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ADS1015 Noise?

Thierry Cachat
Intellectual 310 points

Other Parts Discussed in Thread: ADS1015, ADS1113

Dear all, I do not understand the "Noise Plot" in the typical characteristics of the ADS1015 (page 6 of the datasheet). How is it possible that the noise is less than 1 LSB? How is the noise related to the rate?

  • 0
    TI__Guru** 113765 points

    Hi Thierry,

    I can see how the noise plot is a little confusing.  The ADS1015 is capable of having resolution better than 12 bits, but we have restricted the output to 12 bits.  I can't speak for the person who created the datasheet, but if the response were a straight line, then it might be misunderstood that the part has 0 noise.  If the plot showed steps of 100mV instead of codes, then this might be a little easier to understand, but again the problem is 100mV is 1 LSB at the specified operating conditions.  So this results in having the same issue.  We may have been able to leave the noise plot out entirely, but we would most certainly be asked what is the noise performance of the part.

    So the part has low noise, at high data rates. Your second question related to the data rates.  Delta-Sigma converters oversample the input and noise shape the quantization noise into the higher frequencies of the conversion bandwidth.  A digital filter then acts as a low pass filter to reduce the effects of the noise.  As the data rate increases, so does the bandwidth of the filter which results in higher noise.  So basically higher data rates have increased bandwidth resulting in higher noise.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 310 points

    Hi Bob,


    Thank you for your answer. Do you mean that the ADS1015 has internally more than 12 bits? Great, but we can read only 12 bits. I looked at the datasheet of the ADS1113, where the noise is much easier to understand, and clearly depends on the rate.


    For the ADS1015 we are considering, it would be better to have a single numerical value of the RMS noise, either in LSB or in µV. Well, I know that higher data rates result in higher noise, I would like to have some values.


    Regards,

    Thierry

  • 0 in reply to Thierry Cachat
    TI__Guru** 113765 points

    Hi Thierry,

    What the noise graph in the ADS1015 datasheet tells us is two things.  The first is that the noise is less than 1 LSB at the highest data rate.  The second is the lower data rates will be no worse.  So the noise of the ADS1015 is less than 1 LSB.

    Best regards,

    Bob B