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Important Questions and Answers: Linear Integrated Circuits : Applications of Operational Amplifier

Linear Integrated Circuits (LIC) Subject : Applications of Operational Amplifier - Important Questions and Answers, Book Bank Questions

APPLICATIONS OF OPERATIONAL AMPLIFIERS

PART-A

1. Mention some of the linear applications of op – amps.

Adder, subtractor, voltage –to- current converter, current –to- voltage converters, instrumentation amplifier, analog computation, power amplifier, etc are some of the linear op amp circuits.

2. Mention some of the non – linear applications of op-amps

Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti–log amplifier, multiplier are some of the non – linear op-amp circuits.

3. What are the areas of application of non-linear op- amp circuits?

1. Industrial instrumentation

2. Communication

3. Signal processing

4. What is voltage follower?

A circuit in which output follows the input is called voltage follower.

5. What is the need for an instrumentation amplifier?

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

6. List the features of instrumentation amplifier:

1. High gain accuracy

2. High CMRR

3. High gain stability with low temperature co-efficient

4 Low dc offset

5. Low output impedance

7. What are the applications of V-I converter?

1. Low voltage dc and ac voltmeter

2. LED

3. Zener diode tester

8. Define Band pass filter.

The band pass filter is the combination of high and low pass filters, and this allows a specified range of frequencies to pass through.

9. Write transfer function of op amp as an integer.

The transfer function of the integer is IAI=1/WR1cf

10. What do you mean by a precision rectifier?

The major limitation of ordinary diode is that it cannot rectify voltages below the cut – in voltage of the diode. A circuit designed by placing a diode in the feedback loop of an op – amp is called the precision diode and it is capable of rectifying input signals of the order of millivolt.

11. Write down the applications of precision diode.

1. Half - wave rectifier

2. Full - Wave rectifier

3. Peak – value detector

4. Clipper

5. Clamper

12. Define Logarithmic and antilogarithmic amplifier.

When a logarithmic PN junction is used in the feedback network of op-amp, the circuit exhibits log or antilog response. The logarithmic amplifier is a current to voltage converter with the transfer characteristics v0=vi In(If/Ii) Antilog amplifier is a decoding circuit which converts the logarithmically encoded signal back to the original signal levels as given by vl=vR10-kvi

13. Differentiate Schmitt trigger and comparator.

Comparator.

1.It compares the input signal with references voltage then yields the output voltage . comparator output need not to be square wave

2. It need not consist of feedback

Schmitt trigger

1. It operates between two reference points namely UTP&LTP.

2. It employs positive feedback

3. Its output is square wave.

14. List the applications of Log amplifiers:

1. Analog computation may require functions such as lnx, log x, sin hx etc. These functions can be performed by log amplifiers

2. Log amplifier can perform direct dB display on digital voltmeter and spectrum analyzer

3. Log amplifier can be used to compress the dynamic range of a signal

4. Comparator output need not to be square wave

15. Write down the condition for good differentiation.

1.For good differentiation, the time period of the input signal must be greater than or equal to Rf C1

2. T> =R f C1 Where, R f is the feedback resistance

3. C f is the input capacitance

16. What is a comparator?

A comparator is a circuit which compares a signal voltage applied at one input of an op amp with a known reference voltage at the other input. It is an open loop op - amp with output +Vsat.

17. What are the applications of comparator?

1. Zero crossing detectors

2. Window detector

3. Time marker generator

4. Phase detector

18. What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square wave output. The output of Schmitt trigger swings between upper and lower threshold voltages, which are the reference voltages of the input waveform.

19. What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square wave output. The output of Schmitt trigger swings between upper and lower threshold voltages,

20. Which are the reference voltages of the input waveform?

i. RC phase shift oscillator

ii. Wein bridge oscillator

21. What are the characteristics of a comparator?

1. Speed of operation

2. Accuracy

3. Compatibility of the output

22. What is a filter?

Filter is a frequency selective circuit that passes signal of specified band of frequencies and attenuates the signals of frequencies outside the band

23. What are the demerits of passive filters?

Passive filters works well for high frequencies. But at audio frequencies, the inductors become problematic, as they become large, heavy and expensive. For low frequency applications, more number of turns of wire must be used which in turn adds to the series resistance degrading inductor’s performance ie, low Q, resulting in high power dissipation.

24. What are the advantages of active filters?

Active filters used op- amp as the active element and resistors and capacitors as passive elements.

25. Give the schematic of op-amp based current to voltage converter.

26. Draw the circuit diagram of differentiator and give its output equation

27. Compare the performance of inverting and non-inverting operational amplifier configurations.

Inverting Amplifier:

Gain = -Rf / Ri

Input resistance = Ri

Non Inverting Amplifier:

Gain = 1+Rf / Ri Input resistance = Very large (∞)

28. Why is frequency compensation required in operational amplifier?

To improve Stability of the circuit.

29. How do the precision rectifiers differ from the conventional rectifier

To rectify voltage below the cut in voltage (0.7V) of a diode.

30. What are the important features of an instrumentation amplifier

High gain accuracy, High CMRR, Low DC offset & low output impedance.

31. What is comparator?

It is a circuit which compares a signal voltage applied at one input of an op-amp with a known reference at other input.

32. Give an application of an Inverting Amplifier.

Scale changer, inverting summer.

33. Draw and write equation of an integrator using an op-amp.

34. Give one application of voltage follower, Schmitt Trigger, Clamper and Peak Detector.

Schmitt Trigger – Squarer circuit

Peak Detector – AM communication

35. Define Bandwidth of a filter?

Bandwidth is the difference between the upper and lower cutoff frequencies.

36. What is Hysteresis and mention the purpose of hysteresis in a comparator.

The difference between upper and lower threshold voltages in a comparator is called hysteresis. The voltage span of hysteresis is set to be greater than the peak to peak noise voltage. Therefore there will not be any incorrect variations due to noise signals.

37. Determine the output voltage for the circuit shown in figure 1 when

a.Vin=-2V and

b.Vin=3V

Given V cc=+-10V e+=1.5 e - =Vin

38. Design and sketch an operational amplifier subtractor circuit.

39. What is the difference between basic comparator and Schmitt trigger?

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. ... In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high.

40. Draw the circuit diagram of a comparator. Mention its applications.

Applications of Comparator:

Threshold Detector, Zero Crossing Detector and Schmitt Trigger

41. Mention some of the linear applications of op – amps.

Adder, subtractor, voltage –to- current converter, current –to- voltage converters, instrumentation amplifier, analog computation ,power amplifier, etc are some of the lin ar op-amp circuits.

42. Mention some of the non – linear applications of op-amps.

Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti –log amplifier, multiplier are some of the non – linear op-amp circuits.

43. Define virtual ground property of Op-amp.

Concept of virtual ground says that the two input terminals of the Op-amp are always at the same potential. Thus if one terminal is grounded the other can be assumed to be at ground potential, which is called virtual ground.

44. What is Voltage follower?

• A circuit in which the output voltage follows th input voltage is called voltage follower Circuit.

• In Op-amp if the inverting input and the output terminals are shorted and if any signal is Applied at the non-inverting terminal, it appears at the output without any change.

• It is also called as source follower, unity gain amplifier, buffer amplifier or isolation amplifier.

45. Calculate the output voltage V0 of the circuit shown in fig. 1

46. Draw the circuit diagram of voltage follower using IC 741.

47. For the op-amp shown, determine the voltage gain.

48. List the features of instrumentation amplifier.

·           High gain accuracy

·           High CMRR

·           High gain stability with low temperature co-efficient

·           Low dc offset

·           Low output impedance

49. What are the applications of V-I converter?

·           Low voltage dc and ac voltmeter

·           LED

·           Zener diode tester

50. 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. A circuit designed by placing a diode in the feedback loop of an op – amp is called the precision diode and it is capable of rectifying input signals of the order of milli volt.

51.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 , thereby making the circuit sensitive to high frequency noise.

52. Write down the condition for good differentiation.

For good differentiation, the time period of the input signal must be greater than or equal to RfC1

T > RfC1 Where, Rf is the feedback resistance Cf is the input capacitance

53. What are the applications of comparator?

·           Zero crossing detector

·           Window detector

·           Time marker generator

·           Phase detector

54. What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square wave output. The output of Schmitt trigger swings between upper and lower threshold voltages, which are the reference voltages of the input waveform.

55. Differentiate Schmtt trigger and comparator

56. Define logarithmic and antilogarithmic amplifier.

The Op-amp circuit in which the output is proportional to the logarithmic of the input is called logarithmic amplifier. It employs a diode or a transistor in the gative feedback path.

The Op-amp circuit in which the output is proportional to the antiloga ithmic of the input is called logarithmic amplifier. It employs a diode or a transistor in the input stage.

57. List the applications of Log amplifiers.

·           Analog computation may require functions such as ln x, log x, sin h x etc.

·           These functions can be performed by log amplifiers

·           Log amplifier can perform direct dB display on digital voltmeter and spectrum analyzer

·           Log amplifier can be used to compress the dynamic range of a signal

58. What is a filter?

Filter is a frequency selective circuit that passes signal of specified band of frequencies and attenuates the signals of frequencies outside the band.

59. What are the advantages of active filters?

·           Active filters used op- amp as the active element and resistors and capacitors as passive elements.

·           By enclosing a capacitor in the feedback loop , inductor less active filters can be obtained

·           Op-amp used in non – inverting configuration offers high input impedance and low output impedance, thus improving the load drive capacity.

60.What are the requirements for producing sustained oscillations in feedback circuits?

For sustained oscillations,

·           The total phase shift around the loop must be zero at the desired frequency of oscillation, fo. ie, AB =0 (or) 360°

·           At fo, the magnitude of the loop gain | A β | should be equal to unity

PART-B

1. Design a fourth order Butterworth LPF having a upper cutoff frequency of 1KHz.

2. Design a square wave oscillator for f0 = 1 KHz using 741 op-amp and a DC supply  voltage of +/-12V.

3. a) Discuss the working of instrumentation amplifier . Name two applications of the same.

4. Discuss in detail the working of a RC phase shift oscillator.

5. Design Wien Bridge oscillator of 1 KHz frequency.

6. Design an op – amp Schmitt trigger with VUT= 2V, VLT= -4V & the output swings b/w +10V. If the i /p is 5 sin wt, plot i/p & o/p waveforms.

7. a) Compare the RC phase shift and Wien bridge oscillator.

b) Design a RC phase shift oscillator and a Wien bridge oscillator of frequency 1 KHz. (Assume C= 0.01 μF).

8. With diagram explain the operation of inverting and non-inverting amplifier.

9. Draw the circuit diagram of a second order Butterworth active LPF and derive its transfer function.

10. Draw an instrumentation amplifier whose gain is controlled by adjustable gain and explain its Working concept.

11. Explain the circuit operation of logarithmic amplifier with two op-amps.

12. With neat circuit, explain the operation of Schmitt trigger.

13. Explain about positive and negative clipper.

14. Explain about zero crossing detector and peak detector.

15. With the help of circuits and necessary equations, explain how log and antilog computations are performed using IC741.

16. Explain the operation of the following op-amp applications.

a. Scale Changer

b. Voltage follower

d. Integrator

17. (i) Design a first order Low-pass filter for cut-off frequency of 2 KHz and pass-band gain of 2.

(ii) Explain a positive clipper circuit using an Op-amp and a diode with neat diagrams .

18. (i) Design a circuit to implement V0=0.545V3+ 0.273V4−1.25 V1−2V2.

(ii) Draw and explain a simple Op-amp differentiator. Mention its limitations. Explain with a neat diagram how it can be overcome in a practical differentiator. Design an Op-amp differentiator that will differentiate an input signal with maximum frequency f max =100Hz.

19. With relevant circuits, explain the following applications of OPAMP.

(i) Voltage to current converters

(ii) Multiplier

20. (i) Explain the steps involved in the design of a band pass filter using OPAMP. (ii) Write a note on Schmitt trigger.

21 (i).Sketch the basic circuit using op amp to perform the mathematical operation of differentiation and explain? What are the limitations of an ordinary op-amp differentiator? Draw and explain the operation of a practical differentiator that will eliminate the limitations.

(ii) Draw and explain the circuit of a voltage to current convertor if the load is

(1) Floating (2) Grounded

22. (i) Explain the working of OP-AMP based Schmitt trigger circuit.

(ii)Design OP-AMP based second order active low pass filter with cut off frequency 2 kHz.

23. a) i) What do you understand by an Instrumentation Amplifier?

ii) State the requirements of a good Instrumentation Amplifier.

iii) Draw the circuit diagram and explain the working of Instrumentation Amplifier.

iv) Mention the specific advantages of three op-amp Instrumentation Amplifier circuit.

24. i) What do you understand by an Integrator?

ii) Draw and explain an ideal active op-amp Integrator circuit.

iii) Draw the I/O waveforms for integrator

1) Step input signal.

2) Square wave input signal

3) Sine wave input signal.

Derive the expression for change in output voltage.

iv) List the applications of practical Integrator.

v) Design a practical integrator circuit with a dc gain of 10, to integrate a square wave of 10 KHz.

25. Explain the working of i) Instrumentation Amplifier ii) Schmitt Trigger , ,

26. Explain the working of i) Precision Full wave rectifier ii) Integrator ,

27. With the neat diagram explain logarithmic amplifier and Antilogarithmic Amplifier

28. With neat diagram explain the application of op amp as precision rectifier, Clipper, and Clamper.

29. Explain in detail about V –I and I-V convertor.

30. Design a wide band pass filter with fL= 400Hz, fH= 2 kHz and a pass band gain of4.Find the value Q of the filter.

31. Determine the rate of change of the output voltage in response to the first input pulse as shown below for the integrator. The output voltage is initially zero. Also describe the output after the first pulse. Draw the output waveform.

32. Explain in detail about the V to I and I to V converters.

33. With a neat circuit diagram, explain the working of the precision rectifier.

34. Explain the application of operational amplifier as differentiator.

35. Mention two advantages of active filter over passive filter. Also design a second order low pass filter using operational amplifier for the upper cut off frequency of 2 kHz. Assume the value of capacitor to be 0.1μF.

36. With a neat circuit diagram explain the working of voltage to current converter.

37. Explain the working of an op-amp differentiator and derive its output equation.

38. What is the need for V to I and I to V converter? How are they realized using op-amp?

39. What is the purpose of a precision rectifier? How are they realized using op-amp? Explain

40. Draw the regenerator comparison circuit and obtain expression for UTP and LTP

41. Draw the circuit diagram of an instrumentation amplifier and explain its operation. List few applications.

42. How an op-amp can be used as an Log amplifier

43. Design a second order high pass Butterworth filter having cut off frequency of 5Khz.

44. What is a precision rectifier? With circuit schematic explain the working principle of full wave rectifier.

45. Using IC741,design a capacitor coupled non inverting amplifier circuit to operate with a 24v supply. The voltage gain is 100,output amplitude is 6V and lower cut –off frequency is to be 100 Hz to drive a minimum load resistance of 5.6kΩ.

46. For the instrumentation amplifier using two ideal opamp shown in Fig.1 verify the equation

Vo = (1 + R2/R1 + 2R2/R3 ) (V2-V1)

47. Prove that the voltage gain and input resistance with feedback of an inverting amplifier is given by Avf = ( - Arf) / (R1(1+A)+ Rf) and Rif = (R1+ Rf/(1+A)) ║Ri

48. Design an adder circuit using an opamp to get the output expression as Vo= - (0.1 V1+V2+10V3).

49. Design an opamp differentiator that will differentiate an input signal with Fmax=100 Hz.

Draw the output waveform for a sinewave of 1V peak at 100 Hz applied to the differentiator.

50. Consider the lossy integrator.For component values R1=10K, Rf= 100K, Cf=10nF, Determine the lower limit of integration.

51. Design a second order butterworth Low pass filter having upper cut off frequency 1 KHz.

52. Find the output voltage vo of the given circuit when input Vi=10mV,Vi=100 mv and Vi=1V.

53. Design a circuit to implement Vo =0.545V3+0.273V4- 1.25  V1- 2V2.

54. Calculate Vo of the output current in given circuit if E1 equals i)+5V ii) – 2V. For each situation, state if the opamp sources or sinks.

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