Large signal sp analysis in virtuoso

Dear Transin,

> How is it possible to perform a large

> signal analysis for a varactor?

I have answered this question multiple times in this forum. You might want to review the methodologies outlined at URL:

community.cadence.com/.../plotting-output-capacitor-of-the-mosfet

community.cadence.com/.../simulating-mos-varactor

Let me know if either of these posts do not provide the information or insight you were hoping to find!

Shawn

 so by plotting the imaginary part of Iprb0/(2*Pi*Vac*f)  I will get the right result? Should I change something? 

Dear Transign,

Transign said:

so by plotting the imaginary part of Iprb0/(2*Pi*Vac*f)  I will get the right result? Should I change something? 

1. The impedance is given by the following: Z = V/I. and the resulting imaginary part is Im{Z} = Im{V/I}. The effective capacitance is derived as:

Xc = 1/(jwCeff) where Xc is the imaginary part of V/I. Hence, the effective capacitance is: Ceff = -1/(2*pi()*f*Xc). I don't think this is equivalent to your expression "Im{ Iprb0/(2*Pi*Vac*f)}".

2. Since I wrote some of those posts, the analogLib now contains an "ac resistor" model for its res. You might consider using this in lieu of the 100 H inductor. I have found, in some cases, using the 100 H inductor presents convergence issues while the use of a high value ac resistor does not.  Figure 1 details where to specify the value for the AC resistance model of an analogLib res.

Shawn

Figure 1

Yes, now it works thanks! One last question, how could large signal analysis performed in the case of a varactor (for Ceff)? I would like to take into consideration the non-linearities when it comes to VCO design

Dear Transign,

Transign said:

One last question, how could large signal analysis performed in the case of a varactor (for Ceff)? I would like to take into consideration the non-linearities when it comes to

There is no difference in the methodology with the exception you perform a transient analysis at one or more frequencies, determine the real and imaginary impedances at the applied frequency and compute the effective capacitance at the applied frequency. Note you must compute the impedance at the applied frequency.

Shawn

I am trying to perform but it seems unable to give rational results. Is there something wrong in the setup ?

Dear Transign,

I am sorry, but you have not provided me with enough information to resolve your question. I do not know your expressions nor what "rational results" might be.

Shawm