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ADS1278: - Buffer Amp Necessity

Gerald Heisenberg
Prodigy 10 points
Part Number: ADS1278

Hello! I have recently started work on a development board and wanted to ask about the performance trade offs of not using a buffer amp stage before the input of the ADS 1278 - will the device continue to function in the absence of the amplifiers (and if so, how well)? Thank you for your time!

  • 0
    TI__Guru 57296 points
    Hi Gerald,

    Thanks for your question!

    The ADS1278 does not have a built-in amplifier at the input of the ADC. This means that the input pins are connected directly to the switch-capacitor sampling stage of the delta-sigma modulator. See Figure 67 for an equivalent model.

    The inputs of the ADS1278 are not high-impedance. You'll notice that some current is drawn during each sample when the S1 switches close, causing the voltage at the inputs to droop and recover. The combination of a differential capacitor across the input pins and a driver amplifier helps to minimize this voltage droop and facilitate the voltage settling before the S1 switches reopen. An unsettled input signal translates to poor performance, specifically distortion (THD).

    While not "required" per say, an amplifier at the inputs is strongly recommended; otherwise, you will not achieve the performance listed in the ADS1278 datasheet.

    Best Regards,