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About the MOS capacitance simulation

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gaom9

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capacitance simulation

Hi,
I am design a VCO with the MOS capacitance as the varactor, I want to know how to simulate the value of the MOS capacitance in spectre.
As I know in hspice, we can use the LX18 parameter to print the value of Cgs+Cgd+Cgb, can spectre do that? And I want to use the dc simulation to know the capacitance of the MOS change with the biasing voltage, how to probe this wave, please?
And is there any method to know the capacitance between two node by simulate tools?

Thank you!
Best regards!
 

spectre + capacitance simulation

You can use CAPTAB option in Spectre.

In transient analysis window, choose Options...

Then click captab at bottom of option.

You can see nodetoground or nodetonode

Threshold means minimum capacitance you want to see.

Below that value, capacitance value is ignored.

Hope that can help.

Regards.
 

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    gaom9

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spectre capacitance simulation

becareful, if i remember currently CAPTAB only reports absolute value of capacitance at a particular node. It does not reveal the effect of AC capacitance. So miller effect and etc... is completely ignored.

there should be a parasitic extraction tool that will extract all the caps b/w different nodes. I am not sure if they have this built into SPICE, but I have used tools that effectively extract parasitic caps post-layout.
 

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