Column ADC Two-Step Ramp Conversion for Faster CMOS Sensing
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Solution Overview
Problem
Existing imaging devices face a low frame rate due to the increased time required for multiple comparisons in analog-to-digital conversion processes, which hampers the efficiency of converting analog pixel output signals into digital data.
Innovation Solution
The implementation of a column ADC system that operates in two steps: a 'coarse' operational step using a first ramped reference signal to determine the operating point, followed by a 'fine' operational step using a second ramped reference signal that ramps multiple times around the operating point, with a feedback switch control circuit to manage the reference signals and counters for efficient conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple comparisons of the pixel output signal with the ramped reference signal are performed to increase conversion accuracy, then the analog-to-digital conversion precision is improved, but the conversion time increases resulting in low frame rate
Solution Approach 1:
The patent divides the analog-to-digital conversion process into two distinct stages: a coarse conversion stage that quickly determines the most significant bits, and a fine conversion stage that precisely determines the least significant bits. This segmentation allows the system to achieve high conversion accuracy through multiple comparisons while maintaining high frame rate by performing only one quick coarse comparison and one precise fine comparison, rather than requiring many sequential comparisons.
2Measurement precision
If multiple comparisons are performed to increase conversion accuracy, then the digital data precision is improved, but the time required for conversion increases
Solution Approach 1:
The patent performs a preliminary coarse conversion that quickly establishes the most significant bits of the digital output. This preliminary action provides an initial approximation that narrows down the range for subsequent fine conversion, thereby reducing the total time required to achieve high precision digital data while maintaining accurate conversion results.
3Productivity
If a single ramped reference signal is used for conversion, then the conversion process is simple and fast, but the conversion accuracy is limited
Solution Approach 1:
The patent dynamically switches between two different reference signal modes: a first ramped reference signal for coarse conversion and a second ramped reference signal for fine conversion. This dynamic adaptation allows the system to maintain high conversion speed through the efficient coarse stage while achieving high accuracy through the precise fine stage, optimizing both speed and accuracy throughout the conversion process.
Data Source
AI summary
A system and method is disclosed for an imaging device and/or an analog to digital converter which converts an analog input signal to a digital data signal using a comparator which compares the analog input signal to a first ramped reference signal to determine an operating point and then uses the same comparator to compare the analog input signal to a second ramped reference signal multiple times about the determined operating point.