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ADuCM350 FAQ AFE TIA

Q: What is the maximum common mode ? ADC input range ? Etc

A: Please refer to the "AFE Signal Swings" section in AFE Excitation Loop chapter of UG-587 and the ADC Measurement section

in ADC Chapter of UG-587.

Q: Details on main TIA specifications such as noise drift.

A:

  • Gain/Offset Calibration on power up.
  • Offset Calibration with respect to 0uA input current ( leakage current from switch matrix calibrated out )
  • TIA_O is sensed with respect to TIA_I (not VBIAS) so TIA OpAmp offset drift and noise rejected

Q: Can I adjust the Common Mode / VBIAS of the TIA ?

A:The default configuration for the common mode of the TIA is 1.1V or set by the VBIAS buffer. The part is characterised and tested with this common mode value. However it is possible to change the common mode voltage.

As figure shows below, use a potential divider off the REF_EXCITE pin to control the VBIAS from a default of 1.1V.

Be aware of the measurement channel rails when adjusting the common mode.

It is possible to make this Common Mode Software configurable by adding a resistor between VREF and VBIAS. In this case:

  • REF_EXCITE = 0 and VBIAS-BUF_EN = 1 for Default option where VBIAS = 1.1V.
  • REF_EXCITE = 1 and VBIAS_BUF = 0 for user desired Common Mode level.

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