Viva Questions on Transistor as an Amplifier
Viva Questions on Transistor as an Amplifier
Short Viva Questions with Answers on Transistor as an Amplifier
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 Cbc
is 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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