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