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Adau1701 Phase Coherency DA to AD

Question asked by FugAzi on Mar 29, 2016
Latest reply on Mar 31, 2016 by FugAzi

Hi There,

 

I am trying to implement a predistortion loop with the adau1701. This means that a signal will be send out to the DA converter of the ADAU1701 and goes into a DUT ( which is a non linear process ). The resulting signal is sampled back in via the AD converter of the ADAU1701.

 

I would assume there is a fixed (phase )delay between the DA and AD ports which is equivalent to the sample blocksize.

In other words, if i output a 1khz sine to the DA and sample it back in via the AD, i would suspect a delay.

This delay should be frequency independent., however after doing some tests i found out that this delay is frequency dependent.  This is quite odd.

 

The test is as following:

Create a 500Hz sine block output it to DA0, sample this signal back in with a cable via AD0 and output the AD0 signal to DA1. Connect the oscilloscope to DA0 and DA1 ( 2 channel scope ). Look at the phase shift. Now change the frequency to 2000 Hz and observe the phase shift again. This is not a constant value as i would assume.

 

Is this an architectural issue?

 

BR

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