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Design >> RF Design >> temperature variation of accumulation MOS varactor
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Message started by arunm on Feb 10^th, 2007, 7:53am

Title: temperature variation of accumulation MOS varactor
Post by arunm on Feb 10^th, 2007, 7:53am

Hi,
I am building an LC VCO with a total cap of around 500fF in which the accumulation varactor used for tuning accounts for around 150fF. Right now, I am using a varactor model which doesn't incorporate variation due to temperature. Can the temperature sensitivity of the varactor be neglected or will it be large enough to affect the freq range?

Thanks,
Arun

Title: Re: temperature variation of accumulation MOS vara
Post by topquark on Feb 12^th, 2007, 2:23am

Arun,

You're right- usually the temp behaviour of caps are not modeled, in particular the varactor.
They just have the voltage gradient specified in ppm/V
In contrast, you've got the linear and quadratic tempco reported for a resistor.

What I did for a process was do a.c simulation with temp sweep and observed that tempco for mos-caps varies between +ve and -ve values.
For LC-VCO design, you're better off doing such a simulation, just with the varactor and also the whole oscillator to see how temperature's affecting it.

Cheers,
Gau