Patent ID: 6130948
Filing Date: 2000-10-10
Classification: H04S

Abstract:
A sound field expanding apparatus comprising:first and second adders that respectively receive left and right stereophonic input signals of two channels;first and second inversion amplifiers coupled to the first and second adders, respectively, the first and second inversion amplifiers having inversion input terminals that receive signal outputs from the first and second adders, respectively;a first amplitude/phase characteristic changing circuit connected between the first inversion amplifier and the first adder, the first amplitude/phase characteristic changing circuit for adding a first specified amplitude/phase characteristic to a signal output from the first inversion amplifier;a second amplifier/phase characteristic changing circuit connected between the second inversion amplifier and the second adder, the second amplitude/phase characteristic changing circuit for adding a second specified amplitude/phase characteristic to a signal output from the second inversion amplifier;a third adder that adds an output signal from the first inversion amplifier and an output signal from the second amplitude/phase characteristic changing circuit; anda fourth adder that adds an output signal from the second inversion amplifier and an output signal from the first amplitude/phase characteristic changing circuit; wherein the first and second amplitude/phase characteristic changing circuits are formed on a single IC chip, each of the first and second amplitude/phase characteristic changing circuits being formed from a plurality of switched capacitor filters,wherein each of the first and second amplitude/phase characteristic changing circuits includes,an input terminal,first and second inversion operation amplifiers, each of the first and second inversion operation amplifier having a normal input terminal being grounded, an inversion input terminal, and an output terminal,a first switched capacitor connected between the input terminal and the inversion input terminal of the first inversion operation amplifier,a first capacitor connected between the output terminal and the inversion input terminal of the first inversion operation amplifier,a second switched capacitor connected between the output terminal of the first inversion operation amplifier and the inversion input terminal of the second inversion operation amplifier,a second capacitor connected between the output terminal and the inversion input terminal of the second inversion operation amplifier,a buffer amplifier having an input terminal and an output terminal, the input terminal of the buffer amplifier being connected to the output terminal of the second inversion operation amplifier for inversing an output signal from the second inversion operation amplifier,a third switched capacitor connected between the output terminal of the buffer amplifier and the inverse input terminal of the first inversion operation amplifier, anda fourth switched capacitor connected between the output terminal of the buffer amplifier and the inverse input terminal of the second inversion operation amplifier.