SBAA507 March   2021 ADS8578S , ADS8584S , ADS8586S , ADS8588H , ADS8588S , ADS8598H , ADS8598S , ADS8661 , ADS8664 , ADS8665 , ADS8668 , ADS8671 , ADS8674 , ADS8675 , ADS8678 , ADS8681 , ADS8684 , ADS8684A , ADS8685 , ADS8688 , ADS8688A , ADS8688AT , ADS8689 , ADS8691 , ADS8694 , ADS8695 , ADS8698 , ADS8699 , OPA2990 , OPA4990 , OPA990

 

  1.   1
  2.   Design Description
  3.   Specifications
  4.   Design Notes
  5.   Component Selection
  6.   DC Transfer Characteristics
  7.   Simulation Verification for Floating Input
  8.   AC Transfer Characteristics
  9.   Noise Simulation
  10.   Stability Simulation
  11.   Design References
  12.   Design Featured Devices

Design Notes

  1. The resistors (R1 and R2) divide the power supply (HVDD) to create a biasing voltage, VT, that is outside of the expected input voltage range which is used to detect whether the VG input is floating.
  2. The amplifier (OPA990) is configured as a non-inverting unity gain buffer to offer a high input impedance for the signal source (VG).
  3. The resistors (R3 and R4) are used to scale down the input signal for a margin to detect if the input is floating.
  4. Select 0.1% or better accuracy resistors for R3 and R4 to minimize the gain error.
  5. Select C0G type capacitor for C1 in the front-end RC filter to minimize the distortion.