TOF Pixel Layout With Shared Readout for Wide-Range Distance Sensing
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Solution Overview
Problem
Conventional solid-state imaging devices using the time-of-flight (TOF) method face challenges in achieving high distance measurement accuracy while maintaining a wide distance measurement range, as increasing the pulse width of the light source to expand the range results in decreased accuracy, and existing methods for background light removal are either complex, reduce sensitivity, or require significant resources.
Innovation Solution
A solid-state imaging device configuration that includes two adjacent pixels sharing a floating diffusion and amplification transistor, with a specific drive timing and pulse signal management to accurately adjust delay times and enhance aperture ratio, allowing for expanded distance measurement range without compromising accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the pulse width of the light source is increased to expand the distance measurement range, then the distance measurement range is improved, but the distance measurement accuracy is decreased
Solution Approach 1:
The imaging device divides the pixel array into multiple regions, with different exposure periods assigned to different regions. This segmentation allows simultaneous measurement at multiple time points, enabling accurate distance measurement across extended ranges without requiring a single long pulse width that would reduce accuracy.
Solution Approach 2:
The device uses periodic exposure cycles with multiple exposure periods (first, second, and third exposure periods) within each cycle. By repeating measurements across multiple periods and using phase difference calculation, the system achieves both extended range and high accuracy without relying on increased pulse width.
2Measurement precision
If three charge accumulation nodes are used for background light removal, then the distance measurement accuracy is improved, but the aperture ratio drops significantly
Solution Approach 1:
Adjacent pixels share common floating diffusion regions and amplification transistors. This merging allows background light subtraction to be performed using shared circuitry rather than requiring separate charge accumulation nodes for each pixel, maintaining high aperture ratio while achieving accurate background removal.
Solution Approach 2:
The shared floating diffusion regions serve multiple functions: they act as charge accumulation nodes for signal pixels, provide reference regions for background light measurement, and enable amplification for multiple pixels simultaneously. This multi-functionality eliminates the need for dedicated background removal hardware that would reduce aperture ratio.
3Measurement precision
If the pulse width of the light source is reduced to improve distance measurement accuracy, then the distance measurement accuracy is improved, but the distance measurement range is decreased
Solution Approach 1:
By using multiple exposure periods within each measurement cycle and calculating phase differences between these periods, the system achieves high accuracy with short pulses while extending the measurable range through the temporal distribution of multiple measurements rather than relying on a single long pulse.
Solution Approach 2:
The system transitions from measuring distance using only the temporal width of a single pulse to using the temporal distribution across multiple exposure periods. This adds a dimensional aspect of periodic measurement cycles, allowing both high accuracy (from precise phase detection) and extended range (from multiple measurement opportunities within each cycle).
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
The proposed solution enables a solid-state imaging device to achieve high distance measurement accuracy over a wide range without the trade-offs of reduced sensitivity or increased complexity, by effectively managing signal charge accumulation and background light subtraction.
Implementation Method 1
a photoelectric converter 1A that converts incident light into signal charge
Data Source
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AI summary
A plurality of pixels (50A) of a solid-state imaging device (100) include: a photoelectric converter (1A), two exposure controllers (6A), two readers (12A1 and 12A2), and two charge accumulators (2A and 4A), and the gate electrodes of the two readers (12A1 and 12A2) are axisymmetrically arranged and are disposed on an identical side of the outer edge of a light-receiving region of the photoelectric converter (1A).