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ADS1299: AC Input impedance

Darren Jenkins
Genius 12541 points
Part Number: ADS1299

Hello ADS1299 support,

Please help with these questions about specs for the ADS1299:

  1. Do we have a plot of AC input impedance versus frequency?
    1. Can you provide this for Differential
    2. And Single-ended
  2. The datasheet shows DC input impedance of 1000 MOhm minimum. Is this Single-ended or Differential?

Thanks,

Darren

  • 0
    TI__Guru 66516 points
    Hi Darren,

    The DC input impedance spec in the datasheet is the common-mode impedance. Differential impedance will be 2x = 2G Ohm.

    We do not specify AC impedance on this device or measure it at final test. The inputs on the ADS1299 connect to a high-impedance PGA input stage and remains relatively constant. This is different from other devices in our portfolio which connect directly to the switched-capacitor sampling stage of the ADC modulator. The impedance in those devices scale with the modulator clock frequency.

    The only AC component of the ADS1299 input impedance is the typical 20pF input capacitance, which is part of the 3-MHz EMI filter. This may come into play as the PGA inputs are chopped; however, the noise that this would produce will be knocked off by the digital sinc filter anyway and should not cause any issues.

    Best Regards,