Time-of-Flight Sensor with Dual Near-Infrared Illumination
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Solution Overview
Problem
Existing active imaging systems face challenges in achieving improved dynamic range, background light stability, and efficient power consumption, particularly when dealing with changing lighting conditions and the need for multiple image acquisitions to subtract background light.
Innovation Solution
The implementation of a time-of-flight imaging system using two different near-infrared illumination sources, one structured and one uniform, with synchronized and temporally modulated illumination, allows for in-pixel background light cancellation and reduced modulation frequencies, enabling robust depth measurement and intensity imaging with lower power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two separate images are acquired with illumination on and off for background subtraction, then background light stability is improved, but system complexity and acquisition time increase
Solution Approach 1:
The patent combines background light cancellation and depth measurement into a single image acquisition process. By using two illumination sources with different wavelengths simultaneously and capturing them with a single sensor that has separate storage nodes for each wavelength, the system eliminates the need for separate on/off image acquisitions while maintaining background light stability.
Solution Approach 2:
The imaging sensor is designed to perform multiple functions simultaneously: it captures images from two different illumination wavelengths, stores them in separate storage nodes, and enables both background light cancellation and depth measurement from a single acquisition. This multi-functional approach reduces system complexity while maintaining reliability.
2Reliability
If two separate images are acquired for background subtraction, then background light stability is improved, but acquisition time increases
Solution Approach 1:
The patent merges background light cancellation and depth measurement into a single simultaneous image acquisition process. By illuminating with two wavelengths at once and capturing both in one exposure, the system achieves background stability without the time penalty of sequential acquisitions.
Solution Approach 2:
The system maintains continuous illumination from both sources during a single acquisition, allowing background light cancellation and depth measurement to occur simultaneously without interruption. This eliminates the time loss associated with switching illumination states in traditional methods.
3Measurement precision
If full dynamic signal range is used to capture both background light and active light, then measurement range is improved, but dynamic range for active light decreases
Solution Approach 1:
The patent segments the dynamic range by creating separate storage nodes for different illumination wavelengths. Each storage node captures only its assigned wavelength, allowing the full dynamic range to be optimized for each individual wavelength without being consumed by the other, thereby improving both measurement range and per-wavelength dynamic range.
Solution Approach 2:
Different regions of the sensor (storage nodes) are assigned different functional qualities: one node captures background light while another captures active light. This local differentiation allows each node to operate within its optimal dynamic range for its specific purpose, improving overall measurement precision without sacrificing illumination intensity capability.
4Measurement precision
If high modulation frequencies are used for TOF measurement, then depth measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent changes the modulation frequency parameter to a lower range that is sufficient for the specific application requirements. By carefully selecting an optimized modulation frequency that balances depth measurement precision with reduced power consumption, the system achieves adequate performance without the excessive energy costs of higher frequencies.
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 approach enhances the dynamic range and resolution of imaging systems, reduces optical power consumption, and allows for three-dimensional measurement with improved robustness against changing lighting conditions, while enabling the use of existing high-speed time-of-flight image sensors with lower modulation frequencies.
Implementation Method 1
TOF image sensor pixels are dedicated pixels designs to guarantee an extremely fast transfer of the photo-generated charges to their storage nodes
Implementation Method 2
Time of flight image sensor pixels are dedicated pixels designs to guarantee an extremely fast transfer of the photo-generated charges to their storage nodes. Higher modulation frequencies result in better depth noise performance.
Implementation Method 3
an imaging system including an imaging sensor adapted to process an image of a scene being illuminated by at least two different illumination sources each having a wavelength in the near infrared range
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 2
AI summary
The present invention relates to vision sensors based on an active illumination. An imaging system includes an imaging sensor and is adapted to process an image of a scene being illuminated by at least two different illumination sources each having a wavelength in the near infrared range. In a variant, the imaging system is adapted to use an illumination source having a modulation frequency below the modulation frequency used to perform a three dimensional time of flight measurement. In a variant, the imaging system is adapted to acquire a reduced number of samples per frame than used in time of flight measurements.