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Phase Issues PCM4202

Ron Sullivan
Prodigy 20 points
Other Parts Discussed in Thread: PCM4202, PCM4202EVM

 

Customer has complaints of the PCM4202 having large phase delays .

Setup:

1) Using PCM4202 eval board

2) Providing a quadrature signal Sin to L and cosine to R channel as Inputs

3) Fs = *KHz.

4) Sweeping frequency range 250Hz. to 2500Hz.

 

Issue:

1) See only 90 deg phase difference at 250 Hz. (due to quad signal inputs; thus, no phase delay between L and R)

2) See 180 deg phase difference at 2500 Hz. (seems to have an extra and unwanted 90 deg phase change)

 

Verified the following:

1) Input signal is not saturating ADC

2) Customer claims the source is NOT distorted (i.e., at 2500HZ no extra phase distortion other than the expected 90 deg)

 

Any ideas ?

 

-RON

 

  • 0
    TI__Guru**** 189399 points

    Hi, Ron,

    Not that it matters, but are you a TI authorized distributor? You make it sound like you are, but you don't have the disty icon next to your name.

    We are pretty backed up right now. It may be a week, or even more, until we can get back to you, but I have put it in one of my apps engineer's queues...

    -d2

  • 0
    Prodigy 20 points

    Yes, I am an Apps Engineer for Arrow.

     

    I am not familiar with  any such ICON to which you are referring.  I was told to just "sign up and use the forum".

    I tried to help my FAE and his customer troubleshoot this issue and needed more information and help.

    I asked the TI rep and Arrow TI Liaison  for a TI support contact to help with this issue...he indicated that I needed to use this forum...

    Any help is appreciated...

    More details:

     Customer is experiencing unusually large phase shift between L and R channels of the PCM4202 (Burr Brown acquired) CODEC using the TI PCM4202EVM Evaluation module.
    At low freq., no or very little phase shift is seen; however at higher frequencies (within Nyquist rages based on Fs=8KHz), the phase shift increases as much as 90 degrees.
    In the setup, a sine and cosine is being used, so an initial 90 degrees phase shift is expected; however as the frequency is increase from 500Hz to 2500Hz, the phase increases from 90 deg to 180 degrees.
    For this CODEC, it is:
    1) It is not expected to see any noticable phase differences between the L and R channels (i.e. IF they shift, they should shift by the same amount at the same given frequecy) . Is this true?
    2) Fs=8KHz inplies a maximum input rrequency of 4KHz, per Nyquist. The offending frequecy is only 1/2 of that, and thus a small phase shift might be expected, but not an additional 90 degress of shift AND one would expect the L and R channels to behave the same. True?
    Can you confirm the assumptions of no shift between L and R channels?
    Can you provide possible causes of the large phase shift?


     Fs = 8K Input Freq Range = 500Hz-2500Hz L = sine wave R = Cosine wave (quadrature component derived from L channel) Checked: 1) Source - Measured the source at the input to the differential buffers on the board; it shows no phase increase between L and R channels across the freq range 2) Checked board for misatched passive components between L and R channels ; it showed no difference 3) Ensured source was not over driving buffers and within input voltage ranges 4) Considering maybe the PCM4202EVM is "bad"... Any suggestions
  • 0 in reply to Ron Sullivan
    TI__Guru**** 189399 points

    Hi, Ron,

    if you look under my name, it shows I am a TI employee. Most distributors say "distributor" under their name. Did you register with your arrow email address? if so, it should have identified you as a disty.... Anyway, it's not a big deal... 

    I really apologize, but the responsible apps engineer for this product is out of the country until late next week, and I've got no back-up for him... I appreciate your patience.

    -d2