Signal processing method for use with an optical navigation system

iiiiiiiA signal processor and method are provided for detecting movement of a surface relative to an optical sensor having an array of photosensitive elements. Generally, the method involves: (i) sampling each of a number (M) of phase signals from the photosensitive elements, each of the M signals having a magnitude (A) 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; (ii) eliminating the offset to the tracking signal due to the background signal to generate M non-offset phase signals having a magnitude (A′); (iii) adjusting phase angles (θ) of the non-offset phase signals to generate M weighted phase signals (A′θ′); and (iv) combining each of the M weighted phase signals (A′θ′) 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.