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Analog Electronics – Problems Page 24

Mixed Concept & Numerical Problems

This section includes mixed questions from diode circuits, BJT amplifiers, operational amplifiers and oscillators for GATE preparation.

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Problem 1

Find the thermal voltage at room temperature (300 K).

Solution

VT = kT / q

VT ≈ 25 mV

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Problem 2

A BJT has β = 120 and base current 20 μA. Find collector current.

Solution

Ic = β × Ib

Ic = 120 × 20 μA Ic = 2.4 mA

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Problem 3

Calculate the voltage gain of an inverting op-amp with Rf = 100 kΩ and Rin = 10 kΩ.

Solution

Av = −Rf / Rin

Av = −100k / 10k Av = −10

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Problem 4

An LC oscillator has L = 5 mH and C = 100 pF. Find oscillation frequency.

Solution

f = 1 / (2π√LC)

f ≈ 225 kHz

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Problem 5

What is the ripple factor of a full wave rectifier?

Ripple Factor = 0.482

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Problem 6

What is the ideal input impedance of an operational amplifier?

Infinite

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Problem 7

What is the ideal output impedance of an op-amp?

Zero

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Problem 8

For oscillations to occur, what should be the loop gain?

Aβ = 1

This is the Barkhausen criterion.