Signal conditioning circuitry

Signal conditioning circuitry for an optical pointing device, the circuitry comprising:

• a differentiator having an input to which a signal generated on periodic illumination of a photodetector is supplied, the differentiator being operable to determine the rate of change of the signal input thereto and to output a 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 in 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 representative 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.