SPAD Sensor Dynamic Bias Modulation for High Dynamic Range Imaging
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Solution Overview
Problem
Conventional image sensors suffer from limited functionality, including inability to determine object distance, lower-than-desired image quality, and lower dynamic range, especially when using single-photon avalanche diodes (SPADs) which have a limited dynamic range due to high sensitivity leading to saturation in high light conditions.
Innovation Solution
Implementing a SPAD-based semiconductor device that dynamically switches between low and high photon detection efficiencies by modulating the over-bias voltage, using multiple sub-exposures with different photon detection efficiencies to generate a high dynamic range depth map, allowing optimal performance in both low and high ambient light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-photon avalanche diodes (SPADs) are used to improve sensitivity to incident light, then sensitivity is improved, but dynamic range deteriorates due to saturation in high light conditions
Solution Approach 1:
The patent implements dynamic switching between multiple operational modes (photon counting mode and analog integration mode) based on ambient light conditions. The system dynamically adjusts the over-bias voltage and selects appropriate readout circuits to optimize performance across varying light levels, resolving the contradiction between high sensitivity and broad dynamic range.
Solution Approach 2:
The patent changes key operational parameters including over-bias voltage levels, integration time, and readout circuit selection based on ambient light conditions. By modulating these parameters, the system maintains optimal sensitivity in low light while preventing saturation in high light conditions, thereby expanding the effective dynamic range.
2Adaptability or versatility
If conventional image sensors are used, then dynamic range is maintained, but sensitivity to incident light deteriorates
Solution Approach 1:
The patent segments the sensor array into multiple regions with different operational characteristics. Some pixels operate in photon counting mode for high sensitivity in low light, while others operate in analog integration mode for high dynamic range in bright conditions. This segmentation allows the system to achieve both high sensitivity and broad dynamic range simultaneously.
Solution Approach 2:
The patent creates a multi-functional imaging system where each pixel can operate in multiple modes (photon counting, analog integration, depth sensing) depending on conditions. This universality allows the sensor to adapt to various lighting scenarios, achieving both high sensitivity and broad dynamic range across different operating conditions.
3Adaptability or versatility
If multiple sub-exposures with different photon detection efficiencies are used, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple functional capabilities (photon counting, analog integration, depth sensing) into a single unified sensor array. By combining these functions in one device with shared readout circuitry and control logic, the system achieves high dynamic range without proportionally increasing device complexity.
Solution Approach 2:
The patent implements self-service through automatic mode selection and parameter adjustment based on ambient light detection. The system autonomously determines the appropriate operational mode and configuration without requiring complex external control, thereby reducing the effective complexity burden on the user while maintaining high dynamic range performance.
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 solution enhances the dynamic range and detection probability of the SPAD-based semiconductor device, maintaining high sensitivity in low light conditions while reducing saturation in high light conditions, resulting in improved image quality and distance measurement accuracy across a wide range of ambient light levels.
Implementation Method 1
single-photon avalanche diodes (SPADs) for single photon detection
Implementation Method 2
Each pixel typically includes a photosensitive element (such as a photodiode) that receives incident photons (light) and converts the photons into electrical signals
Implementation Method 3
Each pixel may also include a microlens that overlaps and focuses light onto the photosensitive element
Data Source
AI summary
An imaging device may include single-photon avalanche diodes (SPADs). To improve the sensitivity and signal-to-noise ratio of the SPADs, photon detection efficiency (PDE) may be increased. However increased photon detection efficiency may result in a decreased saturation rate and lower than desired dynamic range. To increase the dynamic range, a SPAD-based semiconductor device may operate with multiple sub-exposures. During the first sub-exposure, an over-bias voltage may be set to a first voltage level so that the SPADs have a first photon detection efficiency. During the second sub-exposure, the over-bias voltage may be set to a second voltage level so that the SPADs have a second photon detection efficiency that is different than the first photon detection efficiency. Image data from the first and second sub-exposures may then be combined into a single high dynamic range depth map.