Question

Which of the following is an expression for gm0?

(a) gm0 = IDSS/Vp

(b) gm0 = 2IDSS/|Vp|

(c) gm0 = IDSS/5Vp

(d) gm0 = IDSS/2Vp

I had been asked this question in an interview.

I'd like to ask this question from The FET Small-Signal Model in section Field-Effect Transistors of Electronic Devices & Circuits

Answer 1

Right answer is (b) gm0 = 2IDSS/|Vp|

The explanation is: gm0  is the value of gm when VGS=0, we have seen that  trans conductance is the ratio of drain current to change  in gate to source voltage, but this is an exceptional case, here the transistor will be working in cut off region.