#### surreyian

##### Member level 3

There are 3 gm equations that can be used

1/ gm=2Id/Vgs-Vth

2/ gm= sqrt(2k(W/L)Id)

3/ gm= k(W/L)(Vgs-Vth)

when do u know which equations to use to determine the gm?

Equation 1, if u have Id constant, gm will decrease with increasing vgs-vth. I can connect a common source with ideal current, increasing vgs will cause gm to decrease. Is that right?

Equation 3. what kind of circuits will use equation 3 to determine the gm. can u give me an example.

thanks