A/D CONVERTER

PURPOSE:To attain high resolution of the A/D converter efficiently by applying noise resulting from shaping quantization noise to the A/D converter so as to shift the quantization noise to a high frequency region. CONSTITUTION:An analog input signal is fed to an A/D converter ADC 3 via an adder 1 and fed to a subtractor 13. While an output of the ADC 3 is inputted to a digital filter section 4, the output is fed to the subtractor 13 via a D/A converter 11 and a delay element 12. The subtractor 13 outputs a difference between an output of the DAC 11 in a preceding sample and an input signal with a delay by the element 12. Then an integration device 14 integrates the difference and the adder 1 adds the result to the input signal through a switch 2. Thus, shaping noise is superimposed on the input signal and high resolution is executed efficiently.