Patent ID: 7075577

Claim:
An auto-exposure power-saving device for controlling the operational status of a central processing unit of a digital still camera when said digital still camera operates in an auto-exposure mode, said auto-exposure power-saving device comprising: said central processing unit setting an upper brightness limit value and a lower brightness limit value for said auto-exposure mode responsive to said digital still camera entering said auto-exposure mode, said central processing unit entering a power-saving sleep mode subsequent to said calculations being completed; an image brightness calculation unit for calculating a brightness value of an image taken by a CCD of said digital still camera; a first comparator and a second comparator each having a first input connected to said image brightness calculation unit for input of said brightness value thereto, said first comparator having a second input for receiving said upper brightness limit value and comparison thereof with said image brightness value for generating a first limit signal at an output thereof if said image brightness value is greater than said upper brightness limit value, said second comparator having a second input for receiving said lower brightness limit value and comparison thereof with said image brightness value for generating a second limit signal at an output thereof if said image brightness value is less than said lower brightness limit value; an OR gate having a first input coupled to said output of said first comparator, a second input coupled to said output of said second comparator, and an output coupled to said central processing unit, said OR gate generating a wakeup signal at said output thereof responsive to input of one of said first limit signal or said second limit signal, said central processing unit exiting said power-saving sleep mode to enter an active mode and calculating new upper and lower limit values responsive to input of said wakeup signal.