1.

If both the MOSFET’s are identical, what is the voltage gain from V1 to node S?(a) Vcc – 2R1* µn Cox* (W/L) * (V1-Vth)^2(b) VccR1* \(\frac{1}{2}\)µn Cox(W/L) * (V1-Vth)^2(c) Vcc– R1* µn Cox(W/L) * (V1-Vth)^2(d) Vcc– 4R1* \(\frac{1}{2}\)µn Cox * (W/L) * (V1-Vth)^2I have been asked this question during an interview.Enquiry is from MOSFET Amplifier with CS Configuration in chapter FET Amplifiers of Analog Circuits

Answer»

The correct answer is (c) Vcc– R1* µn Cox(W/L) * (V1-Vth)^2

For explanation I would SAY: SINCE M1 and M2 receive the same bias voltage V1, the current generated by both the MOSFET’s are same i.e. \(\frac{1}{2}\)µn Cox(W/L) * (V1-Vth)^2. Both the currents enter node S and hence the voltage at node S is VccR1* \(\frac{1}{2}\)µn Cox(W/L) * (V1-Vth)^2.


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