why does SPDIF signal need a transformer?

[ilikebbs]

I have seen a circuit.
It convert SPDIF signal to differential signal. And it connects the differential signal to a connector via transformer.

so I do not know why the circuit is designed like this.
does the transformer must be needed?

thanks,

 

[Externet]

To match impedances of the circuitry to the standard, to isolate grounds to prevent loops; to convert unbalanced/balanced signals.

https://www.cirrus.com/en/pubs/appNote/AN134REV5.pdf

 

[flatulent]

In some LAN networks on military aircraft, the transformer circuit includes two series resistors. That way an open or short fault in the semiconductors do not bring the network down.