Image Sensor Pixel Charge Storage for High Dynamic Range Noise Reduction
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Solution Overview
Problem
Image sensors face issues with noise amplification and image signal degradation due to charge leakage and noise amplification when implementing high dynamic range (HDR) functionality, particularly in configurations where accumulated charge is directly shared between low gain capacitors and floating diffusion regions.
Innovation Solution
Incorporating a dedicated storage structure for overflow charge, such as a capacitor with similar capacitance to the low gain capacitor, to isolate noise amplification during readout operations, and providing a separate blooming path and floating diffusion region reset path to mitigate these issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple frames are captured with different exposure times to generate HDR image, then high dynamic range functionality is achieved, but additional frame storage is required
Solution Approach 1:
The pixel is segmented into multiple independent charge storage regions (first charge storage region, second charge storage region, third charge storage region) that can independently store charge from different exposure times. This segmentation allows simultaneous storage of multiple exposure frames within a single pixel structure, eliminating the need for additional frame storage while maintaining HDR functionality.
Solution Approach 2:
The patent transitions from temporal separation (capturing multiple frames at different times) to spatial separation (storing charges from different exposures in different regions within the same pixel). By adding a spatial dimension to charge storage, the system can hold multiple exposure frames simultaneously without requiring additional frame storage capacity.
2Adaptability or versatility
If multiple image signals are generated based on a single integration time, then HDR functionality is achieved, but leakage and noise may be amplified
Solution Approach 1:
The pixel is divided into multiple isolated charge storage regions (first, second, and third charge storage regions) with separate readout paths. By segmenting the charge storage and readout paths, noise and leakage in one region do not affect other regions, preventing noise amplification while enabling HDR functionality through differential readout of the stored charges.
Solution Approach 2:
The patent introduces separate readout circuitry and control mechanisms as intermediaries between the charge storage regions and the output. These intermediary elements allow independent control and readout of each charge storage region, enabling the system to selectively read out charges from different exposure times without cross-contamination of noise and leakage signals.
3Device complexity
If accumulated charge is directly shared between low gain capacitors and floating diffusion regions, then readout is simplified, but noise amplification and image signal degradation occur
Solution Approach 1:
The readout structure is segmented into separate paths: one path reads out from the first charge storage region through a first readout amplifier, and another path reads out from the second and third charge storage regions through a second readout amplifier. This segmentation prevents noise amplification by isolating the charge sharing processes, while the overall readout structure remains relatively simple due to the systematic arrangement of the separate paths.
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 solution reduces noise amplification and improves image signal quality by decoupling the low gain capacitor from the floating diffusion region, allowing for more accurate and clear HDR image generation with reduced noise and leakage.
Implementation Method 1
A typical image pixel contains a photodiode for generating charge in response to incident light.
Data Source
AI summary
An imaging system may include an image sensor having an image sensor. The image sensor may include an image sensor pixel array coupled to row control circuitry and column readout circuitry. The image sensor pixel array may include a plurality of image sensor pixels. Each image sensor pixel may include a photosensitive element configured to generate charge in response to incident light, a first charge storage structure configured to accumulate an overflow portion of the generated charge for a low gain signal and a second charge storage structure configured to store a remaining portion of the generated charge for a high gain signal. Each image sensor pixel may also include a dedicated overflow charge storage structure interposed between the first charge storage structure and a floating diffusion region.