Patent ID: 7382302

Claim:
An A/D (analog-to-digital) converter, comprising: a first voltage generation circuit configured to generate a first output voltage; a second voltage generation circuit configured to generate a second output voltage; a comparator which has first and second input terminals and a first output terminal, and outputs from the first output terminal a signal in accordance with a potential difference between the first and second input terminals; first and second switch circuits connected in series between an input terminal of an analog input voltage and an output terminal of the first voltage generation circuit; a first capacitor inserted between a connection node between the first and second switch circuits and the first input terminal; a second capacitor inserted between an output terminal of the second voltage generation circuit and the second input terminal; a third switch circuit, one end of which is connected to the first input terminal, and which can set the first input terminal to an output common mode voltage or a predetermined voltage at conductive time; a fourth switch circuit, one end of which is connected to the second input terminal, and which can set the second input terminal to the output common mode voltage or the predetermined voltage at conductive time; an A/D conversion control circuit which generates a digital signal in accordance with signal level of the first output terminal; and a voltage setting circuit which sets voltages to be outputted from the first and second voltage generation circuits based on the digital signal, wherein the first to fourth switch circuit switch ON/OFF in an initial period for sampling the analog input voltage, a first period for gradually changing the first output voltage and comparing the first output voltage with the analog input voltage after the initial period, and a second period for gradually changing the second output voltage and comparing the second output voltage with the analog input voltage and wherein the second voltage generation circuit generates the second output voltage having a maximum voltage level capable of being outputted by the second voltage generation circuit during the initial period and the first period, and gradually changes the second output voltage by using a final first output voltage without changing a value thereof.