How to calculate the capacitance of a Varactor?

 Hi Hamid,

 When you compute the capacitance using Y11, what frequency are you using? Are you familiar with this:

Hi Shawn

Thanks for your answer.

The frequency I have used is the same for both analyses. Both are in 40GHz.

Besides, what you mentioned, is it a link? Definitely I have no idea about it :-)

Best

Hamid 

 Hi Hamid,

The URL was pointing to a Cadence solution concerning the derivation of y11 from the sp analysis. The support number is:

 20148716. I was able to access the support article by doing a search with this number. Perhaps you can try, The title of the article is " How to calculate y parameters using SpectreMDL?". I appears the expected syntax to obtain y11 is not the expected syntax.

Shawn

Hi Shawn

Thanks again for your response. It seems that at Cornell I do not have access to those support files. Is there any way for me to get that link?

Best

Hamid 

Hi Hamid,

I am only a Cadence customer and hence can not provide any information as to why you cannot access their support site. Sorry! Perhaps you need to speak with your Cadence representative at Cornell.

Sorry,

Shawn 

 HI Hamid,

One other thought cam to mind. You mentioned that the capacitances matched between the two analyses at a few points, but the slopes were significantly different. I was wondering if the frequencies used in the sp analysis and AC analysis were different and if the frequency step size is not sufficiently small. Specifically, if one analysis used only a few points per decade and the other contained a few points per linear range, since the C-V characteristic is non-linear and your delta frequency step is different between the two analyses, you may compute a significantly different slope. Have you tried using the same frequency scales for both analyses and increasing the number of frequency steps per decade?

Shawn

Hi Shawn

Both analyses are done only at 40GHz. 

 Hi Hamid,

I guess without any further information, I would try to run a large signal analysis using a 40 GHz sinusoid at a few amplitudes (one to mimic small signal case) and compute the varactor capacitance from the resulting impedance. This is what I typically do to determine the impact of its non-linear capacitance as a function of waveform amplitude. Hence, perform a transient analysis, determine the impedance at 40 GHz (DFT function at 40 GHz) and compute the effective capacitance to compare with your AC and sp analyses.

I hope this helps resolve the issue.

Shawn