Imaging Detector Stray Capacitance Error Correction
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Solution Overview
Problem
Imaging sensors utilizing charge transfer mechanisms face errors due to stray and parasitic capacitance, particularly evident in rapidly changing operating conditions, which can limit system performance and require frequent calibration in infra-red detectors.
Innovation Solution
A method to correct output errors by measuring and comparing signal voltages across capacitors, calculating a correction factor based on the ratio of stray to pixel capacitance, and applying it to derive a corrected output value, allowing for individual pixel corrections without physical detector alteration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge transfer mechanism is used in imaging sensors, then detection capability is achieved, but errors due to stray and parasitic capacitance occur
Solution Approach 1:
The patent converts the harmful stray capacitance effect into a beneficial correction mechanism by measuring the output signal before and after charge transfer, calculating the error based on the difference, and applying a correction factor to compensate for the stray capacitance impact on detector output accuracy
Solution Approach 2:
The patent implements feedback by measuring the output signal Vm after charge transfer, comparing it with the previous output signal Vm-1, calculating the error based on the difference, and applying a correction factor to produce a corrected output value, thereby continuously improving measurement precision
2Measurement precision
If calibration is performed for each frame, then detector accuracy is maintained, but system complexity and processing time increase
Solution Approach 1:
The patent applies preliminary action by determining the correction factor during a calibration process before actual detection, storing it for use during operation. This pre-computed correction factor can then be applied to each detector element's output without requiring complex real-time calibration, reducing processing complexity while maintaining accuracy
Solution Approach 2:
The patent changes the approach from performing complex calibration for each frame to using a pre-determined correction factor that accounts for stray capacitance effects. The correction factor is calculated based on the ratio of stray capacitance to pixel capacitance and is applied as a parameter adjustment to the output signal, simplifying the overall system complexity
3Ease of manufacture
If detector elements are mismatched, then manufacturing tolerances are realistic, but ongoing calibration checks are required
Solution Approach 1:
The patent applies local quality by determining and applying individual correction factors to each detector element's output signal. Instead of requiring uniform performance across all elements, the system accounts for local variations and mismatches by measuring and correcting each element's output individually, thereby maintaining reliability despite manufacturing tolerances
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 method improves the accuracy of detector outputs, increases the range of detector applications, and enhances system performance by effectively mitigating errors caused by stray capacitance, especially in infra-red detectors used in fast-changing environments.
Implementation Method 1
measuring an output signal (V m ) of a capacitor (C sh ) holding a voltage corresponding to a signal detected by the detector element
Implementation Method 2
the charge transfer mechanism comprises a charge being transferred from the capacitor C pix to the capacitor C sh
Implementation Method 3
the charge transfer mechanism further includes a stray or parasitic capacitance C str within the image detector
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
A method of correcting errors in the output of an image detector is disclosed. The method comprises measuring an output signal (Vm) of a capacitor (Csh) holding a voltage corresponding to a signal detected by the image detector;comparing the value of output signal (Vm) to the value of the previously measured output signal (Vm-1) of the capacitor (Csh);calculating the error in the output signal (Vm) using a predetermined correction factor and the difference between the value of the output signal (Vm) and the value of the previously measured output signal (Vm-1); and providing a corrected output value (Vcrt) in accordance with the calculated error. Detectors, methods of calibrating detectors, image correction apparatus and guidance systems comprising the detectors are also disclosed.