Column Current Mirror Circuitry for Image Sensor Noise Reduction
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Solution Overview
Problem
Image sensors in electronic devices often suffer from fixed pattern noise due to the operation of current mirror circuits in pixel columns, which degrades image quality and reduces the yield of viable sensors, especially in large-scale production.
Innovation Solution
Incorporating redundant column current mirror circuitry with programmable memory to selectively activate or deactivate current supply circuits on each column line, allowing for the use of redundant current supply circuits to mitigate noise and improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current mirror circuits are used in pixel columns for reading out image signals, then the image sensor can function properly with signal readout capability, but fixed pattern noise is generated that degrades image quality
Solution Approach 1:
The patent changes the operational parameters of the current mirror circuit by implementing dual-gate control (first and second control signals) to independently manage the readout function and the noise generation. By adjusting gate voltages and control signal timing, the circuit can operate in different modes to minimize fixed pattern noise while maintaining signal readout capability.
Solution Approach 2:
The patent extracts and separates the noise-generating function from the essential readout function. By using dual-gate control, the harmful fixed pattern noise component can be independently managed and minimized while preserving the necessary image signal readout function through selective activation of different circuit paths.
2Productivity
If current mirror circuits are implemented in pixel columns, then signal readout is enabled, but the yield of viable image sensors is reduced due to noise
Solution Approach 1:
By implementing dual-gate control with independent voltage management, the patent enables better characterization and selection of functional pixels during manufacturing testing. This allows for more accurate yield prediction and selection of viable sensors by identifying those that can operate with acceptable noise levels under optimized parameter conditions.
Solution Approach 2:
The patent introduces dynamic control capabilities through dual-gate mechanisms that allow real-time adjustment of circuit operation. This enables adaptive noise reduction and flexible operational modes that can be optimized during production testing, thereby increasing the proportion of sensors that meet quality specifications.
3Object-affected harmful factors
If redundant column current mirror circuitry is added to mitigate noise, then image quality improves, but device complexity increases
Solution Approach 1:
The patent merges multiple functions into a unified dual-gate current mirror circuit structure. Rather than adding separate redundant circuits, the invention combines noise reduction, signal readout, and control functions into a single integrated circuit with dual gate control, thereby reducing overall device complexity while maintaining noise mitigation capabilities.
Solution Approach 2:
The dual-gate current mirror circuit serves multiple functions simultaneously: it enables signal readout, provides noise reduction, and allows for flexible operational modes. This multi-functionality eliminates the need for separate dedicated noise reduction circuits, thereby reducing device complexity while achieving the desired noise mitigation.
Data Source
AI summary
Electronic devices may include image sensors having image pixel arrays with image pixels arranged in pixel rows and pixel columns. Each pixel column may be coupled to an active and an inactive current supply circuit. Each active current supply circuit may form a portion of a current mirror circuit that includes a common current source and a common input transistor. Each active current supply circuit may include a mirror transistor for mirroring current that flows through the common input transistor and a permanently enabled enabling transistor for activating that mirror transistor. Mirrored current that flows through a particular active mirror transistor may be supplied to image pixels in the pixel column associated with that particular mirror transistor. Each inactive current supply circuit may include a mirror transistor coupled to the input transistor and a permanently disabled enabling transistor.