Varactor

Hi,
I'm trying to simulate a differential varactor (1.2V) with cadence. I
do a simple ac analysis to have as result the impedance of the
varactor at a specified frequency. Before to run the simulation I set
the object properties to have a certain starting capacitance.
I have some problem when I try to graph the value of the immaginary
part of the impedance. The value shown in the graph is completely
different from the value which I set before in the object propierties
(two order of magnitude).
There is someone of you who have been the same problem and then can
help me?
Thanks
Bye Pierpaolo

 

[Andrew Beckett]

pierpaolo.stabile@gmail.com wrote, on 09/22/08 15:14:

Hi,
I'm trying to simulate a differential varactor (1.2V) with cadence. I
do a simple ac analysis to have as result the impedance of the
varactor at a specified frequency. Before to run the simulation I set
the object properties to have a certain starting capacitance.
I have some problem when I try to graph the value of the immaginary
part of the impedance. The value shown in the graph is completely
different from the value which I set before in the object propierties
(two order of magnitude).
There is someone of you who have been the same problem and then can
help me?
Thanks
Bye Pierpaolo

How are you computing the impedance? I would imagine it's some expression using
the current through the component, and if so, please make sure you have the
option "useprobes=yes" set (in ADE this is on the Outputs->Save All form,
heading something like "Save AC Currents").

Otherwise the default method of outputting the currents from many primitive
devices is not correct for AC analyses (anything that outputs a complex
waveform), and so you need to tell the simulator to insert a current probe
automatically instead.

Best Regards,

Andrew.