In the AD9910's datasheet, it shows a circuit like Figure 1, used for LVPECL
and LVDS input clock. For Termination, I am not sure how to consider it. For
LVDS or LVPECL, I think the termination is different.
If you wanted a LVDS termination, the termination box (shown below) would be
replaced with a 100 ohm resistor across source’s outputs and still ac-coupled
to the AD9910. If PECL, there’s many different PECL termination schemes. As
long as the PECL signals are ac coupled, you should be fine. Maybe go to the
ADCLK944 or the AD9516 for PECL termination schemes.