SPAD Pixel Array Brightness Adaptation for Photon Counting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Imaging devices with single-photon avalanche diodes (SPADs) face challenges in capturing both dark and bright scenes effectively due to high photon detection frequency in bright conditions, making it difficult to maintain image quality across varying light levels.
Innovation Solution
An imaging device with a setting unit to control the active or inactive state of avalanche photodiodes in each pixel, allowing the number of active photodiodes to be adjusted based on the brightness of the object, enabling flexible photoelectric gain and uniform sensitivity across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of active avalanche photodiodes is increased to improve sensitivity for dark scene capture, then detection capability in low-light conditions is improved, but photon detection frequency becomes too high in bright situations causing saturation and loss of photon-counting accuracy
Solution Approach 1:
The patent implements dynamic control of the number of active SPAD pixels based on scene brightness. The control unit adjusts the operational state of SPAD pixels in real-time, switching between high-sensitivity mode (more active pixels) for dark scenes and low-sensitivity mode (fewer active pixels) for bright scenes, enabling the system to adapt to varying light conditions while maintaining photon-counting accuracy
Solution Approach 2:
The patent changes the operational parameter of the imaging device by varying the number of active SPAD pixels. This parameter adjustment allows the system to optimize its detection sensitivity according to the brightness of the captured scene, resolving the contradiction between needing high sensitivity for dark scenes and avoiding saturation in bright scenes
2Measurement precision
If all avalanche photodiodes are kept in active state to maximize detection capability, then sensitivity is improved, but dark count rate noise increases and reduces signal-to-noise ratio
Solution Approach 1:
The patent extracts only the necessary number of SPAD pixels from the active state based on scene brightness requirements. By keeping only the required number of pixels active and placing others in an inactive or low-power state, the system reduces dark count rate noise while maintaining sufficient detection capability, thereby improving the signal-to-noise ratio
Solution Approach 2:
The patent applies partial action by activating only the necessary portion of SPAD pixels rather than all pixels. This selective activation reduces the total dark count rate noise generated by inactive pixels while providing sufficient detection sensitivity for the current lighting conditions
3Measurement precision
If aperture mechanism is used to reduce light amount for bright scene capture, then saturation is prevented, but detection frequency becomes too low for effective photon-counting in dark scenes
Solution Approach 1:
The patent segments the pixel array into multiple independently controllable groups of SPAD pixels. By controlling the activation state of different pixel groups rather than uniformly reducing light through aperture, the system can maintain high detection frequency for photon-counting accuracy in dark scenes while preventing saturation in bright scenes through selective pixel deactivation
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 allows for accurate photon counting in both low-light and high-light conditions, expanding the dynamic range of captured images and improving image quality by adjusting the sensitivity of pixels according to the lighting environment.
Implementation Method 1
An APD can amplify the amount of signal charges excited by photons by around several times to million times by using an avalanche amplification phenomenon caused by an intense electric field induced at a p-n junction of a semiconductor
Implementation Method 2
a use of a photodetector element in which a signal corresponding to a single photon is larger than a noise at signal readout allows for so called photon-counting
Data Source
AI summary
An imaging device includes a plurality of pixels each including a plurality of avalanche photodiodes, a setting unit configured to set the plurality of avalanche photodiodes to an active state or an inactive state separately, and a counter circuit that counts and outputs number of photons determined by the avalanche photodiode(s) set to the active state out of the plurality of avalanche photodiodes, wherein the imaging device is configured to change the number of avalanche photodiodes set to the active state out of the plurality of avalanche photodiodes in accordance with brightness of an object.