Patent ID: 8055923

Claim:
An electronic control unit comprising: a microcomputer that operatively switches to any one of a normal operation mode and a low power consumption operation mode; and a signal monitoring circuit that cyclically operates at least when the microcomputer is in the low power consumption operation mode, and outputs a wakeup signal that instructs the microcomputer to shift from the low power consumption operation mode to the normal operation mode upon detecting that a relationship between an analog signal received from an external side a reference voltage satisfies a predetermined relationship, wherein the signal monitoring circuit includes: a capacitor; a constant current circuit for charging the capacitor with a constant current; a memory that stores a charging time during which the constant current circuit charges the capacitor; a timer circuit that allows the constant current circuit to charge the capacitor for only the charging time that is stored in the memory during an operation of the signal monitoring circuit; a discharging circuit for discharging the capacitor while stopping the operation of the signal monitoring circuit; and a comparator that compares the analog signal with a charge voltage of the capacitor, wherein the charging time for allowing the charge voltage at charging completion of the capacitor to be used as the reference voltage is stored in the memory, and the wakeup signal is output to the microcomputer based on comparison results of the comparator.