Image Sensor Comparator with Dual Ramp ADC Switching
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in reducing data conversion time and power consumption, leading to increased power consumption and noise due to the difficulty in minimizing the number of counts required for data conversion.
Innovation Solution
A CMOS image sensor design that selects either an upper or lower ramp signal based on the magnitude of a pixel signal compared to a reference voltage, reducing data conversion time and the number of counts needed, thereby enhancing data processing speed and minimizing power consumption and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional analog-to-digital conversion method is used, then data conversion is performed, but data conversion time is increased and power consumption is increased
Solution Approach 1:
The patent divides the analog-to-digital conversion process into two segments: a first comparison operation using a first ramp signal to determine a coarse value, and a second comparison operation using a second ramp signal to determine a fine value. This segmentation allows the conversion to be performed in stages, reducing the total time and power consumption compared to a single lengthy conversion process.
Solution Approach 2:
The patent performs a preliminary comparison operation using the first ramp signal before the final comparison operation. This preliminary action establishes a baseline or coarse value that guides the subsequent fine comparison, thereby reducing the overall conversion time and power consumption by avoiding a single lengthy conversion process.
2Measurement precision
If conventional analog-to-digital conversion method is used, then data conversion is performed, but the number of counts is increased and noise is increased
Solution Approach 1:
The patent segments the conversion process into coarse and fine comparison stages. The coarse stage using the first ramp signal quickly establishes a baseline value, while the fine stage using the second ramp signal refines the measurement. This segmentation reduces the total number of counts required compared to a single high-precision conversion, thereby reducing counting noise.
Solution Approach 2:
The first ramp signal and first comparison operation act as an intermediary step between the input analog signal and the final digital output. This intermediary coarse comparison reduces the range of values that the second comparison must resolve, thereby reducing the total count number and associated noise while maintaining overall precision.
Data Source
AI summary
A comparison device includes a comparison block suitable for comparing an upper ramp signal or a lower ramp signal with a pixel signal, and outputting a comparison signal; a CDS block provided between a first input terminal into which the pixel signal is inputted and a negative input terminal of the comparison block, and configured to perform correlated double sampling; a second switch provided between a second input terminal into which the lower ramp signal is inputted and a positive input terminal of the comparison block; a third switch provided between a third input terminal into which the upper ramp signal is inputted and the positive input terminal of the comparison block; and a feedback control unit suitable for checking a magnitude of the pixel signal according the comparison signal and outputting a second control signal or a third control signal for controlling the second or third switch.