Active filter having series resonant active filter terminated by parallel resonant active filter

摘要

A fourth (or higher) order filter has a series resonant section terminated by a parallel resonant section, both based on frequency dependent negative resistance (FDNR). The FDNR, resistance and capacitance (representing damping) of the series section are provided by a capacitive potential divider (C41,C42) connected between low impedance input (A) to the filter and an intermediate terminal forming the input of a unity-gain amplifier (A4) whose output is connected via a resistance (R4O) to the tapping point of the divider; the intermediate terminal is connected via a second resistance (R1) to the parallel section.