Patent ID: 7486218

Claim:
An A/D converter comprising: an A/D conversion circuit; a residue voltage generation circuit having an input terminal connected to an input of the A/D conversion circuit, the residue voltage generation circuit generating a residue voltage by amplifying a difference between an input voltage applied to the input terminal and a reference analog voltage by a predetermined gain; a signal terminal for receiving an external signal voltage; a switch circuit having a first end connected to the input terminal of the residue voltage generation circuit and a second end connectable to the signal terminal or an output terminal of the residue voltage generation circuit; and a control circuit that performs an amplification operation and an A/D conversion operation followed by the amplification operation, wherein in the amplification operation, the control circuit keeps the reference analog voltage at a predetermined voltage level, wherein in the amplification operation, the control circuit controls the switch circuit so that the residue voltage generation circuit receives the external signal voltage as the input voltage and outputs an output voltage, wherein in the amplification operation, the control circuit controls the switch circuit so that the output voltage is recycled through the switch circuit and the residue voltage generation circuit a first certain number of times to amplify the output voltage; wherein in the A/D conversion operation, an analog value into which a digital value outputted from the A/D conversion circuit is converted is used as the reference analog voltage, and wherein in the A/D conversion circuit, the control circuit controls the switch circuit so that the amplified voltage is recycled through the switch circuit, the A/D conversion circuit, and the residue voltage generation circuit a second certain number of times to convert the amplified voltage into the digital value.