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Modeling >> Behavioral Models >> monitoring frequency to adjust for drift
https://designers-guide.org/forum/YaBB.pl?num=1132391021

Message started by svensl on Nov 19^th, 2005, 1:03am

Title: monitoring frequency to adjust for drift
Post by svensl on Nov 19^th, 2005, 1:03am

Hello All,

I was wondering how I would be able to determine the centre-frequency of a VCO by looking at its pulse-train output.
Naturally, the frequency of a VCO will drift with temperature and; therefore, might not be centered at the desired free-running frequency anymore. Essentially, I would like to extract the free-running frequency (or “middle”) by monitoring the output of the VCO to use the obtained signal as a clock for some other circuit. The more constant the period of the obtained signal the better.

I considered using a PLL with the VCO output as a reference signal and choosing the capacitance and resistor of the low-pass so that the time constant gets very large and the PLL outputs the free-running frequency of the VCO. This however, requires large values for the capacitance. Are there any other possibilities?

Thanks for any feedback.

Regards,
Sven

Title: Re: monitoring frequency to adjust for drift
Post by jbdavid on Apr 1^st, 2006, 10:20pm

I think you'd need to know something about the input voltage that was generating the frequency..
I.e keep track of the frequency, but onl y record it when the loop filter voltage was at the level you think of a "free running" .. ?

But there aren't a lot of device models who model thermal transients, and if you don't use ones that do, you will not get any variation due to temperature increase..
jbd