A common-source stage on a supply uses an n-channel MOSFET with transconductance parameter

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-source stage on a

15\,\mathrm{V}

supply uses an n-channel MOSFET with transconductance parameter

k_n = 25\,\mathrm{mA\,V^{-2}}

, biased at an overdrive voltage

V_{GS} - V_{GS(\rm th)} = 0.40\,\mathrm{V}

, with drain resistor

R_D = 4.7\,\mathrm{k}\Omega

and the source grounded. Take the output resistance

r_o

to be much larger than

R_D

and neglect it. ((a)) Predict the quiescent drain current and the mid-band voltage gain. ((b)) Predict the largest peak input (gate) amplitude before the output clips, taking the boundary of the triode region as

V_{DS} = V_{GS} - V_{GS(\rm th)}

, with

V_{GS}

the instantaneous gate-source voltage and the drain current following the square law. Both figures can be checked on a bench: the gain from input and output traces, the clipping amplitude by raising the gate drive until the bottom of the drain waveform flattens.

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