Variable Integration Time TDI Image Sensor for High Dynamic Range
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Solution Overview
Problem
TDI CCD image sensors face limitations in dynamic range, particularly when capturing scenes with high contrast, as they often exceed the charge capacity of integrating CCD stages, leading to issues like charge blooming and ambiguity in integration time determination.
Innovation Solution
The solution involves selectively controlling the projection of light onto the image sensor and resetting stages of the integrating CCDs based on prior-captured images, using an optical mask or sense nodes to manage photocharge accumulation, allowing for dynamic adjustment of integration time and preventing charge blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the integration time is increased to capture more photocharge, then the sensitivity is improved, but the charge capacity is exceeded causing charge blooming
Solution Approach 1:
The integrating CCD is divided into multiple independently controllable stages, allowing different integration times for different regions. Bright areas can use fewer stages while dark areas use more stages, preventing charge blooming in bright regions while maintaining sensitivity in dark regions.
Solution Approach 2:
The integration time is made dynamically adjustable for each stage of the integrating CCD. The system can change the number of stages used for integration based on the brightness of the scene, allowing optimal performance across varying illumination conditions without charge blooming.
2Adaptability or versatility
If a fixed integration time is used, then the device complexity is reduced, but the adaptability to different brightness levels is limited
Solution Approach 1:
A leading sensor captures a preliminary image of the scene before the main TDI sensor. This leading image is used to determine the brightness distribution, allowing the system to pre-calculate which stages should be used for integration in each column, simplifying the control of the multi-stage integrating CCD.
Solution Approach 2:
The leading sensor acts as an intermediary that provides brightness information about the scene. This information is used to control the integrating CCD stages, allowing the system to adapt to different brightness levels without requiring complex real-time monitoring of charge accumulation.
3Adaptability or versatility
If multiple linear arrays are used to capture color images, then the color capture capability is improved, but the device complexity increases
Solution Approach 1:
The TDI sensor with variable integration times can serve multiple functions: it can capture monochrome images with high sensitivity, capture color images when combined with color filters, and adapt to different brightness conditions. This multi-functionality reduces the need for separate specialized sensors.
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 significantly increases the dynamic range of TDI CCD image sensors by enabling tailored integration times for different brightness levels, reducing charge blooming, and providing clear integration time information for each pixel, thus enhancing image capture capabilities in high-contrast scenarios.
Implementation Method 1
multiple integrating CCDs (ICCDs) that accumulate photocharge in response to exposure to light
Implementation Method 2
an optical mask selectively altering the intensity of light projected to at least portions of the ICCDs
Data Source
AI summary
In various embodiments, a time-delay-and-integrate (TDI) image sensor includes (i) a plurality of integrating CCDs (ICCDs), arranged in parallel, that accumulate photocharge in response to exposure to light, (ii) electrically coupled to the plurality of ICCDs, a readout CCD (RCCD) for receiving photocharge from the plurality of ICCDs, and (iii) electrically coupled to the RCCD, readout circuitry for converting charge received from the RCCD into voltage.