capacitor extration issue?

[tonywai]

Dear all
I use IC 5.0.33，Calibre Interactive -PEX v9.3_2.5 to extract metel capacitor. When I set outputs->netlist type->C; inputs->Calibre-xRC,
the Result is 3.00pF.
But when I set input->xCalibre-PX(Flat), the result is 3.244pF.
Who can explain this difference to me?
Which result is more exact and why ??
Thanks

 

[DoctorX]

I have not used Calibre exactly, but my guess is that somehow the extraction rule included different geometry shapes in the two trials.

A sure way to test it is to use one Rectangular piece of metal, do the two trials as you said, and do one hand calculation.

If successful, move on to give it more complex shapes. Verify it thoroughly this way.