On a custom AD9162 board, measuring NCO "leakage" of about -41dBm. Setup : Sending a 50us pulsed 12MHz tone. NCO is programmed to 1200MHz. Below is the output. Pulsed tone at 1212MHz and a spur at 1200MHz (NCO frequency). During deadtime (or when the pulsed tone is not transmitted on the JESD Lanes) all zeros are fed to the DAC.
I reconfigured the FPGA to transmit all zeros to the DAC and still get the spur at -41dBm
Is there a reason for this spur?