| 摘要 |
PURPOSE:To stop the singing in a telephone set such as an automobile telephone set by providing a singing detector and a phase shift circuit to a talking device, using the phase shift circuit to change the phase of the signal and decreasing the closed loop gain to the singing component. CONSTITUTION:The hand free talking device is provided with the singing detector 11 and the phase shift circuit 12. Then the singing detector 11 detects the singing by utilizing that the singing has a single frequency and is consecutive for a prescribed time and outputs the signal to start the phase shift circuit 12 when the singing reaches a prescribed level or over. Thus, the phase shift circuit 12 changes the phase of the signal from a variable loss circuit 6 and gives an output to a power amplifier 5. Since the phase of the singing component is changed, the gain of the singing component in the closed loop comprising a path of speaker 4 - microphone 1 - transmission system circuit (amplifier 2 - transmission terminal T) - hybrid or the like (not shown in figure) - reception system circuit (reception terminal R - power amplifier 5) - speaker 4 is decreased to stop the singing.
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