Calven,
If you are going to build a PLL model for Spectre, then the models need to written
in Verilog-A. AMS Designer supports Verilog-AMS. There are some model templates,
on this site under the Verilog-AMS link
http://www.designers-guide.org/VerilogAMS/There is a lot of information about PLL modeling under the Analysis link including
http://www.designers-guide.org/Analysis/PLLnoise+jitter.pdfKen's classic paper of behavioral modeling of PLLs. One other library that may be useful
in the Cadence libraries is bmslib it contains Verilog-A primitives for logic gates that can
be used to create Phase/Frequency Detectors.
Best Regards,
Sheldon