Light Sensor Distance Measurement Using Histogram Center Positions
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Solution Overview
Problem
Current methods for measuring distance using single photon avalanche diodes in applications like auto focus require high resolution and accuracy, but are hindered by crosstalk components, leading to increased processing time and circuit complexity, especially at longer distances or low reflectance conditions.
Innovation Solution
A light sensor system that includes a light emitting element, first and second photon count-type light receiving units, and histogram generation units to compute distance based on the center positions of reflection and reference light distributions in histograms, accounting for crosstalk and disturbance components, thereby eliminating the need for delay locked loop circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high resolution distance measurement is implemented using conventional methods, then measurement precision is improved, but device complexity and processing time increase significantly
Solution Approach 1:
The patent segments the light receiving process into two independent channels: a first light receiving unit for receiving reflected light from the sensing object, and a second light receiving unit for receiving reference light directly from the light emitting element. This segmentation allows parallel processing of reference and measurement signals, eliminating the need for complex delay locked loop circuits while maintaining high measurement resolution.
Solution Approach 2:
The patent introduces a computation unit as an intermediary that processes histograms generated from both light receiving units. This computation unit calculates the center positions of the histograms and determines distance based on their difference, replacing complex conventional processing circuits with a more straightforward computational approach that reduces device complexity.
2Measurement precision
If high resolution distance measurement is implemented using conventional methods, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs preliminary action by generating histograms from the light receiving units and calculating their center positions in advance. This preprocessing allows the final distance calculation to be performed quickly by simply comparing the pre-computed center positions, significantly reducing the time required for high-resolution distance measurement compared to conventional methods.
Solution Approach 2:
The patent maintains continuous useful action by operating both light receiving units simultaneously and continuously accumulating photon detection events into histograms. This parallel continuous operation ensures that measurement is ongoing without interruption, improving measurement speed while maintaining high resolution through continuous data accumulation.
3Measurement precision
If conventional distance measurement methods are used, then measurement precision is maintained, but crosstalk components reduce accuracy at long distances
Solution Approach 1:
The patent extracts the reference light signal from the reflected light signal by using a separate second light receiving unit dedicated to receiving reference light. This extraction isolates the harmful crosstalk components that would otherwise contaminate the measurement, allowing the computation unit to calculate distance based on the difference between the two independent histograms, thereby eliminating crosstalk-induced errors even at long distances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances measurement speed and resolution while reducing the complexity and cost of the measurement process by directly computing distance through histogram analysis, effectively mitigating the effects of crosstalk and disturbance components.
Implementation Method 1
reflection light by the sensing object
Implementation Method 2
an avalanche photodiode utilizing an avalanche amplification (avalanche) effect of a photodiode
Implementation Method 3
a photodiode, an active quenching resistor (resistor component of a MOS transistor), and a buffer
Implementation Method 4
When the current flows through the aforementioned active quenching resistor connected in series to the photodiode, a voltage between terminals of the active quenching resistor increases, and the bias voltage of the photodiode drops accordingly
Data Source
AI summary
A light sensor or the like that has an improved measurement speed is realized. A light sensor includes a computation unit that computes a distance between the light sensor and a sensing object on the basis of a difference between a center position of reflection light, which indicates a center position of distribution of light reception probability of a first light receiving unit in a first histogram, and a center position of reference light, which indicates a center position of distribution of light reception probability of a second light receiving unit in a second histogram.