How to get the derivation of a graph ?

[Stefan Joeres]

Hi alltogether,

I measured the output frequency of a VCO, and plotted it against the control
voltage.
Now I want to determine the steepness (Kvco).
Does anyone know how to do this with the Cadence calculator ?
A simple deriv(waveform) produces something that really doesn't look like
the thing I'm searching for ....

Thanks a lot,

Stefan Joeres

 

[Andrew Beckett]

Well, deriv should be OK. May be a bit noisy, because it's using just the points
which came out of the simulator.

You could always write a verilog-A model to do the derivative using ddt().
Are you measuring the frequency of the VCO with Verilog-A? (the benefit of
doing it with verilog-a is that the crossing points are controlled, and so you
don't get jitter from numerical interpolation). There's a component, freq_meter,
in ahdlLib.

Andrew.

On Tue, 2 Mar 2004 14:11:34 +0100, "Stefan Joeres"
<joeres@halifax.rwth-aachen.de> wrote:

Hi alltogether,

I measured the output frequency of a VCO, and plotted it against the control
voltage.
Now I want to determine the steepness (Kvco).
Does anyone know how to do this with the Cadence calculator ?
A simple deriv(waveform) produces something that really doesn't look like
the thing I'm searching for ....

Thanks a lot,

Stefan Joeres

--
Andrew Beckett
Senior Technical Leader
Custom IC Solutions
Cadence Design Systems Ltd