Varying Sensitivity Reference Pixel Array for TOF Sensor Calibration
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Solution Overview
Problem
In 3D imaging systems with multiple light elements, synchronization and calibration of light elements are challenging due to temperature changes, manufacturing tolerances, and differences in behavior among light elements, making it difficult to achieve accurate distance measurements and high signal-to-noise ratios.
Innovation Solution
A demodulation sensor with a reference pixel array on the same chip as the imaging pixel array, using a light guide to transmit reference modulation light and varying the sensitivity of reference pixels to achieve synchronized control and exposure times, allowing for accurate phase measurements and improved signal-to-noise ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photodetection area is enlarged to get higher sensitivities, then sensitivity is improved, but parasitic capacitances increase which detrimentally impacts the speed of the device
Solution Approach 1:
The pixel is divided into multiple photo-gates with different resistances. Each photo-gate has a specific resistance value that is different from other photo-gates in the array. This segmentation allows each gate to have optimized capacitance and resistance characteristics, enabling high sensitivity while maintaining fast demodulation speed by preventing excessive charge accumulation in any single gate.
Solution Approach 2:
Different regions of the pixel have different properties - specifically, different photo-gates have different resistance values. This local variation in resistance creates different capacitance characteristics in different regions, allowing the pixel to achieve both high sensitivity (through appropriate resistance) and high speed (through controlled capacitance) simultaneously.
2Measurement precision
If the transport path is lengthened to increase photodetection area, then sensitivity is improved, but the time required for photo-generated charges to reach storage increases
Solution Approach 1:
The transport path is segmented into multiple regions with different resistance values. Each segment has optimized dimensions and resistance characteristics that allow charges to be collected efficiently without requiring excessively long transport paths. The segmentation creates multiple parallel charge collection pathways, reducing overall transport time while maintaining high sensitivity.
3Adaptability or versatility
If multiple light elements are used in 3D imaging systems, then imaging capability is improved, but synchronization and calibration become challenging due to temperature changes and manufacturing tolerances
Solution Approach 1:
A reference pixel array is integrated into the sensor chip to provide feedback signals for synchronization and calibration. The reference pixels receive light from the same light elements as the imaging pixels and generate reference signals that are used to compensate for timing differences and calibration drift caused by temperature changes and manufacturing tolerances, ensuring reliable synchronization across multiple light elements.
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 solution enables precise synchronization and calibration of light elements, enhancing the accuracy of distance measurements and signal-to-noise ratios in 3D imaging systems, particularly in systems with multiple light elements, by ensuring consistent control signals and exposure times across all pixels.
Implementation Method 1
using a light guide to transmit reference modulation light
Implementation Method 2
In these sensors light is converted into electrical charge carriers, usually electrons
Data Source
Figure 1~2B
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AI summary
The sensitivity of a reference pixel array RPA to the reference modulated light MLR is varied for different reference pixels RP of the reference pixel array RPA. In one embodiment the different sensitivities of the reference pixels RP in the RPA is achieved by designing the pixels to have different light sensitivities with respect to each other. In another embodiment, the different sensitivities are achieved by changing optical coupling between the separate reference pixels RP of the reference pixel array RPA to the reference modulated light MLR such as by changing how the different reference pixels RP couple to the aperture LGA of the light guide LG.