Pole-Zero analysis

Ram,

Well, pz analysis is the way to do it. It would have helped if you'd given some details of what was wrong?

Do you have any components which have values which are frequency dependent? For example, transmission lines, or laplace controlled sources, or Verilog-A components using the laplace functions? If so, you'll need to specify the frequency of evaluation (this defaults to 1Hz).

For most normal circuits, you don't have to do anything... so some details would help.

Regards,

Andrew.

Andrew,

thanks a lot for your reply!!

I was simulating the passive filter along with opamp (veriloga model) and trying to see how the filter cut-off frequency varies with op-amp gain-bandwidth.

So I am using verilogA - components using the laplace function in my circuit - for pz analysis.

Should I specify the frequency of evaluation from 1 Hz(default value) to my desired frequency(filter cut-off frequency) ?

Thanks,

Ramesh




Ramesh

Actually you can't really analyze the poles and zeros of a circuit using the laplace function, using the method that pz analysis uses. So I don't think moving the evaluation frequency will help.

Regards,

Andrew.

One comment to add:

I didn't use the laplace function.   All I want to simulate the passive filter loading an op-amp (verilog-a model) and analyze the variation of poles resulting from passive filter!!

Ramesh

I'm confused. Previously you said you were using the laplace function.

Perhaps you need to report this to Cadence Customer Support - so we can take a proper look at this?

Regards,

Andrew.

 Hi,

I tried to simulate pole-zero of a 4th order passive filter  using pz analysis.The cutoff frequency is around 1GHz. When I specify the "component eval freq" under 900MHz, there is no pole/zero founded. Only when I specify it over 900MHz, there are poles/zeros. However, I don't think it is linear >900MHz. What/how should I set the component eval freq?

Thank you!

In general it's better to start a new thread (you can always include a link to the old one) rather than continuing a very old one... I thought about splitting this into a new thread, but I'll leave this one for now.

Anyway, the behaviour you describe sounds very odd - unless you have frequency dependent (i.e. where the component value varies with frequency) components in your circuit, as I pointed out towards the top of this thread.

What is the make up of your passive filter? How is it represented?

Regards,

Andrew.