SPAD Pixel Array Signal Sharing for Low-Crosstalk Ranging
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Solution Overview
Problem
In range image sensors using single photon avalanche diodes (SPADs), the large number of signal lines required for outputting detection signals leads to concerns about crosstalk, delay, and increased wiring complexity, which limits the ability to set multiple pixels in the same row as active simultaneously.
Innovation Solution
A light receiving element and ranging system where a pixel array with SPADs is arranged in a matrix, and a pixel driving unit controls pixels to be active in units of spots (N×M pixels) with one signal line outputting detection signals for multiple spot constituent pixels within a unit (L×L pixels).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If individual signal lines are provided for each pixel, then detection signal output capability is improved, but the number of wirings becomes extremely large leading to crosstalk and delay
Solution Approach 1:
The patent merges signal lines by making them common in units of row for pixels selected as active pixels in units of column. Specifically, multiple pixels in the same row share a common signal line, reducing the total number of signal lines from potentially thousands (if each pixel had its own line) to just the number of rows in the pixel array.
Solution Approach 2:
The patent segments the pixel array into units where pixels are selected as active in columns and organized in rows, with signal lines commoned within each row segment. This segmentation allows systematic reduction of signal lines while maintaining detection capability.
2Device complexity
If pixels in the same row share common signal lines, then the number of wirings is reduced, but multiple pixels in the same row cannot be set as active pixels at the same time
Solution Approach 1:
The patent implements periodic action by sequentially selecting different columns as active columns in different time periods. During each period, only pixels in the selected active column can be active, but they can be active simultaneously since they are in different rows with different signal lines. This temporal multiplexing resolves the conflict between signal line sharing and simultaneous activation.
3Reliability
If the number of signal lines is reduced, then crosstalk and delay are minimized, but the ability to simultaneously activate multiple pixels in the same row is lost
Solution Approach 1:
By using periodic column selection, the system allows multiple pixels to be simultaneously active within each active column during each period, while maintaining reduced wiring. The sequential activation of different columns across periods ensures comprehensive coverage without requiring excessive simultaneous signal lines.
Solution Approach 2:
The system dynamically adjusts which columns are active at different time periods, allowing flexible configuration of active pixels adapt. This dynamic column selection enables the system to optimize between signal line usage and simultaneous active pixel capability based on current measurement requirements.
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 configuration reduces the number of signal lines, minimizing crosstalk and signal delay while allowing for efficient control of active pixels, thereby improving the accuracy and reliability of range measurements.
Implementation Method 1
In the SPAD, avalanche amplification occurs if one photon enters a high-field PN junction region in a state where a voltage higher than a breakdown voltage is applied
Implementation Method 2
a pixel array in which a plurality of pixels including SPADs in units of pixel is arranged in a matrix
Data Source
AI summary
There is provided a light receiving element and a ranging system which achieve reduction in the number of signal lines which output detection signals. The light receiving element includes a pixel array in which a plurality of pixels is arranged in a matrix, and a pixel driving unit configured to control respective pixels of the pixel array to be active pixels or non-active pixels, in which the pixel driving unit controls the pixels to be the active pixels in units of spot including N×M pixels (N>0, M>0, where N and M do not become 1 at a same time), and one signal line which outputs a detection signal is disposed at the pixel array for a plurality of spot constituent pixels of a same type within one unit where the one unit includes L×L pixels (L>1).