how to simulate Vth mismatch in spectre

Hi guys,

I would like to simulate a simple matched differentail amplifier.
If I am interested in only Vth variation, how can I simulate the
mismatch effect?

I put the dc voltage source (2sigma_vth variation) in series with gate
of + input transistor and put dc voltage source(-2sigma_vth variation)
in series with gate of - input transistor.

Is this way correct?
And usually how many sigma_vth variation are used for mismatch
simulation?

Thanks.

h.s

 

[John O'Donovan]

Hi,

If you are using bsim3v3 or bsim4 models, you can use the instance
parameter "delvto" to change Vth for the individual transistors, i.e.

m1 d g s b nmos ..... delvto=2*sigma_vth variation
m2 1 2 3 4 nmos ..... delvto=-2*sigma_vth variation

Regards,
John