I'm using the AD9957 evaluation board and software and modulating at 40MHz and using the multiplier (x25) to obtain a 1GHz clock in QDUC mode. Also, we designed our PLL loop filter from the tool provided and populated the board. For the most part, we see what we expected from the simulations, however there are a few questions I was hoping to get answered:
- We seem to lose the PLL in quadrature modulating mode, the light on the software control window blinks. This doesn't happen in singletone mode. As far as I understand from the data sheets these modes shouldn't affect that, so why is it losing the PLL lock in quadrature mode?
- Is it normal to see spurs on the spectrum analyzer every 25MHz (clock frequency) from the center frequency? I attached a picture of this phenomenon.
- What is PFD and Antibacklash PW? The data sheet and user guild seemed to skip what those are, but they're on the Control view window for the evaluation software. How do these affect the performance?
Thanks in advance for any assistance you are able to provide.