Patent ID: 8648610

Claim:
A signal input circuit comprising: a signal input device having a signal input terminal, through which an input signal is input into the signal input device, the input signal having a voltage variable within a predetermined variation range; an inspection capacitor having one end connected to the signal input terminal and the other end connected to a reference potential; a connection unit arranged in the signal input device and connecting and disconnecting an inspection path between the inspection capacitor and the signal input terminal; a charge and discharge unit arranged in the signal input device and charging and discharging the inspection capacitor so that a voltage between both ends of the inspection capacitor is set to be within the predetermined variation range; and a determination processing unit arranged in the signal input device and carrying out a terminal failure detection processing, wherein the determination processing unit sequentially carries out a charge and discharge procedure and a continuity establishing procedure in the terminal failure detection processing, wherein, in the charge and discharge procedure, the determination processing unit controls the connection unit to disconnect the inspection path and controls the charge and discharge unit to set the voltage between both ends of the inspection capacitor to be a predetermined terminal inspection voltage, wherein, in the continuity establishing procedure, the determination processing unit controls the connection unit to connect the inspection path, wherein the determination processing unit detects the terminal failure based on a voltage of the inspection path after the terminal failure detection processing is executed, and wherein the terminal failure occurs at the signal input terminal or a communication path of the input signal input from the signal input terminal.