Patent ID: 7129882

Claim:
A successive approximation AD converter, comprising: a sampling capacitor adapted to receive an analog signal; a reference voltage supply section adapted to provide a reference voltage; a voltage comparator having an input terminal for receiving the analog signal via the sampling capacitor, and a second terminal into which the reference voltage is input from the reference voltage supply section; a successive approximation register connected to an output terminal of the voltage comparator; and a DA converter for converting data in the successive approximation register into an analog signal and inputting the analog signal into the first input terminal of the voltage comparator, wherein: the voltage comparator comprises: a capacitance pair; two differential amplifiers connected in series via the capacitance pair; a first switch connected between the sampling capacitor and a first one of the differential amplifiers; a second switch connected between a connection point between the first switch and the sampling capacitor and the reference voltage supply section; and a third switch connected between a connection point between the first switch and the first one of the differential amplifiers and the reference voltage supply section, when the input analog signal is applied to the voltage comparator input terminal to be sampled, the first switch is switched OFF, and the second switch and third switch are switched ON, and when a voltage comparison is executed, the first switch is switched ON, and the second switch and third switch are switched OFF.