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How to acquire the small-signal capacitances of a MOSFET from a DC operating point simulation?

Hi there,

 

I am DC sweeping the drain and gate voltages of some MOSFET devices in Multisim to build a model that can be used for design optimization purposes. One of the key inputs to the models I am building are the MOSFET small-signal capacitors (e.g., Cgs, Cds, Cbd, etc.). However, when I run a DC Sweep or a DC Operating point simulation, I find that Multisim reports zero-valued capacitances for the various capacitors I am attempting to extract -- this is clearly not correct.

 

I have taken a look at the following thread:

 

https://forums.ni.com/t5/Multisim-and-Ultiboard/quot-Weird-quot-result-in-MOSFET-Capacitance-calcula...

 

but it seems that this similar issue was supposed to be resolved several years ago, and I am still experiencing a similar issue. To be clear, though, my question is a bit different from the one above -- I don't plan on running AC or transient simulations, I'm just running DC Sweep and DC Operating Point simulations, and want the correct values for Cgs, Cds, Cdb, etc. to be reported so that I can take those and do something else.

 

Is there a workaround for this, or is this still something that has not been resolved?

 

(Note that I have observed this same behavior with several different MOSFET model files, from 0.35um models to 65nm models, so I am fairly certain there isn't anything wrong with the models I am using.)

 

Software details: I am currently using Multisim 14.

 

Thanks in advance for your help.

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I'm having to switch to LTSpice, since this tool is not even supported. Does anyone at NI even monitor these boards?

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