GATE 2021 BM – Question 44
The shown saturated NMOS has μₙCox=200 μA/V²,W=40 μm,L=1 μm, threshold 0.4 V and gmb/gm=0.1. A small input is applied at the bulk terminal. Neglect channel-length modulation and intrinsic capacitances. Find DC small-signal gain Vout/Vin.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: (A) −0.4
Explanation
The equal ten-kilohm bias resistors set the gate to .9 V from the 1.8 V supply; source is grounded. Overdrive=.9−.4=.5 V. Thus gm=200×10⁻⁶×40×.5=.004 S and gmb=.0004 S. A bulk input changes drain current by gmbvin, producing gain −gmbRD=−.0004×1000=−.4, A.