CMOS Image Sensor Noise Elimination via Single Transfer Capacitor
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Solution Overview
Problem
Conventional imaging devices with CMOS sensors face challenges in noise elimination due to the need for multiple capacitors per pixel column, which hinders miniaturization and degrades signal-to-noise ratio, especially when transmitting images over long distances through endoscopes where noise mixing is a significant issue.
Innovation Solution
The imaging device employs a noise elimination unit that uses a transfer capacitor and a reference voltage generating unit to alternately output imaging signals and noise signals, eliminating the need for sampling capacitors and allowing effective noise subtraction without degrading image quality, while also transmitting only alternating current components over long distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple capacitors (AC coupling capacitor and sampling capacitor) are provided for each pixel column to eliminate noise, then noise elimination capability is improved, but device area increases and miniaturization is hindered
Solution Approach 1:
The patent merges the AC coupling capacitor and sampling capacitor into a single capacitor structure. The same capacitor serves dual purposes: coupling AC signals and sampling noise signals for elimination. This integration eliminates the need for separate capacitors, reducing device area while maintaining noise elimination functionality.
Solution Approach 2:
The single capacitor in the invention performs multiple functions that were previously requiring separate components. It acts as both an AC coupling element for signal transmission and a sampling capacitor for noise capture. This multi-functionality resolves the contradiction by providing the same noise elimination capability with reduced component count and smaller area.
2Reliability
If multiple capacitors are provided for noise elimination, then noise reduction is improved, but signal-to-noise ratio deteriorates due to capacity division
Solution Approach 1:
By combining the AC coupling and sampling functions into a single capacitor, the invention eliminates capacity division between multiple capacitors. The full capacitance value is available for both AC signal coupling and noise sampling, preventing signal attenuation and maintaining high signal-to-noise ratio while still achieving effective noise reduction.
3Adaptability or versatility
If imaging signals are transmitted over long distances through endoscopes, then imaging capability is improved, but noise mixing increases significantly
Solution Approach 1:
The invention performs preliminary noise elimination at the image sensor before signal transmission through the endoscope. By capturing and subtracting noise signals in advance using the single capacitor-based noise elimination unit, the transmitted signal already has reduced noise content, preventing further noise mixing during long-distance transmission and maintaining image quality.
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 enables miniaturization of the imaging device without compromising image quality and effectively eliminates noise during transmission, improving signal-to-noise ratio and reducing the area occupied by noise elimination units.
Implementation Method 1
a photoelectric conversion element that performs photoelectric conversion according to an amount of light received and accumulates a charge
Implementation Method 2
a transfer capacitor connected to the first transfer line; a second transfer unit that is connected to the first transfer line via the transfer capacitor and to which a signal is output from the first transfer line due to coupling by a capacity of the transfer capacitor
Data Source
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AI summary
An imaging device includes: a photoelectric conversion element, a first transfer unit, a charge converter, a charge converter resetting unit, a signal output unit, a first transfer line, a transfer capacitor, a second transfer unit, a transfer capacitor resetting unit, a second transfer line, and a drive unit, and causes a signal to be output from the first transfer line via the second transfer unit by a noise signal reading operation and a light-noise sum signal reading operation, the noise signal reading operation resetting the transfer capacitor when a signal of the charge converter is output to the first transfer line after the first transfer unit is turned into an OFF state and the charge converter is reset, and the light-noise sum signal reading operation outputting the signal of the charge converter to the first transfer line after the transfer capacitor resetting unit is turned into an OFF state, the first transfer unit is turned into an ON state, and a charge accumulated by the photoelectric conversion element is transferred.