Pixel-Wise Coded Exposure Control for CMOS Image Sensors
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Solution Overview
Problem
CMOS Image Sensors (CIS) face limitations in flexible pixel exposure control, leading to constraints on frame rate, signal-to-noise ratio (SNR), and dynamic range due to inflexible exposure times, which result in motion blur and reduced performance.
Innovation Solution
A CMOS-based pixel-wise coded-exposure system with in-pixel memory and circuit-reset-modulation techniques allows for variable exposure control of each pixel, eliminating the need for additional optical elements and enabling on-chip exposure coding, thereby allowing for flexible exposure times and improved dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long exposure time is used to improve pixel SNR, then signal-to-noise ratio is improved, but motion blur increases and frame rate decreases
Solution Approach 1:
The pixel array is divided into multiple independently controllable pixel units, each capable of having different exposure times. This segmentation allows simultaneous capture of multiple exposure-coded images with different exposure durations within a single frame period, enabling high frame rate video and HDR imaging without motion blur while maintaining high pixel SNR.
Solution Approach 2:
The patent implements dynamic exposure control where each pixel's exposure time can be individually adjusted and changed over time. The exposure time for each pixel is controlled by reset signals that can be dynamically programmed, allowing the system to adapt exposure duration to scene conditions and achieve optimal SNR without sacrificing frame rate.
2Speed
If short exposure time is used to capture blur-less fast motion, then motion blur is reduced, but pixel SNR decreases at low light intensity
Solution Approach 1:
By segmenting the pixel array into independently controllable units with variable exposure times, the system can assign different exposure durations to different pixels based on local scene conditions. This allows fast motion capture in bright regions while maintaining long exposure for low-light regions, optimizing both frame rate and pixel SNR simultaneously.
Solution Approach 2:
The patent applies local quality by allowing each pixel to have customized exposure parameters based on its local scene requirements. Pixels in low-light regions can use longer exposure times for high SNR, while pixels in bright or fast-motion regions use shorter exposure times to avoid saturation and motion blur, achieving optimal performance locally across the entire image.
3Measurement precision
If optical spatial light modulators are used for exposure control, then exposure-coded imaging performance is improved, but system size and power dissipation increase significantly
Solution Approach 1:
The patent extracts the exposure control function from external optical components and integrates it directly into the pixel circuitry. By implementing in-pixel reset switches and control logic, the system eliminates the need for separate spatial light modulators, dramatically reducing system size and power consumption while maintaining exposure-coded imaging capabilities.
Solution Approach 2:
The exposure control functionality is merged with the pixel structure itself. The reset switch and control circuitry are integrated within each pixel unit, combining the functions of light sensing, exposure control, and signal readout into a unified on-chip architecture, thereby eliminating external optical modulators and reducing overall system complexity.
4Ease of operation
If frame-based image sensor architecture is used, then simple readout is achieved, but exposure control flexibility is limited and dynamic range is reduced
Solution Approach 1:
The patent introduces dynamic exposure control into the frame-based architecture by implementing programmable reset signals for each pixel. This allows the exposure time to be dynamically adjusted on a per-pixel basis while maintaining the simple frame-based readout structure, achieving both operational simplicity and exposure flexibility simultaneously.
Solution Approach 2:
The system changes the exposure parameter dynamically by controlling the reset timing of each pixel independently. By varying the reset signal timing, the effective exposure duration for each pixel can be changed without altering the fundamental frame-based readout architecture, enabling flexible exposure control and extended dynamic range while preserving readout simplicity.
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 solution enhances the CMOS Image Sensor's performance by enabling flexible exposure control, reducing system size and power consumption, and allowing for high-frame-rate video and high-dynamic-range imaging without the need for additional optical modulators, thus overcoming the limitations of traditional CIS architectures.
Implementation Method 1
a photodiode, a buffer and a memory element and a switching mechanism
Data Source
AI summary
A pixel having a variable exposure for a scene capture device, the pixel comprising a photodiode, a buffer and a memory element and a switching mechanism. The memory element is configured to store an exposure control bit and the switching mechanism configured to control a variable exposure period of the photodiode based on the exposure control bit and to reset a voltage on said photodiode to a reference voltage.