| 摘要 |
PROBLEM TO BE SOLVED: To provide a delta-sigma modulator capable of attaining the compatibility between a high S/N ratio and system stability, a switching method for the delta-sigma modulator, and a digital amplifier. SOLUTION: A delta-signal modulation circuit includes: a quantization bit rate detection unit 9 that detects the quantization bit rate of a digital audio signal; a volume setting detection unit 10 that detects a volume setting of the digital audio signal; a filter 11 that includes plural sets of filter coefficients having different shaping properties and makes the quantization noise pass; and a filter coefficient switcher 17 that switches the filter coefficients of the filter 11 in accordance with the detected results of the quantization bit rate detection unit 9 and the volume setting detection unit 10. The delta-sigma modulator detects the quantization bit rate of an input signal, switches the filter coefficients to the low-order filter coefficient set when a source has a low quantization bit rate, switches the filter coefficients to the low-order coefficient set when the source has a high quantization bit rate and the volume setting value is a prescribed value or over, and switches the filter coefficients to the high-order coefficient set when the source has a high quantization bit rate and the volume setting value is less than the prescribed value. COPYRIGHT: (C)2004,JPO |
