PLL -- Phase Locked Loop

Wireless & IoT
1

Dear expert

I had to get your advice on troubleshooting the PLL circuit. The PLL is the feedback path,thus it make me confuse during the thoubleshooting.

PLL circuit consists of Phase Detector,Loop Filter,VCO,Divider and amplifier.

There is not output frequency “not signal”.

Q: As it is the feedback path so it hard to know which component having the problem becos all the component in the loop having the chances to cause not output.May I know what is the best way to troubleshoot this feedback circuit?

Please advice.

Thank you very much

Peter.

2

I’m not an expert but I would start by disconnecting the input of the VCO from the loop filter and putting a known voltage there. Then you can test that the VCO works and is controlled by its input, and then test that the divider, amplifier, and phase detector work in turn. PLLs are hard to diagnose but the usual problems are that they won’t lock or that they have too much noise.