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Varactor CV curve (Read 5968 times)
pumba007
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Varactor CV curve
Feb 24th, 2012, 8:12am
 
Hi All,

I need someone to comment on my testbench for simulating varactor CV curve in cadence spectre. Pls find the attached image.

I calculate the capacitance from calculator -imag(i/v)/(2*pi*f).

I run ac simulation and sweep the control voltage of the varactor. I am not sure if this setup is correct because when i plug in this value in LC oscillator, i do not get the expected oscillation frequency. The frequency deviation is too large. Am i missing something in the setup?

Is there other methods to obtain CV plots more efficiently?

Regards

Mani
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varactor_t.jpg
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rfidea
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Re: Varactor CV curve
Reply #1 - Feb 24th, 2012, 8:24am
 
It looks like you are using a MOS varactor. Those varactors has a very sharp transistion from min cap to max cap over tuning voltage. Your oscillator has probably a larger voltage sving compared to the voltage transition region of the varactor. This means that your effective large signal capacitance will have another value compared to the small signal value.
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