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ADS125H02EVM: Testing lowest possible noise with EVM

Dave Young
Intellectual 520 points
Part Number: ADS125H02EVM
Other Parts Discussed in Thread: ADS125H02

Hello-

I've been testing the ADS125H02EVM and would like to get an idea of the lowest possible noise using the EVM as a baseline for my design. I took 30k readings and saw ENOB of 19.6 and noise-free bits of 16.4. Is this expected?, or is it possible to improve on it? Here is my setup:

Hardware setup:

  • EVM in stock condition with on-board +/-15V supplies enabled
  • Plugged into my laptop which is on battery (unplugged from the wall).

Register setup is default configuration except:

  • Set 0x03 MODE1 register to 0x21: Enable autozero
  • Set 0x06 REF register to 0x10: Enable internal reference, use int refP and int refN for the reference
  • Set 0x10 MODE4 register to 0x5B: Connect MUX as internal short to (HV_AVDD + HV_AVSS) / 2 and apply a gain of 128V/V

Here are my register settings and associated result:

  • +1
    TI__Mastermind 42051 points

    Hi Dave,

    According to the ADS125H02 datasheet, the measured RMS noise at G=128, ODR = 20 SPS, and using the FIR filter is 74 nVRMS. You can input these values into equation 1 in the datasheet, along with the selected value of VREF = 2.5V, to calculate the estimated effective resolution.

    So, effective resolution = 3.32 * log(2 * VREF / gain / noise) = 3.32 * log(2 * 2.5 / 128 / 74*10^-9) = 19 bits.

    Since you got 19.6 bits in your measurements, I would say you are getting the lowest noise possible.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Intellectual 520 points

    Awesome! Thanks so much for the sanity check and the excellent explanation with calculation. This is great.