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If g is the transconductance and r is the resistance due to channel length modulation – what is the total voltage gain if only M1 has channel length modulation?(a) R / ((1/g || r ) + R) * g *R * R / (1/g + R)(b) R / ((1/g || r ) + R) * g *R * R * g(c) R / ((1/g || r )) * g *R * R / (1/g + R)(d) R / ((1/g ) + R) * g *R * R / (1/g + R)I got this question in semester exam.I need to ask this question from MOSFET Amplifier with CD Configuration topic in portion FET Amplifiers of Analog Circuits

Answer»

The correct option is (a) R / ((1/g || r ) + R) * g *R * R / (1/g + R)

To explain I would say: This is a cascade of a follower stage follower by a CS stage which precedes another follower stage. The gain due to each stage gets MULTIPLIED until we reach the output. For the first stage, the gain is R/ ((1/g || r)+ R) since M1 has CHANNEL length modulation. The second stage has a gain of g * R while the final stage has a gain of R/ (1/g + R). After MULTIPLYING the gains, we get R/ ((1/g || r )+ R) * g *R * R/ (1/g + R).


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