I've been studying the ADAU1361 evaluation board and noticed an odd thing how the differential input and output connectors are connected in their schematic on its user guide, page 7, focus on the left differential connectors:
Notice how the ring and sleeve of the TRS connectors are both connected to differential output negative terminal.
While the left differential input terminal is hooked up as follows:
Notice how the sleeve is connected to ground, ring to the positive left input and tip to the negative left input. (the MIC_BIAS is off and J15 is open, the parts with "OPEN" mean they're unpopulated in default configuration)
So the questions about this implementation, considering the case if the left differential input and output was looped back with a TRS cable, are:
- Wouldn't the ring signal get simply shorted to ground, losing the negative input?
- Why tip on output connector is connected to positive output, while the tip on input connector is connected to the negative input? Wouldn't this immediately cause an inverted 180 degree phase shifted signal being read by the ADC?
- Is there a true TRS standard for balanced differential signals? Is it the same for both input and output directions? (one resource on sound system interconnection by Rane shows tip for positive terminal, ring for negative, sleeve for shield/ground.)
