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ADS58J64: How is the output if an ADC's input is floating?

Wenhao Wu
Genius 9046 points
Part Number: ADS58J64

Hi Team,

I have a question when designing ADC. I found for some ADCs, like MCU's integrated 12-bit ADC, or ADS58J64, when its input is floating, the output often has value.

Do you know the reason behind this? Any application note? Thank you.

-Wenhao

  • 0
    TI__Guru 66184 points

    Hi Wenhao,

    The ADS58J64 input is internally biased by a common mode VCM. The input will need to be AC coupled or biased at VCM (if DC coupled). If the input is floating (with bias), the ADC output will have an average code of the "midscale) (i.e. 2^13 code with full range of 2^14 for 14-bit ADC). The variance of the code will be the noise distribution. 

    -Kang