Dear Cadence SpectreRF Experts:
I am running HB analysis on a PLL. PLL reference is 20MHz and its output is 240MHz. Its VCO operates at 480MHz and there is a fixed divide-by-2 at the VCO output and a feedback divider that divides by 12. The total divide ratio is therefore 24. At this stage, I am only interested to have a HB analysis of the PLL to have its periodic steady state.
I use HB analysis and the setting I am using is as attached in the picture. The convergence is achieved and the simulation is successfully finished.
However, the problem is, the PLL output, the VCO output, and the feedback divider output are all at 0 from HB td results. The VCO control voltage is approximately at VDD/2 (720mV on a supply of 1.5V), the only signal that appears to be periodic in the output is the reference which has a correct period of 1/20MHz. I have attached a picture of the output.
Can you explain why is the outputs (VCO, PLL, and feedback divider) flat at 0?
Thanks!
Br,
