Image Sensor ADC Multiplexing for Fast Readout
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in increasing pixel signal readout speed without proportionally increasing the circuit scale of the analog/digital converter (ADC) portion, which is particularly problematic for applications like moving image capture and photometry where rapid signal processing is required.
Innovation Solution
The implementation of an image sensor with a pixel portion arranged in a matrix, featuring a plurality of A/D converters corresponding to pixel columns, an adding unit to combine signals from multiple columns, and a connecting mechanism to input the summed signal to any A/D converter, allowing for efficient high-speed readout while maintaining a controlled circuit scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If multiple ADCs are provided to one pixel column to improve readout speed, then the readout speed of pixel signal is increased, but the circuit scale of ADC portion increases and chip size considerably increases
Solution Approach 1:
The patent segments the pixel columns into multiple groups, with each group assigned to a single ADC. Instead of providing one ADC per pixel column, the system divides N pixel columns into M groups (where M < N), and each group is processed by one ADC through time-division multiplexing. This segmentation reduces the number of ADCs needed from N to M, thereby reducing chip size while maintaining high readout speed through parallel group processing.
Solution Approach 2:
The patent implements dynamic switching between different pixel column groups using switching elements that can dynamically connect different groups to the same ADC at different time periods. This dynamic reconfiguration allows the system to process multiple pixel columns through a reduced number of ADCs without permanent physical connections, enabling flexible resource allocation and reducing the overall ADC circuit scale.
2Speed
If ADC circuit scale is increased to improve readout speed, then pixel signal readout speed is increased, but device complexity increases
Solution Approach 1:
The patent makes each ADC universal by enabling it to process multiple pixel column groups through time-division multiplexing. Each ADC can sequentially serve different pixel column groups during different time periods, making a single ADC perform the function of multiple ADCs. This multi-functionality reduces the total number of ADCs needed, thereby reducing device complexity and ADC circuit scale while maintaining high readout speed.
Solution Approach 2:
The patent introduces switching elements as intermediaries between pixel columns and ADCs. These switching elements dynamically route signals from different pixel column groups to the appropriate ADCs, enabling flexible resource allocation without direct permanent connections. This intermediary mechanism simplifies the overall circuit architecture by reducing the number of direct ADC-column connections while maintaining high-speed readout capability.
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 faster pixel signal readout without enlarging the ADC circuit scale, enhancing performance in applications requiring rapid signal processing such as moving image capture and photometry.
Implementation Method 1
a pixel portion formed by arraying pixels including photoelectric conversion portions in a matrix
Data Source
AI summary
An image sensor comprises a pixel portion formed by arraying pixels including photoelectric conversion portions in a matrix, a plurality of A/D converters which are provided in a one-to-one correspondence to pixel columns of the pixel portion, an adding unit which adds pixel signals from a plurality of pixel columns to each other, and a connecting portion capable of inputting, to an arbitrary A/D converter, a sum signal obtained by adding the pixel signals by the adding unit.