Diode connected transistors

[Aravind_tucson]

Can we always convert a diode connected transistor to (1/gm // ro) for small signal analysis irrespective of its source voltage...? even if a resistance is connected to the src.. Am i right?

 

[rfzheng]

just in small singal analysis in my mind

 

[ravitest]

this is applicable to small signal analysis not for large signal analysis.

 

[Fahmy]

You are right except if you are using NMOS transistor with bulk and source not connected to each other , in this special case gm will be reduced by gmb due to bulk effect, where gmb is δId/δVsb .

 

[santosh.manabala]

in low frequency small signal analysis we can have a eqivalent circuit which will have a VCCS(one for transconductance and the other for
body current, RESISTOR).
1. this body current is dominant in NMOS but neglisible in PMOS
2.gm << rd( see the smaa signal circuit)
hence the fina expression depend on
1.type of MOS