Image Sensor Read-Out Circuitry Dynamic Gain Conversion Curve
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing CMOS-based image sensors struggle to accurately image regions of interest while maintaining contrast in areas with higher light intensities, as they saturate quickly and cannot effectively handle high photon fluxes without losing detail in other regions.
Innovation Solution
The image sensor introduces a conversion curve with a first and second knee point, allowing the photodiode to switch operational modes based on photon flux thresholds, enabling a linear response for regions of interest and a non-linear response for higher photon flux areas, thereby enhancing dynamic range and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linear conversion between pixel voltage and digital number is used, then measurement precision is improved for low photon flux, but saturation occurs quickly at high photon flux causing loss of information
Solution Approach 1:
The conversion gain is made dynamic by switching between a first gain value for low photon flux regions and a second gain value for high photon flux regions. This allows the system to adapt its response characteristics based on the local intensity conditions, preventing saturation in bright areas while maintaining precision in dim areas.
Solution Approach 2:
Different regions of the image are processed with different conversion characteristics. Pixels identified as being in high photon flux regions use a second conversion curve with a second gain value, while other pixels use a first conversion curve with a first gain value. This local differentiation allows each region to be optimized for its specific lighting conditions.
2Stability of the object's composition
If the photodiode operates only in the first mode with constant capacitance, then linearity is maintained, but dynamic range is limited and cannot handle high photon flux effectively
Solution Approach 1:
The photodiode is designed to operate in two distinct modes: a first mode with constant capacitance for linearity at low flux, and a second mode with voltage-dependent capacitance for extended dynamic range at high flux. The system dynamically transitions between these modes based on the photon flux level, combining the advantages of both operational characteristics.
Solution Approach 2:
The capacitance parameter of the photodiode is changed based on the operating conditions. In the first mode, the capacitance is substantially constant, providing linear response. In the second mode, the capacitance varies as a function of the photo voltage, enabling the system to handle high photon flux levels without saturation while extending the dynamic range.
3Measurement precision
If exposure settings are optimized for a region of interest, then sensitivity is improved for that region, but contrast is lost in areas with higher light intensities
Solution Approach 1:
The image processing is divided into regions based on photon flux characteristics. The region of interest is processed with a first conversion curve optimized for sensitivity, while regions with higher light intensities are processed with a second conversion curve that preserves contrast. This local processing strategy allows each region to maintain its optimal characteristics without compromising others.
Solution Approach 2:
The image data is segmented into different photon flux regions, with each segment processed using an appropriate conversion curve. This segmentation allows the system to apply different processing strategies to different parts of the image, maintaining sensitivity in dim regions while preserving contrast in bright regions.
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 allows for high sensitivity in linear regions of interest and high dynamic range in areas with higher photon flux, preventing saturation and maintaining detail across varying light intensities.
Implementation Method 1
The photodiode is configured to generate a photocurrent as a result of photons that fall onto the pixel during an integration time, and to generate a photo voltage by charging the storage capacitor using the generated photo current
Data Source
AI summary
The present invention relates to an image sensor and to an imaging system comprising such a sensor. According to the invention, the overall conversion curve describing the conversion between photon flux and digital number comprises a first region in which the conversion is essentially linear and a second region in which the conversion is essentially non-linear.According to the invention, the non-linearity of the second region is obtained by operating the photodiode of the image sensor in its non-linear range and by changing the gain associated with the conversion between pixel voltage and digital number.