drain-source conductance gds

[hyc]

gm gds

I follow the gm/Id methodology and precharacterize a few parameters against gm/Id, I then try with a typical two stage OTA, although gm, vdsat, and Id values seem to agree with spice well, the gds value seems to be way off. Does anyone have the same expericence and how to correct this discrepency? Also, is there is way to find out the VA (early voltage) value?

thanks,

Hau

 

[antonio_eda]

gm/gds

gds is very difficult to model in modern processes. Always the simple hand-model is far from reality...

 

[hyc]

gm, gds, hspice

However, one of important parameters that gm/Id methodology claims to characterize is the intrinsic gain Avi, which is gm/gds, if gds can not be characterized well, it seems the whole gm/Id methodology will fall apart.

 

[DenisMark]

drain source

At the first Gds isn't a part of original Gm/Id methodology. Gds can't be predicted well because dependce from many factors: Vds, current (IC), channel length. So use prediction of Gds and Gain=Gm/Gds just for first order estimation.

Early voltage = Ids/Gds.

 

[haoshs]

Just as hyc said, the gds value of simulation is far small. that is 75e^-9, however, the intrinsic gain is only about 20(meg) for gm = 123uS


So, what kind of method is it to evalulate the intrinsic gain?