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Measurements >> Other Measurements >> measuring mosfet parasitic caps cgs,cgd in AC simulation.
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Message started by yvkrishna on Nov 3^rd, 2012, 9:04am

Title: measuring mosfet parasitic caps cgs,cgd in AC simulation.
Post by yvkrishna on Nov 3^rd, 2012, 9:04am

Hi all,

I am trying to create a testup for measuring cgd,cgs etc.
(ofcourse they are available in DCOP, here idea is to use this setup for a new composite device)

using AC=1 at gate of a mos and finding the imaginary part of the current gives the cap loading at that node, but how to find the junction caps cgd,cgs only?

tried using 'sp1tswitch' from analogLib but was not successful.

can someone please help with a simple test setup for measuring them in any simulation.

Thanks,
yvkrishna.

Title: Re: measuring mosfet parasitic caps cgs,cgd in AC simulation.
Post by Maks on Nov 29^th, 2012, 12:00pm

Apply AC signal to the gate, and measure the AC current at the nodes you are interested in (source, drain, bulk,...) - you will get the respective capacitive coupling components you are interested in. The sum of them should be equal to the total gate capacitance.

Title: Re: measuring mosfet parasitic caps cgs,cgd in AC simulation.
Post by yvkrishna on Nov 30^th, 2012, 7:57am

Thats not so simple, how do you eliminate the effect of other caps like cgd,csb which come in series/shunt while doing this experiment?

Title: Re: measuring mosfet parasitic caps cgs,cgd in AC simulation.
Post by Maks on Dec 12^th, 2012, 11:03pm

yvkrishna wrote on Nov 30^th, 2012, 7:57am:

Thats not so simple, how do you eliminate the effect of other caps like cgd,csb which come in series/shunt while doing this experiment?

I don't think so.

In an N-port system - apply an AC signal to port i, and ground all other ports. The AC current through port j (its imaginary part) will give you Cij component.