Amplifier Interview Questions & Answers

Question 1. Explain What Is An Operational Amplifier?

Answer :

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.

Question 2. State Assumptions Made For Analyzing Ideal Op-amp?

Answer :

Assumptions made for analyzing ideal op-amp are:

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

Question 3. Explain What Are Differential Gain And Common-mode Gain Of A Differential Amplifier?

Answer :

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.

Question 4. Define Cmrr?

Answer :

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

Question 5. Explain Why Does An Op-amp Have High Cmrr?

Answer :

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.

Question 6. Explain Why Open-loop Op-amp Configurations Are Not Used In Linear Applications?

Answer :

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.

Question 7. List The Parameters That Should Be Considered For Ac And Dc Applications?

Answer :

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

Question 8. Define Offset Voltage As Applied To An Op-amp?

Answer :

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

Question 9. Define Slew Rate?

Answer :

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.

Question 10. Explain What Is A Voltage Follower?

Answer :

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

Question 11. Explain What Are The Advantages Of Using A Voltage Follower Amplifier?

Answer :

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.

Question 12. In Explain What Way Is The Voltage Follower A Special Case Of The Non-inverting Amplifier?

Answer :

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

Question 13. Explain What Is An Inverting Amplifier?

Answer :

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

Question 14. Explain What Are The Applications Of An Inverting Amplifier?

Answer :

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, and differentiator.

Question 15. Explain What Is A Differential Amplifier?

Answer :

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

Question 16. Give Examples Of Linear Circuits?

Answer :

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

Question 17. Explain What Is An Adder Or Summing Amplifier?

Answer :

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.

Question 18. Explain What Is An Integrator?

Answer :

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

Question 19. Explain What Are The Applications Of Integrator?

Answer :

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

Question 20. Op-amp Is Used Mostly As An Integrator Than A Differentiation. Explain Why?

Answer :

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.

Question 21. What Is Characteristic Of Ideal Op Amp?

Answer :

Characteristic of ideal OP AMP are

1. Infinite voltage gain
2. Zero output impedance
3. Infinite input impedance
4. Infinite slew rate
5. Characteristics not drifting with temperature
6. Infinite bandwidth

Question 22. What Is Amplifier?

Answer :

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

Question 23. What Is The Formula For Non Inverting Amplifier?

Answer :

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

Question 24. What Is Perfect Balance In Op Amp?

Answer :

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

Question 25. Which Opamp Don’t Have Feedback Loop?

Answer :

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

Question 26. Why Opamp Called Direct Coupled High Differential Circuit?

Answer :

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.

Question 27. Why Opamp Called Operational Amplifier?

Answer :

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.

Question 28. What Is The Output Differentiation And Integrator?

Answer :

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.

Question 29. For The Cmrr To Be Infinite What Will Be The Condition?

Answer :

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.

Question 30. Explain What Is Meant By Small Signal Amplifier?

Answer :

When the input signal is quite weak and produces less small fluctuations in the output current in comparison to its quiescent value, the amplifier is called the small signal or voltage amplifier.

Question 31. Explain What Is Meant By Phase Reversal?

Answer :

In a CE configuration, the output voltage increases in the negative direction when the input signal voltage increases in the positive direction and vice-versa. This is called the phase reversal and and causes a phase difference of 180o between the input signal and output voltage.

Question 32. Explain What Is An Ac Emitter Resistance?

Answer :

The dynamic resistance of the emitter-base junction diode is called the ac emitter resistance.

Question 33. Explain What Do You Mean By Operating Point?

Answer :

The zero signal values of IC and VCE are known as the operating point. It is called operating point because the variations of IC and VCE take place about this point when signal is applied. It is also known as the quiescent or Q-point.

Question 34. Explain What Is Transistor Biasing?

Answer :

The proper flow of zero signal collector current and the maintenance of proper collector emitter voltage during the passage of signal is called the transistor biasing.

Question 35. Explain What Is Faithful Amplification?

Answer :

The process of raising the strength of a weak signal without any change in its general shape is referred to as faithful amplification.

Question 36. Explain What Is The Effect Of Removal Of Bypass Capacitor In A Ce Amplifier Circuit?

Answer :

Removal of bypass capacitor in a CE amplifier circuit causes excessive degeneration in the amplifier circuit and therefore reduction in voltage gain.

Question 37. Explain Why Common-collector Circuit Is Known As An Emitter Follower?

Answer :

The CC circuit amplifier is called an emitter follower because in this circuit the output voltage at the emitter terminal follows the input signal applied to the base terminal.

Question 38. Explain What Are The Main Purposes For Which A Common-collector Amplifier May Be Used?

Answer :

For a common collector amplifier, current gain is as high as for CE amplifier, voltage gain is less than unity, input resistance is the highest and the output resistance is the lowest of all the three (CE, ,CC and CB) configurations. This circuit finds wide applications as a buffer amplifier between a high impedance source and a low load.