1.

If g is the transconductance, r is the resistance due to channel length modulation and if M2 and M1 has channel length modulation but M3 doesn’t, what is the total voltage gain for only M2?(a) g * {(1 + gr)* (R || 1/g || r) + (R || 1/g || r)} || R(b) g * {(1 + gr)* R + R} || 4R(c) g * {(1 + gr)* R + 3R} || 4R(d) g * {(1 + 2gr)* R + R} || 4RI have been asked this question by my college professor while I was bunking the class.My question is taken from MOSFET Amplifier with CD Configuration in chapter FET Amplifiers of Analog Circuits

Answer»

Correct choice is (a) G * {(1 + GR)* (R || 1/g || r) + (R || 1/g || r)} || R

The explanation is: The voltage gain for M2 will be due to a CG stage. M2 has CHANNEL length modulation and is degenerated by (R || 1/g || r). Thus the output IMPEDANCE rises to {(1 + gr)* (R || 1/g || r) + (R || 1/g || r)} ||R and hence the gain for only M2 is g * {(1 + gr)* (R || 1/g || r) + (R || 1/g || r)} || R.


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