Variable Capacitance Charge Storing Circuit for Dynamic Range Adaptation
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Solution Overview
Problem
Conventional Focal Plane Array (FPA) unit cell circuits face inefficiencies in managing variations in flux levels during integration periods, leading to unpredictable capacitive charge-sharing accuracy and inefficient management of unit cells, as they typically require modifying the integration period for low and high flux levels, which is cumbersome and ineffective.
Innovation Solution
A variable capacitance charge storing circuit that dynamically adapts by cycling through operation phases to accommodate low and high flux levels, increasing well capacity and noise tolerance accordingly, using a sequence of switching phases and charge-sharing between multiple capacitors to maintain a high dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single capacitive element is used to accumulate charge, then the circuit structure is simple, but the dynamic range is limited and cannot accommodate both low flux levels (requiring low noise floor) and high flux levels (requiring high well capacity)
Solution Approach 1:
The single capacitive element is divided into multiple capacitive elements (first capacitive element and second capacitive element). Each capacitive element can be independently selected to accumulate charge based on flux level conditions, enabling the circuit to accommodate both low flux levels (using first capacitive element for low noise floor) and high flux levels (using second capacitive element for high well capacity).
Solution Approach 2:
The circuit dynamically selects which capacitive element to use based on real-time flux level conditions. The control circuit monitors the flux level and switches between the first and second capacitive elements accordingly, making the charge accumulation capability adaptable rather than fixed, thus achieving high dynamic range.
2Adaptability or versatility
If the integration period is modified for low and high flux levels, then the flux variations can be accommodated, but the management becomes cumbersome and inefficient
Solution Approach 1:
Instead of modifying the integration period, the invention changes the capacitive element parameter (capacitance value) to accommodate flux variations. The control circuit selects between capacitive elements with different capacitance values based on flux level, which is simpler and more efficient than dynamically adjusting integration period while achieving the same adaptability goal.
3Quantity of substance
If conventional circuits are used, then the noise floor is low for low flux conditions, but the well capacity is insufficient for high flux conditions
Solution Approach 1:
The charge storage function is segmented across multiple capacitive elements with different capacitance values. The first capacitive element has smaller capacitance optimized for low flux conditions with low noise floor, while the second capacitive element has larger capacitance optimized for high flux conditions with high well capacity. This segmentation allows the system to achieve both low noise floor and high well capacity by selecting the appropriate element for each condition.
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 feasibility and performance of FPA unit cells by providing a low noise floor for low flux conditions and a high well capacity for high flux conditions, effectively managing flux variations during integration periods, improving imaging system efficiency and accuracy.
Implementation Method 1
A unit cell circuit includes a photodetector configured to generate a photocurrent in response to receiving wavelengths of light
Implementation Method 2
A variable capacitance charge storing circuit is coupled to the photodetector and configured to integrate the photocurrent to produce an integrated voltage signal
Data Source
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AI summary
An imaging system unit cell and method of detecting an image. One example of an imaging system unit cell includes a photodetector configured to generate a photo-current in response to receiving optical radiation, a variable capacitance charge storing circuit in electrical communication with the photodetector and configured to integrate an electrical charge accumulated from the photo-current, a control circuit configured to monitor an integration voltage across the variable capacitance charge storing circuit and adjust a capacitance of the variable capacitance charge storing circuit based on the integration voltage, and an output configured to provide an output voltage based at least in part on the integrated voltage.