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Measurements >> Phase Noise and Jitter Measurements >> Ken, I have a basic question
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Message started by James on Mar 29^th, 2005, 10:30pm

Title: Ken, I have a basic question
Post by James on Mar 29^th, 2005, 10:30pm

Ken,

I'm a beginer on PLL design and encounter a problem on PSS analysis.

In your paper "Predicting Pnoise and Jitter on PLL", you show that for a periodic PLL, we can use PSS ann Pnoise to see the pnoise and jitter in a PLL and I do this. Here is the question:

1. I put a pulse source in the pll schematic as the input reference frequency: 24MHz. I config the PSS and in the section of "Fundemental Tones", it shows the 24M ref input. Then I set the "Beat Frequency" as 24M too and config other sections in PSS.

2. I started the simulation and it failed. It shows "Error found by spectre during periodic steady state analysis `pss'.`V7' is a periodic input signal, which is inconsistent with autonomous circuits." V7 is the name of my input reference pulse source.

3. I deleted the V7 so there is no reference frequency input in this PLL. I still set "Beat frequency" as 24M and start simulation. It failed again and said "It cannot converge"

4. My PLL structrue is almost the same as yours in Fig1 in your paper except that there is no OSC in my pll. Instead, I use a pulse source. My divider is 8 and the VCO is suppose to oscillate at 192MHz. It works well when I do the transient simulation.

The problem is I don't know how to perform PSS simulation correctly since I've never done this before.

Best Regards

James

Title: Re: Ken, I have a basic question
Post by Ken Kundert on Mar 30^th, 2005, 1:01am

Don't specify the output of the circuit to the PSS analysis. Spectre uses this as a cue to enable its "autonomous" algorithm. A PLL is not autonomous, it is driven.

-Ken