Dual Readout Circuit for Image Pickup Device Focus Detection
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Solution Overview
Problem
Existing image pickup devices with focus detection pixels face inefficiencies in readout processes, leading to potential image quality deterioration and increased power consumption, particularly when focusing detection pixels are discretely arranged and read out in a thinned manner.
Innovation Solution
The implementation of a dual AD conversion system, where a first readout circuit converts signals from image pickup pixels to digital signals and a second readout circuit converts signals from focus detection pixels to digital signals, allowing for optimized readout sequences that reduce power consumption and maintain image quality by independently controlling the operation of these circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus detection pixels are discretely arranged in the image pickup pixel group, then phase difference detection capability is improved, but readout efficiency deteriorates due to the need for thinned readout
Solution Approach 1:
The pixel array is segmented into two distinct groups: image pickup pixels for normal image capture and focus detection pixels for phase difference detection. Each group has its own dedicated readout circuit, allowing independent optimization of readout paths and improving overall readout efficiency
Solution Approach 2:
A signal charge transfer mechanism acts as an intermediary to move signal charges from focus detection pixels to the second readout circuit. This enables efficient readout of focus detection pixels without directly reading them out in the conventional thinned manner
2Device complexity
If focus detection pixels are read out in a thinned manner, then readout processing is simplified, but image quality deteriorates
Solution Approach 1:
The readout system is divided into two independent paths: the first readout circuit handles image pickup pixels with full resolution for high-quality image output, while the second readout circuit processes focus detection pixels separately. This segmentation prevents image quality deterioration while maintaining simplified processing for focus detection
Solution Approach 2:
Signal charges from focus detection pixels are transferred to the second readout circuit through an intermediate transfer mechanism, allowing the main image readout path to remain unchanged and preserve image quality while enabling efficient focus detection processing
3Speed
If all AD conversion circuits operate simultaneously, then readout speed is maximized, but power consumption increases
Solution Approach 1:
The readout system dynamically switches between different operational modes: both readout circuits can operate simultaneously when high-speed readout is needed, or only the necessary circuit operates when power saving is prioritized. This dynamic control optimizes the balance between readout speed and power consumption based on real-time requirements
Solution Approach 2:
The system can selectively deactivate unnecessary AD conversion circuits during operation to reduce power consumption, and reactivate them when high-speed readout is required. This on-demand operation pattern allows the system to discard power consumption when not needed and recover full performance when required
4Measurement precision
If the number of focus detection pixels is increased, then focus detection accuracy is improved, but device complexity increases
Solution Approach 1:
Focus detection pixels are segmented into a dedicated group with their own specialized readout circuit (second ADC), separating them from the main image pickup pixel group. This segmentation allows increasing the number of focus detection pixels for improved accuracy without proportionally increasing the complexity of the main image processing path
Solution Approach 2:
The second readout circuit is designed to handle multiple focus detection pixels efficiently through a unified processing path, allowing the system to scale the number of focus detection pixels without linearly increasing device complexity. The multi-functional design accommodates varying numbers of focus detection pixels while maintaining manageable system 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
This approach enables efficient and high-speed readout with reduced power consumption by selectively turning off unnecessary AD conversion circuits, thereby improving the overall performance and efficiency of the image pickup process while minimizing image quality deterioration.
Implementation Method 1
a first readout circuit including a first AD converter that converts only signals from pixels belonging to the image pickup pixel group to digital signals
Implementation Method 2
a second readout circuit including a second AD converter that converts only signals from pixels belonging to the focus detection pixel group to digital signals
Implementation Method 3
focus detection pixels that receive and photoelectrically convert light fluxes resulting from pupil division
Data Source
AI summary
Provided is an image pickup device including: an image pickup pixel group including a plurality of pixels arrayed in a matrix; a focus detection pixel group of focus detection pixels discretely arranged in the image pickup pixel group; a first readout circuit including a first AD converter that converts only pixel signals from the image pickup pixel group to digital signals; and a second readout circuit including a second AD converter that converts only pixel signals R, L, T and B from the focus detection pixel group to digital signals.