Viva Questions on Transistor as an Amplifier

 Viva Questions on  Transistor as an Amplifier

Viva Questions on  Transistor as an Amplifier, Viva Questions on Transistor as an Amplifier, Short Viva Questions Questions on Transistor as an Amplifier, Engineering Viva Questions, Electronics Devices Viva Questions

Short Viva Questions with Answers

Q.1. What are the Hybrid Parameters (h-parameters)? Explain.

Ans. Hybrid parameters are also called as h-parameters. Characteristics of amplifier can be specified easily in terms of h-parameters. The hybrid or h-parameters are very popular and widely used because them give accurate result and can be measured very easily.

We know that a transistor is a three terminals device. If one terminal is made common to the Input and output, then the transistor can be represented as a two-port network.

Q.2. What do you mean by cascade amplifier?

Ans. Cascade amplifier is a composite amplifier pair with a large bandwidth used for RF applications and as a video amplifier. It consists of a CE stage followed by a CB stage directly to each  other and combines some of the features of both the amplifiers.

For high frequency applications, CB configuration has the most desirable characteristics. However, it  suffers from low input impedance. The cascade configuration is designed to have the input impedance  essentially that of CE amplifier, the current gain that of CE amplifier, the voltage gain that of CB amplifier and good isolation between the input and output.

Q.3. What is an amplifier?

Ans. The device that amplifiers the amplitude of the input signal is called the amplifier. An amplifier may be defined as a device that increase the current, voltage or power of an input signal with the help of transistor by furnishing the additional power from a separate source of supply.

Q.4. What is meant by small signal amplifier?

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

Q.5. What is meant by phase reversal?

Ans. 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 causes a phase difference of 180° between the input signal voltage and output voltage.

Q.6. What is an ac emitter resistance?

Ans. The dynamic resistance of the emitter-base junction diode is called the ac emitter resistance. It is given as 25 mV/IE , where IE is the dc emitter current at Q-point.

Q.7. What is the effect of source resistance on voltage gain of a common base transistor amplifier?

Ans. The voltage gain of a CB transistor amplifier will decrease if source resistance is considered because in such a case, there will be a voltage drop across the source resistance and output voltage will decrease.

Q.8. What is the effect of removal of emitter bypass capacitor in a CE amplifier circuit?

Ans. Removal of bypass capacitor in a CE amplifier circuit causes excessive degeneration in the amplifier circuit.

Q.9. Why common-collector circuit is known as an emitter follower?

Ans. 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.

Q.10. What are the main purposes for which a common-collector amplifier may be used?

Ans. 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 application as a buffer amplifier between a high impedance source and a low impedance load.

Q.11. What is meant by frequency response of an amplifier?

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

Q.12. Define fT of a BJT.

Ans. The fT of a BJT is defined as the frequency at which the short-circuit common emitter current gain β falls to unity. It is equal to β fβ.

Q.13. What is Miller effect?

Ans. According to Miller effect, when viewed from input base terminal of a CE connected transistor the collector-base capacitance Cbc appears to be (1 + Av) Cbc, i.e., the Cbcis amplified by a factor (1 + Av).

Q.14. What is meant by distortion in an amplifier?

Ans. Change in amplified output signal waveform is called the distortion.

Q.15. Why distortion in amplifier is considered harmful?

Ans. Because distortion may change the intelligence (useful information) carried by the signal.

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