Patent ID: 6177837
Filing Date: 2001-01-23
Classification: H03F,H03H

Abstract:
An active low-pass filter comprising:cascade-connected amplifying circuits of a plurality of stages, each comprising:an amplifying elements; anda capacitor for setting cut-off frequency, said capacitor being connected between a connecting point of the amplifying circuits and the ground,wherein said amplifying element has an input electrode and an output electrode; anda feedback circuit connected between the input electrode of said amplifying element in an initial amplifying circuit and an output electrode of said amplifying element in a final amplifying circuit,wherein said feedback circuit comprises of a serial circuit of a voltage dropping means, which results in almost constant voltage drop regardless of an increase or decrease of current and a feedback resistance, and a bias voltage is supplied to the input electrode of the amplifying element in the initial amplifying circuit from an output electrode of the amplifying element in the final amplifying circuit via said feedback circuit.