Image Sensor Readout for HDR and Phase Difference AF
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Solution Overview
Problem
Existing image sensor technologies face challenges in simultaneously achieving high-dynamic range expansion and phase difference detection, as the methods for reading out high-gain and low-gain image signals differ, leading to issues like offset shifts due to dark current components and wiring resistance changes, which affect the accuracy of on-imaging plane phase difference AF, especially in long exposures or high-temperature environments.
Innovation Solution
An image sensor with a pixel region of microlenses and photoelectric conversion portions, equipped with amplifiers applying different gains and a scanning circuit that reads out partial and added signals in parallel, allowing for simultaneous focus detection and dynamic range expansion, while a processor expands the dynamic range using the added signal and a focus detection circuit performs phase difference focus detection using both partial and added signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If different readout methods are used for high-gain and low-gain image signals to expand dynamic range, then dynamic range expansion is achieved, but offset shifts occur due to dark current components and wiring resistance changes
Solution Approach 1:
The pixel array is divided into first pixel regions and second pixel regions, where first pixel regions read out image signals for dynamic range expansion and second pixel regions read out image signals for phase difference detection. This spatial segmentation allows different readout methods to be applied to different regions simultaneously, avoiding offset shifts while maintaining dynamic range expansion capability.
Solution Approach 2:
Different readout characteristics are applied to different spatial regions of the pixel array. The first pixel regions use readout characteristics optimized for dynamic range expansion, while the second pixel regions use readout characteristics optimized for phase difference detection. This local differentiation ensures that each region's specific requirements are met without compromising the other function.
2Temperature
If high-gain and low-gain image signals are read out using different methods, then dynamic range is expanded, but phase difference detection accuracy deteriorates due to offset shifts
Solution Approach 1:
The pixel array is segmented into dedicated first pixel regions for dynamic range expansion and second pixel regions for phase difference detection. By reading out image signals from second pixel regions using methods that avoid offset shifts, phase difference detection accuracy is maintained while first pixel regions simultaneously provide dynamic range expansion.
Solution Approach 2:
The readout system applies different readout characteristics to different spatial regions: first pixel regions use characteristics that maximize dynamic range expansion, while second pixel regions use characteristics that ensure accurate phase difference detection. This local optimization resolves the contradiction between dynamic range expansion and detection accuracy.
3Productivity
If readout driving is switched between dynamic range expansion and phase difference detection to maintain high framerate, then framerate is maintained, but dynamic range expansion is lost in alternating rows
Solution Approach 1:
The pixel array is divided into first pixel regions and second pixel regions that operate simultaneously with different readout characteristics. This allows both dynamic range expansion and phase difference detection to occur in the same frame period, achieving high framerate without alternating between modes, thereby maintaining dynamic range expansion in all rows.
Solution Approach 2:
The system merges the functions of dynamic range expansion and phase difference detection by reading out image signals from both first pixel regions and second pixel regions simultaneously within the same frame period. This combination allows both functions to operate concurrently, maintaining high framerate while preserving dynamic range expansion capability in all pixel regions.
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 enables the acquisition of suitable image signals for dynamic range expansion and focus detection within the same frame, maintaining high framerate and accurate phase difference focus detection, even under varying environmental conditions.
Implementation Method 1
a pixel region including a plurality of microlenses arranged in a matrix, and a plurality of photoelectric conversion portions provided for each of the microlenses
Data Source
AI summary
An image sensor comprises: a pixel region including a plurality of microlenses arranged in a matrix, and a plurality of photoelectric conversion portions provided for each of the microlenses; a plurality of amplifiers that apply a plurality of different gains to signals output from the pixel region; and a scanning circuit that scans the pixel region so that a partial signal and an added signal are read out, the partial signal being a signal from some of the plurality of photoelectric conversion portions, and the added signal being a signal obtained by adding the signals from the plurality of photoelectric conversion portions.