I am using the AD9637-80, and it works fine up to 65Msps.
But when I increase the sampling frequency to 75MHz, I get corrupted data.
I checked the timing with my scope, and found that at 65Msps (=780Mbit/s line rate), I see the data lines changing app. 600ps after the DCO edge.
But at 75Msps (=900Mbit/s line rate), I found that data changes app. 90ps prior to the DCO edge.
For a better visualisation of the problem, I attached two scope shots, taken at 65Msps and 75Msps.
CH1 and 2 are always DCO+-
CH3 and 4 are always D+-H
Can you explain this behavior to me?
Thanks in advance,