Signal conditioning circuitry

Signal conditioning circuitry for an optical pointing device comprising a photodetector which upon periodic illumination generates a periodic signal, the circuitry comprising:

• a differentiator receiving as input said periodic signal, the differentiator being operable to determine the rate of change of said periodic signal independently of the amplitude of said periodic signal and to generate an output signal representative of said determined rate of change, and
• a Schmitt trigger operable to compare said output signal to a predetermined reference voltage.

Signal conditioning circuitry for an optical pointing device, said circuitry comprising a circuit for outputting signals proportional to X-direction movement and a circuit for outputting signals proportional to Y-direction movement, each said circuit comprising a detector arrangement for detecting movement of a respective body of said X- and Y-direction movement and outputting a signal in response thereto, means for determining a rate of change of said signal and outputting a signal representative of said determined rate of change and means for comparing said signal output by said determining means to a reference voltage.