Patent ID: 7248345

Claim:
A method for detecting movement of a surface relative to an optical sensor having an array including a plurality of photosensitive elements, the method comprising steps of: sampling each of a number (M) of phase signals from the plurality of photosensitive elements, each of the M signals having a magnitude (A i ) and including a tracking signal at a frequency being tracked and a background signal at other frequencies that offsets the tracking signal, where i, an index of the signals, is a whole number between 0 and M-1; eliminating the offset to the tracking signal due to the background signal to generate M non-offset phase signals having a magnitude (A′ i ); adjusting phase angles (θ i ) of the non-offset phase signals to generate M weighted phase signals (A′ i θ′ i ); and combining each of the M weighted phase signals (A′ i θ′ i ) to generate an average weighted phase having a phase angle (θ), that when tracked over time indicates a direction and velocity of the movement of an image of the surface mapped to the array.