Apparatus and method for finding optimal sensitivity level for optical encoding circuit
First Claim
1. A user input device including an optical encoder apparatus comprising:
- one or more light sources;
first and second light detectors positioned near the one or more light sources, each light detector providing an electrical output representative of the amount of light received by the light detector;
a rotatable encoder wheel having light-blocking regions alternating circumferentially with light-transmitting regions and positioned between the light detectors and the one or more light sources such that the amount of light received by the light detectors, and the output of the light detectors, varies periodically with the rotation of the encoder wheel, the light detectors being positioned relative to the encoder wheel and the one or more light sources such that the periodic output of the second light detector is about 90°
out of phase with the periodic output of the first light detector;
first and second single-bit analog-to-digital converters connected respectively to the outputs of the first and second light detectors and converting the outputs to first and second single-bit digital outputs at a digitization threshold;
a sensitivity level adjuster for adjusting the relative levels of the output of the light detectors and the digitization threshold of the first and second analog-to-digital converters; and
a threshold locator for locating the sensitivity threshold of a prescribed state of the first and second digital outputs;
wherein the sensitivity level adjuster adjusts the relative levels of the output of the light detectors and the digitization threshold of the first and second analog-to-digital converters as a function of the sensitivity threshold detected by the threshold locator.
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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.
10 Citations
26 Claims
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1. A user input device including an optical encoder apparatus comprising:
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one or more light sources; first and second light detectors positioned near the one or more light sources, each light detector providing an electrical output representative of the amount of light received by the light detector; a rotatable encoder wheel having light-blocking regions alternating circumferentially with light-transmitting regions and positioned between the light detectors and the one or more light sources such that the amount of light received by the light detectors, and the output of the light detectors, varies periodically with the rotation of the encoder wheel, the light detectors being positioned relative to the encoder wheel and the one or more light sources such that the periodic output of the second light detector is about 90°
out of phase with the periodic output of the first light detector;first and second single-bit analog-to-digital converters connected respectively to the outputs of the first and second light detectors and converting the outputs to first and second single-bit digital outputs at a digitization threshold; a sensitivity level adjuster for adjusting the relative levels of the output of the light detectors and the digitization threshold of the first and second analog-to-digital converters; and a threshold locator for locating the sensitivity threshold of a prescribed state of the first and second digital outputs;
wherein the sensitivity level adjuster adjusts the relative levels of the output of the light detectors and the digitization threshold of the first and second analog-to-digital converters as a function of the sensitivity threshold detected by the threshold locator. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for setting an adjustable sensitivity level of an optical encoding device having an optical encoding wheel and first and second digital outputs in quadrature representative of the rotational position of the optical encoding wheel, the adjustable sensitivity level compensating for variations in LED-phototransistor pairs used with the optical encoding wheel, the method comprising the steps of:
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setting the adjustable sensitivity level to a first level at an extreme of the total range of the adjustable sensitivity level that yields the greatest probability of the outputs matching prescribed output values; repeatedly sampling the outputs during motion of the encoding wheel to obtain search output values; whenever the search output values match the prescribed output values, changing the adjustable sensitivity level to a new first level at a small change from the previous first level, the change being in the direction away from the extreme;
the change yielding an equal or lessor probability of the outputs matching the prescribed output values. - View Dependent Claims (22, 23, 24, 25, 26)
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Specification