CMOS TDI Sensor Zero Desynchronization via Segmented Integration
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Solution Overview
Problem
Conventional CMOS image sensors lack the mechanism to perform time-delayed integration (TDI) imaging due to the absence of a mechanism for adding multiple samples of a ground pixel as it traverses the imaging array, leading to low signal-to-noise ratio (SNR) and spatial desynchronization issues.
Innovation Solution
The implementation of a CMOS TDI sensor with zero desynchronization, where the integration time is reduced to allow for additional time for pixel reset and data transfer operations, maintaining synchronization by increasing the pixel data rate and adding extra TDI stages to ensure synchronous addition of samples, thereby maintaining the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the integration time is increased to improve signal-to-noise ratio, then the signal level increases, but the pixel reset and data transfer operations cannot be completed in time, causing spatial desynchronization
Solution Approach 1:
The imaging array is divided into multiple TDI stages (first TDI stage, second TDI stage, etc.), each handling a portion of the integration process. This segmentation allows the system to process multiple samples sequentially while maintaining synchronization, enabling longer effective integration times without losing spatial alignment.
Solution Approach 2:
The patent introduces a temporal dimension to the imaging process by implementing multiple TDI stages that process samples at different time points. This transforms the traditional single-exposure spatial imaging into a multi-temporal integration process, where samples taken at different times are combined across multiple stages to achieve both high SNR and spatial synchronization.
2Reliability
If conventional CMOS readout is used with sequential row-by-row sampling, then device complexity is low, but multiple samples of the same ground pixel cannot be added, resulting in low signal-to-noise ratio
Solution Approach 1:
Each TDI stage is designed with multi-functionality, serving both as a sample acquisition unit and an addition unit. The same hardware structure (photosensitive elements, switches, and addition circuits) is replicated across multiple stages, allowing the system to achieve TDI functionality without requiring fundamentally different components, thus controlling complexity while enabling multiple sample integration.
Solution Approach 2:
The patent implements multiple copies of the TDI stage structure (first TDI stage, second TDI stage, etc.), where each stage is a replicated version of the basic TDI unit. This copying approach allows the system to accumulate multiple samples by simply adding more identical stages, making the complexity increase linear and predictable rather than exponentially.
3Duration of action of moving object
If the pixel data rate is increased to allow more samples per ground pixel, then integration periods increase, but the readout speed must increase accordingly, affecting device operation
Solution Approach 1:
The high data rate requirement is segmented across multiple TDI stages, each operating at a manageable data rate. Instead of requiring one stage to process all samples at high speed, the total integration is distributed across multiple stages that each handle a portion of the samples, reducing the instantaneous data rate burden on any single component.
Solution Approach 2:
The TDI stages operate continuously to accumulate samples, with each stage constantly receiving and processing incoming pixel data. This continuous operation allows the system to maintain high effective integration times without requiring periodic high-speed bursts, smoothing out the data rate requirements and enabling sustained long-duration integration.
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 enhances the signal-to-noise ratio and maintains spatial frequency resolution without degrading the modulation transfer function, allowing for efficient TDI imaging with increased integration periods per ground scene pixel.
Implementation Method 1
Solid-state image sensors use an array of picture elements (pixels), typically arranged in rows and columns, to convert electromagnetic (EM) energy (e.g., infrared, visible light, ultraviolet light, x-rays, etc) into a charge that can be detected and processed to generate a digital image.
Data Source
AI summary
A time delayed integration image sensor provides over-sampled image data on a time-shared column bus to maintain data synchronization.