A common-emitter stage has an input resistance (the parallel combination of the bias…

PHYSICS · Subjective · Fermi University Physics · Electronics, Instrumentation & Communication · Circuit foundations and passive networks · Semiconductor devices and analogue circuits

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

Problem

A common-emitter stage has an input resistance

R_{\rm in} = 3.0\,\mathrm{k}\Omega

(the parallel combination of the bias network's Thevenin resistance and

r_\pi

). Its measured low-frequency response, plotted as gain magnitude in decibels against frequency on a logarithmic axis, is flat above about

1\,\mathrm{kHz}

, falls towards a slope of

20\,\mathrm{dB}

per decade well below

200\,\mathrm{Hz}

, and crosses

3\,\mathrm{dB}

below the flat-band level at

f_c = 200\,\mathrm{Hz}

. This corner is set by the coupling capacitor

C

feeding the stage's input, in series with

R_{\rm in}

. Find

C

, and state the nearest E12 preferred value.

Browse the problem library