Pinned Photodiode Sensor for Time-of-Flight and Greyscale Imaging
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Solution Overview
Problem
Existing single-photon avalanche diode (SPAD) sensors for LiDAR have low spatial resolution, high power consumption, and lack intensity imaging capability alongside range information, with single-ended time-to-analog converters resulting in low range accuracy.
Innovation Solution
A pixel design incorporating a pinned photodiode (PPD), switching device, and output circuit that enables both time-of-flight range measurement and greyscale intensity measurement using separate charge transfers and output paths, allowing for synchronized laser source-based 3D TOF information and ambient light integration for 2D imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a time-to-digital counter (TDC) is placed inside each pixel of a sensor array, then range measurement capability is achieved, but power consumption increases and device complexity increases
Solution Approach 1:
The patent extracts the complex TDC circuitry from individual pixels and replaces it with a simpler time-to-analog converter (TAC) that generates a voltage signal proportional to time-of-flight. This extracted approach eliminates the need for complex digital counters in each pixel, thereby reducing power consumption while maintaining range measurement capability through the voltage signal that can be read out centrally.
Solution Approach 2:
The patent substitutes the digital counting mechanism (TDC) with an analog voltage generation mechanism (TAC). Instead of using complex digital electronics to count time intervals, the system uses analog voltage proportional to time-of-flight, which can be generated with simpler circuitry and read out more efficiently, thereby reducing power consumption.
2Use of energy by moving object
If a single-ended time-to-analog converter (TAC) is used instead of a TDC, then power consumption is reduced, but range accuracy deteriorates
Solution Approach 1:
The patent merges the time-of-flight measurement function with intensity measurement function into a single pixel structure. By combining these functions, the system uses the same photodetector and readout circuitry for both measurements, improving overall system efficiency and accuracy while maintaining low power consumption through shared hardware resources.
Solution Approach 2:
The patent implements a universal pixel design that can perform both time-of-flight range measurement and intensity imaging using the same hardware components. The pinned photodiode serves dual purposes: measuring photon arrival time for range and integrating photon counts for intensity, thereby achieving multi-functionality without requiring separate specialized circuits for each measurement type.
3Measurement precision
If existing SPAD sensors are used for LiDAR, then range information is obtained, but intensity imaging capability is lost
Solution Approach 1:
The patent implements a universal pixel design that can perform both time-of-flight range measurement and intensity imaging using the same hardware components. The pinned photodiode serves dual purposes: measuring photon arrival time for range and integrating photon counts for intensity, thereby achieving multi-functionality without requiring separate specialized circuits for each measurement type.
Solution Approach 2:
The patent uses periodic gating signals to control charge transfer from the pinned photodiode to the floating diffusion. By applying gate signals at different times (first gate signal for intensity, second gate signal for range), the system periodically switches between measurement modes, enabling both intensity imaging and range measurement from the same photodetector through time-multiplexed operation.
4Measurement precision
If separate measurement systems are used for range and intensity, then measurement accuracy is maintained, but device complexity increases
Solution Approach 1:
The patent merges the time-of-flight measurement function with intensity measurement function into a single pixel structure. By combining these functions, the system uses the same photodetector and readout circuitry for both measurements, improving overall system efficiency and accuracy while maintaining low power consumption through shared hardware resources.
Solution Approach 2:
The patent uses periodic gating signals to control charge transfer from the pinned photodiode to the floating diffusion. By applying gate signals at different times (first gate signal for intensity, second gate signal for range), the system periodically switches between measurement modes, enabling both intensity imaging and range measurement from the same photodetector through time-multiplexed operation.
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 solution enhances spatial resolution, reduces power consumption, and provides aligned range and intensity imaging without the need for image fusion, improving performance in low-light and ambient-light conditions.
Implementation Method 1
a pinned photodiode (PPD)... Photon Detection and Ranging (LiDAR)
Data Source
AI summary
A pixel of an image sensor includes a pinned photodiode (PPD), a switching device and an output circuit. A first terminal of the switching device is coupled to the PPD. A second terminal of the switching device is coupled to a floating diffusion (FD). A third terminal of the switching device is coupled to a first enable signal and a second enable signal. The switching device is responsive to the first enable signal to transfer a first charge on the PPD to the FD, and responsive to the second enable signal to transfer a second charge on the PPD to the FD. The output circuit outputs a first voltage based on the first charge and outputs a second voltage based on the second charge in which the first voltage corresponds to a time of flight of one or more detected photons and the second voltage corresponds to a greyscale image.