Analog Electronics – Problems Page 26
GATE Previous Year Type Questions
This section contains important conceptual and numerical questions inspired by previous GATE examinations.
Problem 1
A silicon diode is forward biased with voltage 0.7 V. The thermal voltage is 25 mV. Calculate exponential factor V/VT.
Solution
V / VT = 0.7 / 0.025
V/VT = 28
Problem 2
A transistor has β = 150 and emitter current IE = 3 mA. Find collector current IC.
Solution
Relation:
IC ≈ α IE
Where
α = β / (1 + β)
α = 150 / 151 ≈ 0.993
IC ≈ 2.98 mA
Problem 3
An op-amp has open loop gain 10⁵. If feedback factor β = 0.01, find closed loop gain.
Solution
Acl = A / (1 + Aβ)
Acl = 10⁵ / (1 + 10⁵ × 0.01)
Acl ≈ 100
Problem 4
A low pass filter has R = 1 kΩ and C = 0.1 μF. Find cutoff frequency.
Solution
fc = 1 / (2πRC)
fc ≈ 1591 Hz
Problem 5
In an RC phase shift oscillator, how many RC sections are used?
3 RC sections
Problem 6
A Wien bridge oscillator has R = 20 kΩ and C = 0.005 μF. Calculate oscillation frequency.
Solution
f = 1 / (2πRC)
f ≈ 1592 Hz
Problem 7
What is the ideal value of CMRR for an op-amp?
Infinite
Problem 8
Which oscillator is commonly used in RF circuits?
Hartley or Colpitts oscillator
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