Simulation of stray capacitances (Cgs, Cgd,Cds) with double pulse test

nugzari

I would like to make a sweep of capacities. As I see in the .lib file there are Cgs, Cgd and Cds functions of voltage.

1. I would like to keep the voltage dependencies and sweep at the same time? If it works can you tell me how?

What I have already tried with 1). I define in SpiceLine2 Cgs = {Cgs} and then I try to perform sweep unfortunately did not work.

1. I would like to delete the function and sweep without voltage dependency.
   But I do not understand why in .lib file occur several times. Which function should I delete? Assuming I want to sweep Cgs, Cgd and Cds from CAB425M12XM3.

For example Cgs occurs 63 times. In total 29 MOSFETS are executed in .lib file. I expect a number which I can divide by 29.

Thanks!

Forum_Moderator

Thank you for your post, it has been approved and we will respond as soon as possible.

Bdeboi

Hello,

There are ways to sweep the device capacitances in the model file. For your benefit, the dependencies in the model for the Cgd, Cds, and Cgs capacitances are shown below.

You can use the scaling parameters that already exist - 'ags', 'ads', 'agd', and 'CgdOffset'.

ags, ads, and agd scale the Cgs, Cds, and Cgd capacitance by their respective scalar. So, for example, if you set 'ags = 0.5' in the spiceline, then it will scale the entire Cgs capacitance curve by 0.5.

The 'CgdOffset' parameter adds an offset to the Cgd capacitance (this offset is not multiplied by agd).

By default, these parameters are not set to 1. So, for your sweeps, you may consider setting them all to 1 (0 for CgdOffset) to establish your baseline.

Let me know if this level of control works for you. If not, we can explore some other options.

By the way - here is how you can identify the MOSFET subcircuit that is being used by your model.

First, find your module .subckt statement. Below is for the CAB425M12XM3. You'll see two parameters - 'die' and 'level'. Sum these parameters to get 23 — this is the subcircuit number you want to look for. If you change the 'level' parameter in the spiceline it will change which model is used.

Thanks,

Brian

BlakeNelson

I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.

Blake