Question about the plot for gm/Id methodology

[peterlau1984]

Hi everyone,
I am confused about why the vgs is set to be vt+200mV when gm*ro versus Vds is plot? Dose the vgs has to be vt+200mV?
thanks!!

 

[peterlau1984]

Perhaps, I should repeat my question above more clearly.

first, why the Vgs should be vt+200mV while ploting gm*ro versus vds?

second, while sweeping vds, the actual threshold voltage would change as well, how should we define the value of "vt" in the "vt+200mV". Is the "vt" equal to "vth0" listed in the technology file?

Thanks!

 

[holddreams]

v*=vgs-vt, usually use v*=200mv for design.
vth≠vth0

Just my points.

Perhaps, I should repeat my question above more clearly.

first, why the Vgs should be vt+200mV while ploting gm*ro versus vds?

second, while sweeping vds, the actual threshold voltage would change as well, how should we define the value of "vt" in the "vt+200mV". Is the "vt" equal to "vth0" listed in the technology file?

Thanks!

 

[peterlau1984]

Thanks for holddreams's reply.
If vth is not equal to vth0, how should I set Vgs in spectre? is there any ideas?