Successive approximation a/d converter comparing analog input voltage to reference voltages

Abstract

An analog-to-digital converter includes a resistance type potential divider, connected between a supply voltage and a ground terminal, for generating plural reference voltages; and plural switches for selecting one of the reference voltages in response to a select signal. The analog-to-digital converter also includes a capacitor for storing an analog voltage applied to an input node and having its one plate connected to the input node and its other plate connected to the midpoint of the resistance type potential divider. The midpoint has an intermediate potential placed between the power supply voltage and the ground voltage, which is insensitive to noise transmitted from a logic circuit. It is thus possible to reduce the influence exerted by the noise transmitted from the logic circuit without newly providing the supply voltage and ground terminals to the analog-to-digital converter in order to connect the converter and the logic circuit independently to each other.