I have previously successfully synchronised two AD9954s by simply using a common clock and a common IO-UPDATE. I am currently attempting to do something similar with the AD9910.
I am using a REFCLK of 1GHz and generating a frequency of 200MHz. When I power up the circuit, I set all registers to their default values except for some slight variations such as enabling 3-wire serial mode and turning the SYNC_CLK output off.
Instead of the signals always being in phase, it varies every time I restart the circuit. The time difference between the two signals randomly vary between approximately 0ns, 0.9ns, 1.8ns, 2.84ns and 3.9 ns. When the signals are not in phase, there is also an amplitude difference between the signals of up to 60mV.
Could you please advise me as to what could be causing this and suggest any possible solutions?