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  • TI Thinks Resolved

PCM1840: DC coupled inputs?

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Replies: 1

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Part Number: PCM1840

Hi there,

Is it possible to use a DC coupled input signal to the PCM1840?.

I note that the input bias on the PCM1840's inputs is 1.48V.  If I set my ADC driver circuitry to have a mid point of 1.48V, should that work?.

thanks!

Stephen Turner

AudioScience, Inc

  • Hi Stephen,

    While it is technically possible, I would strongly discourage DC coupling the inputs of this device because of it's unique architecture. The input needs to be held within +/-50mV of the internal common-mode bias to avoid degradation in performance and unfortunately there is not a suitable reference voltage to use to bias your circuitry that will guarantee this condition over device variation, temperature, etc. 

    If you absolutely must DC couple the inputs, the one workaround I can suggest is if you are not using all 4 channels of the device you can short the inputs of one of the unused channels together and bypass to ground with an AC coupling capacitor. This node can then be used with a high impedance buffer to measure the input bias and this can be used as a reference for your op amp circuit. 

    Another thing worth mentioning is that if you do DC couple the inputs, even with the method above the DRE function cannot be used and you should make sure to leave it disabled.

    Best,

    Zak

    Regards,

    Zak Kaye
    Precision Data Converter Applications

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