A common-emitter stage is biased at with a transistor of and Early voltage

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Semiconductor devices and analogue circuits · Semiconductor devices and analogue circuits

Electronics for Measurement, Ch Transistors: a current controlled by a third terminal

Problem

A common-emitter stage is biased at

I_C = 2.0\,\mathrm{mA}

with a transistor of

\beta_F = 100

and Early voltage

V_A = 100\,\mathrm{V}

, collector resistor

R_C = 2.2\,\mathrm{k}\Omega

. Take

V_T = 25.7\,\mathrm{mV}

. Someone argues: “the voltage gain of a common-emitter stage is set by the transistor's current gain, so with

\beta_F = 100

the voltage gain is about

100

; if this part were replaced by one with

\beta_F = 300

from the same production batch, the voltage gain would triple to about

300

.” ((a)) Calculate the actual mid-band voltage gain of the stage. ((b)) State what happens to the gain if the transistor is replaced by one with

\beta_F = 300

at the same bias current, and explain in one or two sentences why the claim is wrong.

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