Hi Jim,
Thanks for your reply - however, these facts I can read from the ADL5566 datasheet and as mentioned we have been using said device for two years now.
I am more looking for experience reports on using ADL5566 and AD9681. And specificaations on AD9681 input impedance.
That is: is the AD9681 input impedance roughly constant/benign over the frequency range of 100..350MHZ - in the datasheet it is given as 160Ohms (but at which frequency? are there s-parameter or other files?)
In order to leverage optimum performance I would add some 20ohms on both diff lines when connecting the output of the ADL5566 (such that I load it with the desired 200ohms). Having a 10dBm output at the driver, (2Vpp, 200Ohms) I reach around 1.6Vpp at the ADC input.
(I am especially asking this because our current ADC has an input impedance of 50Ohms differential - so at a 10dBm output, I add around 50-80Ohms on each diffline, and end up having ~400..500mVpp, which is a factor of 3..4 lower => max SNR I loose 1..2 bits)
Thanks for any input.