Hi, I'm designing a circuit with 2x PCM1794a in Mono mode and differential outputs where absolute phase is important.
It is pretty obvious from the datasheet that in Mono mode, one channel gets phase inverted, otherwise the application in Figure27 would not work.The assumption would be that the opposite channel is inverted, so that if it's strapped to Mono Mode Left Channel, the right channel is inverted and vice versa.
The polarities don't make sense to me though. Going through the logic:
- The Figure25 circuit retains absolute phase, where a positive-level digital input translates to a positive analog output voltage at the summing buffer.
- In the Figure27 mono application, there is no phase inversion on either the left or right channels
- The output of the left channel Figure25 section is called "OUT+" and the right channel "OUT-"
- However, the OUT+ signal is tied to XLR pin3, which is the negative/cold pin and thus results in a phase inversion. Why is this done?
Similarly, if one has two identical circuits for left&right channel with only the Mono mode strap being different between the two, one has to also invert the polarity of one output XLR to achieve similar phase between the two channels?
