| 摘要 |
PROBLEM TO BE SOLVED: To enhance power supply efficiency of a class-D amplifier circuit in a small output power state. SOLUTION: An analog input signal AIN is amplitude-controlled by a gain control unit 10, applied to a pulsewidth modulation unit 30, converted into a pulsewidth modulation signal PWM having a duty ratio corresponding to its amplitude and applied to a driving signal generation unit 40. In the driving signal generation unit 40, driving signals PGC, NGC to an output driver 50 are generated on the basis of the pulsewidth modulation signal PWM. The output driver 50 includes a first driver constituted of a PMOS 51 and an NMOS 52 which are constantly driven, and a second driver constituted of a PMOS 53 and an NMOS 54 of which operation is controlled by a drive control signal ROC. In a drive control unit 20, when a low level is set by a volume control signal VOL, the drive control signa ROC is outputted that stops driving the second driver. Thus, while output power is small, charging/discharging currents of gate capacitance of the second driver are eliminated, thereby enhancing power supply efficiency. COPYRIGHT: (C)2009,JPO&INPIT
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