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Abstract

An apparatus and method for setting a sensitivity level of an optical encoding circuit in an input device includes an adjuster for adjusting the sensitivity level, a threshold locator for detecting a sensitivity threshold of the occurrence of a prescribed output from a light detector circuit, and a motion encoder for encoding motion from the output of the light detector circuit. The threshold locator locates a sensitivity threshold by setting the sensitivity level to one extreme, then repeatedly sampling the light detector circuit output for a prescribed state most likely at the one extreme, while incrementally changing the sensitivity level each time the prescribed state is detected. The sensitivity level used by the threshold locator thus approaches the sensitivity threshold of the prescribed state. A sensitivity level for motion encoding is set based on the sensitivity level for threshold location. Motion encoding samples from the output of the light detector may be interleaved with threshold location samples, and the absolute total motion is tracked. When the sensitivity level has not changed through a prescribed amount of total motion, the threshold location process terminates, the sensitivity level is set for motion encoding, all samples are used for motion encoding, and encoded motion is reported by the device. The prescribed amount of total motion is selected such that the threshold location process completes within a finite displacement, with an optimal-level resulting set point for motion encoding, regardless of the motion of the device throughout the process.

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