Place an RC filter in front of the
isolated amplifier to improve the signal-to-noise performance of the signal path.
Design the input filter such that:
The cutoff frequency of the filter is at least one order of magnitude
lower than the sampling frequency (20 MHz) of the ΔΣ modulator
The input bias current does not generate a significant voltage
drop across the DC impedance of the input filter
The impedances measured from the analog inputs are equal
For most applications, the structure
shown in Figure 8-2 achieves excellent performance.