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ADS1292RECG-FE: Problem reading out PGA

Jonathan Engel
Intellectual 285 points
Part Number: ADS1292RECG-FE
Other Parts Discussed in Thread: ADS1292, ADS1292R, , ADS1298R, ADS1298

We are having difficulty reading the output across the PGA ouput pins on the ADS1292RECG-FE evaluation module (demonstration kit). We're feeding in good clean ECG which is easily seen in the LabView runtime executable provided by TI. However, when we connect a scope or high-res data acquisition device across the PGA output capacitor on pins 7 and 8 or 1 and 2 we see nothing or some square wave artifact (at about 6Hz). We are not able to see the ECG signal that the ADS1292R is clearly measuring and digitizing. We've been able to easily visualize the output of the PGA amp on the ADS1298R using the same measurement hardware. We've tried a lot of permutations and register settings but nothing coming out of the PGA pins on the ADS1292 makes sense. Suggestions?

  • 0
    TI__Guru 57296 points

    Hello Jonathan,

    Thank you for your post.

    What is the expected amplitude of the signal after the PGA gain stage? Remember that the PGA is only applying gain to the differential signal path, not the common-mode.

    Where were you probing the PGA outputs on the ADS1298? Were you routing a given channel through the PACE amplifiers? These amplifiers will convert the differential PGA output to a single-ended signal with a gain of 0.4 V/V. This may make it a lot easier to see on a scope.

    Best regards,

  • 0 in reply to Ryan Andrews
    Intellectual 285 points

    The input is a 1mV NSR (normal sinus rhythm) ECG signal at 60 BPM from a patient simulator. The PGA gain did not effect the signal observed across the PGA cap. We have tried to capture the ADS1292 signal using bipolar inputs on the DAQ as well as two single ended inputs combined to create a differential signal and still the signal measured is null (with square wave as noted). The PACEOUT pins on the ADS1298 is what we had accessed in the past because there is no provision on that part for direct PGA output like on the ADS1292. If there is no configuration register value on the ADS1292 that we are missing or otherwise misconfigured then I guess it must be our measurement method. Any suggestions? Viewing other threads on reading PGA output, it shouldn't be that hard. See below:

    https://e2e.ti.com/support/data-converters/f/73/t/506058

  • 0 in reply to Jonathan Engel
    TI__Guru 57296 points

    Hi Jonathan,

    My only suggestion would be to increase the signal amplitude. Remember that the ADS1292 has about 2x the noise of the ADS1298. It's possible that that 1-mV signal x PGA gain is still too small to be observed this way. Much of the noise is removed through the ADS1292 digital filter, which is why you're able to resolve the signal in the GUI.

    To prove your setup is correct, configure the ADS1292 to use the internal square wave test signal. The differential amplitude will be 1 mVp times the PGA gain. Alternatively, apply a larger input, such as a 100-mVp sine wave at 10 Hz, to INxP with a mid-supply offset. Connect INxN of the same channel to mid-supply as well.

    Best regards,