a circular shift register. The output of the last shift register is fed to the input of the first register. For example, in a 4-register counter, with initial register values of 1100, the repeating pattern is: 1100, 0110, 0011, 1001, 1100, so on.
5. Compare and Contrast Synchronous and Asynchronous reset.
Answer
Synchronous reset logic will synthesize to smaller flip-flops, particularly if the reset is gated with the logic generating the d-input. But in such a case, the combinational logic gate count grows, so the overall gate count savings may not be that significant. The clock works as a filter for small reset glitches; however, if these glitches occur near the active clock edge, the Flip-flop could go metastable. In some designs, the reset must be generated by a set of internal conditions. A synchronous reset is recommended for these types of designs because it will filter the logic equation glitches between clock.
Problem with synchronous resets is that the synthesis tool cannot easily distinguish the reset signal from any other data signal. Synchronous resets may need a pulse stretcher to guarantee a reset pulse width wide enough to ensure reset is present during an active edge of the clock, if you have a gated clock to save power, the clock may be disabled coincident with the assertion of reset. Only an asynchronous reset will work in this situation, as the reset might be removed prior to the resumption of the clock. Designs that are pushing the limit for data path timing, can not afford to have added gates and additional net delays in the data path due to logic inserted to handle synchronous resets.
Asynchronous reset: The major problem with asynchronous resets is the reset release, also called reset removal. Using an asynchronous reset, the designer is guaranteed not to have the reset added to the data path. Another advantage favoring asynchronous resets is that the circuit can be reset with or without a clock present. Ensure that the release of the reset can occur within one clock period else if the release of the reset occurred on or near a clock edge then flip-flops may go into metastable state.
6. What is a Johnson counter?
Answer
Johnson counter connects the complement of the output of the last shift register to its input and circulates a stream of ones followed by zeros around the ring. For example, in a 4-register counter, the repeating pattern is: 0000, 1000, 1100, 1110, 1111, 0111, 0011, 0001, so on.
7. An assembly line has 3 fail safe sensors and one emergency shutdown switch.The line should keep moving unless any of the following conditions arise:
(1) If the emergency switch is pressed
(2) If the senor1 and sensor2 are activated at the same time.
(3) If sensor 2 and sensor3 are activated at the same time.
(4) If all the sensors are activated at the same time
Suppose a combinational circuit for above case is to be implemented only with NAND Gates. How many minimum number of 2 input NAND gates are required?
Answer
Solve it out!
8. In a 4-bit Johnson counter How many unused states are present?
Answer
4-bit Johnson counter: 0000, 1000, 1100, 1110, 1111, 0111, 0011, 0001, 0000.
8 unused states are present.
9. Design a 3 input NAND gate using minimum number of 2 input NAND gates.
Answer
10. How can you convert a JK flip-flop to a D flip-flop?
Answer
Connect the inverted J input to K input.
11. What are the differences between a flip-flop and a latch?
Answer
Flip-flops are edge-sensitive devices where as latches are level sensitive devices.
Flip-flops are immune to glitches where are latches are sensitive to glitches.
Latches require less number of gates (and hence less power) than flip-flops.
Latches are faster than flip-flops.
12. What is the difference between Mealy and Moore FSM?
Answer
Mealy FSM uses only input actions, i.e. output depends on input and state. The use of a Mealy FSM leads often to a reduction of the number of states.
Moore FSM uses only entry actions, i.e. output depends only on the state. The advantage of the Moore model is a simplification of the behavior.
13. What are various types of state encoding techniques? Explain them.
Answer
One-Hot encoding: Each state is represented by a bit flip-flop). If there are four states then it requires four bits (four flip-flops) to represent the current state. The valid state values are 1000, 0100, 0010, and 0001. If the value is 0100, then it means second state is the current state.
One-Cold encoding: Same as one-hot encoding except that '0' is the valid value. If there are four states then it requires four bits (four flip-flops) to represent the current state. The valid state values are 0111, 1011, 1101, and 1110.
Binary encoding: Each state is represented by a binary code. A FSM having '2 power N' states requires only N flip-flops.
Gray encoding: Each state is represented by a Gray code. A FSM having '2 power N' states requires only N flip-flops.
14. Define Clock Skew , Negative Clock Skew, Positive Clock Skew.
Answer
Clock skew is a phenomenon in synchronous circuits in which the clock signal (sent from the clock circuit) arrives at different components at different times. This can be caused by many different things, such as wire-interconnect length, temperature variations, variation in intermediate devices, capacitive coupling, material imperfections, and differences in input capacitance on the clock inputs of devices using the clock.
There are two types of clock skew: negative skew and positive skew. Positive skew occurs when the clock reaches the receiving register later than it reaches the register sending data to the receiving register. Negative skew is the opposite: the receiving register gets the clock earlier than the sending register.
15. Give the transistor level circuit of a CMOS NAND gate.
Answer
16. Design a 4-bit comparator circuit.
Answer
17. Design a Transmission Gate based XOR. Now, how do you convert it to XNOR (without inverting the output)?
Answer
18. Define Metastability.
Answer
If there are setup and hold time violations in any sequential circuit, it enters a state where its output is unpredictable, this state is known as metastable state or quasi stable state, at the end of metastable state, the flip-flop settles down to either logic high or logic low. This whole process is known as metastability.
19. Compare and contrast between 1's complement and 2's complement notation.
Answer
20. Give the transistor level circuit of CMOS, nMOS, pMOS, and TTL inverter gate.
Answer
21. What are set up time and hold time constraints?
Answer
Set up time is the amount of time before the clock edge that the input signal needs to be stable to guarantee it is accepted properly on the clock edge.
Hold time is the amount of time after the clock edge that same input signal has to be held before changing it to make sure it is sensed properly at the clock edge.
Whenever there are setup and hold time violations in any flip-flop, it enters a state where its output is unpredictable, which is known as as metastable state or quasi stable state. At the end of metastable state, the flip-flop settles down to either logic high or logic low. This whole process is known as metastability.
22. Give a circuit to divide frequency of clock cycle by two.
Answer
23. Design a divide-by-3 sequential circuit with 50% duty circle.
Answer
24. Explain different types of adder circuits.
Answer
25. Give two ways of converting a two input NAND gate to an inverter.
Answer
26. Draw a Transmission Gate-based D-Latch.
Answer
27. Design a FSM which detects the sequence 10101 from a serial line without overlapping.
Answer
28. Design a FSM which detects the sequence 10101 from a serial line with overlapping.
Answer
29. Give the design of 8x1 multiplexer using 2x1 multiplexers.
Answer
30. Design a counter which counts from 1 to 10 ( Resets to 1, after 10 ).
Answer
31. Design 2 input AND, OR, and EXOR gates using 2 input NAND gate.
Answer
32. Design a circuit which doubles the frequency of a given input clock signal.
Answer
33. Implement a D-latch using 2x1 multiplexer(s).
Answer
34. Give the excitation table of a JK flip-flop.
Answer
35. Give the Binary, Hexadecimal, BCD, and Excess-3 code for decimal 14.
Answer
14:
Binary: 1110
Hexadecimal: E
BCD: 0001 0100
Excess-3: 10001
36. What is race condition?
Answer
37. Give 1's and 2's complement of 19.
Answer
19: 10011
1's complement: 01100
2's complement: 01101
38. Design a 3:6 decoder.
Answer
39. If A*B=C and C*A=B then, what is the Boolean operator * ?
Answer
* is Exclusive-OR.
40. Design a 3 bit Gray Counter.
Answer
41. Expand the following: PLA, PAL, CPLD, FPGA.
Answer
PLA - Programmable Logic Array
PAL - Programmable Array Logic
CPLD - Complex Programmable Logic Device
FPGA - Field-Programmable Gate Array
42. Implement the functions: X = A'BC + ABC + A'B'C' and Y = ABC + AB'C using a PLA.
Answer
43. What are PLA and PAL? Give the differences between them.
Answer
Programmable Logic Array is a programmable device used to implement combinational logic circuits. The PLA has a set of programmable AND planes, which link to a set of programmable OR planes, which can then be conditionally complemented to produce an output.
PAL is programmable array logic, like PLA, it also has a wide, programmable AND plane. Unlike a PLA, the OR plane is fixed, limiting the number of terms that can be ORed together.
Due to fixed OR plane PAL allows extra space, which is used for other basic logic devices, such as multiplexers, exclusive-ORs, and latches. Most importantly, clocked elements, typically flip-flops, could be included in PALs. PALs are also extremely fast.
44. What is LUT?
Answer
LUT - Look-Up Table. An n-bit look-up table can be implemented with a multiplexer whose select lines are the inputs of the LUT and whose inputs are constants. An n-bit LUT can encode any n-input Boolean function by modeling such functions as truth tables. This is an efficient way of encoding Boolean logic functions, and LUTs with 4-6 bits of input are in fact the key component of modern FPGAs.
45. What is the significance of FPGAs in modern day electronics? (Applications
of FPGA.)
Answer
- ASIC prototyping: Due to high cost of ASIC chips, the logic of the application is first verified by dumping HDL code in a FPGA. This helps for faster and cheaper testing. Once the logic is verified then they are made into ASICs.
- Very useful in applications that can make use of the massive parallelism offered by their architecture. Example: code breaking, in particular brute-force attack, of cryptographic algorithms.
- FPGAs are sued for computational kernels such as FFT or Convolution instead of a microprocessor.
- Applications include digital signal processing, software-defined radio, aerospace and defense systems, medical imaging, computer vision, speech recognition, cryptography, bio-informatics, computer hardware emulation and a growing range of other areas.
46. What are the differences between CPLD and FPGA.
Answer
47. Compare and contrast FPGA and ASIC digital designing.
Answer
48. Give True or False.
(a) CPLD consumes less power per gate when compared to FPGA.
(b) CPLD has more complexity than FPGA
(c) FPGA design is slower than corresponding ASIC design.
(d) FPGA can be used to verify the design before making a ASIC.
(e) PALs have programmable OR plane.
(f) FPGA designs are cheaper than corresponding ASIC, irrespective of design
complexity.
Answer
(a) False
(b) False
(c) True
(d) True
(e) False
(f) False
49. Arrange the following in the increasing order of their complexity: FPGA,PLA,CPLD,PAL.
Answer
Increasing order of complexity: PLA, PAL, CPLD, FPGA.
50. Give the FPGA digital design cycle.
Answer
51. What is DeMorgan's theorem?
Answer
For N variables, DeMorgan’s theorems are expressed in the following formulas:
(ABC..N)' = A' + B' + C' + ... + N' -- The complement of the product is equivalent to the sum of the complements.
(A + B + C + ... + N)' = A'B'C'...N' -- The complement of the sum is equivalent to the product of the complements.
This relationship so induced is called DeMorgan's duality.
52. F'(A, B, C, D) = C'D + ABC' + ABCD + D. Express F in Product of Sum form.
Answer
Complementing both sides and applying DeMorgan's Theorem:
F(A, B, C, D) = (C + D')(A' + B' + C)(A' + B' + C' + D')(D')
53. How many squares/cells will be present in the k-map of F(A, B, C)?
Answer
F(A, B, C) has three variables/inputs.
Therefore, number of squares/cells in k-map of F = 2(Number of variables) = 23 = 8.
54. Simplify F(A, B, C, D) = S ( 0, 1, 4, 5, 7, 8, 9, 12, 13)
Answer
The four variable k-map of the given expression is:
The grouping is also shown in the diagram. Hence we get,
F(A, B, C, D) = C' + A'BD
55. Simplify F(A, B, C) = S (0, 2, 4, 5, 6) into Product of Sums.
Answer
The three variable k-map of the given expression is:
The 0's are grouped to get the F'.
F' = A'C + BC
Complementing both sides and using DeMorgan's theorem we get F,
F = (A + C')(B' + C')
56. The simplified expression obtained by using k-map method is unique. True or False. Explain your answer.
Answer
False. The simplest form obtained is not necessarily unique as grouping can be made in different ways.
57. Give the characteristic tables of RS, JK, D and T flip-flops.
Answer
RS flip-flop.
| S | R | Q(t+1) |
| 0 | 0 | Q(t) |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | ? |
JK flip-flop
| J | K | Q(t+1) |
| 0 | 0 | Q(t) |
| 0 | 1 | 0 |
| 1 | 0 | 1 |
| 1 | 1 | Q'(t) |
D flip-flop
| D | Q(t+1) |
| 0 | 0 |
| 1 | 1 |
T flip-flop
| T | Q(t+1) |
| 0 | Q(t) |
| 1 | Q'(t) |
58. Give excitation tables of RS, JK, D and T flip-flops.
Answer
RS flip-flop.
| Q(t) | Q(t+1) | S | R |
| 0 | 0 | 0 | X |
| 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 |
| 1 | 1 | X | 0 |
JK flip-flop
| Q(t) | Q(t+1) | J | K |
| 0 | 0 | 0 | X |
| 0 | 1 | 1 | X |
| 1 | 0 | X | 1 |
| 1 | 1 | X | 0 |
D flip-flop
| Q(t) | Q(t+1) | D |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
T flip-flop
| Q(t) | Q(t+1) | T |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
59. Design a BCD counter with JK flip-flops
Answer
60. Design a counter with the following binary sequence 0, 1, 9, 3, 2, 8, 4 and repeat. Use T flip-flops.
Answer
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