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TLV320AIC3254: Audio-in interference issue

Liao JengAn
Prodigy 120 points
Part Number: TLV320AIC3254


Hi,

I have used the TLV320AIC3254 in our system design, and recently found an audio noise issue on the following configuration.

Here is our system I/O interface (included: VGA-In, Audio-In, Audio-out and internal speaker). If we connected the VGA and Audio-in source form the same NB(ex: Fig 1 &3), it got the audible noise on the internal speaker or external headphone/AVR through the audio-out port. However, if we separated the VGA and Audio-in form different NB(ex: Fig.2), the noise was just disappeared. Does anyone have seen the same phenomenon before, thank you. 

  • 0
    TI__Mastermind 30220 points

    Liao, 

    The Audio output is Analog?   do both cables have a ground connection? What kind of noise are you seeing?  do you have an FFT? 

    best regards,

    -Steve Wilson

  • 0 in reply to Steve-Wilson
    Prodigy 120 points

    Hi Steve,

    Thanks for you quickly reply.

    Yes, it’s analog audio output, and both cables have the ground connection inside of the VGA cable ground pin 5, 6, 7, 8,10 & Audio 3.5mm cable ground pin. The noise sounds like ground noise (ZiZi…), and I have no idea how to measure it with scope. Could you please tell me more detail about the FFT measurement?

    BTW, here is another finding. If we do a Ground cable connection between the NB-1 & NB-2 on Fig2, the noise was show up but sounds smaller than Fig 1&3 configuration. The noise will always be noticed if we stop playing the music.

  • 0 in reply to Liao JengAn
    TI__Mastermind 30220 points

    Liao, 

    This sounds like a simple ground loop,  doesn't really have anything to do with the TLV320AIC3254.  If you were to float the ground on the Audio Cable and connect it and the VGA cable to NB-1 my guess is that the noise would go away.  This is a system level issue.  do both the PJ and NBs use proper Star grounding?  

    best regards,

    -Steve Wilson