Low power image sensor adjusting reference voltage automatically and optical pointing device comprising the same

Abstract

The low power image sensor includes: an image sensing unit which senses light from an object, converts the light into an electric signal, and outputs the electric signal; a comparing unit which receives an electric signal from the image sensor, compares a voltage level of the electric signal with a reference voltage, and outputs an image signal as a 1 bit signal per pixel; and an effective image adjuster which compares bit value distribution of an image signal output from the comperator with a preset effective range, and adjusts the effective image to output an effective image. Further, an optical pointing device includes: an image sensor which senses light from an object and outputs an image signal; and a motion computing unit which receives the image signal and compares before and after images to calculate a motion vector.

1 . An optical pointing device comprising:
 an image sensor which senses light from an object and outputs an image signal; and   a motion computing unit which receives the image signal and compares before and after images to calculate a motion vector, the motion computing unit comprising:
 a temporary storage unit to temporarily store image data output from the image sensor; 
   a comparing unit to compare the image data output from the image sensor with the image data stored in the temporary storage unit;
 a direction selector to calculate a motion vector from a value output from the comparing unit; and 
 a controller to control operation of the motion computing unit. 
   
     
     
         2 . The optical pointing device according to  claim 1 , wherein the image sensor comprises:
 an image sensing unit which senses light from an object, converts the light into an electric signal, and outputs the electric signal; and   a comparing unit which receives the electric signal from the image sensing unit, compares a voltage level of the electric signal with a reference voltage, and outputs an image signal as a 1 bit signal per pixel.   
     
     
         3 . The optical pointing device according to  claim 1 , wherein the motion computing unit comprises an operating state selector to determine an operating state of an object with respect to the number of focused effective frames and unfocused ineffective frames to a current image frame or with respect to time. 
     
     
         4 . The optical pointing device according to  claim 3 , wherein the operating state selector determines an operation as a click if the number of effective frames following an ineffective frame or time is smaller than a predetermined critical value N 0 . 
     
     
         5 . The optical pointing device according to  claim 3 , wherein the operating state selector determines an operation as a double-click if the number of first effective frames following a first ineffective frame or time is smaller than the critical value N 0 , if the number of second ineffective frames following the first ineffective frame or time is smaller than a predetermined critical value N 1 , and if the number of second effective frames following the second ineffective frame or time is smaller than the critical value N 0 . 
     
     
         6 . The optical pointing device according to  claim 3 , wherein the operating state selector determines an operation as a drag if the number of effective frames following the ineffective frame or time is larger than a predetermined critical value N 0 . 
     
     
         7 . The optical pointing device according to  claim 1 , wherein the motion computing unit comprises a power controller to control the image sensor and the computing unit to consume minimum power when there is no input, when the object is unfocused, and when the object remains stopped for a predetermined period. 
     
     
         8 . An integrated circuit comprising the optical pointing device according to  claim 1  and integrated on a single chip.