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ADS1232: ENOB & Noise Free

Brian Wang0928
Genius 15130 points

Part Number: ADS1232

According to the Table 1 in the ADS1232 datasheet,

1. We found the calculation of the noise free bits are wrong. only 18.4 is correct at GAIN=128, right?

2. How to get the RMS NOISE and PEAK-TO-PEAK NOISE values? From measurement in practical? or using formula?

Also, why the higher GAIN is, the lower RMS NOISE is?

  • 0
    TI__Guru** 113765 points

    Hi Brian,

    The calculations for noise-free bits were done by direct measurement of the peak-to-peak noise.  The formula for calculation is shown for both the ENOB (RMS) calculation as well as the Noise-Free Bits calculation on page 5 above the tables.  So when making the calculation you must make sure you are using the correct full-scale range which is +/- 0.5*Vref/Gain.

    You can calculate the RMS noise as standard deviation of a number of samples.  We often use 1024 samples.  The noise should appear Gaussian when plotted as a Histogram.  The peak-to-peak noise is based on the min/max of the data set.  Both the ENOB (RMS) and Noise-Free measurements are conducted with the inputs shorted, which would be the best case scenario for the ADS1232 and excludes the noise of the reference in the measurement as well as external input noise.

    The advantage of using an integrated PGA with Delta-Sigma ADCs is a reduction of input referred noise as opposed to using most external amplifiers.  I would suggest taking a look at the following blog for additional information regarding noise:

    https://e2e.ti.com/blogs_/b/analogwire/archive/2019/01/17/top-10-questions-about-noise-in-high-resolution-delta-sigma-adcs

    Best regards,

    Bob B