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Sync Problem with AD9914

Question asked by MichaelK on Feb 16, 2016
Latest reply on Mar 3, 2016 by JLKeip

Hi all,

 

i want to sync four AD9914. The setup is shown in the attached pic.Blockdiagramm.png

The REF-clock is distributed by an AD9508, also the Master-Sync_out signal is distributed by an AD9508.

The IO-Update signal is synced with the Master-Sync-Clock via D-FlipFlops and is applied to all DDS simultaneously all the time.

All traces are length-matched. The REF-Clock-signals are in phase, also the Sync-in signals are in phase.

 

I do the sync procedure described in AN-1254.

 

Everytime i do the sync sequence, i get the same fixed phase offsets between the 4 channnels.

The phase offsets are constant.

I tried to change the the SYNC_OUT delay on the Master (Reg 0x1B [5:3]) to sync the REF-Clock to the SYNC-IN but i always get phase-offsets between the output signals.

 

If i skip step 5 (AN-1254) "set the CAL with SYNC-bit (Reg 0x1B [6])" and perform another DAC CAL to each device, i get random-phase-offsets.

 

I think, there is some kind of synchronisation, but i always get these fixed phase-offsets.

 

Unfortunately i cannot check the SYNC-Clock outputs of all four DDS-devices.

 

Is my setup in general correct?

Any suggestions?

 

Best regards,

Michael

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