Multistage Amplifiers Viva Questions

Multistage Amplifiers Viva Questions

Multistage Amplifiers Viva Questions, Viva Questions Multistage Amplifiers, Short Questions with Answers on Multistage Amplifiers, Engineering Viva Question, Electronics Device Circuits Viva Questions,

Short Questions with Answers

Q.1. What is gain?

Ans. The ratio of output to the input of an amplifier is known as the gain of the amplifier. The output quantity may be current, voltage, or power. Generally, it is represented by the letter ā€˜Gā€™ or ā€˜Aā€™.

Q.2. What do you mean by Decibel?

Ans. The gain of an amplifier is the ratio of the output signal to the input signal of an amplifier, where input and output are of similar quantities having the same units. The telephone industry proposed a logarithmic unit named bel (or decibel dB) after Alexander Graham Bell.

Q.3. Explain the reasons for expressing the gain in dB.

Ans.

  • When the gains are expressed in dB, the overall gains of a multi-stage amplifier can be determined by simply adding them. On the other hand, the absolute gain is obtained by multiplying the gains of individual stages.
  • Use of dB permits us to denote very, large gains on linear scale by conveniently small figures on dB (logarithmic) scale. For instance, a power gain of 12000 is just 40.79 dB.
  • The output of most of the amplifiers is ultimately converted into sound. Experiments reveal the fact that our ears do not respond according to the intensity of sound but they respond according to the log of intensity of sound. Hence, if the intensity of sound given by speaker increases by 100 times then the hearing level will increase only by 2 times (log10 100 = 2). Since dB unit tallies with the natural response of human ears, therefore, it has become more popular compared to linear scales.

Q.4. What do you mean by frequency response?

Ans. A curve drawn between voltage gain and signal frequency of an amplifier is known as the frequency response of the amplifier.

Q.5. What do you mean by the bandwidth of an amplifier?

Ans. The range of frequency over which the gain of an amplifier is equal to or greater than 70.7% of its maximum gain is known as the bandwidth of the amplifier.

Q.6. What are the requirements of an ideal coupling network?

Ans. An ideal coupling network should satisfy the following requirements.

  • It must not disturb the d.c. bias conditions of the amplifier being coupled. This means that the direct currents must not pass through the coupling network.
  • The coupling network must transfer ac signal waveform from one amplifier to the next amplifier without any distortion.
  • Although a small amount of voltage loss of signal cannot be avoided in the coupling network but the loss must he minimum. 
  • The coupling network must offer equal impedance to the various frequencies of signal wave. Following are the four coupling schemes, often used in amplifiers.

Q.7. What is main advantage of an impedance coupled amplifier?

Ans. The main advantage of an impedance coupled amplifier is that it can be operated at low collector supply voltage, since there is hardly any drop across inductor (L). The drawback of an impedance coupled amplifier is that it is relatively expensive because of the use of inductors. In addition to this, the impedance of the inductor drops off at lower frequencies. Hence, as a rule, an impedance coupled amplifier is suitable only at frequency above 20 kHz (also called radio frequencies).

Q.8. What are the advantages of a transformer coupled amplifier?

Ans. Advantages:

  • No signal power is lost in the collector or base resistors because of the low winding resistance of the transformer.
  • It provides a higher voltage gain than the RC coupled amplifier.
  • It provides an excellent resistance (or impedance) matching between the stage. The resistance matching is desirable for maximum power transfer.

Q.9. What are the drawbacks of transformer coupled amplifier?

Ans. Disadvantages:

  • The coupling transformer is expensive and bulky, particularly when operated at audio frequencies.
  • At radio frequencies, the winding inductance and distributed capacitance produces reverse frequency distortion.
  • It tends to produce ‘hum’ in the circuit which is highly undesirable.

Q.10. Write the advantages of a direct coupled amplifier?

Ans. Advantages:

  • The circuit arrangement is very simple because it uses a minimum number of resistors.
  • The circuit cost is low because of the absence of expensive coupling devices.
  • It can amplify very low frequency signals down to zero frequency.

Q.11. Write the drawbacks of a direct coupled amplifier?

Ans. Disadvantages:

  • It cannot amplify high frequency signals.
  • It has a poor temperature stability. Because of this, its, Q-point shifts. In a multistage direct coupled amplifier, the Q-point shifts are amplified in succeeding stages. Thus a small d.c. shift in the first stage can cause the final stage to be either saturated or cut-off. All integrated circuit amplifiers are direct coupled because of the difficulty of fabricating large integrated capacitors. It leads to special problems in their design.

Q.12. What are the applications of a direct coupled amplifier?

Ans. The direct coupled amplifier are used in several electronic systems that handle signals which change very slowly with time. Some of the important applications can be listed as under:

  • Analog computation
  • Power supply regulators
  •  Bioelectric measurements
  •  Linear integrated circuits (LICs)

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