US 4,230,904 AGranted

Signal control circuit

AssigneeMatsushita Electric Industrial Co., Ltd.

InventorsKazuyoshi Fujiyoshi, Kyoji Murakami

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Abstract

An antisidetalk signal control circuit for preventing transmission of signals from a first source connected with a first input circuit to an output circuit while allowing the transmission of signals from a second source connected with a second input circuit to the output circuit. The signal control circuit comprises a first switching circuit having an input coupled to the first input circuit, a second switching circuit having an input coupled to the first output circuit through a phase inverter and a third switching circuit having an input coupled to the outputs of the first and second switching circuits. An oscillator drives the first switching circuit with signals having a given phase and the second and third switching circuits with signals of opposite phase. A low-pass filter couples the junction of the first and second switching circuits to the second input circuit and a feedback circuit couples the second input circuit to the junction of the first and second switching circuits. The reduction in sidetalk is not affected by variations in the impedances of the first and second signal sources.

A signal control circuit comprising:

first input means connected to a first signal source circuit;
second input means connected to a second signal source circuit;
output means;
an oscillator having first and second outputs for generating first and second output signals, respectively, said second output signal being in opposite phase with respect to said first output signal;
a first switching circuit having inputs thereto connected respectively to said first input to said signal control circuit to and said first output of said oscillator, said first switching circuit being driven by said first output signal from said oscillator to provide a first switched output signal at an output thereof;
a second switching circuit having inputs thereto connected respectively to said first input to said signal control circuit through a phase inverter circuit and to said second output of said oscillator, said second switching circuit being driven by said second output signal from said oscillator to provide a second switched output signal at an output thereof;
a low-pass filter having an input thereto connected to a junction point of the outputs of said first and second switching circuits, the output of said low-pass filter being connected to said second input of said signal control circuit;
a feedback circuit having an input thereto connected to said second input of said signal control circuit and an output thereof connected to said junction point of the outputs of said first and second switching circuits;
and
a third switching circuit having inputs thereto connected respectively to said junction point of the outputs of said first and second switching circuits and to said second output of said oscillator, said third switching circuit having an output thereof connected to said output of said signal control circuit and driven by said second output signal from said oscillator to provide a third switched output signal at said output of said signal control circuit, said signal control circuit preventing transmission of signals from said first input means to said output means despite changes in the impedances of a signal source circuit.

7 more elements

Abstract

Claims3