Image Sensor Variable Charge Accumulation Time Control
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Solution Overview
Problem
Spectroscopic devices face challenges in performing high-sensitivity measurements across all wavelengths due to charge accumulation limitations in image sensors, leading to noise components interfering with signal components in low-intensity wavelength ranges.
Innovation Solution
The implementation of an image sensor with a switching instruction part and gate circuits that control the charge accumulation time of photodiodes, allowing for variable charge accumulation periods and a signal processor with a variable capacitance portion to optimize charge handling and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the charge accumulation time is set to be as long as possible to prevent saturation at peak wavelengths, then measurement sensitivity is improved at wavelengths where (I(λ)•D(λ)) is large, but noise components cannot be disregarded at wavelengths where (I(λ)•D(λ)) is small, resulting in low sensitivity
Solution Approach 1:
The patent applies dynamics by making the charge accumulation time variable rather than fixed. The control unit dynamically adjusts the charge accumulation time for each photodiode based on the intensity spectrum I(λ) and detecting sensitivity spectrum D(λ), allowing the accumulation time to be optimized for each wavelength range. This resolves the contradiction by enabling long accumulation time for high-intensity wavelengths (improving sensitivity) while using shorter accumulation time for low-intensity wavelengths (reducing noise interference).
Solution Approach 2:
The patent changes the parameter of charge accumulation time from a fixed value to a variable parameter that adapts to different operating conditions. By calculating the product (I(λ)•D(λ)) for each wavelength and adjusting the accumulation time accordingly, the system optimizes the balance between signal strength and noise. This parameter change allows the system to achieve high measurement precision across all wavelength ranges without being constrained by a single fixed accumulation time setting.
2Measurement precision
If the charge accumulation time is extended to maximize sensitivity, then the accumulated charge amount increases, but the junction capacitance portion becomes saturated at wavelengths where (I(λ)•D(λ)) has a peak
Solution Approach 1:
The system dynamically adjusts the charge accumulation time based on the expected signal strength at different wavelengths. By calculating (I(λ)•D(λ)) and using this information to control the accumulation time, the system prevents saturation at wavelengths with high intensity peaks while maintaining sufficient accumulation time for wavelengths with lower intensity. This dynamic control resolves the contradiction between maximizing sensitivity and preventing saturation.
Solution Approach 2:
The control unit uses feedback information from the intensity spectrum I(λ) and detecting sensitivity spectrum D(λ) to adjust the charge accumulation time. By continuously monitoring these parameters and adjusting the accumulation time accordingly, the system ensures that the junction capacitance portion remains within its linear response range while maximizing charge accumulation for optimal sensitivity. This feedback mechanism prevents saturation while maintaining high measurement precision.
3Device complexity
If a fixed charge accumulation time is used for all wavelengths, then the device complexity is reduced, but the measurement precision deteriorates in wavelength ranges where (I(λ)•D(λ)) is small due to noise interference
Solution Approach 1:
The patent changes the charge accumulation time parameter from fixed to variable, allowing it to adapt to different wavelength ranges. This parameter change enables the system to optimize measurement precision for each wavelength by adjusting the accumulation time according to the calculated (I(λ)•D(λ)) value. While this increases control complexity, the benefit of achieving high measurement precision across all wavelength ranges outweighs the additional complexity.
Solution Approach 2:
The system applies local quality by tailoring the charge accumulation time to specific local conditions (wavelength ranges) rather than using a uniform setting for all wavelengths. For wavelength ranges where (I(λ)•D(λ)) is large, longer accumulation time is used to maximize sensitivity. For wavelength ranges where (I(λ)•D(λ)) is small, shorter accumulation time is used to minimize noise interference. This localized optimization resolves the contradiction between device complexity and measurement precision.
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 configuration enables high-sensitivity spectroscopic measurements across all wavelengths by preventing charge saturation and minimizing noise interference, thereby enhancing measurement sensitivity.
Implementation Method 1
the photodiode generates charges whose amount corresponds to the amount of light received
Data Source
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AI summary
An image sensor 20A contains a photodiode array portion 21, a signal processor 22, a switching instruction part 23A and a control part 24A. Each switch SWn is provided between the corresponding photodiode PDn and the common output line L, and instructed to carry out the switching operation by the switching instruction part 23A so as to be closed, whereby the charges accumulated in the junction capacitance portion of the photodiode PDn are output to the common output line L. On the basis of the instruction from the switching instruction part 23A, the N switches SW1 to SWN carry out the switching operation so that the N switches SW1 to SWN are set to the close state in the different periods and the interval at which each switch SWn is set to the close state is equal to an integral multiple of a base period. As described above, the charge accumulation time of each of the N photodiodes PD1 to PDN is set to an integral multiple of the base period.