TTL -> SPDIF -> TTL (why the capacitors?)

[snoopy33]

Just wondering why 0.1uF capacitors are used pre and post transmission?

When I put a scope on the line the skew of the signal is considerably worse. It may not matter (haven't got that far) but I don't see a reason to degrade a digital signal?

 

[Tiido]

The signal is supposed to be AC centered around 0V and these capacitors will help to achieve it.

 

[MarcelvdG]

On the receiving side a capacitor is needed to bias the first inverter as an amplifying stage, which is necessary because the S/PDIF swing is much less than the levels that an inverter normally works with. On the transmitting side, it's probably needed to meet the S/PDIF DC voltage spec. A DC level of 0 is convenient when you want to transformer-couple the signal to eliminate ground loops (you don't need to worry about DC current saturating the transformer core).

 

[snoopy33]

Ah of course, on the receiver is stops the 3.3v bias draining away. Got it!