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ADS127L01: how to get the 1.34 µVRMS of input-referred noise in ADS127L01 d/s

Steven Sim
Prodigy 65 points
Part Number: ADS127L01

Hi Gent.,

Happy Christmas Holiday!

May I know how to get the 1.34 µVRMS of input-referred noise in ADS127L01 d/s? thanks.

best regards,

Steven

  • 0
    TI__Mastermind 45285 points

    Hi Steven,

    The apps engineers who support this device are on vacation. Are you talking about the Vrms_noise in the table 2 on page 25?

    Best regards

    Dale

  • 0 in reply to Dale Li
    TI__Mastermind 46200 points

    Thanks Dale,

    Hi Steven,

    The 1.34uVrms noise is a combination of input clock frequency, filter type and OSR setting.  The clock frequency applied to the CLK, pin 24, should be adjusted to 4.096MHz. 

    CLK(pin24)=4.096MHz

    OSR=2048: OSR1(pin15)=1=DVDD, OSR0(pin16)=1=DVDD

    Low-latency filter (LL):  FILTER1(pin12)=1=DVDD, FILTER0(pin13)=0=DGND

    LP,VLP mode:  HR(pin29)=0=DGND

    Since you are operating at a lower clock frequency, you can further reduce power by adjusting REXT(pin7) to 120kOhm(VLP mode), but this is not necessary. 

    Please note that in order to reduce the input noise to 1.34uVrms, you are reducing the data rate to 2000sps, and the resulting input signal bandwidth is 900Hz.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 65 points

    Thank Keith for detailed explanation. 

    btw, how to get this 1.34uV rms, by calculation or simulation or measurement / test in lab? 

    thanks.

    Steven

  • 0 in reply to Steven Sim
    TI__Mastermind 46200 points

    Hi Steven,

    These numbers were measured in the lab by shorting the inputs (0V input) and recording a large number of ADC conversion readings (16k), and then calculating the 1-sigma value of the data set.

    Many of the newer EVM's provide this calculation in the Histogram section, but unfortunately, the EVM for the ADS127L01 does not provide this capability.  However, if you have the EVM, you can collect the sample set, export to Excel, and then calculate the 1-sigma value of the dataset using Excel or another similar spreadsheet tool.

    Regards,
    Keith