| 摘要 |
PROBLEM TO BE SOLVED: To provide a low-noise voice output apparatus. SOLUTION: The apparatus comprises an output amplifier 5 for amplifying an input signal, an amplitude detector circuit 10 for detecting amplitude information of the input signal, and a bias current setting circuit 11 for controlling the bias current density of the output amplifier 1. The amplitude detector circuit 10 converts the input signal of the output amplifier 5 to e.g. a DC voltage proportional to the signal amplitude, and the bias current setting circuit 11 controls the bias current of the output amplifier 5 according to the DC voltage value and increases the bias current especially while no signal or low-amplitude signal is coming. The bias current flowing in an operational amplifier may be increased to lower the thermal noise owing to its thermal noise characteristics. The current may be reduced in the usual operation but increased only when no signal or low-amplitude signal is coming, thereby reducing the power consumption for the entire voice output apparatus. COPYRIGHT: (C)2003,JPO
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