Dear all,

I have a simulation set-up problem when it comes to simulating a varactor (actually 2) of which I want to determine the capacitance versus the tune voltage using following SPICE setup:

Code:

Xvar1 tune test nvar_rf finger=nf w=wvar l=lvar
Xvar2 tune vss  nvar_rf finger=nf w=wvar l=lvar

Vtune tune vss dc 'vtune'

Itest test vss dc 0 ac 1

.ac dec 100 100 100e6 sweep vtune -0.9 0.9 0.1

 

The problem is that the Vtune source acts as a short to ground during an AC analysis. Therefore, my setup returns the effective capacitance C of 1 varactor instead of the correct C/2.

I can solve this problem by inserting a 1GOhm resistor between the vtune source and the controlling node of the varactors. I was wondering if there is another approach to tackle this (setup) problem?


Kind Regards


Peter