Imaging Device Pixel Charge Separation for Global Shutter Noise
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Solution Overview
Problem
Imaging devices with global electronic shutters face image quality deterioration due to false signals such as dark current, leakage, and noise components accumulated in holding units, which existing technologies struggle to correct effectively.
Innovation Solution
The implementation of a pixel configuration with multiple holding units and transfer switches that allow for the separation and correction of actual and false signal charges during exposure and readout periods, enabling accurate signal processing and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If holding units are used to temporarily store charges in global electronic shutter operation, then image distortion of moving objects is avoided, but false signals (dark current, leakage, noise) accumulate in the holding units deteriorating image quality
Solution Approach 1:
The pixel is divided into multiple holding units (first holding unit and second holding unit) that can be independently controlled. During the exposure period, only the first holding unit receives and stores signal charges from the photoelectric conversion unit, while the second holding unit remains isolated. This segmentation prevents false signals from accumulating in both holding units simultaneously, allowing the system to maintain global shutter functionality while reducing false signal contamination.
Solution Approach 2:
The patent applies preliminary action by controlling the transfer switches to ensure that the second holding unit does not receive actual signal charges during the exposure period. Instead, it only accumulates false signals generated during the readout period. This preliminary isolation of the second holding unit from actual signals enables subsequent subtraction of false signals to accurately recover the original image signal.
2Measurement precision
If multiple holding units are used to separate actual and false signal charges, then false signal correction becomes possible, but the circuit configuration becomes more complex with additional transfer switches
Solution Approach 1:
The transfer switches (first transfer switch, second transfer switch, third transfer switch, and fourth transfer switch) serve multiple functions throughout the exposure and readout periods. For example, the first transfer switch not only transfers signal charges to the first holding unit but also enables the readout of both actual and false signals from the first holding unit. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity despite the enhanced signal correction capability.
3Object-generated harmful factors
If the second transfer switch remains off during exposure period, then false signal charges are not mixed with actual signal charges, but the readout process requires additional time periods
Solution Approach 1:
The patent implements periodic action by dividing the readout process into distinct time periods: a first readout period for reading actual signal charges from the first holding unit, and a second readout period for reading false signal charges from the second holding unit. This periodic readout approach allows the system to maintain clean separation between actual and false signals while systematically processing each type of charge in its designated time window, optimizing the balance between signal purity and readout efficiency.
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 allows for the reduction of false signal influence, resulting in improved image quality and simplified system design by enabling accurate signal correction and reduced noise in imaging systems with global electronic shutter operation.
Implementation Method 1
a photoelectric conversion unit configured to accumulate charges generated by an incident light
Data Source
AI summary
Provided is an imaging device that includes a plurality of pixels, each of the plurality of pixels including a photoelectric conversion unit configured to accumulate charges generated by an incident light, a first holding unit and a second holding unit configured to hold the charges, an amplification unit configured to output a signal based on the charges, a first transfer switch provided between the photoelectric conversion unit and the first holding unit, a second transfer switch provided between the photoelectric conversion unit and the second holding unit, a third transfer switch provided between the first holding unit and the amplification unit, and a fourth transfer switch provided between the second holding unit and the amplification unit, and outputs a signal including a signal based on actual signal charges and a signal including a signal based on false signal charges.