Hello , There is this good single ended to differential converter.
two questions:
1.my input single ended signal is AC, I gues that Vocm is common mode.
What do I need to do with the Vocm input?
2.our goal is to convert single ended to differential , what is the role of feedback resistor Rf Rg?
feedback is good for bandwidth and gain.gain bandwidth product.

How can I know to what purpose I should tune them for good functionality.
https://www.analog.com/en/resources...-ended-to-differential-signal-conversion.html

 

you need to study OpAmps and read the article, everything is there. you can connect Vref to 0VDC if you do not need offset. if you want it, connect to a wiper of linear potentiometer and connect ends to +5V and -5V. Rf and Rg set overall gain of the circuit.

 

ALSO, study the application drawings for that amplifier.
Your "single ended circuit" has a return path someplace. So where do the application circuits connect the input signal return side?? It certainly looks like the input return ties to "Vref" in this case. Before yu power it, though, be sure that neither input connection exceedsthe voltage ratings.