Filtering with the LMF100

The LMF100 is a chip that contains two independent switched capacitor filters. With just a few added external resistors, it can be used to create 1st-4th order lowpass, highpass, notch, and bandpass filters. Independently each filter is either first or second order (depending on the external resistor configuration), but they can be cascaded to create up to a fourth order filter. This page will focus primarily on what the device's datasheet calls "Mode 1" (a bandpass filter), although the other modes described in the datasheet are quite similar. The bandpass gain plot is shown to the right.

In general, the second order bandpass response is given by: $H_{BP}(s)={\frac {H_{OBP}\cdot {\frac {\omega _{0}}{Q}}\cdot s}{s^{2}+{\frac {s\omega _{0}}{Q}}+\omega _{0}^{2}}}$

References

• LMF100 Datasheet, National Semiconductor