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Synchronizing AD9874 to aquire on symbol center

Question asked by bmackenzie on Jun 25, 2011
Latest reply on Jul 5, 2011 by PMH



I am using an AD9874 in a four-level FSK demodulation scheme. And, mathematically, i'm able to configure the AD9874 to digitize my IF at a frequency that is exactly an integer multiple of my symbol period. Everything is working smoothly, i'm aquiring data as would be expected, and the data is good.


However, here's the catch: Due to the fact that the AD9874 is operating off it's own clock, there's nothing to ensure that AD9874 is capturing in the middle of the symbol period. The device is going to capture at some arbitrary point within the symbol period, then at the symbol period from that point on. Also, not the end of the world, I can determine "center symbol" in several ways. However, it doesnt seem that i'm able to effectively tune the AD9874 during this process such that I know when, exactly, during the symbol the AD9874 is going to capture.


Is there any way to skew the timing on the AD9874 such that I could "tune" the capture rate to achieve what i've outlined? I see that there are standby modes and whatnot, but none of them seem to have definite timings associated with their startup times (ie: values are depicted as <1ms).


I understand that this approach (eg: sampling once at "center frequency") isn't ideal. This is more of a matter of curiosityfor me -- I'm trying to take the easy way out of a problem


In the event that the AD9874 isn't able to be reliably tuned to center frequency, I suppose i'd have to take the approach of capturing as many samples as possible then determine center symbol in post processing. Does this seem more logical?