Dual Comparator Circuit for Image Sensor Linearity and Power
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Solution Overview
Problem
Existing image sensor comparator circuits face challenges with low power consumption and limited dynamic range due to nonlinear output signals when the required voltage is not maintained, limiting their performance in advanced applications.
Innovation Solution
The implementation of a dual comparator circuit structure, comprising NIN and PIN comparators, with differential inputs and current mirror circuits, along with auxiliary comparator circuits to selectively activate each comparator based on pixel signal levels, extending the input range and improving linearity without increasing power supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a certain amount of voltage is maintained to ensure adequate impedance for accurate current source, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The comparator circuit is divided into two separate comparators: a first comparator for comparing the pixel signal with a first reference voltage, and a second comparator for comparing the pixel signal with a second reference voltage. This segmentation allows each comparator to operate within optimized voltage ranges, improving measurement precision across the full dynamic range while maintaining lower overall power consumption through selective activation.
Solution Approach 2:
The patent implements dynamic selection between different comparator configurations based on the pixel signal level. An auxiliary comparator dynamically determines which main comparator to activate, allowing the system to adapt its operating state according to the input signal characteristics. This dynamic operation ensures optimal measurement precision for each signal range while minimizing power consumption by activating only the necessary comparator.
2Use of energy by moving object
If the required voltage is not maintained, then use of energy is reduced, but measurement precision deteriorates due to nonlinear output signals
Solution Approach 1:
The patent changes the reference voltage parameter dynamically by selecting between a first reference voltage and a second reference voltage based on the pixel signal level. This parameter change allows the comparator to maintain accurate and linear output signals across different input ranges without requiring a constantly high voltage supply, thereby reducing power consumption while preserving measurement precision.
Solution Approach 2:
The auxiliary comparator acts as an intermediary that monitors the pixel signal level and controls the activation of the main comparators. This intermediary component enables the system to switch between different operating modes, ensuring that measurement precision is maintained through appropriate comparator selection while minimizing power consumption by keeping comparators in a low-power state when not actively needed.
3Device complexity
If a single comparator circuit is used, then device complexity is reduced, but measurement precision is limited due to low dynamic range
Solution Approach 1:
The comparator system is segmented into multiple specialized comparators, each optimized for specific reference voltage levels. This segmentation extends the overall dynamic range of the measurement system, allowing accurate measurements across a wider range of input signals. The modular segmented structure manages complexity through functional specialization rather than requiring a single overly complex comparator design.
Solution Approach 2:
The multiple comparators work together as a universal measurement system that can handle various pixel signal levels through selective activation. Each comparator serves multiple functions: signal comparison, reference voltage selection, and dynamic range extension. This multi-functionality approach achieves extended dynamic range and improved measurement precision while managing system complexity through coordinated operation of standardized comparator units.
Data Source
AI summary
A comparator circuit of an image sensor that is configured to compare a pixel signal and a ramp signal is introduced. The comparator circuit includes a first comparator circuit and a second comparator circuit. The first comparator circuit includes differential inputs that receive the pixel signal and the ramp signal, respectively. The second comparator circuit includes differential inputs that receive the pixel signal and the ramp signal, respectively. The second comparator circuit is activated when a level of the pixel signal is smaller than a first threshold value, the first comparator circuit is activated when the level of the pixel signal is greater than a second threshold value, and the first threshold value is greater than the second threshold value.