Optical navigation chip used in an optical mouse

An optical navigation system cooperated with a light source for being used in a mouse is provided. The mouse transmits a mouse signal to a computer for navigation control. The optical navigation system includes an optical sensing array and a circuitry. The optical sensing array is utilized for receiving a reflected light from a surface indicating features of the surface for generating a digital frame corresponding to intensity variation caused by the reflected light. The circuitry is coupled to the optical sensing array, and utilized for generating a digital displacement signal by monitoring the intensity variation of two different digital frames, wherein the two digital frames are captured by the optical sensing array at two different time. Additionally, the mouse suspends the mouse signal to the computer if the intensity variation is flat.