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ADS1299 Discrete Channels V Cross Over?

mileece petre
Prodigy 30 points
Other Parts Discussed in Thread: ADS1299

Hello, 

We are using the ADS1299 with the intention of gathering discrete channels of micro-volt emissions from each channel monitoring individual bio-electrical sources. 

It isn't entirely clear to us if you can indeed have discrete differential signal per N+P channel?

Since our sources are independent, we don't need the SRB reference pin to be in use. In fact, don't want it.

With both SRB pins turned off, we still see our independent channel signals crossover/bleed into adjacent channels. 

We would like to know where this problem lies. Which stage of our set-up that is happening and would like to eliminate the actual chip design from that equation from the start. 

Can you help elucidate this for us please? 

P.S. it's a bit (very) urgent ;) 

Thank you!!

  • 0
    TI__Mastermind 18285 points

    Mileece,

    I'm moving your post to the precision data converters forum. They will be better equipped to answer your questions.

  • 0
    TI__Mastermind 38745 points
    Hey Mileece,

    The phenomenon you are describing (if it is indeed the chip) is known as "cross-talk" and its effect is quantified on the datasheet on the electrical characteristics table. We measure it by shorting one of the channel's inputs, and apply a signal of a known frequency and amplitude to another input. We then measure the magnitude of that signal's content at the output of the shorted channel. Ideally that value is zero, but there is always at least a little. For the ADS1299, the value is -110 dB, which is nearly negligible. However, I'd encourage you to test it yourself in the way I described. If you see cross-talk numbers similar to what is specified in the datasheet, then the source of the "bleeding" is at the system level.

    Regards,
    Brian Pisani