| 摘要 |
PROBLEM TO BE SOLVED: To minimize output distortion of the amplifier by applying a boosted voltage to an amplifier section when the amplitude of an amplified signal is high and applying a constant voltage via a bypass circuit to the amplifier section as a power supply voltage when small. SOLUTION: When the level of an amplified signal ZS is increased and a level at a point (a) is a reference voltage Vref or over, the output of a comparator 14A goes to H, a switching transistor(TR) SW12 is conductive and a boosted voltage boosted by a boosting chopper 12 is fed to an amplifier 15 as a power supply voltage. The level of the amplified signal ZS is small and when the potential at the point (a) is lower than the reference voltage Vref , the output of the comparator 14A goes to L and a power supply voltage applied to an amplifier 15 reaches a constant voltage +Vb applied again via a bias circuit 13. Thus, the power supply voltage changed depending on the level of the amplified signal is fed to the amplifier thereby amplifying the input signal AS and producing the amplified signal ZS. |
