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Input signal distortion – ADS 1298

AlexSG
Prodigy 10 points
Other Parts Discussed in Thread: ADS1298ECGFE-PDK, ADS1298

Hello !

We have been testing the ADS1298ECGFE-PDK with our own software and DSP. The MMB0 is only used to power the ADS and the ADS board is accessed with SPI. The input test signal is provided by a Tek signal generator with a simple short wire.

At the input of the ADS (INPx) , our oscilloscope shows correctly the signals of the signal generator. However, recovering the same signal from the ADS by SPI, we get a signal that is similar to the “probe overcompensating” problem.

Should we buffer the input or use a RC compensation circuit as in oscilloscope probes ?

Any help would be greatly appreciated !

Thanks, Alex.

  • 0
    TI__Guru**** 180931 points

    Hi Alex,

    "Step change" inputs to the ADS1298 might cause distortion when looking at the unfiltered digitized results.  Let us know the details of your configuration registers as I'd like to try and reproduce that in the lab to give you a 'do this to compensate' based solution/answer to your question.  What does the digital code look like when using a sine instead of a square wave?

  • 0
    Genius 3585 points

    Your picture shows a typical HP filtered pulse train. As far as I know, the ECGFE-PDK has a 2nd order passive HP filter on every input so if you had the signal feeded into the DB15 connector that could cause that deformation (depending on the frequency of the signal, of course). I'd try to feed the generator signal at the appropriate J5 pins, after the HP section.