Question

If channel length modulation is neglected, what is the voltage gain for the following CG stage?

(a) Rd/(1/gm – Rs)

(b) Rd/(3/gm + Rs)

(c) Rd/(1/gm + Rs)

(d) Rd/(2/gm + Rs)

I had been asked this question in an interview for internship.

The query is from MOSFET Amplifier with CG Configuration topic in portion FET Amplifiers of Analog Circuits

Answer 1

Right option is (c) Rd/(1/gm + Rs)

The best I can explain: The above circuit is quite similar to the CS stage with degeneration. But the CG stage doesn’t invert and after performing a small signal analysis, the voltage gain comes out to be Rd/(1/gm + Rs).