ADV7842 analog input resistances

this is interesting to read, I don't think I found this info in the datasheet but I could be mistaken. I guess this wasn't the case for ADV7800 right? if it is a must, then I will follow it.

to my understanding, I should put those 2 resistors as close as possible to video connector itself not the adv7842 pins right? then use 50R routing for each individual trace from the 2 resistors to adv7842 pins right?

notice that the input video will come from 75-ohm terminated cables, how will that affect the operation? and maybe it will come from non-terminated cables... please advise if there is a difference.

thanks

Yes, place 2 resistors close to the connector.  Use 50 Ohm traces from there.  Don't forget the DC blocking caps.

The 25 + 50 to ground will match the 75 Ohm cable.  The 7842 input is high impedance so it really doesn't affect the cable.  The eval. board works fine up to UXGA60 which is ~154MHz data rate.

In general you want to place the 7842 close to the connector too.  Don't run it across the board.  Although your formats are so slow the whole layout is rather tolerant.  Running long distances with poor impedance matching at high pixel rates can cause reflections causing image ghosting.  Been there, done that.  Copy the eval board.

Older designs where based on 75 Ohm PCBs.  You'd really need to check the layout to see that it's designed that way.