GATE Electrical Engineering - Complete Master Library

 

GATE Electrical – Analog Electronics

Practice Problems – Page 4

This section contains problems based on BJT Amplifier Configurations and Gain Calculations.

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Problem 31

Question:

A BJT has current gain β = 100. If base current is 20 μA, find collector current.

Solution:

Ic = β × Ib

Ic = 100 × 20 μA

Ic = 2000 μA = 2 mA

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Problem 32

Question:

If α = 0.98, find β.

Formula:

β = α / (1 − α)

Solution:

β = 0.98 / (1 − 0.98)

β = 49

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Problem 33

Question:

A common emitter amplifier has voltage gain of −50. What does the negative sign indicate?

Answer:

It indicates 180° phase shift between input and output.

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Problem 34

Question:

Which amplifier configuration provides highest current gain?

Answer:

Common Emitter Amplifier

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Problem 35

Question:

Which amplifier configuration has voltage gain approximately equal to 1?

Answer:

Common Collector (Emitter Follower)

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Problem 36

Question:

Which amplifier configuration has the lowest input impedance?

Answer:

Common Base Amplifier

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Problem 37

Question:

Which amplifier configuration has the highest output impedance?

Answer:

Common Emitter amplifier.

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Problem 38

Question:

Define transconductance (gm) of a transistor.

Answer:

gm = Ic / VT

Where VT ≈ 25 mV at room temperature.

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Problem 39

Question:

If collector current Ic = 2 mA, find transconductance.

Solution:

gm = Ic / VT

gm = 2 mA / 25 mV

gm = 0.08 S

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Problem 40

Question:

Why is emitter resistor used in CE amplifier?

Answer:

Emitter resistor provides thermal stability and stabilizes operating point.