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How to find overlap cap from the Spectre or Hspice sim?

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ee484

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overlap cap estimation??

How to find overlap cap from the spectre or hspice simulation?

Is it possible?

Thanks!
 

Re: overlap cap estimation??

If you are referring to CGSO and CGDO, then you can take a look at your transistor model parameters.

You can find your transistor model parameters in a text file. You can determine the path to this text file by doing the following:

Open analog environment -> Setup -> Model libraries... In my case the text file has a .scs extension.

Greetz!
 

Re: overlap cap estimation??

Wow...thank you for your reply so fast!

Actually, I am trying to consider the junction cap. at the drain of a transitor into my design.

In OP parameter of spectre, "cjd" indicates the junction capacitance of a transistor.
Does this junction cap. only talk about the junction capacitance between drain and substrate?

Thanks!
 

Re: overlap cap estimation??

I think so...

When I calculated the junction capacitances according to a formula, which I found in the book "CMOS, circuit design, layout and simulation" by Baker:

\[C_{js,d} = \frac{cj.A_{S, D}}{(1+\frac{V_{S,DB}}{pb})^{mj}}+\frac{cjsw .P_{S, D}}{(1+\frac{V_{S,DB}}{pbsw})^{mjsw}}\]

And estimated VS,DB by 1V (other parameters can be derived from your transistor model parameters) it delivered me a result pretty close to the result I found by the OP parameters: cjd, cjs.

I hope it was helpful.
 

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    ee484

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Re: overlap cap estimation??

Thanks alot!

It's helpful.
But, actually I am designing a opamp based on gm/iD method.
(Surprisingly, the result comes out faily good....I loved it)


The equation is good estimate, but I believe (I heard) that the equation does not hold any longer in short channel.

I wanted to know what Cjd means in spectre op point profile.

After I designed 1 opamp...I believe what I said was correct.

Thank you for your answers. It definitely helped me.
 

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