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PCM1804 Dynamic Range - Input?

Richard Meidl
Intellectual 370 points
Other Parts Discussed in Thread: PCM1804

The data sheet for the PCM1804 says the typical dynamic range is 112 dB.  Is that the dynamic range of the analog input?  The data sheet says that the Analog input voltage, full scale is 5 V p-to-p which is about 7 dBu.  Can the PCM1804 digitize signals down to -105 dBu?  What are the preferred input levels or input range for best performance?

Thanks,

Rich

  • 0
    TI__Guru**** 189401 points

    Hi, Richard,

    I've asked my colleague to look into this for you next week. 

    D2

  • 0
    TI__Expert 6715 points

    Hi Rich,

    In short, yes the device can digital signals down to a very low level with a recommended analog input level of 5Vp-p.

    To explain a little more, the dynamic range of the device is 112dB (analog in and digital out). For this case, as it is a 24-bit ADC, it has a theoretical maximum of around 144dB (24 bits). However, there is always some noise, which the least signifcant bit(s) are susceptible to. From the data sheet (page 7), the THD+N is typically -101/-102dB, this is the limit on which the device can effectively (noise free) digitize the signal.

    As for the recommended input level, (bottom of page 5 on the datasheet) the full-scale (-0dB) input is 5Vp-p. If you use a smaller range input, the 24 bit data coming from the ADC will not hit full-scale (a data line of all - or mostly - ones). This is assuming that the recommended Vcc of 5V is also being used.

    I hope this fully answers your questions.

    Regards,

    ~John

  • 0 in reply to John Fedak
    Intellectual 370 points

    Hi John,

    Thank you for your reply.  I would like to connect the PCM1804 to a microphone amplifier.  Would the PCM1804 be able to operate with input signals from 5Vp-p (+7dBu) down to 0.16Vp-p (-23dBu)?  Or would low level inputs like -23dBu be totally lost in the noise?

    Thanks,

    Rich

  • 0 in reply to Richard Meidl
    TI__Expert 6715 points

    Hi Rich,

    The noise floor is substantially lower than 0.16 Vp-p, so noise is not an issue at that level. An audio input at a 0.16 Vp-p level will be much quieter compared to an input at 5Vp-p and would not take full advantage of the 24bits in the ADC.

    Although, if I'm understanding correctly and you are saying that the microphone amplifier has a 5Vp-p when the loudest sounds are coming through and 0.16Vp-p with quieter sounds, the PCM1804 will work.

    Regards,

    ~John

  • 0 in reply to John Fedak
    Intellectual 370 points

    Hello John,

    You are understanding correctly, the loudest sounds will be at 5Vp-p and the quieter sounds will be 0.16Vp-p and sometimes lower.  A majority of the time, the signals should be in the 1.55Vp-p to 4.5Vp-p range.

    Thanks again,

    Rich