| 摘要 |
PURPOSE:To improve the sound volume control characteristic at low sound volume by providing a 1st A/D converter receiving an input data signal and a 2nd D/A converter using an output voltage of the 1st D/A converter as a reference voltage to convert the input data signal into an analog voltage and using the output voltage of the 2nd converter thereby controlling the amplitude of the input signal. CONSTITUTION:A D/A converter 22 converts an input data signal into an analog voltage signal. A D/A converter 23 uses an output voltage of the converter 22 as a reference voltage to convert the input data signal into an analog voltage as the output. A sound volume control circuit 21 controls the amplitude of the input signal based on the output voltage of the converter 23. Thus, the output voltage of the converter 23 is decided by the reference voltage varied by the input data signal and the input data signal itself. As a result, smoother sound volume change is realized at low sound volume.
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