The filter shown in the figure, suggested by National Semiconductor, only allows frequencies above 100 HZ to pass through the values of the components used. These components, basically C1 and C2, can have their values changed for other cutoff frequencies. It is a unit gain filter with Sallen-Key topology, characterized by a relatively low Q factor. The power supply must be symmetrical, and the values indicated are for components with smaller tolerances. Closer commercial values can be used if high cutoff frequency accuracy is not desired. When choosing the component values, the frequency characteristics of the operational amplifier used must be taken into account.
