Differential to Single Ended with transformer?

[youngguns21]

I have a RF switch that I would like to select between two clocks (125MHz and 150MHz). The clocks are both LVPECL signals, 100ohm diff pairs. The SP2T inputs are 50ohm single ended.

Can I use a balun for the Diff to SE transform?
What kind of termination would I need on the diff pair side? 100 ohm resistor?
W
What is going to happen to the signal level at the 50 ohm side?

 

[mtwieg]

RF transformers are often used for this purpose for RF ICs. They can also be used for various logic families, so long as you respect the needs of the biasing and impedance matching on both ends.

For interfacing a 100ohm diff pair to 50ohm SE, use a 2:1 transformer. The 50ohm on the SE side will present the required 100ohm on the diff side, but only at high frequencies. IIRC the outputs of LVPECL need external DC biasing as well. Using a center tapped transformer might make this easier.

 

[youngguns21]

That is what I thought. And to be clear, the 100 ohm diff pair would be connected to the side of the balun with the higher turns ratio? And no resistor is needed for termination on either side of the balun?