Hybrid SPAD-PPD Image Sensor for Wide-Range Photon Counting
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Solution Overview
Problem
Conventional PPD-based image sensors struggle with low linearity in photon counting in low-illuminance situations, while SPAD-based sensors face challenges with high power consumption and photon counting limitations in high-illuminance conditions.
Innovation Solution
An image sensor incorporating hybrid pixels with both SPAD and PPD, utilizing a digital detection unit for SPAD and an analog detection unit for PPD, with a connection unit to transfer electric charges, allowing for high dynamic range operation through APC and CA modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If PPD-based image sensor is used, then device size is reduced and power consumption is lowered, but measurement precision of photon counting deteriorates in low-illuminance situations
Solution Approach 1:
The patent combines SPAD and PPD into a hybrid pixel structure where both detectors coexist and can operate in different modes. The SPAD provides precise photon counting in low-illuminance conditions, while the PPD handles higher illuminance scenarios, allowing the system to achieve accurate photon counting without the high power consumption of pure SPAD architecture.
2Measurement precision
If SPAD-based image sensor is used, then measurement precision of photon counting is improved in low-illuminance situations, but device area and power consumption increase
Solution Approach 1:
The patent implements dynamic operation modes that allow the hybrid pixel to switch between SPAD-based photon counting mode and PPD-based operation. This dynamic switching enables the system to use the high-precision SPAD only when necessary (low-illuminance conditions), thereby achieving accurate photon counting while minimizing overall power consumption by utilizing the lower-power PPD in higher illuminance scenarios.
3Measurement precision
If SPAD-based image sensor is used, then measurement precision of photon counting is improved in low-illuminance situations, but device area increases
Solution Approach 1:
The patent merges SPAD and PPD functionalities into a shared pixel structure with common components such as the micro lens, charge storage region, and readout circuitry. This merging allows the system to achieve SPAD-level photon counting precision without the full area overhead of a dedicated SPAD sensor, as the PPD shares the physical infrastructure and can handle scenarios where SPAD operation is not required.
4Area of stationary object
If PPD-based image sensor is used, then device size is reduced, but adaptability to different illuminance conditions deteriorates
Solution Approach 1:
The patent creates a universal hybrid pixel that can operate in multiple modes depending on illuminance conditions. The same physical structure supports both SPAD-based photon counting for precise low-illuminance detection and PPD-based operation for higher illuminance scenarios, giving the sensor universal adaptability across the full dynamic range from very low to high illuminance without requiring separate sensor systems.
5Adaptability or versatility
If hybrid pixels with both SPAD and PPD are used, then adaptability to different illuminance conditions is improved, but device complexity increases
Solution Approach 1:
The patent merges SPAD and PPD into a single hybrid pixel structure with shared components including the micro lens, charge storage region, and readout circuitry. This merging approach reduces the overall system complexity compared to having separate SPAD and PPD sensors, as common infrastructure is shared between the two detector types while still maintaining the ability to operate in different modes for extended dynamic range.
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
Enables accurate photon counting in both high and low illuminance conditions, achieving a smaller sensor size and reduced power consumption by leveraging the strengths of both SPAD and PPD technologies.
Implementation Method 1
a digital detection unit configured to detect light based on a single photon avalanche diode (SPAD)
Implementation Method 2
an analog detection unit configured to detect light based on a pinned photodiode (PPD)
Data Source
AI summary
Provided are an image sensor and a control method thereof. The image sensor includes a digital detection unit configured to detect light based on a single photon avalanche diode (SPAD), an analog detection unit configured to detect light based on a pinned photodiode (PPD), and a connection unit configured to transfer a specific amount of electric charges to the analog detection unit in detection of the light by the digital detection unit, in which the analog detection unit is further configured to count a number of photons based on an amount of electric charges accumulated during a specific time.