**OP-AMP Interview Questions :-**

**1. What is an operational amplifier?**

An operational amplifier, abbreviated as op-amp, is basically a multi-stage, very high gain, direct-coupled, negative feedback amplifier that uses voltage shunt feedback to provide a stabilized voltage gain.

**2. State assumptions made for analyzing ideal op-amp.**

Assumptions made for analyzing ideal op-amp are :

- Infinite open-loop gain
- Infinite input impedance
- Zero output impedance
- Perfect balance
- Infinite frqeuency bandwidth
- Infinite slew rate
- Infinite common-mode rejection ratio
- Nil drift of characteristics with temperature

**3. Explain what is a voltage transfer curve of an op-amp?**

The curve drawn between output voltage and input differential voltage, for an op-amp, keeping voltage gain A constant is known as voltage transfer curve.

**4. What are differential gain and common-mode gain of a differential amplifier?**

When the difference of the two inputs applied to the two terminals of a differential amplifier is amplified, the resultant gain is termed as differential gain. But when the two input terminals are connected to the same input source then the gain established by the differential amplifier is called the common mode gain.

**5. Define CMRR.**

CMRR is defined as the ration of differential voltage gain to common-mode voltage gain and it is given as CMRR = Ad/Acm

**6. Why does an op-amp have high CMRR?**

High CMRR ensures that the common mode signals such as noise are rejected successfully and the output voltage is proportional only to the differential input voltage.

**7. Why open-loop op-amp configurations are not used in linear applications?**

When an op-amp is operated in the open-loop configuration, the output either goes to positive saturation or negative saturation levels or switches between positive and negative saturation levels and thus clips the output above these levels. So open-loop op-amp configurations are not used in linear applications.

**8. List the parameters that should be considered for ac and dc applications.**

The parameters to be considered for dc applications are:

- Input offset voltage
- Input offset current
- Input bias current
- Drift

The parameters to be considered for ac applications are:

- Gain bandwidth product (GBW)
- Rise time
- Slew rate
- Full-power response
- AC noise

**9. Define offset voltage as applied to an op-amp.**

Input offset voltage may be defined as that voltage which is to be applied between the input terminals to balance the amplifier.

**10. Give the typical value of bias current for CA741 operational amplifier.**

80nA

**11. Define slew rate.**

Slew rate of an op-amp is defined as the maximum rate of change of output voltage per unit time and is expresses in V/µs.

**12. Explain what kind of negative feedback is present in a noninverting op-amp.**

Negative voltage-series feedback.

**13. Explain what is a voltage follower?**

Voltage follower is an electronic circuit in which output voltage tracts the input voltage both in sign and magnitude.

**14. What are the advantages of using a voltage follower amplifier?**

Voltage follower has three unique characteristics viz. extremely high input impedance, extremely low output impedance and unity transmission gain and is , therefore, an ideal circuit device for use as a buffer amplifier.

**15. In Explain what way is the voltage follower a special case of the non-inverting amplifier?**

If feedback resistor is made zero or R1 is made ∞(by keeping it open-circuited) in a noninverting amplifier circuit, voltage follower is obtained.

*OPERATIONAL AMPLIFIERS Questions and Answers*

**16. What is an inverting amplifier?**

In an inverting amplifier, the input is connected to the minus or inverting terminal of op-amp.

**17. What are the applications of an inverting amplifier?**

Inverting amplifier is a very versatile component and can be used for performing number of mathematical stimulation such as analog inverter, paraphrase amplifier, phase shifter, adder, integrator, differentiator.

**18. What is a differential amplifier?**

Differential amplifier is a combination of inverting and noninverting amplifiers and amplifies the voltage difference between input lines neither of which is grounded.

**19. Give examples of linear circuits.**

Adder, subtractor, differentiator, integrator fall under the category of linear circuits.

**20. Explain what is an adder or summing amplifier?**

Adder or summing amplifier is a circuit that provides an output voltage proportional to or equal to the algebraic sum of two or more input voltages multiplied by a constant gain factor.

**21. What is an integrator?**

An integrator is a circuit that performs a mathematical operation called integration.

**22. What are the applications of integrators?**

Integrators are widely used in ramp or sweep generators, filters, analog computers etc.

**23. Op-amp is used mostly as an integrator than a differentiator. Explain why?**

Op-amp is used mostly as an integrator than a differentiator because in differentiator at high frequency, gain is high and so high-frequency noise is also amplified which absolutely abstract the differentiated signal.

**24. What is CMRR?**

CMRR is defined as the ratio of differential voltage gain (Ad) to common mode voltage gain (Acm). The formula for CMRR is given below:

CMRR = Ad/Acm

**25. What is characteristic of Ideal OPAMP? Important Interview questions on OPAMP**

Characteristic of ideal OPAMP are

- Infinite voltage gain
- Zero output impedance
- infinite input impedance
- Infinite slew rate
- Characteristics not drifting with temperature
- Infinite bandwidth

**26. What is Amplifier? Important Interview questions on OPAMP**

Amplifier is a device that makes sound louder and signal level greater.

**27 What is the Formula for Non Inverting Amplifier?**

The formula for non inverting amplifier is given as 1+Rf/R1

**28. What is perfect balance in OPAMP? Important Interview questions on OPAMP**

Perfect balance is the characteristics of ideal OPAMP and if there is same input applied then we will get the output zero. In this condition it is known as perfect balance.

**29. Which OPAMP don’t have feedback loop?**

Comparator OPAMP (operational amplifier) don’t have feedback loop.

**30. Why OPAMP called direct coupled high differential circuit?**

OPAMP is called direct coupled because the input of one OPAMP is inserted into the input of another OPAMP. It is called high gain differential circuit because the difference of the two input is amplified.

**31. Why OPAMP called operational Amplifier? Important Interview questions on OPAMP**

OPAMP it is a direct coupled high gain differential input amplifier. It is called operational amplifier because it is used for performing different functions like differentiation, addition, integration, subtraction. It has infinite voltage gain, infinite slew rate, infinite input impedance, zero output impedance, infinite bandwidth.

**32. What is the output Differentiator and Integrator?**

If we give the sinusoidal input in differentiator we will get the output of differentiator as a square output. If we give the sinusoidal input in integrator we will get the output of integrator as a ramp output.

**33. For the CMRR to be infinite what will be the condition?**

CMRR is defined as the ratio of differential voltage gain (Ad) to common mode voltage gain (Acm). The formula for CMRR is given below:

CMRR = Ad/Acm

If Acm will be zero then only it will be infinite.

**34. An ideal operational amplifier has**

A. infinite output impedance

B. zero input impedance

C. infinite bandwidth

D. All of the above

Answer: C

**35. Another name for a unity gain amplifier is:**

A. difference amplifier

B. comparator

C. single ended

D. voltage follower

Answer: D

**36. The open-loop voltage gain (Aol) of an op-amp is the**

A. external voltage gain the device is capable of

B. internal voltage gain the device is capable of

C. most controlled parameter

D. same as Acl

Answer: B

**37. A series dissipative regulator is an example of a:**

A. linear regulator

B. switching regulator

C. shunt regulator

D. dc-to-dc converter

Answer: A

**38. A noninverting closed-loop op-amp circuit generally has a gain factor:**

A. less than one

B. greater than one

C. of zero

D. equal to one

Answer: B

**39. In order for an output to swing above and below a zero reference, the op-amp circuit requires:**

A. a resistive feedback network

B. zero offset

C. a wide bandwidth

D. a negative and positive supply

Answer: D

**40. Op-amps used as high- and low-pass filter circuits employ which configuration?**

A. noninverting

B. comparator

C. open-loop

D. inverting

Answer: D

**41. If ground is applied to the (+) terminal of an inverting op-amp, the (–) terminal will:**

A. not need an input resistor

B. be virtual ground

C. have high reverse current

D. not invert the signal

Answer: B

**42. An astable multivibrator is also known as a:**

A. one-shot multivibrator

B. free-running multivibrator

C. bistable multivibrator

D. monostable multivibrator

Answer: B

**43. With negative feedback, the returning signal:**

A. aids the input signal

B. is proportional to output current

C. opposes the input signal

D. is proportional to differential voltage gain

Answer: C

**44. What starts a free-running multivibrator?**

A. a trigger

B. an input signal

C. an external circuit

D. nothing

Answer: D

**45. A portion of the output that provides circuit stabilization is considered to be:**

A. negative feedback

B. distortion

C. open-loop

D. positive feedback

Answer: A

**46. The closed-loop voltage gain of an inverting amplifier equals:**

A. the ratio of the input resistance to the feedback resistance

B. the open-loop voltage gain

C. the feedback resistance divided by the input resistance

D. the input resistance

Answer: C

**47. All of the following are basic op-amp input modes of operation EXCEPT**

A. inverting mode

B. common-mode

C. double-ended

D. single-ended

Answer: A

**48. A circuit whose output is proportional to the difference between the input signals is considered to be which type of amplifier?**

A. common-mode

B. darlington

C. differential

D. operational

Answer: C

**49. With negative feedback, the returning signal**

A. is proportional to the output current

B. is proportional to the differential voltage gain

C. opposes the input signal

D. aids the input signal

Answer: C

**50. The ratio between differential gain and common-mode gain is called:**

A. amplitude

B. differential-mode rejection

C. common-mode rejection

D. phase

Answer: C