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AD9106/AD9102 clock issue

I have a really strange issue with SPI communication on the AD9106.

When I disable my DAC clock (TI CDC421 156 MHz LVPECL), SPI communication (330 kHz) works great, but when I turn the DAC clock on, I lose SPI communication-- I can no longer read from the registers.

How could the DAC clock affect SPI communication?

Perhaps I'm not terminating my DAC clock or AC-coupling it properly, but I think it's fine:

I see the common mode voltage properly sitting at 0.9 V and I see a 500 mV peak-to-peak swing from CLKP to CLKN

One thought is that there might be a setup time issue that arises with using the faster clock.

Or, if I'm not terminating it correctly, there's some sort of over-current issue?

I'd really appreciate some insight into what might be going on.


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