| 摘要 |
[Problem] The purpose is to provide an amplifier capable of reducing the quantization error caused by conversion accuracy in an A/D converter circuit and, particularly, capable of improving the S/N ratio and distortion rate when an input audio signal is small. [Solution] In an amplifier (1) using a voltage variable power supply (73) as a power supply to follow an input audio signal level (S1) to the amplifier (1) in order to increase or decrease the level of supply voltage supplied to a power amplifier stage (4), when the level of source power of the power amplifier stage (4) is changed, the voltage level of a reference voltage supplied to an A/D converter (62) of a negative feedback circuit is controlled.
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