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ADS1299 + ADS1292R

twistx77
Intellectual 480 points
Other Parts Discussed in Thread: ADS1299, INA129, ADS1292R, ADS1292

Hello,

I'm working in a device where we need a EEG device with a single ECG channel and respiration circuit. I already have a EEG device without the ECG and I started designing the second device using the ADS1299 for the EEG and a discrete channel of ECG using a INA129 and a passband filter. The output of the filter was sampled by a MCU's ADC. 

Then, yesterday I discovered what I think might be a better solution that is to use a ADS1292R which gives me more ECG signals and also has the respiration circuitry for less money and less space that my previous solution.

Regarding this setup I have a couple of questions.

First, Could I supply the ADS1292R with the same +-2.5V (AVDD) supply I'm using for the ADS1299? The datasheet specifies that it can work with up to 5.25V fo AVDD so I guess there would be no problem there but in that case, will the internal reference have the same values specifies in the datasheet?

Second, Since I will hace a bias voltage already connected to the body that is provided by the ADS1299, would it cause any problem if I connect the BIASINV of the ADS1299 and the RLDINV ADS1292R as shown in figure 53 of page 56 of the ADS1292R datasheet? Theoretically both the BIAS and the RLD are the same thing but called different in both devices I think.

Am I correct or am I missing something?

Thank you.

  • 0
    Intellectual 480 points

    Hi,

    Can't anyone give me some information about the RLD - BIAS connection for both devices?

  • 0 in reply to twistx77
    TI__Guru 57296 points

    Hi Alex,

    I realize some time has passed, but have you made some progress in your ADS1292R + ADS1299 design?

    To your original questions, the same +/- 2.5 V supplies could also be used on both ADS129x devices. The internal reference would be set in the CONFIG2 register as always.

    I'm not sure about connecting the RLD and BIAS outputs together. My guess would be that you do not want these signals fighting each other. Tying them together may not make a significant improvement anyhow. The real goal, as you mentioned, is to drive the patient and ensure the input signals are within the input common-mode range of the ADCs. Either one could work, assuming they are generated with the correct DC common-mode voltage at the  BIAS/RLD amplifier non-inverting input (i.e. RLDREF in ADS1292) . As you pointed out, they are essentially the same function, so both is likely not necessary. For ECG, closing the RLD loop helps to improve 50/60 Hz CMRR. 

    I hope this helps.

    Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 480 points

    Hi Ryan,

    Thank you for your reply. About the RLD/BIAS signals, I've followed the instructions in figure 53 of page 56 of the ADS1292 datasheet. So the RLDINV input is connected through a solder jumper to BIASINV and then I use the BIAS OUT to drive the pacient. 

    I'm using +-2.5V supply. I haven't tested it yet since I was working in another project while waiting for the boards to be manufactured. I will be testing it soon though. 

    I will try to remeber to post the results back in here.

    Regards!

  • 0 in reply to Ryan Andrews
    Intellectual 480 points

    Hello Ryan,

    It is done. I've done what is specified in the ADS1292 datasheet and connected BIASINV to RLDINV and it is working ok so far but with two "small" problems.

    One is a lot of DC offset. And the other one is that lead off detection is not working but that might be a problem with the cables we are using since they are provisional because we will be using a custom cable for our device and we don't have it yet.