| 摘要 |
PROBLEM TO BE SOLVED: To enable stable negative feedback in a power amplifier circuit employing a PWM circuit by reducing the phase rotation in the circuit. SOLUTION: The PWM circuit 10 comprises a comparator 11 having hysteresis characteristics applied with positive feedback and an integrator 20. In the circuit 10, an input signal from a signal source 16 which is inputted via an amplifier 15 is compared with an integrated output by the comparator 11, thereby outputting a PWM signal having a leading phase characteristic which is obtained by differentiating an input signal. This PWM signal is amplified in a switching circuit 21, is applied to a speaker 27 via an LC filter 26, and is negatively fed back to an input side via a resistor 28. The PWM signal which is leading in phase passes through the filter 26, thereby reducing the phase rotation of the output to enable an stable negative feedback operation.
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