| 摘要 |
The present invention discloses a method of reducing a noise generated from a speaker at the time of power on/off with a simple configuration in an audio output device that drives a speaker. For its achievement, the audio output device using the noise reduction method according to the present invention is provided with a digital DC attenuator, a D/A converter, and an operational amplifier. The digital DC attenuator functions to gradually change an output digital value from a first digital value to a second digital value. The D/A converter functions to convert an output from the digital DC attenuator into an analog signal. The operational amplifier functions to amplify an output from the D/A converter and thus drives a speaker. At the time of power on, the output from the digital DC attenuator is gradually changed from a digital value corresponding to the ground level to a digital value corresponding to the signal ground value. On the other hand, at the time of power off or the system reset, the output from the digital DC 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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