| 摘要 |
A method of reducing a noise generated from a speaker at the time of power on/off in an audio output device that drives the speaker. The device includes a digital DC attenuator, a D/A converter, and an operational amplifier. The attenuator gradually changes an output digital value from a first digital value to a second digital value. The converter converts an output from the attenuator into an analog signal. The amplifier amplifies an output from the converter and drives a speaker. At the time of power on, the output from the attenuator is gradually changed from a digital value corresponding to the ground level to a digital value corresponding to the signal ground value. At the time of power off or system reset, the output from the attenuator is gradually changed from the digital value corresponding to the signal ground value to the digital value corresponding to the ground level.
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