Hybrid SPAD CMOS Image Sensor for Dynamic Range and Power Optimization
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Solution Overview
Problem
Conventional image sensors face challenges with high power consumption and count errors when using avalanche photodiodes in Geiger mode, particularly when capturing high-brightness subjects, due to the avalanche phenomenon and Random Telegraph Signal (RTS) noise.
Innovation Solution
An image capturing apparatus is designed with a combination of Single Photon Avalanche Diode (SPAD) and CMOS image sensors, where SPAD-type pixels count photons and CMOS-type pixels perform charge accumulation, allowing for dynamic range expansion and sensitivity adjustment based on luminance thresholds to optimize image quality and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche photodiodes are operated in Geiger mode to enable single photon detection, then measurement precision is improved, but power consumption increases due to high electric field requirements and large avalanche currents
Solution Approach 1:
The image sensor is divided into two distinct types of pixels: SPAD pixels for low-luminance photon counting and CMOS pixels for high-luminance charge accumulation. This segmentation allows each pixel type to operate in its optimal mode, reducing overall power consumption while maintaining measurement precision across different lighting conditions.
Solution Approach 2:
The system dynamically switches between SPAD and CMOS pixel modes based on luminance thresholds. The generator selects which pixel type to use for each pixel location depending on the measured luminance level, enabling adaptive operation that optimizes both precision and power consumption for varying scene brightness.
2Measurement precision
If SPAD pixels are used for photon counting in low luminance conditions, then measurement precision is improved, but count errors occur when multiple photons are incident during the dead time period
Solution Approach 1:
The system dynamically adapts the pixel operating mode based on luminance conditions. When luminance exceeds the first threshold, the generator switches from SPAD photon counting mode to CMOS charge accumulation mode, preventing count errors while maintaining measurement capability through appropriate mode selection.
Solution Approach 2:
The generator acts as an intermediary that mediates between SPAD and CMOS pixel outputs based on luminance thresholds. It selects the appropriate pixel type for each imaging location, ensuring reliable measurements across the full range of luminance conditions by avoiding SPAD saturation in high-light scenarios.
3Device complexity
If a single image sensor type is used, then device complexity is reduced, but adaptability to varying luminance conditions deteriorates
Solution Approach 1:
The image sensor achieves multi-functionality by incorporating both SPAD and CMOS pixels within the same sensor array. This universal design enables the sensor to handle both low-luminance photon counting and high-luminance charge accumulation tasks, adapting to varying lighting conditions without requiring separate sensors.
Solution Approach 2:
The sensor is segmented into SPAD pixel regions and CMOS pixel regions, with the generator allocating imaging tasks to appropriate segments based on luminance thresholds. This segmentation enables specialized optimization for different luminance ranges while maintaining a unified sensor structure.
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 image quality by minimizing noise and power consumption, enabling effective photon counting and charge conversion, while reducing count errors and improving dynamic range in varying lighting conditions.
Implementation Method 1
an avalanche phenomenon occurring when avalanche photodiodes (APDs) are operated in Geiger mode to measure the number of incoming photons themselves
Implementation Method 2
when light is incident on a photodiode (PD) in a fixed period, the PD generates and accumulates a charge substantially linearly with respect to an amount of incident light
Data Source
AI summary
An image capturing apparatus comprises: a first image sensor having a plurality of pixels each counts a number of entering photons and outputs a count value as a first image signal; a second image sensor having a plurality of pixels each outputs an electric signal corresponding to a charge amount obtained by performing photoelectric conversion on entering light as a second image signal; and a generator that generates an image by selecting one of the first image signal and the second image signal.