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PCM1862: Question for PCM1862 regarding internal PGA

Kazuki Kuramochi
Expert 7190 points
Part Number: PCM1862

Hello Expert,

I have questions for PCM1862's internal PGA.
Would you answer following questions?

1. Would you provide the min/Max data of PGA gain error against configuration step(0.5dB)?(For example, it is 0.5dB+-0.2dB)
2. Is there any issue except output data spatulation when we configure PGA gain as causing saturation?(For example, configure gain as +32dB for 2.1Vrms input)
3.Is there any risk as like as causing damage on device when we change  I2S BCLK's frequency without stopping I2S?
4.We expect that we can convert audio input signal to 0dB but we observed distorted audio data at approx -2db under specific condition as below. Would you tell me following behavior is expected?
 We configured ch as differential and 15.5dB and input analog audio signal that is smaller than 2.1V. Then, we expect we can observed undistorted signal until 0dB on digital audio output. However. digital audio data have  distortion from -2.1dB.

I'm looking forward to hearing back from you.


Best regards,
Kazuki Kuramochi

  • 0
    TI__Genius 13610 points

    Hello Kazuki,

    I will take a look at these questions you have and return by week's end.

    Best,

    Carson

  • 0
    TI__Genius 13610 points

    Hello Kazuki,

    1. This spec does not currently exist, but it should be expected within 5%

    2. Its unadvisable to intentionally clip as it can unanticipated higher levels of THD+N.

    3. It would not damage device but it could introduce a clock error and possible irregular data output

    4. Not 100% if I understand what your asking but if you take a look at figure below you can observe how distortion shoots up right before 0dB is reached

    Let me know if this answer your questions

    Best Regards,

    Carson

    Low Power Audio Applications

  • 0 in reply to Carson Allen
    TI__Expert 7190 points

    Hello Carson,

    Thank you for your reply and sorry for my response.
    1. I understood
    2. We can accept clipping on output data by excessive gain for the input amplitude.
    3. We will disable the device that receive I2S signal from PCM1862 during this on-the-fly I2S clock change. Therefore clock error and irregular I2S can be ignored.
    4. Sorry for my cheap explanation. Customer observed "clip" at approx. -2dB. Your showed graph said THD+N @0dBFS input is -80dB so I think we shouldn't be any clip until input signal exceed 0dB including 15.5dB internal gain.
    Also, they haven't any clip until output data reached at 0dBFS when they used single-ended input mode.
    However, they observed clip at -2dB when they used differential mode input using as single-ended input(short one side of input to GND).
    Would you tell me why unexpected clip happened only with differential input mode?

    Also, I received new question for this device.
    Would you also answer following question?
    5.Our customer want to assert signal on INT pin when detect clipping input. Therefore they enabled 0x60 bit4 POSTPGA_CP.
    However, PCM1862's behavior only monitoring analog signal and ignore Digital PGA due to output data is clipped even though INT pin haven't asserted.
    Also, I found the register that is DPGA_CLIP_EN(0x05 bit 5)
    Should I enable DPGA_CLIP_EN for monitoring clip including DPGA?

    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Genius 13610 points

    Hey Kazuki,

    Thanks for providing more explanation, I will look further into it along with your 5th question.

    Best Regards,

    Carson

  • 0 in reply to Carson Allen
    TI__Expert 7190 points

    Hi Allen,

    Is there any update?


    Best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Genius 13610 points

    Hey Kazuki,

    Thanks for your patience in regards to 5. I would enable DPGA_CLIP_EN in order to get clipping detection since clipping detection only occurs post digital pga. The DPGA_CLIP_EN is the actual bit to enable system to detect while POSTPGA_CP is actually just enabling interrupt for that detection. This seems like the datasheet should be more clear, thanks for pointing out.

    As for 4. could you provide me how you set the gain to 15.5dB like how much gain does analog vs digital have? Also are using MICBIAS and what are resistor values if you are.

    Also have you considered using automatic gain control in situation and see what the gain is changed to?

    I look forward to hearing back

    Best Regards,

    Carson

  • 0 in reply to Carson Allen
    TI__Expert 7190 points

    Hello Allen-san,

    I got detailed waveform regarding question4 and will share it by mail.


    Thank you and best regards,
    Kazuki Kuramochi

  • 0 in reply to Kazuki Kuramochi
    TI__Genius 13610 points

    Hello Kazuki,

    I see your email and will respond to the spreadsheet there and close this thread.

    Best,

    Carson