'freq' parameter in ac analysis

[Nilay]

Hello,

I would like to have a resistor whose value is a function of 'freq'
parameter in ac analysis (spectre simulator), so for each simulation
step the value of the resistor will change. How can I call this
parameter?

My goal is to mimic a delay cell which will cause 90deg phase shift
with constant gain regardless of its input's frequency. This is
necessary to simplify the model of a mechanical system.

 

[Andrew Beckett]

Nilay wrote, on 04/20/11 10:13:

Hello,

I would like to have a resistor whose value is a function of 'freq'
parameter in ac analysis (spectre simulator), so for each simulation
step the value of the resistor will change. How can I call this
parameter?

My goal is to mimic a delay cell which will cause 90deg phase shift
with constant gain regardless of its input's frequency. This is
necessary to simplify the model of a mechanical system.

You can't do this with Verilog-A or a bsource (which is essentially a convenient
way of describing a simplified Verilog-A model in spectre syntax) because the
languages are designed such that you describe in the time domain, from which you
can easily generate a frequency domain model. If you describe in the frequency
domain, generating a stable, causal, time domain model is hard (or impossible).
For example, a constant 90-degree phase shift is not causal in the time domain
so trying to simulate this in transient would cause no end of trouble.

One way you could do it however is to create an ideal s-parameter description
representing the constant phase shift - and then ensure that you only simulate
in an ac analysis.

Regards,

Andrew.