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PCM1742: Output noise due to all-zero data

Sadanori Kato
Guru 36530 points
Part Number: PCM1742
Other Parts Discussed in Thread: PCM1789

Hi,

When all-zero data was input to the PCM1742, 70Hz with a noise level of about -108dB and odd-order harmonics appeared from the delta-sigma modulation output. Is this a known symptom?
These noises can be improved by inputting minute signal data to the PCM1742.

Best regards,
Kato

  • +1
    TI__Mastermind 24260 points

    Hello Kato,

    Yes, I have seen this in other DACs of similar family. You can MUTE  it in this case.

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Guru 36530 points

    Hi Arash-san,

    Thank you for your prompt reply.

    Could you please tell me the reason why continuous input of all-zero data causes tone noise with the delta-sigma modulator?
    This symptom doesn't occur with the PCM1789 and other PCM DACs.
    Additionally, the software mute functions cannot be used since PCM1742 is used with hardware control(default setting). So, please let me know any other workaround if possible.

    Best regards,
    Kato

  • +1 in reply to Sadanori Kato
    TI__Mastermind 24260 points

    Hello Kato-san, 

    This device is very mature and i don't have any documents for its internal design. Without the internal information about this device and PCM1789,  I can not comment on differences but my guess is that modulator and  OSR are not the same and thus have some different performance. 

    This device has zero detect and  can be used to operate external mute circuits. In fact this is what datasheet suggests as possible use of these flags.

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Guru 36530 points

    Hi Arash-san,

    Thank you for the information.

    I understand and will contact you if I get any additional questions from our customer.

    Best regards,
    Kato