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Simulators >> RF Simulators >> how to plot VCO tuning characteristics spectreRF?
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Message started by EE student on Jul 9^th, 2004, 11:47am

Title: how to plot VCO tuning characteristics spectreRF?
Post by EE student on Jul 9^th, 2004, 11:47am

I am designing a LC VCO in 0.18u CMOS.

How do I plot the tuning characteristics of the VCO ( Freq vs control voltage) in spectre RF?

thanks

Title: Re: how to plot VCO tuning characteristics spectre
Post by froggy on Jul 19^th, 2004, 8:43pm

Hope the following is useful to you.

You can run a transient simulation and use the "clip" and "frequency" special function in the calculator from Analog Circuit Design (ACD) to determine the frequency of the VCO at a particular control voltage. Example: "frequency(clip(VT("/net065"),20n ,50n))"

Next you can use parametric analysis to run the VCO simulation for a different set control voltage, after the simulation is done, you can plot the VCO tuning charactertics.

Title: Re: how to plot VCO tuning characteristics spectre
Post by Andrew Beckett on Jul 21^st, 2004, 12:46am

A few things you can do:

a) A sweep of the control voltage and then do an autonomous PSS
to get the oscillator frequency. This is probably quite expensive
in terms of simulation time though.

b) A transient analysis, using the Verilog-A model freq_meter from
ahdlLib at the output of your oscillator - this measures the
times between zero-crossings and outputs this as a frequency.
The benefit of using the Verilog-A model is that the crossing
is resolved in the simulator, and so minimises interpolation
error. However, you need to sweep the control voltage slowly
over time to avoid impacting the instantaneous frequency too
much.

You can then change the x-axis to be the control voltage,
and plot the frequency against that.

c) As an alternative to using freq_meter, a calculator function
that I wrote can be used. I can't post it here (it is too long,
and the system won't let me post it), but it is available
on http://sourcelink.cadence.com as solution number
11015938.

Regards,

Andrew.