SIGMA-DELTA ANALOG-DIGITAL CONVERTER USING MIXED-MODE INTEGRATOR

PURPOSE: A converter is provided to achieve a high resolution of the converter without causing an instability to system. CONSTITUTION: A converter comprises an overload estimating unit having a sigma-delta modulator used for the converter so as to judge a saturation or overload of an analog integrator; a mixed-mode integrator constituted by a digital integrator including an analog integrator, a digital adder and a digital storing element, and which performs analog and digital integration to an output of the overload estimating unit; and a quantizing unit for analog-to-digital converting an output of the mixed-mode integrator, and outputting the result. The quantizing unit includes a 1-bit A/D converter for performing 1-bit A/D conversion to an output of the analog integrator and feeding back the result to the overload estimating unit; a 3-bit A/D converter for performing 3-bit A/D conversion to an output of the analog integrator; a digital adder for adding the output of the 3-bit A/D converter and the output of the digital integrator; and a digital adder for adding the output of the 1-bit A/D converter and the final output of the modulator, and feeding back the result to the overload estimating unit.