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ADS1298 Noise verification

rafael cruz
Prodigy 150 points
Other Parts Discussed in Thread: ADS1298R

Hello,

I have an issue with verifying the input referred noise levels according to table 4 on the data sheet for my ADS1298R mmb0 evaluation board, my ADC register settings are the following:

I'm trying to read the input refered noise in Low power mode 5V analog supply and 4V reference, what I can verify is the noise for a PGA Gain = 1 this reads values close to 11.9uVpp like the spec sheet states:

 

however when I start increasing the PGA gain these numbers are not decreasing, for example for a gain of 12, I'm not reading anything close to 2.2uVpp and 0.4uVrms

using the scope analysis this is what I see:

I know the scope could be a little off but a quick visual inspection doesn't show the peak to peak voltage being close to 2.2uV

I feel like I'm missing something, any help will be appreciate it (I read the noise measurements notes on page 9 of the data sheet, it mentioned shorting the inputs, I also did this and no change).

Thanks in advanced

Rafael

  • 0
    TI__Guru 66186 points

    Hi Rafael, 

    The noise specifications in the datasheet are input-referred. Make sure to select the checkbox "Analysis data is input referred" near the top-right of the screen. The last image shows results for a gain of 12, correct? Some channels are still slightly high after dividing by 12, ranging from 2.31 uV - 2.98 uV, but they are much more reasonable. :)

    Also, just FYI, when you configured the channels as Input Short on the front panel, the internal MUX is configured to short the inputs internally. This is why you did not notice a difference after shorting the external input jumpers on the EVM. When you start using an external signal source with cables, a neat test might be to short the ends of your cables, configure the ADC channels as Normal Electrode, and measure how much noise is added to your system in comparison to the internal short measurement.

     

    Best Regards,