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AFE7700: Random signal phase delays in DAC channels

Oleksii Shako
Prodigy 50 points
Part Number: AFE7700

Hi!

I`ve figured out during measurements, that in DAC channels signal has different phases as shown in the picture:

And these delays a bit varies from board powerup to powerup

I expect to have fully coherent signals since the board layout and cable lengths are fully equal between channels and the test setup coherence was calibrated and verified.

What can cause this issue?

During the AFE configuration Sysref is in continuous mode, may this affect on this behavior?

Thanks and waiting for your prompt response!

  • 0
    TI__Genius 10865 points

    Hi Oleksii,

    Because of differences in routing lengths in AFE7700, there will be some phase difference between channels. However this difference should not change from powerup to powerup. If phase difference between channels of only one device is considered, continuous SYSREF should work. 

    If delays are varying only slightly, it may just be due to noise. Please average the phase difference over many cycles in each power-up and check if it remains constant. 

    Regards,

    Vijay

  • 0 in reply to Vijayendra Varma Siddamsetty
    Prodigy 50 points

    This behaviour could be simply reproduced on EVM:

    1. After the configuration in the latte was done successfully, I enabled the signal generator using these functions:

    AFE.TOP.enableSigGen(1)

    AFE.setSigGenTone(True,15,-5)

    2. Each next call AFE.setSigGenTone(True,15,-5) cause random phase jumps in DAC sine waves relative to each other.

    Could you please double-check this behaviour on your boards?

    Thanks,

    Oleksii Shako

  • 0 in reply to Oleksii Shako
    TI__Genius 10865 points

    Hi Oleksii,

    The internal test tone phases are not synchronized. Only the main signal path from JESD204 interface to DAC output delays and phases are synchronized based on SYSREF.

    Regards,

    Vijay