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RE: Abe, Here is My Take on the REGEN and Jitterbug

John Westlake has measured the Regen & found that it reduces (practically eliminates) low frequency fluctuations that he found were riding on the USB signal & were correlated with activity of the PC. His digital scope measurements used colouring of the waveform & showed some USB waveforms which fell far outside the eye pattern. These were all but eliminated after the Regen.

It seems he disagrees with Swenson regarding the underlying issue being the ramping up of the processing of the USB PHY as the USB signal integrity worsens. According to him there is no mechanism in USB 2.0 for such increased processing, only in USB 3.0 is this mechanism seen - I've looked into it & it would seem correct

I can summarise my current understanding of the USB scenario & what has been common practise for some time in USB PHYs:
- Blind oversampled clock & data recovery (BOCDR) techniques are used in current USB PHY to recover the clock & data samples (clock accuracy is not hugely important because it's only longer term drift that matters between USB transmitter & receiver)
- BOCDR does not work any harder if the signal integrity of the signal is worsened



Edits: 09/26/15

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