Order of the Low Pass Filters

General

If the filter is enabled, the basic data of the AD converters are filtered respectively per channel (ideal range). For defining the filter order and the respective cutoff frequency for configuring the low pass filter, the following registers are available: Internal filter orders exceeding 1 (up to 4) are realized as cascaded filters of the first order. Since the filter is calculated in the sampling cycle, the filter properties are directly connected to the sampling cycle time settings.

Calculation of the Effective Cascaded Cutoff Frequency of the Filter of the nth Order

fc1 = fcN / (2^1/N - 1)^1/2

Approximate Calculation Filter Cascade Sample Time Ts

yn = a * xn + b * y (n - 1)

a = Ts / (Ts + 1/fc)

b = 1 - a

NOTE: Due to the fixed-point arithmetic calculation of the low pass filter used here, detected errors occur depending on the sample time and the filter order.