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Design Languages >> Verilog-AMS >> frequency dependent capacitor modeling
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Message started by rajdeep on Dec 22^nd, 2010, 4:37am

Title: frequency dependent capacitor modeling
Post by rajdeep on Dec 22^nd, 2010, 4:37am

Hi all,

I have a requirement where I would like to model a capacitor as a function of frequency.
Its like C(s) = C*H(s) where H(s) is a transfer function.

To start with, I tried to write the simple frequency model of a capacitor i.e.
V = I*(1/sC). I could only think of writing it in the following way:
V(p,n) <+ laplace_nd(I(p,n),{1},{0,C}); whre C is constant.
[My next step would be to make this C dependent on frequency.]
But it doesnt give me expected result, what I usually get if I use a standard capacitor or use I(p,n)<+C*ddt(V(p,n)).

I am no longer very fluent with laplace transform, but I would think thats the correct frequency domain model of a capacitor with initial voltage 0.

I also wonder is there any other way to express a quantity w.r.t frequency other than laplace transform?

By the way, I am using this model for ac analysis only.

Thanks,
Rajdeep

Title: Re: frequency dependent capacitor modeling
Post by Marq Kole on Feb 2^nd, 2011, 6:25am

You cannot access frequency directly in Verilog-A. Next to that: AC is a small-signal analysis so in many simulators you will see that non-linear code is only evaluated during DC and the AC behavior is derived from the linearization around the DC solution. The simulator does not need to re-evaluate the model code for that. The AC analysis will only do what you want if you can rewrite your frequency-dependent capacitor as another LTI transfer function.

Cheers,
Marq