Microphone or mouthpiece signal suppression circuit
AssigneeThomson-CSF
InventorJean C. Kaire
Life of this patent
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Abstract
The invention relates to a circuit for a telephone set. In order to eliminate the mouthpiece signal between the receiver and the telephone set, there are provided a subtraction means receiving the mouthpiece signal and the composite signal present on the telephone line, one of the two being produced by different compensation impedances, and on the other hand a mixer controlled by a circuit as a function of the telephone line impedance. The two compensation impedances respectively correspond to the compensation of a long line and the compensation of a short line and the output of the mixer supplies a signal mixture, with variable proportions, which effectively suppresses the mouthpiece signal, no matter what the length of the telephone line.
Claims8
A mouthpiece signal suppression circuit for a telephone set, which telephone set includes a mouthpiece amplifier supplying a mouthpiece signal to a line amplifier, which transmits this mouthpiece signal on a telephone line, a receiver amplifier supplying a signal to a receiver with the mouthpiece signal suppression circuit receiving on the one hand the mouthpiece signal and on the other hand a composite signal from the line, in order to supply the telephone receiver with a signal essentially corresponding to the composite signal, from which has been subtracted the mouthpiece signal, wherein said suppression circuit comprises:
- two different compensation impedances, one of which provides an impedance matching for a short telephone line and the other an impedance matching for a long telephone line,
- a signal mixer for mixing signals modified by said two impedances with controlled variable proportions,
- a control circuit receiving a signal representing the impedance of said telephone line and controlling said signal mixer in order to check the proportions of the mixture of said mixing signal as a function of the impedance of said line, and
- a signed addition function means receiving the composite line signal and the mouthpiece signal wherein at least one of said composite line signal and said mouthpiece signal is modified by said compensation impedances.
Dependencies are inferred from the claim text.