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ADS1298R: Input common-range and offset

user6529224
Prodigy 130 points
Part Number: ADS1298R
Other Parts Discussed in Thread: ADS1298

Dear TI team,

EN60601-2-25 §201.12.4.107.2 specifies:

"The ECG shall be capable of recording a +/- 5mV input signal (biphasic polarity applied to any lead).

With an input signal producing a peak-to-valley deflection of 10mV at the center of the effective recording width the recorded amplitude shall not change by more than 5% (+/-500uV) when the recorded signal is shifted over the whole of the effective recording width

This requirement shall be met in the presence of differential and common mode DC offset voltages of +/- 300mV. These offset voltages shall not be applied simultaneously."


Assuming:

a) the ADS1298 is programmed with an input voltage range of +/- 5mV

b) RLD is used

Will the +/- 300mV offset be removed by the RLD or will it hide the useful signal (by "saturating" the op amp) ?

Thanks,

Paul-Alexandre,

  • 0
    TI__Genius 11550 points

    Hi Paul-Alexandre,

    Thanks for the post. 

    The RLD will not help with eliminating the +/-300mV offset of the electrode. The use of RLD will help set the proper common-mode voltage for the PGA and improve the CMRR. You will need to use a lower PGA gain setting so that your input will not saturate the input channel PGA. The use of lower PGA gain and a high-resolution (24-bit) ADC in the ADS1298 will help to meet this requirement.

    Thanks

    -TC

  • 0 in reply to TCT
    Prodigy 130 points

    Hello TC,

    Thank you very much for your quick and crystal clear answer.

    Paul-Alexandre,