Triple Conversion Gain Image Sensor Pixels for High Dynamic Range
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Solution Overview
Problem
Conventional image sensors are limited in capturing high-dynamic-range images as they can only operate in either high or low gain modes, leading to issues like blown out highlights or overexposed shadows in varying light conditions.
Innovation Solution
The development of image sensor pixels capable of operating in multiple conversion gain modes, including high, medium, and low conversion gain modes, using a pixel circuitry configuration with shared floating diffusion nodes and control transistors to adjust capacitance and gain settings dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single image sensor operates in high gain mode, then shadow detail is improved, but highlight detail is lost (blown out highlights)
Solution Approach 1:
The pixel circuit dynamically switches between high conversion gain mode and low conversion gain mode based on the intensity of incident light. This is achieved through automatic gain selection circuitry that monitors the signal level and transitions between gain modes to optimize both shadow and highlight capture across varying light conditions.
Solution Approach 2:
The image sensor is designed with multi-functionality to operate in both high gain mode for low-light conditions and low gain mode for bright-light conditions within the same pixel structure. This eliminates the need for separate sensors for different lighting scenarios and enables high-dynamic-range imaging capability.
2Measurement precision
If a single image sensor operates in low gain mode, then highlight detail is improved, but shadow detail is lost (overexposed shadows)
Solution Approach 1:
The pixel circuit dynamically switches between low conversion gain mode and high conversion gain mode based on the intensity of incident light. This is achieved through automatic gain selection circuitry that monitors the signal level and transitions between gain modes to optimize both shadow and highlight capture across varying light conditions.
3Measurement precision
If multiple separate image sensors are used to capture high-dynamic-range images, then both highlight and shadow detail are retained, but device complexity increases
Solution Approach 1:
The patent merges multiple gain modes into a single pixel structure, combining high conversion gain and low conversion gain capabilities in one sensor. This is achieved through shared photodiodes and floating diffusion nodes with dynamic gain selection, eliminating the need for multiple separate sensors while maintaining high-dynamic-range imaging capability.
Solution Approach 2:
The image sensor is designed with multi-functionality to operate in both high gain mode for low-light conditions and low gain mode for bright-light conditions within the same pixel structure. This eliminates the need for separate sensors for different lighting scenarios and enables high-dynamic-range imaging capability.
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 allows for enhanced dynamic range in captured images by effectively managing light exposure across different conditions, retaining both highlight and shadow details without the limitations of single-mode sensors.
Implementation Method 1
The pixel circuitry may include a first photodiode coupled to a first floating diffusion node via a first charge transfer gate, and a second photodiode coupled to the second floating diffusion node via a second charge transfer gate
Data Source
AI summary
An image sensor having pixel circuitry operable in multiple gain modes is provided. The pixel circuitry may include first and second floating diffusion (FD) regions, a first photodiode coupled to the first FD region via a first transfer gate, a second photodiode coupled to the first FD region via a second transfer gate, a third photodiode coupled to the second FD region via a third transfer gate, and a fourth photodiode coupled to the second FD region via a fourth transfer gate. The first FD region may be coupled to the second FD region via first and second control transistors. The control transistors may be connected to a shared reset transistor. During readout, both control transistors may be deactivated to provide a high gain mode, only one transistor may be activated to provide an intermediate gain mode, or both control transistors may be activated to provide a low gain mode.