I was looking at a design recently that had a 100 ohm differential pair feeding into an LVPECL Line Driver/Receiver and on the far side they took the Q! and grounded it through a 150ohm resistor and then took the Q and feed it to a 50ohm SMA in addition to pulling it to ground with an additional 150ohm resistor. Of course I can't get a hold of anyone to ask how they came up with that system, but I am a little perplexed. I tried looking around for some app notes, but couldn't come up with anything. I am sure it is something simple I am overlooking, but it is a little odd to me on first glace. Anyone know why you would do it like this (and come up with those resistor values) as opposed to going through an RF transformer (like they do other places in the same design)?