Heterogeneous ADC Image Sensor Horizontal Noise Filtering
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Solution Overview
Problem
CMOS image sensors face challenges in effectively removing horizontal noise during the conversion of analog signals to digital signals, particularly due to random noise, which affects image quality without increasing the number of pixels or analog-to-digital converters.
Innovation Solution
The implementation of a heterogeneous analog-to-digital converter system in the image sensor, comprising distinct first and second analog-to-digital converters for active and optical black pixel sensors, respectively, allows for effective noise filtering and reduction of horizontal noise without increasing the number of pixels or converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single type of analog to digital converter is used for all pixel sensors, then the device complexity is low and manufacturing is simple, but horizontal noise cannot be effectively removed due to random noise characteristics
Solution Approach 1:
The pixel sensor array is segmented into active pixel sensors and optical black pixel sensors, each with dedicated analog to digital converters. The analog to digital converters are further segmented into first and second converters with different noise characteristics, allowing separate processing paths for different signal types to effectively filter horizontal noise.
Solution Approach 2:
Different analog to digital converters are assigned to different regions (active pixels vs. optical black pixels) with different noise characteristics. The first analog to digital converter processes signals from active pixels while the second converter processes signals from optical black pixels, providing locally optimized noise filtering for each region.
2Reliability
If the number of analog to digital converters is increased to improve noise filtering, then horizontal noise reduction capability is enhanced, but the chip area and resource overhead increase
Solution Approach 1:
The optical black pixel sensors and their dedicated second analog to digital converter serve multiple functions: they provide dark current reference signals for noise compensation and simultaneously enable horizontal noise filtering through their distinct noise characteristics. This multi-functionality allows effective noise reduction without proportionally increasing chip area.
Solution Approach 2:
The patent utilizes the inherent random noise characteristics of the second analog to digital converter as a beneficial feature rather than a drawback. By designing the second converter with different noise characteristics, the random noise becomes a tool for differentiating and filtering horizontal noise patterns, converting what would normally be a harmful interference into a useful filtering mechanism.
Data Source
AI summary
An image sensor in accordance with exemplary embodiments of the inventive concept may include a pixel sensor array which includes an active pixel sensor and an optical black pixel sensor; a first analog to digital converter configured to convert a first sensing signal, which is provided from the active pixel sensor, to a first digital signal; a second analog to digital converter configured to convert a second sensing signal, which is provided from the optical black pixel sensor, to a second digital signal; and an output buffer configured to temporarily store and output the first digital signal and the second digital signal, wherein a plurality of noise characteristics of the second analog to digital converter is different from a plurality of noise characteristics of the first analog to digital converter.