Placing an RC filter in front of the isolated modulator improves signal-to-noise performance of the signal path. In practice, however, the impedance of the resistor divider is high and only a small value filter capacitor can be used not to limit the signal bandwidth to an unacceptable low value. Design the input filter such that the cutoff frequency of the filter is at least one order of magnitude lower than the sampling frequency (10 MHz) of the internal ΔΣ modulator.

Most voltage-sensing applications use high-impedance resistor dividers in front of the isolated amplifier to scale down the input voltage. In this case, an additional resistor is not required and a single capacitor (as shown in Figure 8-2) is sufficient to filter the input signal.