Re: Can a transformer be used to convert single ended signal to differential signal?
Yes.
Transformer...due to the symmetry of the windings, will guarantee a good 180 deg phase shift, and a good amplitude balance. And does not need a DC power source, and is immune to ESD damage. The drawbacks are the size, and sometimes the cost is higher. A benefit...if the differential output windings are center tapped, that is an excellent way to inject DC bias into the follow on circuitry.
How would you use an op amp? One inverting, and one non inverting stage? They are different topologies, so phase and amplitude tracking are questionable, also as the frequency increases, they might deviate even more since the basic op amp has limited bandwidth. Also the active device can have compression point issues generating harmonics or distorting your waveform.