| 摘要 |
PROBLEM TO BE SOLVED: To set an output level to an optimal level automatically, so as to keep a maximum output level to a fixed level regardless of the size of a supply voltage while the supply voltage is high enough, and not to be clipped to an output dynamic range when the supply voltage falls. SOLUTION: The voice signal amplifier is provided with a variable gain amplifier circuit 101 which amplifies a voice signal at an amplifying rate according to a gain control signal; a detection level control circuit 200 which outputs a detection signal feedback amount control signal that a level is fixed regardless of a supply voltage in a state that the supply voltage is higher than a predetermined value, and that a level changes dependent on the supply voltage in a state that the supply voltage is lower than the predetermined value; and a detection circuit 102 which outputs a detection signal by detecting an output of the variable gain amplifier circuit 101, inputs the detection signal as feedback to a gain control terminal 122 of the variable gain amplifier circuit 101, and changes the level of the detection signal according to the level of a detection signal feedback amount control signal that is output from the detection level control circuit 200. COPYRIGHT: (C)2008,JPO&INPIT
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