Dual Conversion Gain Image Sensor for Dynamic Range and Noise Optimization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional CMOS image sensors face challenges in achieving high dynamic range and low noise performance, particularly in applications requiring high reliability and stability, where existing technologies struggle to effectively adjust conversion gain and manage noise levels.
Innovation Solution
The implementation of a dual conversion gain (DCG) pixel array with a scaler, ramp generator, comparator, and counter, which adjusts conversion gain to output high and low conversion gain signals, scales voltage levels, and compares signals with ramp signals to generate comparison results, thereby enhancing dynamic range and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional CMOS image sensors use fixed conversion gain, then device complexity is low, but dynamic range and noise performance cannot be optimized for different application requirements
Solution Approach 1:
The patent implements dynamic conversion gain adjustment by switching between high conversion gain mode (for low light conditions) and low conversion gain mode (for bright light conditions). The conversion gain control circuit dynamically selects the appropriate gain level based on scene brightness, enabling the sensor to adapt to varying lighting conditions and optimize both dynamic range and noise performance.
Solution Approach 2:
The patent changes the conversion gain parameter by adjusting the capacitance values in the floating diffusion node. By controlling the switch connections between different capacitance elements (C1, C2, C3), the conversion gain parameter is varied to match different lighting conditions, thereby optimizing dynamic range and noise characteristics without requiring multiple separate sensors.
2Reliability
If high conversion gain is used, then noise performance improves in low light conditions, but dynamic range is reduced for bright scenes
Solution Approach 1:
The system dynamically switches between high and low conversion gain modes based on scene brightness detection. In low light conditions, high conversion gain is applied to improve noise performance and signal sensitivity. In bright light conditions, low conversion gain is used to preserve dynamic range and prevent saturation, thus adapting to different lighting scenarios optimally.
Solution Approach 2:
The conversion gain parameter is changed by reconfiguring the capacitance network in the floating diffusion node. High conversion gain is achieved by connecting smaller capacitance values, while low conversion gain uses larger capacitance values. This parameter switching allows the sensor to optimize noise performance for low light while maintaining dynamic range for bright scenes.
3Adaptability or versatility
If low conversion gain is used, then dynamic range is maintained for bright scenes, but noise performance deteriorates in low light conditions
Solution Approach 1:
The system dynamically adjusts conversion gain based on scene brightness. When bright scenes are detected, low conversion gain is applied to maintain adequate dynamic range and prevent highlight saturation. When low light conditions are detected, the system switches to high conversion gain to boost signal levels and improve noise performance, thus adapting to different lighting conditions.
Solution Approach 2:
The conversion gain parameter is reconfigured by switching the capacitance connections in the floating diffusion node. For bright scenes, the parameter is set to low conversion gain using larger capacitance values to preserve dynamic range. For low light scenes, the parameter switches to high conversion gain with smaller capacitance values to enhance signal-to-noise ratio.
4Adaptability or versatility
If dual conversion gain mode is implemented, then both high and low conversion gain signals can be processed, but device complexity increases due to additional scaling and comparison circuits
Solution Approach 1:
The signal processing pipeline is segmented into separate paths for high conversion gain signals and low conversion gain signals. Each path has its own scaler and comparator circuits optimized for the specific gain level. This segmentation allows independent optimization of each processing path while managing complexity through modular design.
Solution Approach 2:
The patent introduces intermediate scaling circuits that adjust the voltage levels of high conversion gain signals before comparison. These intermediary scaling stages act as mediators between the high gain pixel output and the comparator input, enabling proper signal level matching without requiring direct complex high-speed comparison circuits.
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 enables the image sensor to achieve high dynamic range and low noise performance, providing improved reliability and stability by effectively managing signal-to-noise ratio and dynamic range through adjustable conversion gain and noise reduction mechanisms.
Implementation Method 1
a photoelectric converter configured to convert the incident light into a plurality of photocharges
Data Source
AI summary
An image sensor includes a dual conversion gain pixel to output a high conversion gain signal according to a high conversion gain and output a low conversion gain signal according to a low conversion gain, by adjusting a conversion gain; a scaler to scale a voltage level of the high conversion gain signal; a ramp generator to generate a first ramp signal and a second ramp signal, slopes of the first and second ramp signals being different from each other; a comparator to compare the scaled high conversion gain signal and the first ramp signal to output a first comparison result, and compare the low conversion gain signal and the second ramp signal to output a second comparison result; and a counter to output a first counting result value based on the first comparison result and output a second counting result value based on the second comparison result.