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AD9680 channel time alignment delay

Question asked by hyperdyne on Aug 23, 2017
Latest reply on Sep 26, 2017 by UmeshJ


I am looking for any answers to why the 2 channels on the Eval kit board have a time (phase) delay that varies with frequency? The sample rate is 1GHz.  We have tried this in zero IF mode and with the mixer/NCO enabled. 

 

If I sample a 10MHz sinusoid real-valued input and feed it into both channels 1 and 2, I should see the same signal time aligned on both channels.  Using the Analog oscope we see this for 10MHz.  It shows both channels are time (phase) aligned.  However if I move up to a 300 MHz sine, I get a 30 degree phase shift between channels 1 and 2!  Going up to 700MHz and bandpass sampling will result in a 300MHz sine also, but the phase delay between channels 1 and 2 is now 55 deg!

 

This experiment tells us that as we go up in frequency, the alignment between sampling both channels is compromised.  But this shouldnt be happening, as we are synchronizing 2 channels on the SAME chip.  We tried the soft reset and  SYSREF mode with no change.  We even removed the baluns because we thought it might be them, but issue still remains.  We tried this on 2 units with same results.

 

Is the AD9680 capable of synchronizing the sampling of multiple channels?  And if so, how?  We cannot get this to work and is jeopardizing the project.  Which means we are ready to go to a competitor since we have been unable to rectify this issue.

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