| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal amplifier circuit employing an RC filter as a filter at the post-stage of a class D amplifier. SOLUTION: The class D amplifier 20 in an audio output circuit 100 amplifies a one-bit audio signal SIG 12 subjected to pulse width modulation. A low pass filter 30' eliminates a high frequency component of an audio signal SIG 14 outputted from the class D amplifier 20 and converts the resulting audio signal into an audio signal SIG 16 including an analog amplitude component. The low pass filter 30' includes an eighth resistor R8, a ninth resistor R9, a third capacitor C3, and a fourth capacitor C4 provided between one-side ends of the eighth resistor R8, the ninth resistor R9 and a ground level point. A high pass filter 40 eliminates a low frequency component of an audio signal SIG 16. An amplifier 50 amplifies an audio signal SIG 18 outputted from the high pass filter 40 to drive the speaker 60. COPYRIGHT: (C)2006,JPO&NCIPI
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