A common-emitter stage on a supply is biased at ( , 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 on a

9.0\,\mathrm{V}

supply is biased at

I_C = 1.2\,\mathrm{mA}

(

\beta_F = 120

, Early voltage

V_A = 70\,\mathrm{V}

), with

R_C = 3.3\,\mathrm{k}\Omega

and an emitter resistor

R_E = 1.0\,\mathrm{k}\Omega

that is bypassed by a large capacitor. Take

V_T = 25.7\,\mathrm{mV}

, base current negligible compared with the emitter current when finding the quiescent emitter voltage, and

V_{CE(\rm sat)} = 0.2\,\mathrm{V}

. ((a)) Predict the mid-band small-signal voltage gain. ((b)) Predict the largest peak input amplitude that can be applied at the base before the output starts to clip, using the exponential law for the collector current and neglecting

r_o

for this part. Both quantities can be checked on a bench: the gain from an oscilloscope trace of input and output, the clipping amplitude by raising the input sine amplitude until the top or bottom of the output trace flattens.

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