TOP 45+ LINEAR INTEGRATED CIRCUITS LAB VIVA Questions and Answers

LAB VIVA Questions on LINEAR INTEGRATED CIRCUITS

1. What are the advantages of integrated circuits?
increased package density.
Cost reduction .
Increased system reliability.
Improved functional performance.
Increased operating speeds.
Reduction in power consumption.

2. What are the popular IC packages available?
Metal can package.
Dualinlinepackage.
Ceramic flat package.

3. What is an operational amplifier.
An operational amplifier is a directcoupled high gain amplifier consisting of one or more differential amplifiers, it can be used to perform a variety of mathematical operations.

5. What are the characteristics of an ideal op-amp.
Open loop voltage gain is infinity.
Input impedance is infinity.
Output impedance is zero.
Bandwidth is infinity.
Zero offset.
CMRR Infinite.
Slew rate Infinite.

6. What are the DC,AC Characteristics of OP-Amp?
DC Characteristics: Input Bias Current, Input off set Current, Input offset voltage, Thermal Drift.
AC Characteristics: Slew Rate, Frequency compensation

7. What is input offset voltage?
It is the voltage Imbalance b/w two input terminals of op-amp.

8. Define input offset current.
The difference between the bias currents at the input terminals of the

9. Define CMRR of an opamp?
It is the ratio b/w Differential mode gain and common mode gain
CMRR= Ad/Ac

10. What is the effect of high frequency on its performance?
The openloopgain of op-ampdecreases at higher frequencies due to the presence of parasitic capacitance. The closedloopgain increases at higher frequencies and leads to instability.

11. What is the need for frequency compensation in practical op-amps?
When large bandwidth and lower closed loop gain is desired, to improve the stability.

12. What are the frequency compensation methods?
Dominantpolecompensation
Pole-zerocompensation

13. Define slew rate.
The maximum rate of change of output voltage causedby a step input voltage. An ideal slew rate is infinite. Units- v/µs

14. Can we use IC 741 for high frequency applications?
No, IC741 has a low slew rate.

15. Why slew rate is not infinite in Ideal op-amp?
There is a capacitor withinor outside of an op-ampto prevent oscillation.

16. What are the applications of op-amps?
Linear: Adder, subtracter, voltage to current converter, current to voltage converters, instrumentation amplifier, analog computation, power amplifier, Integrator, differentiator etc.
Non linear: Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti-logamplifier, multiplier

17. What is an instrumentation amplifier and the need for?
In a number of industrial and consumer applications, the measurement of physical quantities is usually done with the help oftransducers. The output of transducer has to be amplified So that it can drive the indicator or display system. This function isperformed by an instrumentation amplifier.

18. What are the features of instrumentation amplifier?
high gain accuracy
high CMRR
high gain stability
low dc offset
low output impedance

19. What are the applications of V-I and I-V converters?
V-I:Low voltage dc and ac voltmeter, L E D Tester, Zener diode tester
I-V: Digital to Analog converter, Light intensity indicator, photo diode detector

20. What do you mean by a precision diode?
The major limitation of ordinary diode is that it cannot rectify voltages below the cut in voltage of the diode the precision diode is capable of rectifying input signals of the orderof millivolt.

21. What are the applications of precision diode.
Half waveRectifier
Full Wave rectifier
Peak value detector
Clipper, Clamper

22. What are the applications of Log amplifier?
Multiplier, divider.

23.What are the limitations of the basic differentiator circuit?
At high frequency, a differentiator may become unstable and break into oscillations, The input impedance decreases with increase in frequency.

24. What are the limitations of the basic Integrator circuit?
At low frequency, a integrator may become unstable and break into oscillations, The input impedance decreases with decrees in frequency.

25. What is a comparator?
Which compares a signal with a known reference voltage . its output is either + Vsat or -Vsat .

26. What are the applications of comparator?
Zero crossing detector

27. Why can’t we use comparator to convert sin wave into square wave?
If noise exist in sinusoidal signal at zero volts unwantedly out put varies b/w + Vsat and -Vsat .

28. What is a Schmitt trigger?
It is a regenerative comparator. It converts sinusoidal input into a square wave output.

29. What is a multivibrator?
It is a regenerative circuit that is used extensively in timing applications. It has two states either stable or quasi-stable depending on the type of multivibrator.

30. What is monostable multivibrator?
Generates a single pulse of specified duration in response to each external trigger signal. It has only one stable state. Its is also called as One-shot generator.

31. What is an astable multivibrator?
It is a free running oscillator having two quasi-stable states. So it is a Square wave generator.

32. What is a bistable multivibrator?
Bistable multivibrator is one that maintains a given output voltage level unless an external trigger is applied .Application of an external trigger signal causes a change of state, and this output level is maintained indefinitely until an second trigger applied . Thus, it requires two external triggers before it returns to its initial state

33. What are the requirements for producing sustained oscillations in feedback circuits?
For sustained oscillations,
The total phase shift around the loop must be zero
the magnitude of the loop gain should be equal to unity

34. What are the different oscillators?
AF oscillators: RC phase shift oscillator, Wein bridge oscillator
RF oscillator: Colpitts oscillator, Hartley oscillator

35. What is a filter?
Filter is a frequency selective circuit that passes signal of specified band of frequencies and attenuates the signals of frequenciesoutside the band

35. What are the demerits of passive filters?
Passive filter max gain is unity and its roll off is less.

36. What are the advantages of active filters?
Offers high input impedance and low output impedance, thus improving theload drive capacity. Pass band gain is more than 1, roll off is more.

37. What are the various filters?
Low pass filter
High pass filter
Band pass filter
Band reject filter.

38. What is the use of All pass filter?
it passes all signals to output but provides phase difference of 0 -90 degrees.

39. What Order of the filter Represents?
Order of the filter represents No. of storage elements with in the system (circuit), as order increases Roll off increases.

40. Define cut off frequency?
The cutoff frequency is defined as the frequency at which the ratio of the (input/output) has a magnitude of 0.707. When this magnitude is changed to decibels –3dB mostly referred to as the 3dB down point.

41. Where PLL is widely used?
Radar synchronization, satellite communication systems, air borne navigational systems, FM communication systems,etc.

42. What are the basic building blocks of PLL?
Phase detector/comparator, Low pass filter, Error amplifier, Voltage controlled oscillator

43. What are the three stages through which PLL operates?
Free running, Capture, Locked/ tracking.

44. Define lock-inrange, capture range, and Pullintime of a PLL
*The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lockin range or trackingrange.
*The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range.
*The total time taken by the PLL to establish lok is called pullintime.It depends on the initial phase and frequency differencebetween the two signals as well as on the overall loop gain and loop filter characteristics.

45. What is a voltage controlled oscillator?
Voltage controlled oscillator is a free running multivibrator operating at a set frequency called the free running frequency.Thisfrequency can be shifted to either side by applying a dc control voltage and the frequency deviation is proportional to the dc controlvoltage.

46. On what parameters does the free running frequency of VCO depend on?
*External timing resistor,RT *External timing capacitor,CT *The dc control voltage Vc.

47. Give the expression for the VCO free running frequency.
fo = 0.25 / Rt Ct

48. Mention some typical applications of PLL:
Frequency multiplication/division
Frequency translation
AM detection
FM demodulation
FSK demodulation.