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Simulators >> Circuit Simulators >> How to measure node charge using Spectre
https://designers-guide.org/forum/YaBB.pl?num=1180608728

Message started by JC on May 31^st, 2007, 3:52am

Title: How to measure node charge using Spectre
Post by JC on May 31^st, 2007, 3:52am

I just wonder if it is possible to measure it directly or not? I use the CAPTAB option that allows to print the total capacitance on a node during Transient simualtion.

However, I found the value of capacitance is derived by C=dQ/dV in Spectre, so I think Spectre should know the node charge during simulation. And in my case the capacitance is due to parasitic effect and will change during operating. So I cann't use Q=C*V to calculate the node charge.

Is there a way to measure charge node directly? or How can I calculate node charge by knowing node capactiance?

JC

Title: Re: How to measure node charge using Spectre
Post by Geoffrey_Coram on Jun 1^st, 2007, 9:17am

Please read this thread:
http://www.designers-guide.org/Forum/YaBB.pl?num=1172655940/0#1

Next time, use the search function first!

Title: Re: How to measure node charge using Spectre
Post by JC on Jun 1^st, 2007, 9:34am

I had read that thread yet, but it doesn't answer my question. So I post again.

And I know how to print the node capacitance using CAPTAB option, However my question is

"How to measure the node charge while the capacitance is caused by parasitic effect and is nonliear?"

JC

Title: Re: How to measure node charge using Spectre
Post by Geoffrey_Coram on Jun 4^th, 2007, 4:21am

I'm not aware of any simulator that gives you direct access to the node charge.

You can't get Q from C because C is the partial derivative of Q and there's no (easy) way to integrate back. If you had 2-terminal nonlinear capacitors, you could integrate from 0 to v, but MOSFETs are 4-terminal nonlinear capacitors, and in many MOS models, the capacitance is non-reciprocal, so the integral would be path-dependent: the value of the integral depends on how you get from (0,0,0) to (vgs,vds,vbs)!