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ADS119x / ADS129x vs ADS1299

Sean Grech
Prodigy 50 points
Other Parts Discussed in Thread: ADS1299, ADS1298

Dear TI,

I am looking to build an EEG amplifier with impedance monitoring capabilities. I understand that the ADS119x and ADS129x (except for ADS1299) are catered specifically for use with ECG, but EEG is still possible with them, provided pre-amplifiers are used - https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/69112 - since they are a bit noisy for uV recordings. The use of pre-amplifiers however does not allow for the impedance monitoring to be performed without the implementation of external current sources - https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/136188which essentially defeats the purpose of using the ADS119x and ADS129x in the first place.

I have however found that several people are using the ADS1299 for EEG recordings, whilst also performing impedance measurements. Does this mean that the ADS1299 solves the ADS119x and ADS129x problems of large noise at the inputs? In essence, I am struggling to find the difference between the ADS1298 and ADS1299 IC's. If the ADS1299 does solve the issue of noise, would 4-channel versions of ADS1299 be made available any time soon?

Also, does the ADS1299 cater for anti-aliasing before sampling?

Thanks,

Sean Grech

  • 0
    TI__Mastermind 38745 points
    Hey Sean,

    The ADS1299 is basically a lower noise and higher PGA gain version of the ADS1298. The noise generated by the ADS1299 is specified in tables 1-4 in the ADS1299 datasheet. There are similar tables in the ADS129x datasheet and I would encourage you to compare. The noise on the ADS1299 is very good and it rivals a solution involving a discrete amplifier. There are business reasons (rather than technical reasons) as to why the ADS1299 may not be selected in exchange for the ADS1298.

    The ADS1299's PGA does have low pass characteristics which may satisfy your anti-aliasing requirement. You can see the bandwidth for different gain settings in table 5 of the datasheet. You can get away with modeling those cutoffs like a first order RC filter. You will have to decide if the anti-aliasing performance of the PGA itself is satisfactory. Otherwise you can station a simple RC filter on your inputs to net a second order roll-off.

    Regards,
    Brian Pisani