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PCM3168A: Output of ADC is configured

Shifali N
Expert 2175 points
Part Number: PCM3168A


Hi,

I am using PCM3168APAP in my design for differential audio input and differential audio output. I have attached the signal flow in the attached block diagram. I will be giving differential input audio using mobile phone. And output is connected to speaker. I have few queries regarding Audio.

1. Is the audio input sourced by my Phone balanced audio?

2. Since the input is balanced, the positive and negative data will be out of phase by 180. But they will have similar amplitude. Hence wont the output of amplifier be 0. As Vout of differential amplifier is Vout=Gain(V+-V-).

3. If data sent through balanced input audio is different, how will ADC convert it to signal digital data output. Will it consider data only from positive channel or data only from negative channel.

4. My requirement is Mono Balanced Audio. So I am connecting Audio input in my board to Phone using TRS jack. Currently I have connected Tip to positive, Ring to negative and ground to sleeve. Since TRS can also be used as stereo left and right channel, how will the differential come to know whether the data received is balanced or stereo left and right channels.Audio signal flow.pptx

  • 0
    TI__Mastermind 29765 points

    Hi,

    1. Phone is usually stereo where else balanced audio is differential signal, same amplitude but reversed polarity.
    2. The amplitude will be doubled when it goes thru differential amplifier.
    3. Balanced audio is always same amplitude but reversed polarity. I think you are confused with stereo signal.
    4. The phone is stereo as mentioned above and not balanced, you will need to send this signal say the tip side to a single ended to a differential amplifier to get the balanced audio. Mono means only 1 side sound say left or right, but this sound coming out is single ended or unbalanced so to get balanced audio you need to convert it. What you have connected will only create noise as you are taking the difference between the left and right side which are not same tone/sound. What you can do is to take the tip to VIN+ and GND to VIN- and configure as single ended input instead of differential.

    You can search the web for more information on audio balanced/unbalanced, mono/stereo. 

    Regards,

    Peter