Algorithm for obtaining eye pattern for USB compliance test

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advaita

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USB compliance test

Hi

I read that for compliance test USB output has to satisfy a particular eye diagram.
Can anyone point me to the actual algorithm used by scopes to obtain the eye pattern for this?

Basically, I want to know whether only cycle-cycle peiod differences are important or is the accumulated phase also important. If anybody knows this please tell.

Thanks.
 

Re: USB compliance test

Hi Iouri

Yes, I've seen usb.org but still it is not clear whether it is the cycle-cycle jitter or the phase jitter that'll close the eye. I'll post this question on their forum also.

On first thought it seems that phase jitter will be considere in the eye opening.

But, on second thought as the allowed frequencies are (480M-240K) to (480M+240K), so while doing the compliance test one won't be able to feed the exact clock frequency as expected. So, there will be an undesired phase drift seen in the clock.

There must be way in the scope that it plots the eye with a trigger based on the input signal. This way only cycle-cycle jitter will affect the eye and not the phase jitter.
 

Re: USB compliance test

Hi advaita,

I also want to measure the eye diagram using scope but I still dont know how to measure because the time transfer from CPU to USB mem is so small when I read or write to USB mem.

Have you found out the way to do it? If yes, please share it with me.

Thank you,

Test_out
 

Re: USB compliance test (urgent)

Hi,

I am using Oscilloscope: 54825A for measuring the USB characteristic. But in the analyze option I cant not find the USB test option? Any thing wrong with my oscilloscope. And one more thing, how can I know I have E2645A or not?


Thank you very much
 

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