# Analog Circuits Questions and Answers – Operating Point of Transistor

This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Operating Point of Transistor”.

1. Reverse saturation current of a common emitter transistor is __________
a) Collector current when emitter is open circuited and base-collector junction is reverse biased
b) Emitter current when collector is open circuited and base-collector junction is reverse biased
c) Base current when emitter circuit is open circuited and emitter-collector junction is reverse biased
d) Collector current when base circuit is open circuited

Explanation: Reverse saturation current is the collector current when emitter is open circuited and base-collector junction is reverse bias mode. In this mode of operation collector-base junction act as a reverse biased diode. The current in this reverse biased junction is known as reverse saturation current.

2. Reverse collector saturation current ICBO is __________
a) Collector current when emitter current is zero
b) Collector current when base current is zero
c) Same as reverse saturation current
d) Collector current when either emitter or base current is zero

Explanation: Reverse collector current ICBO is collector-base current when emitter is open. This is same as reverse saturation current in ideal but have slight difference in practical.

3. Reverse collector saturation is greater than Reverse saturation current because of reverse collector saturation __________
a) Is ideal
b) Doesn’t include leakage current
c) They are same
d) Include avalanche multiplication current which is caused by the collision in collector junction

Explanation: One of the reasons why reverse collector current exceeds the reverse saturation current is the introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current. Another major reason is the presence of surface leakage currents flowing in the reverse collector saturation.

4. Reverse collector saturation is greater than Reverse saturation current because reverse collector saturation __________
a) Is ideal
b) Consist leakage current flowing through junction and surface
c) Doesn’t include avalanche multiplication current opposing collector current
d) They are same

Explanation: One of the reasons why reverse collector current exceeds the reverse saturation current is the introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current. Another major reason is the presence of surface leakage currents flowing in the reverse collector saturation.

5. Which of the following statement about a common base transistor is true?
a) Very low input impedance
b) Very low output Impedance
c) Current gain is greater than unity
d) Voltage gain is very low

Explanation: Common base transistor has very low input resistance (20Ω). It also has very high output resistance. Its current gain is less than unity and it has a medium voltage gain.
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6. Which of the following statement about a common emitter transistor is true?
a) Very high input resistance
b) High output resistance
c) Current gain is less than unity
d) Voltage gain is very low

Explanation: Common emitter transistor has high output resistance (about 40k). It has low input resistance (about 1k). Current gain is high (20 to a few hundred). Voltage gain is medium.

7. Which of the following statement about a common collector transistor is true?
a) Very low input impedance
b) Very high output impedance
c) Unity current gain
d) Unity voltage gain

Explanation: Common collector configuration has high input impedance and low output impedance. The current gain is high but voltage gain is low, almost equal to unity.

8. Which of the following configuration is used as input stage of the multistage amplifier?
a) Common base configuration
b) Common emitter configuration
c) Common collector configuration
d) All configurations are equally suited

Explanation: Since input resistance is low and output resistance is high common base configuration is used as an input stage of the multistage amplifier. Common emitter configuration is used for audio signal amplification. Common collector is used for impedance matching.

9. Which of the following configuration is used for audio signal amplification?
a) Common base configuration
b) Common emitter configuration
c) Common collector configuration
d) All configurations are equally suited

Explanation: Common base configuration is used as input stage of multistage amplifier since it has low input resistance and high output resistance. Since voltage gain is high, common emitter configuration is used for audio signal amplification. Common collector is used for impedance matching since the voltage gain is unity.

10. Which of the following configuration is used for impedance matching?
a) Common base configuration
b) Common emitter configuration
c) Common collector configuration
d) All configurations are equally suited

Explanation: Common base configuration is used as input stage of multistage amplifier since it has low input resistance and high output resistance. Since voltage gain is high, common emitter configuration is used for audio signal amplification. Common collector is used for impedance matching since the voltage gain is unity.

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