Patent ID: 8284093

Claim:
A successive approximation A/D converter, comprising: a reference voltage generation circuit that divides a potential difference between a high potential power supply and low potential power supply to output a reference voltage; a sample/hold circuit that converts an input analog voltage to an internal analog voltage representing a difference between the input analog voltage and the reference voltage, and samples and holds the internal analog voltage; a D/A converter circuit that divides a potential difference between the high potential power supply and the low potential power supply to generate a comparison target voltage; a comparator that compares the input analog voltage with the comparison target voltage and outputs a signal representing the result of the comparison; and a control circuit that retrieves a comparison target voltage that is closest to the input analog voltage while successively updating a voltage division ratio in the D/A converter circuit in accordance with the output signal from the comparator and outputs a digital value corresponding to the result of the retrieval, wherein a potential difference between the comparison target voltage generated by the D/A converter circuit and the internal analog voltage is applied to one input terminal of the comparator through a first signal line, and the reference voltage generation circuit is connected to the other input terminal of the comparator through a second signal line and a switching element, a first capacitive element is disposed between the high potential power supply and the second signal line, and a second capacitive element is disposed between the second signal line and the low potential power supply, the control circuit turns ON the switching element to charge the first and second capacitive elements during a period when the sample/hold circuit samples and holds the internal analog voltage and turns OFF the switching element in response to the end of the period, a first switch is disposed between the first capacitive element and the high potential power supply, a second switch is disposed between the second capacitive element and the low potential power supply, the D/A converter includes a plurality of third capacitive elements, each of which has one end connected to the first signal line and the other end connected to a respective one of a plurality of third switches that is provided to select any one of at least the high potential power supply and the low potential power supply, and turning ON and OFF the first switch and the second switch is controlled to adjust each capacitance of the first capacitive element and the second capacitive element so that impedances of the first and second signal lines are uniform with each other.