Different PSS and Pnoise result with different Fund and sample_ratio settings

Hello everyone,

I am using ADE assembler in IC23.1 to simulation my circuit, which include a 25% dutycycle generator (working frequency is fck) followed with a div-4 (driven by 2 stage clock buffer).

I did two experiments with two different settings on PSS+Pnoise to measure the RJ at the 25% dutycycle generator output (rising-edge). But the PSS time domain waveform and edge phase noise looks different.

1st experiment: div-4 was enabled, set "Fundamental frequency" in PSS as 4*fck, and "sample ratio" in sampled jitter as 4;

2nd experiment: disabled div-4, set "Fundamental frequency" in PSS as fck, and "sample ratio" in sampled jitter as 1;

Based on my understanding, 25% dudycycle generator are driving the same loading in above two experiments and I expect PSS time-domain waveform and edge phase noise at generator's output should be the same in above two experiments.

However, PSS time-domain waveform at the generator output with div-4 disabled has slightly slower rising edge than counterpart of with div-4 enabled.

And in edge phase noise curves, low offset frequency range, noise between two cases is almost the same, but in high frequency range, the different is ~4dB.

I would like to know:

1) How does "sample ratio" work in sampled jitter work to measure Jee or edge phase noise?

2) Any explanation to this difference between above two experiments?

Thanks and regards,

Yutao

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