GATE Electrical Engineering - Complete Master Library

 

GATE Electrical – Analog Electronics

Practice Problems – Page 6

This section contains numerical and conceptual problems based on Small Signal BJT Model and Amplifier Analysis.

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Problem 51

Question:

A transistor amplifier has collector resistance Rc = 4 kΩ and transconductance gm = 0.04 S. Find the voltage gain.

Solution:

Av = − gm × Rc

Av = −0.04 × 4000

Av = −160

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Problem 52

Question:

If Ic = 4 mA, calculate small signal emitter resistance re.

Formula:

re = VT / Ic

Solution:

re = 25 mV / 4 mA

re = 6.25 Ω

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Problem 53

Question:

If β = 150 and re = 10 Ω, find input resistance.

Solution:

rin = β × re

rin = 150 × 10

rin = 1500 Ω

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Problem 54

Question:

A CE amplifier has Rc = 3 kΩ and re = 25 Ω. Find voltage gain.

Formula:

Av ≈ − Rc / re

Solution:

Av = −3000 / 25

Av = −120

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Problem 55

Question:

If collector current increases, what happens to transconductance?

Answer:

Transconductance increases because:

gm = Ic / VT

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Problem 56

Question:

Which amplifier configuration has the highest bandwidth?

Answer:

Common Base Amplifier

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Problem 57

Question:

Which amplifier configuration is used as a buffer?

Answer:

Common Collector (Emitter Follower)

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Problem 58

Question:

What is the typical value of thermal voltage at room temperature?

Answer:

VT ≈ 25 mV

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Problem 59

Question:

Why is bypass capacitor used in CE amplifier?

Answer:

To increase voltage gain by bypassing emitter resistor for AC signals.

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Problem 60

Question:

What is the main advantage of emitter follower amplifier?

Answer:

High input impedance and low output impedance.