Shared PPD+SPAD Pixel for Time-of-Flight Range Measurement
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Solution Overview
Problem
Current 3D imaging technologies, such as time-of-flight (TOF) systems, face limitations in accuracy and frame rate due to reset noise and vulnerability to ambient light, especially in short-range measurements and adverse weather conditions, while stereoscopic imaging requires high computational power and is unsuitable for space-constrained applications like autonomous navigation.
Innovation Solution
A TOF-based 3D imaging system using a single-chip solution that combines TOF and analog amplitude modulation within each pixel, employing multiple single photon avalanche diodes (SPADs) with a pinned photo diode (PPD), where spatial-temporal correlation among SPAD outputs controls the PPD to record time-of-flight values, reducing reset noise and enhancing performance in adverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a TOF-based 3D imaging system uses a single-chip solution with multiple SPADs and a PPD to reduce reset noise and improve measurement accuracy, then range measurement precision and frame rate are improved, but device complexity increases due to the integration of multiple diodes and control circuits
Solution Approach 1:
The patent combines multiple SPADs and a PPD within a single pixel structure on one chip to achieve both high measurement precision through spatial-temporal correlation and reduced reset noise. This merging of multiple diode types and control circuits into an integrated pixel design resolves the contradiction by achieving improved range measurement accuracy while managing device complexity through systematic integration
Solution Approach 2:
The shared PPD serves multiple functions by acting as a time-to-charge converter for multiple SPADs simultaneously, enabling the system to perform accurate time-of-flight measurements while reducing reset noise. This multi-functionality allows the pixel structure to achieve high measurement precision without proportionally increasing device complexity
2Reliability
If the system uses spatial-temporal correlation among multiple SPADs to control the PPD operation, then reset noise is reduced and measurement accuracy is improved, but the device requires more components and higher complexity
Solution Approach 1:
The patent merges multiple SPADs with shared control circuits and a common PPD into an integrated structure that achieves reliable performance in adverse weather conditions through spatial-temporal correlation. This integration reduces the relative complexity by sharing components across multiple detection elements while maintaining high reliability
Solution Approach 2:
The PPD acts as an intermediary time-to-charge converter that processes signals from multiple SPADs using spatial-temporal correlation. This intermediary component enables the system to achieve improved reliability in adverse conditions while managing component complexity through the use of a shared conversion mechanism
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 producing accurate 3D and 2D images in all weather conditions, independent of ambient light, with enhanced range measurement accuracy and increased frame rate, and is suitable for space-constrained applications like autonomous vehicles.
Implementation Method 1
Each of the plurality of first type of diodes may detect one or more incident photons
Implementation Method 2
Each of the plurality of first type of diodes may detect one or more incident photons
Implementation Method 3
a time-resolving sensor... to control the operation of a time-to-charge converter, such as a pinned photo diode (PPD), to facilitate recording of TOF values
Data Source
AI summary
An image sensor includes a plurality of a first type of diodes and a time-resolving sensor. The time-resolving sensor outputs first and second reset signals, and first and second measurement signals. The two reset signals respective represent a reset-charge level of a first and a second floating diffusion. The measurement signals are output in response the diodes detecting at least one incident photon. First and second time-of-flight (TOF) signals are formed by respective subtracting the first and second reset signals from the first and second measurement signals. A first ratio of a magnitude of the first signal to a sum of the magnitudes of the first and second signals is proportional to a TOF of the detected photon, and a second ratio of the magnitude of the second signal to the sum of the magnitudes of the first and second signals is proportional to the TOF of the detected photons.