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.pdf

Ken'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

Verilog-A is the "analog only" subset of Verilog-AMS, which is a full analog and mixed-signal language and includes (in principle) everything from IEEE 1364 Verilog.