Image Sensor Two-Step Single-Slope ADC for Lower-Power Conversion
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Solution Overview
Problem
Existing single-slope ADCs in image sensors require a clock cycle that is a multiple of 2, leading to increased power consumption when capturing high-resolution images, necessitating a 2-step signal converting operation to implement a high-resolution ADC without excessively increasing operation frequency.
Innovation Solution
The image sensor employs a 2-step single slope analog-digital converting method, where a voltage obtained by sampling a coarse ramp signal is stored and used to generate a sampling voltage for a fine ramp signal, simplifying voltage control for the fine conversion operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-slope ADC is used for high-resolution image acquisition, then measurement precision is improved, but power consumption increases due to requiring a clock cycle that is a multiple of 2
Solution Approach 1:
The patent divides the ADC conversion process into two separate steps: a first conversion step and a second conversion step. Each step uses its own capacitor (first capacitor C1, second capacitor C2) and ramp signal (first ramp signal RMS1, second ramp signal RMS2). This segmentation allows the system to achieve high-resolution conversion without requiring a single complex high-frequency clock cycle, thereby reducing power consumption while maintaining measurement precision.
2Productivity
If a 1-step analog-digital converting operation is used, then conversion speed is improved, but power consumption increases
Solution Approach 1:
The conversion process is segmented into two sequential steps, each operating at lower frequency requirements. The first conversion step processes the first ramp signal, and the second conversion step processes the second ramp signal. This segmentation maintains overall conversion speed by dividing the workload while reducing the peak frequency requirements and associated power consumption of a single-step high-speed conversion.
Solution Approach 2:
The first conversion step performs preliminary analog-digital conversion before the second conversion step. The result from the first step is used as input for the second step, allowing the system to progressively build the final high-resolution digital output. This preliminary action approach enables high-resolution conversion without requiring all components to operate at maximum speed simultaneously, thereby reducing power consumption.
3Measurement precision
If operation frequency is increased to achieve high-resolution ADC, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent segments the high-resolution ADC operation into two separate conversion steps, each operating at moderate frequency. The first conversion step uses the first ramp signal and first capacitor, while the second conversion step uses the second ramp signal and second capacitor. This segmentation achieves the cumulative resolution of high-frequency operation without requiring any single component to operate at excessively high frequencies, thereby reducing power consumption while maintaining measurement precision.
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 allows for high-resolution analog-digital converting operations in image sensors while reducing power consumption and shortening conversion time compared to a 1-step analog-digital converting operation.
Implementation Method 1
a first capacitor configured to sample a coarse ramp signal
Implementation Method 2
a second capacitor configured to sample a sum of a voltage of the first capacitor and a fine ramp signal
Implementation Method 3
a comparator configured to generate a comparison signal obtained by comparing a pixel voltage received from a pixel with the voltage of the first capacitor or a voltage of the second capacitor
Data Source
AI summary
An image sensor includes a first capacitor for sampling a coarse ramp signal, a second capacitor for sampling a sum of a voltage of the first capacitor and a fine ramp signal, and a comparator for generating a comparison signal obtained by comparing a pixel voltage received from a pixel with the voltage of the first capacitor or a voltage of the second capacitor. The image sensor further includes a data output unit for outputting bit data corresponding to the pixel, based on the comparison signal.