I'm trying to use AD9172-FMC-EBZ in NCO-only mode. I bring up the JESD link and then configure the data chain to use the main 48-bit NCO only, using the ADI no-OS API. It seems to work, but the DAC output signal level is only about -73 dBm, when the DC amplitude register has value 0x7FFF. Decreasing this register value decreases the output signal level correctly.
I have verified that register 0x1E6 bits 0 and 1 are as expected.
Ramp up/down block is disabled. I also verified that forcing ramp down disabled the output signal.
We also bought AD9176-FMC-EBZ, and it behaves exactly the same way, so it is not a FMC module hardware problem. Seems that I just fail to program the converter correctly.
The datasheet says on page 66 that "Mode 3 and Mode 4 can be used to generate a single-channel or dual channel NCO only mode of operation, respectively." Does this mean that the other JESD modes can't be used in NCO-only mode? I don't see why that would be the case. For example, here Matti uses mode 0:
Synchronizing phases of DAC0 and DAC1 in AD9173 NCO only mode
The carrier is our own and well tested with other FMC modules, so I don't believe it causes any troubles here.
I have tried a couple of modes, but the result is always the same. I'm kind of stuck with this, so any advices are warmly welcomed.