Imaging Unit Cell Dynamic Integration Period Scaling
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Solution Overview
Problem
Conventional Focal Plane Arrays (FPAs) unit cells saturate when exposed to high-intensity optical radiation, limiting their dynamic range and ability to image both bright and dark features simultaneously, and existing solutions face challenges in calibration and nonuniformity correction.
Innovation Solution
The imaging system dynamically scales the integration period of each unit cell based on the intensity of received optical radiation, using a transimpedance amplifier circuit and quantization circuitry that compares integration voltage with a voltage ramp signal to generate a digital signal, allowing for simultaneous imaging of both bright and dark features without saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed integration period is used in conventional FPA unit cells, then the circuit structure is simple, but the dynamic range is limited and saturation occurs at high-intensity optical radiation
Solution Approach 1:
The patent implements dynamic integration period scaling by introducing a voltage ramp signal that varies over time during the integration period. The transimpedance amplifier integrates photo-current against this time-varying ramp signal, automatically adjusting the effective integration weight for different intensity levels. This dynamic approach enables the system to capture both bright and dark features simultaneously without saturation, resolving the contradiction between fixed integration simplicity and adaptive dynamic range.
Solution Approach 2:
The patent changes the integration parameter from a fixed time interval to a time-varying voltage ramp signal. By modifying the integration kernel (from constant to linearly varying voltage), the system achieves enhanced dynamic range. The ramp signal's slope and characteristics can be adjusted to optimize performance for different scene conditions, allowing the circuit to adaptively handle varying optical radiation intensities while maintaining a relatively simple circuit architecture.
2Adaptability or versatility
If conventional transimpedance amplification is used, then the circuit is simple, but saturation occurs at high flux levels limiting dynamic range
Solution Approach 1:
The patent introduces a voltage ramp signal as an intermediary element between the photodetector and the output. This ramp signal acts as a time-varying weighting function that modulates the integration process. By multiplying the photo-current with the ramp signal during integration, the system effectively compresses the dynamic range of the input signal, preventing saturation while preserving information from both bright and dark regions. The ramp signal serves as a mediator that transforms the integration behavior without requiring complex adaptive circuitry.
3Adaptability or versatility
If fixed integration time is used, then processing is simple, but both bright and dark features cannot be imaged simultaneously
Solution Approach 1:
The patent employs a periodic voltage ramp signal that resets with each integration period. This periodic ramp action creates a consistent, predictable integration pattern that can be synchronized with the imaging frame rate. The periodic nature of the ramp signal ensures that each integration period follows the same temporal profile, enabling reliable comparison and processing of data from different regions of the image. This periodic approach allows simultaneous capture of varying intensity features while maintaining simple periodic processing logic.
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 dynamic range and feasibility of imaging systems by preventing saturation at high flux levels, enabling the capture of image data from a wide range of intensities and reducing the complexity of auto-exposure algorithms, while maintaining high-resolution image data extraction.
Implementation Method 1
a photodetector configured to generate a photo-current in response to receiving optical radiation
Data Source
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AI summary
Imaging system, imaging system unit cell, and a method of detecting an image. One example of an imaging system unit cell includes a photodetector configured to generate a photo-current, a transimpedance amplifier circuit configured to integrate an electrical charge accumulated from the photo-current during an integration period and provide an integration voltage at an output node, and quantization circuitry configured to generate a digital signal during the integration period based at least in part on the integration voltage, the quantization circuitry including a comparator configured to receive the integration voltage and a voltage ramp signal, compare the integration voltage and the voltage ramp signal, and determine an intersection of the voltage ramp signal and the integration voltage at an intersection time, and a latch coupled to the comparator and configured to latch a digital counter value corresponding to the intersection time, the digital signal including the digital counter value.