CMOS Image Sensor ADC Ramp Circuit for Faster Pixel Sampling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current CMOS image sensors require high-resolution analog-to-digital conversion for converting analog signals from active pixel sensors into digital signals, but existing solutions do not provide high-speed operation necessary for advanced mobile applications.
Innovation Solution
An analog-to-digital conversion circuit with a reference current generating unit, ramp voltage generating unit, and comparison unit, along with current sources, switching units, and a control unit, that adjust and mirror currents to enable high-speed sampling and conversion of pixel signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing analog-to-digital conversion methods are used in CMOS image sensors, then manufacturing cost and integration are improved, but operation speed is insufficient for advanced mobile applications
Solution Approach 1:
The analog-to-digital conversion process is divided into multiple sampling stages, with each stage handling a portion of the conversion task. This segmentation allows parallel processing of different signal components, thereby increasing overall operation speed and reducing total sampling time while maintaining integration benefits of CMOS architecture
Solution Approach 2:
The circuit performs preliminary sampling and conversion operations in advance within each sampling stage, preparing intermediate results that accelerate the final conversion process. This preliminary action reduces the critical path delay and enables faster overall operation without compromising manufacturing simplicity
2Measurement precision
If high-resolution analog-to-digital conversion is implemented, then signal accuracy is improved, but conversion speed deteriorates
Solution Approach 1:
The high-resolution conversion process is segmented into multiple coarse-to-fine sampling stages, where each stage resolves a portion of the signal precision requirement. This allows the system to achieve high overall accuracy through cumulative measurements while maintaining fast operation by avoiding the need for a single lengthy high-precision conversion step
Solution Approach 2:
Each sampling stage performs a partial conversion with sufficient precision for that stage's resolution requirement, rather than attempting full high-resolution conversion in each stage. This partial action approach accumulates to achieve total high-resolution accuracy while significantly reducing the time required compared to performing complete high-precision conversion in a single step
Data Source
AI summary
An analog-to-digital conversion circuit includes a reference current generating unit suitable for generating a reference current varied by a given level in a sampling stage, a ramp voltage generating unit suitable for generating a ramp voltage corresponding to the reference current, and a comparison unit suitable for comparing the ramp voltage with a voltage level of a pixel signal to output a comparison signal.