ADS1299: Can I use an external multiplexer with ADS1299?

Patrice COCHETEUX

Prodigy 20 points

Part Number: ADS1299

Hello,

We are thinking about making a 32 ways acquisition system at 250 SPS from a single ADS1299 and 8 mux ADG659

In order to achieve that we where thinking of :

Setting in the Output data rate at 8kSPS.
Switching of canal every 2 acquisitions ( 1>2>3>4>1).
Ditching 1 acquisition just after the mux switching.

But our conclusion is that the digital Filter stage will prevent us to get good result.

Could you confirm us this conclusion?

Thanks in advance.

Regards

over 5 years ago

0 Tom Hendrick over 5 years ago

TI__Guru**** 168785 points

Hi Patrice!

Thank you for the great ADS1299 questions! We're on Easter break till Monday the 22nd. One of our Bio-Potential experts will be in touch with you after the holiday weekend. In the meantime, please do have a look at some of the frequently asked ADS129x questions here:
e2e.ti.com/.../772058

0 Ryan Andrews over 5 years ago

TI__Guru 57346 points

Hello Patrice,

Welcome to our forum and thank you for your post.

We generally discourage using an external multiplexer in the manner you described because of the digital filter's settling response. Switching the mux input to the ADS1299 will produce a sudden transient or step response. The sinc3 digital filter will require 4 samples at the output data rate to be fully settled, so the first 3 samples after changing the mux will need to be discarded.

In addition, running the ADS1299 at 8 kSPS with a 4:1 mux vs. 1 kSPS for all channels will significantly increase the digital filter bandwidth and degrade noise performance.

Best regards,

0 Patrice COCHETEUX over 4 years ago in reply to Ryan Andrews

Prodigy 20 points

Hello Ryan,

Thanks for this precious answer.

Best regards

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ADS1299: Can I use an external multiplexer with ADS1299?