GATE 2014 EC (EC1) – Question 49
For the amplifier shown, BJT parameters are V_BE = 0.7 V, β = 200 and thermal voltage V_T = 25 mV. Find voltage gain vo/vi.
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Correct answer: -240 to -230
Explanation
The bias divider has Vth=3V and Rth=33kΩ∥11kΩ=8.25kΩ. Including base loading, IE=(3−0.7)/[1010+8250/201]=2.1883mA and IC=(200/201)IE=2.1774mA. Hence gm=IC/25mV=0.08710S. At midband CE bypasses1kΩ but leaves10Ω unbypassed. Thus vo/vi=−gm×5000/[1+gm×10×(201/200)]≈**−232.18**. Neglecting base loading gives about−238.25, also inside the official range.