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eye closure under Jitter mode, but not eye mode

Question asked by ftblr10 on Jul 12, 2019



I recently try to do jitter measurement on DCA-X module 86108 for a 53G PAM4 signal. I have a deembedding function to remove a S4P file, and followed by a CTLE transfer function that applies 4dB peaking. In order to use those, I had pattern locked to PRBS13. 


Under Eye mode, I see that the eye is pretty open with 60+ mV eye height and 250+ mUI eye width. 

However, when I switched to Jitter mode, eye collapsed (complete closure) right after first pattern is acquired, as if CDR lost lock for a sec and we have samples all over the place. But the CDR remained locked seen from the GUI the entire time. 


The question is: if indeed there is a jitter event that is closing the eye, why are we not observing it under Eye mode, but only Jitter mode? We've checked that data acquisition differs in two modes by default and forced them to be the same (smoothing and averaging). That did not make a difference. 


Any idea?