Although the device digital filter attenuates high-frequency noise, use a first order low-pass RC filter at the ADC inputs to further reject out-of-bandwidth noise and avoid aliasing. A differential low-pass RC filter formed by R5, R6, and the differential capacitor CDIFF sets the –3-dB cutoff frequency, fC, given by Equation 14. These filter resistors produce a voltage drop because of the input currents flowing into and out of the ADC. This voltage drop could contribute to an additional gain error. Limit the filter resistor values to below 1 kΩ.
Two common-mode filter capacitors (CCM1 and CCM2) are also added to offer attenuation of high-frequency, common-mode noise components. Select a differential capacitor, CDIFF, that is at least an order of magnitude (10x) larger than these common-mode capacitors because mismatches in these common-mode capacitors can convert common-mode noise into differential noise.