Hi,
I'm working with the AD-FMCDAQ2-EBZ and noticed what looks like a deliberate differential polarity swap on Channel B for both the AD9680 (ADC) and the AD9144 (DAC). I'd like to confirm the intent and whether it's documented anywhere.
1) AD9680 analog inputs
The Channel A and Channel B front-ends (T101/T100 vs. T103/T102, ETC1-1-13 double balun) are topologically identical, but the net labels at the AD9680 are swapped:
- Channel A: top leg (T101 pin 3) = VINA_P, bottom leg = VINA_N
- Channel B: top leg (T103 pin 3) = VINB_N, bottom leg = VINB_P
So for the same signal at IN_A and IN_B, I expect the Channel B digital output to be inverted (180°) relative to Channel A.
2) AD9144 DAC outputs
Same pattern on the DAC side (T3/T12 vs. T4/T13, ADTL1-12+ / ADT2-1T+):
- Channel A: OUT0_P to T3 pin 1, OUT0_N to T3 pin 3
- Channel B: OUT1_N to T4 pin 1, OUT1_P to T4 pin 3
So identical digital samples on DAC0 and DAC1 should produce inverted analog signals at OUT_A vs. OUT_B.
Questions:
1. Is this swap intentional (I assume for routing, given the mirrored OUT0/OUT1 pin order on the AD9144 package)?
2. Is it documented in the AD-FMCDAQ2-EBZ user guide, wiki, or reference design? I couldn't find it.
3. Do the ADI HDL (daq2 project) or the no-OS / Linux drivers compensate for it (e.g. sample negation or a polarity register), or is the user expected to handle it?
4. Do the AD9680 or AD9144 have a per-channel invert setting you'd recommend for correcting it?
This matters for coherent multi-channel work (I/Q, phase alignment, DAC-to-ADC loopback testing). In loopback, A-to-A and B-to-B would come back with the same sign, but A-to-B or B-to-A would be negated, so I'd like to confirm before correcting it in my design.
Thanks!
