Weak inversion MOS ohmic region

[pedrovfr]

Hi,
I am interested in designing a MOS as a voltage controlled resistor, I'm looking for a rough formula for the conductance in weak inversion and in the ohmic region (let's say vds = Vt). I couldn't find anywhere an equation as the equation for strong inversion ( gds= ucoxW/L(Vgs-Vth) ).
Does anyone know that, or can suggest me a book or paper where I can find this information?
Thx

 

[BigBoss]

Almost every texbook mentions about linear reagion of MOS transistors, why couldn't you find it ??

 

[rmanalo]

If in strong inversion triode region, gds=Id_patial/Vds_partial. Then in weak inversion we can apply the same principle, Knowing that drain current in weak region is "Io*exp((Vgs-Vth)/mVt)[1-exp(-Vds/Vt)]".
then gds_weakinversion=Id_patial/Vds_partial = [Io*exp((Vgs-Vth)/mVt)*exp(-Vds/Vt)]/Vt. which is very nonlinear.

 

[BigBoss]

I think you make a mistake.
Regarding to "Analysis and Design of Analog Integrated Circuits" of Meyer-Gray page-74,the Partial derivative of Id aginst V_gs ( so gm) is linear.