| 摘要 |
PROBLEM TO BE SOLVED: To reduce power consumption and to highly efficiently extend a battery operation time by providing a drive current generation circuit which receives the pulse of a pulse generation circuit and generates a current with a current value corresponding to PWM modulation, etc., and driving a speaker in accordance with the output of the drive current generation circuit. SOLUTION: A D/A conversion circuit (D/A) 4 receives the digital value of a bit shifter 3 from its output terminal 3c and converts it into an analog signal. The analog signal output of the D/A 4 is inputted to a PWM switching power amplifier 5. The amplifier 5 consists of a PWM pulse generation circuit 5a and a pulse oscillator 5b oscillating in 500 kHz pulses. Furthermore, the output pulses from the oscillator 5b are transmitted to an L-type filter circuit 6. The circuit 6 converts a PWM signal into a drive current having a current value corresponding to the amplitude of the analog signal by using the coil L, the signal converted into the drive current is applied to a speaker 7 and converted into sound.
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