sheldon
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Matteo,
Spectre RF supports a technology called the Noise-Aware PLL flow. It is an automated tool for PLL behavioral modeling. The key is the VCO model. It will allow you to replace VCO with a behavioral model and still make a good estimate of PLL characteristics, for example, phase noise. While you can simulate at the behavioral level, my usual configuration is PFD/CP/loop filter at transistor level and VCO/divider at behavioral level. This gives a good speed-up and captures most of the nasty non-idealities in the loop: charge pump mismatch, etc. Most of my test data has a 2x VCO so I include the divide by 2 in the VCO characterization. One other comment, you will need to set the VCO number of points per period to a reasonable value. I like 50 but you can get away with less. If you have access and want more information there have been several presentations at CDNLive over the years on the technology.
Best Regards,
Sheldon
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