SPAD-PPD Pixel Spatial-Temporal Correlation for Ambient Light Robustness
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Solution Overview
Problem
Current 3D imaging technologies, such as Time-of-Flight (TOF) and stereoscopic imaging, face limitations in resolution, especially at short distances, and are vulnerable to ambient light, making them impractical for applications like autonomous navigation in inclement weather.
Innovation Solution
A TOF-based 3D imaging system using a pixel array with Single Photon Avalanche Diodes (SPADs) and a Pinned Photo Diode (PPD) that employs spatial-temporal correlation among adjacent SPAD outputs to control the PPD's operation, enabling accurate Time-of-Flight value recording and range measurement, even in high ambient light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional TOF or stereoscopic imaging is used, then 3D imaging capability is provided, but resolution at short distances deteriorates and the system becomes vulnerable to ambient light
Solution Approach 1:
The pixel is divided into multiple SPADs (Single Photon Avalanche Diodes) that operate independently to detect photons. Each SPAD functions as a separate detection element, allowing the system to segment the detection process and improve precision through correlated measurements across multiple segments while maintaining reliability through redundancy
Solution Approach 2:
A time-to-charge converter (TTC) is introduced as an intermediary device that converts time-of-flight measurements into charge values stored in a Pinned Photo Diode (PPD). This intermediary transformation enables precise range measurement by mapping temporal information to electrical charge, while the PPD's integration capability provides robustness against ambient light variations
2Measurement precision
If multiple SPADs are used for spatial-temporal correlation, then measurement precision improves, but device complexity increases
Solution Approach 1:
Multiple SPADs are merged into a single pixel structure with shared readout circuitry. The SPADs collectively perform photon detection and feed into a common time-to-charge converter and PPD, combining their measurement capabilities while sharing the complex conversion and storage infrastructure to reduce overall device complexity
Solution Approach 2:
The Pinned Photo Diode (PPD) serves multiple functions: it stores the analog charge representing time-of-flight information, acts as an integration node for signals from multiple SPADs, and provides a unified readout interface. This multi-functionality reduces the need for separate dedicated circuits for each SPAD, thereby reducing overall device complexity while maintaining high measurement precision
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 system provides improved autonomous navigation capabilities by enabling 3D imaging and 2D grayscale imaging independent of ambient light, with enhanced resolution and robustness in adverse weather conditions.
Implementation Method 1
each SPAD is operable to convert received luminance into a corresponding electrical signal
Implementation Method 2
Single Photon Avalanche Diodes (SPADs)
Implementation Method 3
a Pinned Photo Diode (PPD) operable to store an analog charge
Implementation Method 4
Time-resolving sensor using shared PPD+SPAD pixel and spatial-temporal correlation for range measurement
Data Source
AI summary
A Time-of-Flight (TOF) technique is combined with analog amplitude modulation within each pixel in a pixel array using multiple Single Photon Avalanche Diodes (SPADs) in conjunction with a single Pinned Photo Diode (PPD) in each pixel. A SPAD may be shared among multiple neighboring pixels. The TOF information is added to the received light signal by the analog domain-based single-ended to differential converter inside the pixel itself. The spatial-temporal correlation among outputs of multiple, adjacent SPADs in a pixel is used to control the operation of the PPD to facilitate recording of TOF values and range of an object. Erroneous range measurements due to ambient light are prevented by stopping the charge transfer from the PPD—and, hence, recording a TOF value—only when two or more SPADs in the pixel are triggered within a pre-defined time interval. An autonomous navigation system with multi-SPAD pixels provides improved vision for drivers under difficult driving conditions.