Image Sensor Flicker Detection via Embedded Readout Circuitry
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Solution Overview
Problem
Electronic devices with cameras or image sensors face issues with flicker artifacts in images due to ambient lighting, particularly from sources like fluorescent lights, which can cause horizontal or vertical striations in captured images, and existing solutions often require additional components and increased power consumption.
Innovation Solution
Incorporating flicker current detection circuitry (FCDC) directly into the pixel array on a common semiconductor substrate, which isolates a set of pixels from readout circuit elements to combine light-generated currents and analyze signal patterns to characterize flicker, using a transimpedance amplifier and digital signal processing to detect and compensate for flicker before image capture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional auxiliary sensors are added to detect flicker, then flicker detection capability is improved, but device complexity and power consumption increase
Solution Approach 1:
The pixel array is designed to perform multiple functions: both image capture and flicker detection. During flicker detection mode, the pixel array operates in photodiode-only mode without activating the full readout circuitry, allowing the same hardware to serve dual purposes and eliminating the need for separate auxiliary sensors
Solution Approach 2:
The flicker detection functionality is merged directly into the pixel array by utilizing the photodiodes' inherent current generation capability. The readout circuitry is shared between image capture and flicker detection operations, combining multiple functions into a single integrated structure rather than using separate components
2Measurement precision
If additional auxiliary sensors are added to detect flicker, then flicker detection capability is improved, but power consumption increases
Solution Approach 1:
The system performs flicker detection periodically or selectively rather than continuously, and only activates the necessary photodiodes and readout circuitry during detection intervals. This periodic operation allows the system to maintain flicker detection capability while significantly reducing average power consumption compared to continuous operation or having always-on auxiliary sensors
Solution Approach 2:
The pixel array's photodiodes inherently generate light-generated currents that can be directly used for flicker detection without requiring additional power-hungry auxiliary sensors. The system leverages the natural photodetection capability of the existing image sensor components, eliminating the need for separate powered detection devices
3Device complexity
If pixel array is used for both image capture and flicker detection, then device complexity is reduced, but measurement precision for flicker detection may be compromised
Solution Approach 1:
The pixel array operation is segmented into distinct modes: during flicker detection, only the photodiodes are active and connected to the readout circuitry, while during image capture, the full pixel functionality is engaged. This temporal segmentation allows the same hardware to achieve high precision for both functions without interference
Solution Approach 2:
The system dynamically reconfigures the pixel array operation mode based on the task at hand. The photodiodes can be independently controlled to operate in current-generation mode for flicker detection or in full imaging mode, allowing adaptive optimization of measurement precision for the current operation while maintaining low device complexity
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
Enables effective detection and compensation for flicker in ambient light within the image sensor itself, reducing the need for auxiliary sensors and power consumption while improving image quality by minimizing flicker-related artifacts.
Implementation Method 1
Pixels of the pixel array include respective photodiodes (PDs) electrically connected to readout circuit elements of the pixel
Implementation Method 2
The FCDC may include a transimpedance amplifier that receives the total light-generated current as input
Data Source
AI summary
Disclosed herein are cameras and image sensors, and electronic devices containing them, having pixel arrays operable both for obtaining images and detecting flicker in ambient light. For flicker detection, such as prior to image capture, light-generated current from a set of pixels of the pixel array is received at a transimpedance amplifier (TIA) that is formed in a common semiconductor substrate with the pixel array. An output signal of the TIA is digitized and signal processed to detect the flicker in the ambient light. Also disclosed are image sensors having pixel arrays with an embedded modulated light source. The modulated light source may be used for proximity detection, either by time-of-flight or intensity variation of reflected light.