This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1299 PGA

Other Parts Discussed in Thread: ADS1299

Hi;

I bought an ADS1299 evaluation board. In order to have a single supply EEG system with single-ended electrodes and selectable reference, I did some things in hardware as follow:

- In order to have a single supply, JP2: 2-3 (AVDD=+5V) and JP20: 1-2 (AVSS=AGND=0V).

- In order to have a selectable reference electrode: JP7: 2-3 and JP8: 2-3 (connect SRB2 to SRB1 by onboard buffer).

- Remove all jumpers from JP25 and J6.

- Connect a sine wave (40mV p-p, 10Hz) with +60mV DC offset to CH1+/AGND as a first test signal.

- Connect a DC source (1V) to CH2+/AGND as a second test signal.

- Connect other CHx+ to AGND.

and also some things in software as follow:

- All PGA gain to *1.

- To have CH8 as a ref electrode (CH8+ is connected to AGND), SRB2 of CH8 and SRB1: closed .

Under these conditions, when I make a registration, I have a 40mV p-p sine wave in CH1 with 60mV offset, and a 1V DC on CH2 (as expected). However, when I put the PGA gain of CH1 and CH2 in *2, the result in CH1 become a 14mV p-p sine wave with 40mV offset, and a 0.6V DC in CH2.

I couldn’t understand why it become like this. Is there any mistake in hardware or software setting?

Thanks a lot,  

  • Hi Javad,

    We'll try to re-create your test setup with the ADS1299 and see where the issue might be coming from.  Can you let us know how the entire configuration register bank is setup?  If you can review the register tab and either post a screen shot or simply write down the various register settings, that would be very helpful.  

  • Thanks a lot for your fast reply.

    i attached a photo from my evaluation board, for checking the jumpers.

    also PGA1_out and PGA1_reg when the pga gain is 1 and PGA2_out and PGA2_reg when the pga gain is 2.

  • Hi

    Dear Tom;

    do you have some news for me ?

  • Hi Javad,

    My apologies for the late reply here - I was out of the office on the 15th and meant to get back to you last week to let you know that I too see similar behavior with the settings you have noted above.  I've still not had time to go back and see where the problem is coming from though.

  • please how to can reduce the frequency of sampling by that ADS is very fast and I can not draw the strings?

  • Hello to everyone,

    I have a question about the PGA gain. There are the gain settings of 1,2,4,6,8,12 and 24.

    My problem is, that with a offset of 300mV and a gain of 24, the ADC is in saturation and i have to switch to a gain of 12. But with a gain of 12 my CMRR is getting worse and i will not pass the requirements. I have seen, that there is a not used register setting for the PGA gain with 111. Is it somehow possible to program this 111 to a gain between 12 and 24?

    Regards

    Melanie