Abstract:
An electronic circuit has two similar phase shift networks connected in cascade between a circuit input and the input of an amplifier providing a 180* phase-shift between its input and output. The output of the amplifier and first network are combined and the combination applied to the circuit output, providing an overall frequency response exhibiting a resonant frequency. The networks may be connected together via a buffer amplifier, and each comprises a resistance and a reactance interconnected to provide a phase lead or lag. The resonant frequency may be varied by varying the gain of the amplifier or the resistance or reactance of one or both networks. Variable gain feedback circuitry may be connected between the circuit output and input, so that the circuit is selectively operable as a frequency selective amplifier or oscillator in accordance with the gain of this circuitry.