| 摘要 |
PURPOSE:To reduce substantially a nose offensive to ears by converting a sound signal voltage into a sound signal current in proportion to a mute signal for silencing a sound so as to execute a sound mute action. CONSTITUTION:When the mute signal inputted to a terminal is at a high voltage, the voltage of a capacitor 5 becomes constant and applied to transistors TRs 10, 11 and 15. Then a current (i) equaling values of resistances 12, 13 and 14 is flowed. Assuming that values of resistances 16 and 17 are to be R when a signal DELTAV is applied to terminals 1 and 2, the negative side input current DELTAV/2R of an operational amplifier 23 will not be larger than a constant current 2i. Next, when the mute signal inputted to a terminal 3 is at a low voltage, it is integrated by a resistance 4 and a capacitor 5, whereby the sharp rise and fall of a waveform are smothed. When the voltage is applied to the bases of current source TRs 10, 11 and 15 through TRs 6 and 7, the constant current (i) comes to zero slowly in proportion to a mute integration voltage. And the output voltage of the amplifier 23 is also in proportion to the mute signal integration waveform. Thus a noise due to a high frequency wave will not occur.
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