Image Sensor Pixel Sharing for Parallel A/D Conversion
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Solution Overview
Problem
The existing image capturing apparatuses face challenges in efficiently AD-converting signals from pixels with integrated photoelectric conversion and AD conversion portions, leading to increased circuit complexity and performance drops during focus detection, especially with moving objects.
Innovation Solution
The implementation of a selection circuit that allows AD conversion of signals from one pixel to be performed using the AD converter of another pixel, enabling parallel AD conversion across a group of pixels, thereby reducing circuit scale and maintaining synchronized signal accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single pixel is constituted by two photoelectric conversion portions and two AD conversion portions to enable simultaneous AD conversion, then the AD conversion speed and focus detection performance are improved, but the circuit area increases significantly making it difficult to arrange within the pixel limit area
Solution Approach 1:
The pixel array is divided into first pixel regions and second pixel regions, where each first pixel region contains two photoelectric conversion portions but shares a single AD conversion portion located in the second pixel region. This segmentation allows simultaneous AD conversion capability while reducing per-pixel circuit area.
Solution Approach 2:
The single AD conversion portion in each second pixel region serves multiple first pixel regions, performing universal AD conversion function for all associated photoelectric conversion portions. This multi-functionality reduces the total number of AD conversion portions needed while maintaining simultaneous conversion capability.
2Area of stationary object
If signals are sequentially AD-converted from two photoelectric conversion portions using a single AD conversion portion, then the circuit area is reduced, but the accumulation timing difference causes performance drop in focus detection for moving objects
Solution Approach 1:
The pixel structure is segmented into first pixel regions (containing photoelectric conversion portions) and second pixel regions (containing AD conversion portions). This spatial segmentation enables simultaneous AD conversion of signals from multiple photoelectric conversion portions without accumulation timing differences, maintaining focus detection performance while using fewer AD conversion portions.
3Reliability
If two AD conversion portions are provided per integrated pixel to enable parallel AD conversion, then the focus detection performance is improved, but the number of transistors increases by several hundred making the circuit scale too large
Solution Approach 1:
Each AD conversion portion is designed to universally handle signals from multiple photoelectric conversion portions simultaneously. This multi-functional design reduces the total number of AD conversion portions and associated transistors needed, lowering circuit complexity while maintaining the capability for parallel AD conversion and high-quality focus detection.
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 allows for efficient and flexible AD conversion of signals, preventing performance drops during focus detection and enabling global shutter operations while minimizing circuit complexity.
Implementation Method 1
each pixel including a light-receiving portion that outputs an electrical signal obtained by photoelectrically converting incident light
Data Source
AI summary
An image sensor comprises: a plurality of pixels, each pixel including a light-receiving portion that outputs an electrical signal obtained by photoelectrically converting incident light and an A/D converter that AD-converts the electrical signal, the plurality of pixels configured to be capable of AD-converting a signal output from the light-receiving portion of a first pixel, among a predetermined plurality of pixels, using the A/D converter of another pixel, every predetermined plurality of pixels; and a selection circuit that selects a pixel to AD-convert the electrical signal output from the light-receiving portion of the first pixel, every predetermined plurality of pixels. The A/D converters of the predetermined plurality of pixels carry out the AD conversion in parallel.