Top 100 Analog Electronics Interview Questions And Answers

Table of Contents

Que.51 Which is a better amplifier BJT or MOSFET?


  • Both the BJT and MOSFET include unique features and their own advantages and disadvantages. But, we cannot say which is good in BJT & MOSFET as the matter is extremely subjective. But before selecting the BJT or MOSFET, there are several factors that need to consider like the level of power, efficiency, drive voltage, price, speed of switching, etc. Usually, a MOSFET is used in power supplies more efficiently because the working of MOSFET is faster due to metal oxide usage apart from BJT. Here, BJT depends on the combination of electron-hole.
  • MOSFET works with low power once switching at high frequency because it has a quick switching speed so it leads through grid-oxide controlled field-effect but not through the recombination of an electron or hole like BJT. In MOSFET, the circuit like gate control is very simpler
  • There are numerous reasons that stand out:

Fewer Conduction Losses

  • A bipolar junction transistor includes a stable saturation voltage drop like 0.7 V, whereas the MOSFET includes a 0.001-ohm on-resistance that leads to fewer power losses.

High Input Impedance

  • A bipolar junction transistor uses a low base current for operating a larger collector current. And they perform like a current amplifier. The MOSFET is a voltage-controlled device and it doesn’t include gate current almost. The gate works like a value capacitor and it is a significant benefit in the applications of switching & high current because the gain of the power BJTs has medium to low, which needs high base currents to produce high currents.
  • The area occupied by the MOSFET is less as compared with BJT like 1/5th. The BJT operation is not as simple as compared with MOSFET. So FET can be designed very easily and can be used like passive elements instead of amplifiers.

Que.52 How is BJT biased in integrated circuits?


  • BJT is biased in IC amplifiers by using a special circuit known as a current mirror.
  • Current mirror- here two identical transistors have a large beta in which the collector of one transistor is shorted to its base, i.e. VCB = 0 or VCE = VBE therefore Q1 transistor will remain in the active region, and it will never enter saturation.
C:\Users\Admin\Desktop\current mir.png
Current Mirror Circuit


  • For the two transistors, bases are short and emitters are grounded, therefore,


i.e., IB1 = IB2

  • hence, for an equal value of \beta, IC1 = IC2



I_{in}=I_C+2 \left ( \frac{I_C}{\beta} \right)

I_{in}=I_C\left ( 1+ \frac{2}{\beta} \right)

\boxed{I_C=\frac{I_{in}}{\left(1+\frac{2}{\beta} \right)}}

Que.53 What are the applications of current mirror circuits?


Application of current mirror circuits:

  • A current mirror is used as a constant current source to bias the BJT in IC amplifiers.
  • A current mirror is used as an active load in ICs amplifiers to obtain higher voltage gain.

Que.54 What are the different compensation methods to keep the IC stable?

Answer: It is a method of keeping Ic stable by connecting temperature-dependent devices such as diodes, thermistors, and sensors.

Que.55 What is a buffer circuit? How does BJT act as a buffer circuit?


  • Buffer circuit: A circuit that is used for impedance matching between source and load circuits. So that maximum power is transferred from source to load circuit.
  • A common-collector amplifier in BJT is used as a voltage buffer between source and load as it has large input resistance, smaller output resistance, and unity voltage gain.
C:\Users\Admin\Desktop\cc amp.gif
CC Amplifier
  • The common base amplifier in BJT is used as a current buffer between source and load as it has smaller input resistance, large output resistance, and unity current gain.

Que.56 What are the advantages and applications of RC coupled amplifiers?


  • Advantages of RC coupled amplifier:
  1. It has a better frequency response.
  2. DC isolation between amplifier and load.
  • Application: it is used to amplify the audio and video frequency signal.

Que.57 How are BJT amplifiers classified?


  • On the basis of the interconnection of amplifier and load, BJT amplifiers are divided into three types:
  1. RC coupled amplifier:
RC coupled amplifier


  1. Direct-coupled amplifier: voltage gain does not decrease at low frequencies because of large capacitors but voltage gain reduces at high frequencies due to junction capacitances.
  1. Transformer coupled amplifier: voltage gain decreases at low frequencies due to the inductance of primary and secondary windings. A peak appears in frequency response because of leakage capacitances and inductances.
Transformer coupled BJT amplifier ckt. diag

Que.58 Advantage, disadvantage, and application of direct-coupled amplifier.


Advantages of direct-coupled amplifier:

  • It can amplify DC signals also.
  • It is ideal for fabrication on silicon chips as it doe not have large capacitances.
  • All IC amplifiers are direct-coupled amplifiers.

The disadvantage of direct-coupled amplifier:

  • Maximum power cannot be transferred to the load due to impedance mismatch.
  • No DC isolation, which causes disturbance in biasing condition of the amplifier.

Application of direct-coupled amplifier:

  • It is used as a DC amplifier and very low-frequency amplifier as it can amplify frequency signals of 1hz or 2hz.

Que.59 Advantage, disadvantage, and application of transformer-coupled amplifier.


Advantages of transformer-coupled amplifier:

  • Maximum power can be transferred to the load due to the impedence matching property of the transformer.
  • Dc isolation between amplifier and load.
  • Better efficiency because primary winding does not dissipate DC power.
  • Higher voltage gain than RC  coupled amplifier if turns ratio is greater than 2.

The disadvantage of transformer-coupled amplifier:

  • Improper frequency response.
  • The transformer is bigger in size and costlier.

Application of transformer-coupled amplifier:

  • These are used in power amplifiers.

Que.60 What is a MOSFET? Why MOSFET is a voltage-controlled device.


  • MOSFET refers to metal oxide field effect transistor which is also called voltage controlled capacitor, as a parallel plate is formed at the gate region, with aluminum plate and semiconductor channel acting as two plates of a capacitor and SiO2 act as the dielectric.
  • MOSFETs, can either be of depletion type of enhancement type. depletion type is when a transistor conducts current across the drain-source terminal in the absence of voltage to the gate terminal. Enhancement type transistors are transistors that conduct current across the source-drain region only if the voltage is applied to the gate terminal. In the absence of voltage to the gate terminal in an enhancement type transistor, the transistor will not conduct current across the drain-source region. Only if sufficient voltage is applied to the gate terminal of a transistor for an enhancement type transistor will it conduct current across the drain-source region.
  • It is called a voltage control device because a small change in the gate to source voltage Vgs causes a proportionate change in drain current. But it acts as a constant current source with respect to Vds in the saturation region.

Que.61 What is JFET? How does it differ from MOSFET?


  • JFET refers to the junction field-effect transistor. The operation of the device depends on the electric field intensity produced in the channel. When 0V is fed into the gate of a JFET along with proper biasing to the source and drain terminals, the JFET operates at full conduction. Applying voltage to the gate terminal of JFET makes it more resistive and less current flows. Once the voltage reaches a certain threshold, all current flow from the source-drain terminal ceases.

Difference between JFET and MOSFET:

JFET is a discrete three-terminal device. (source, gate, and drain).It is called an insulated field effect transistor having 4 terminals. ( source, gate, drain, and substrate).
Size more than MOSFET.Smaller in size than JFET.
Not easy to fabricate.Easier to fabricate than JFET.
Slower than MOSFET.MOSFET is faster than JFET.
JFET is always operated under depletion mode.MOSFET operates in depletion as well as enhancement mode.

Que.62 How does the CMOS inverter work as a NOT gate?


  • CMOS inverter is used as NOT gate in digital circuits. When the input voltage is logic 1 or 0.
  • When the input voltage is logic 1 or Vdd- 

Vgsn=Vdd    …… which implies NMOS on.

Vsgp = 0 …………. which implies PMOS off

  • When the input is logic 0 then-

 Vgsn = 0          … implies NMOS off

Vsgp = Vdd       …. implies PMOS on

Hence, Vo = Vdd


Que.63 What is a Darlington amplifier?  Application of Darlington amplifier.


  • Darlington amplifier: it is a cascade of two common collector amplifiers or cascade of two common drain amplifiers. It has very high input resistance, low output resistance, unity voltage gain, and high current gain.
Darlington amplifier
  • Application: it is used as a voltage buffer for impedance matching.

Que.64 What is bootstrap biasing.


  • It is special biasing ckt. which is used in the Darlington amplifier to prevent the decrease in input resistance. If self-bias ckt. is used, then input resistance decreases due to biasing resistors R1 and R2, to prevent this, we use bootstrap biasing ckt. which uses a  large capacitor(microfarad) in between two resistors R1 and R2.
 Bootstrap biasing

Que.65 What is a Cascode amplifier?  Application of the same.


  • It is a cascade of a common emitter and common base amplifier.
  • Its main feature is, that it has large bandwidth, therefore it is used as a wideband amplifier to amplify video frequency signals.
Cascode amplifier

Que.66 What is a tuned amplifier? Application of tuned amplifier circuit.


  • It is a narrow-band amplifier that uses a parallel LC circuit as a load. Its main application is in radio frequency amplifiers.
  • In this type of amplifier, voltage gain is varied with frequency and becomes maximum at a frequency of resonance. Narrow bandwidth is achieved using a parallel LC circuit having a large quality factor. 
C:\Users\Admin\Desktop\tuned amplifier.jpg
C:\Users\Admin\Desktop\tuned ampl.png
Tuned amplifier
  • Application: In a superheterodyne receiver single tuned amplifier is used as an RF amplifier and a double-tuned amplifier is used as an IF amplifier.

Que.67 What type of distortion occurs in amplifiers?


Distortion in amplifier: If the output signal does not resemble an input signal, then the output is said to be distorted.

Distortion in amplifier is of three types: 

  1. Harmonic distortion: occurs in large-signal amplifiers or power amplifiers due to the non-linearity of the transistor. Nonlinearity causes harmonic frequencies in the output signal. Thus the appearance of harmonic frequencies in the output signal is known as harmonic distortion.
  2. Frequency distortion: refers to providing unequal amplification to different frequencies present in the input signal. Frequency distortion occurs due to the presence of reactive elements such as inductors and capacitors.

Example: RC coupled amplifier provide unequal amplification of different frequencies.

  1. Phase shift or delay distortion: refers to providing unequal phase shift to different frequencies present in the input signal. It also occurs due to reactive elements. 

Que.68 Why do we use negative feedback in an amplifier?

Answer: In a basic amplifier (without feedback) gain is unstable due to variation in device parameters with temperature and time.

So negative feedback is used:

  • To make the gain stable against variation in device parameters.
  • To reduce all types of distortions in amplifiers
  • To obtain desired values of input and output resistances.

Que.69 What are the effects of negative feedback on the various characteristics of amplifiers.

Answer: Effect of negative feedback on characteristics of the amplifier:

  • Effect on gain: negative feedback decreases the overall gain.
  • Effect on cut-off frequencies: negative feedback decreases the lower cut-off frequencies and increases the higher cut-off frequencies.
  • Effect on the stability: it decreases the sensitivity of gain towards device parameters.
  • Effect on frequency distortion: when negative feedback is used, bandwidth increases, therefore gain remains constant over a wide range of frequencies, hence amplifier is able to provide a uniform amplification over a wide range of frequencies.
  • Effect on harmonic distortion: negative feedback reduces harmonic distortion by decreasing the non-linearity of the transistor.

Que.70 What is a power amplifier? Where do we use the power amplifier?


  • Power amplifier: it is a large signal amplifier. The power amplifier uses a power transistor that operates at a greater voltage (VCE more than 10V) and the collector current of a few amperes. It supplies large AC output power because it internally converts a part of DC power obtained from biasing supply into AC power.
  • Application: power amplifier is used at the final stage or output stage in a multi-stage amplifier.

Que.71 What are the advantages of using a Class A  power amplifier? Where do we use the class A amplifier?


  • Advantage of using a class A amplifier is that we keep the operating point at the center of the load line, hence the output is undistorted.
C:\Users\Admin\Desktop\class A.jpg
Class A amplifier waveform
  • Class A amplifier is mostly used as a small-signal amplifier or voltage amplifier because it provides undistorted output. It is also used in high-frequency audio systems as an audio frequency power amplifier.

Que.72 What is a complementary push-pull amplifier? What are the disadvantages push-pull amplifier?

Answer: A complimentary push-pull amplifier consists of a pair of complementary transistor i.e. NPN and PNP transistor having identical characteristics.

  • During the positive cycle of input, the NPN transistor conducts and pushes the current through load resistor R.
  • During the negative cycle, the PNP transistor conducts and pulls the current out of the load resistor.
Complimentary push-pull  power amplifier
  • It is suitable for ICs(integrated circuits) as it does not require any transformer.

Disadvantages of push-pull amplifier:

  • Two biasing supplies are required, hence it is difficult to get two complimentary transistors with identical chars.
  • Maximum power transfer to the load is not possible.

Que.73 Define Active filter. What is the difference between active and passive filters?

Answer: A filter consisting of R, C elements and an active device such as opamp, FET, and BJT is called an active filter.

Active filterPassive filter
It consists of R and C elements along with an active device.It consists of passive elements such as R, L, and C only.
It provides filtering as well as amplification.It provides only filtering.
Used as audio frequency amplifier.It is used at high frequency or radio frequency.

Que.74 What is the application of the sample and hold circuit?

Answer: It is used in analog to digital converters.

  • it consists of two voltage followers: input voltage follower and output voltage follower, a MOS switch, and a low leakage capacitor.
C:\Users\Admin\Desktop\sample and hold.png
  • When Vcontrol is logic 1, the MOSFET switch turns on and capacitor voltage follows input voltage. This is called a sampling operation.
  • When Vcontrol is logic 0, the MOSFET switch turns off and capacitor voltage remains constant because the output follower does not allow to discharge, this is called hold operation.

Que.75 What is a voltage follower circuit? What is the application of voltage follower?


  • Voltage follower circuit: A circuit in which output follows the input voltage due to a physical short circuit. It is also called a unity gain non-inverting amplifier.
Voltage follower circuit 

Application of voltage follower:

  1. It is used for impedence matching.
  2. It is used in the sample and hold circuit.
  3. It is used in instrumentation amplifiers.
  4. It is used in 1st order Butterworth filters.

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Hello friends, my name is Trupal Bhavsar, I am the Writer and Founder of this blog. I am Electronics Engineer(2014 pass out), Currently working as Junior Telecom Officer(B.S.N.L.) also I do Project Development, PCB designing and Teaching of Electronics Subjects.

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