Patent ID: 7173556

Claim:
An analog-to-digital converter, including: an AD converter circuit which converts an input analog signal to a digital value of a predetermined bit number; a first amplifier circuit which samples the input analog signal and amplifies the sampled signal by a first predetermined gain; and a second amplifier circuit which amplifies, by a second predetermined gain, a difference between an analog signal outputted from said first amplifier circuit and an analog signal corresponding to the digital value amplified by a gain practically identical to the first predetermined gain, and which feeds the amplified difference back to said AD converter and said first amplifier circuit, wherein said first amplifier circuit includes an amplifier circuit of a capacitive coupling type in which any of the plurality of input signals is inputted to one end of capacitance and a voltage appearing on the other end is sampled, and the amplifier circuit of a capacitive coupling type includes: a plurality of switches for use with input signals, provided respectively at path through which the plurality of input signals lead to one end of the capacitance; and a switch for use with reference, provided at path through which a predetermined reference voltage signal leads to one end of the capacitance, wherein each of the switches for use with input signals is directly connected to one end of the capacitance.