CMOS Image Sensor Readout Paths for High Dynamic Range
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Solution Overview
Problem
CMOS image sensors face limitations in dynamic range and noise reduction, particularly in low-light conditions and capturing wide luminance variations, due to high power consumption and complex column readout circuits required for high bit depth ADCs.
Innovation Solution
The use of multiple readout circuit paths with different amplification responses to generate digital image samples at a higher bit depth, allowing for a combination of these samples to produce a digital image output with improved dynamic range without the need for costly and power-intensive column readout circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high bit depth ADCs are used to improve dynamic range, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The pixel array is divided into multiple independently controllable regions (first pixel array and second pixel array) with different exposure times. Each region can be read out through separate column readout circuits, allowing the system to achieve high dynamic range by combining data from multiple segments rather than requiring a single high-bit-depth ADC for the entire array.
Solution Approach 2:
The patent introduces the time dimension by implementing different exposure times for different pixel regions. This temporal dimension allows short-exposure pixels to capture bright highlights while long-exposure pixels capture dark shadows, effectively expanding the dynamic range without requiring higher bit depth converters.
2Measurement precision
If high bit depth ADCs are used to improve dynamic range, then measurement precision is improved, but power consumption increases
Solution Approach 1:
By segmenting the pixel array into multiple regions with different exposure times and reading them through separate column circuits, the system avoids the need for power-hungry high-bit-depth ADCs. Each segment can be processed with lower bit depth converters, significantly reducing overall power consumption while maintaining high dynamic range performance.
Solution Approach 2:
The introduction of temporal dimension through varied exposure times allows the system to capture both bright and dark regions in the same scene. This approach achieves high dynamic range through time-based differentiation rather than through high-bit-depth conversion, thereby reducing power consumption.
3Illumination intensity
If longer exposure time is used to improve light sensitivity, then light gathering capability is improved, but saturation of bright regions occurs
Solution Approach 1:
The pixel array is segmented into first and second pixel arrays with different exposure times. The first pixel array uses longer exposure for improved light sensitivity in dark regions, while the second pixel array uses shorter exposure to prevent saturation in bright regions. This segmentation allows both requirements to be satisfied simultaneously in different spatial regions.
Solution Approach 2:
Different regions of the pixel array are assigned different exposure times based on local lighting conditions. Regions that require high light sensitivity (dark areas) receive longer exposure, while regions prone to saturation (bright areas) receive shorter exposure. This local differentiation optimizes both light sensitivity and luminance range capture accuracy.
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 CMOS image sensors to achieve high dynamic ranges similar to those with high bit depth ADCs while using simpler and less expensive circuitry, reducing manufacturing and operational costs and enhancing image quality.
Implementation Method 1
Pixel 300 includes a photodetector 305 followed by a transfer transistor 310... The photodetector 305 converts the incident light into an electrical charge.
Data Source
AI summary
An image sensor apparatus comprises an image sensor for generating digital images having a high dynamic range. The image sensor apparatus includes an image sensor for generating a first and a second set of digital image samples at a first bit depth, with each set of digital image samples generated by a different column readout circuit path. A processor combines the first and second set of digital image samples to generate a digital image at a second bit depth, the second bit depth higher than the first bit depth.