SAR ADC Shared Tracking Voltage Generator for CMOS Image Sensors
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Solution Overview
Problem
The application of SAR analog-to-digital converters in CMOS image sensors with numerous column lines is hindered by the need for separate digital-to-analog converters for each column line, leading to increased power consumption, switching noise, and circuit complexity.
Innovation Solution
A SAR analog-to-digital converter that uses a single tracking voltage generator and two comparators to perform N-bit data conversion by repeatedly comparing and modulating the input signal across operating phases, reducing the need for independent digital-to-analog converters and simplifying the circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate digital-to-analog converter (DAC) is employed for each column line of the CIS, then the SAR analog-to-digital converter can achieve higher resolution and shorter converting times, but the power consumption, switching noise, and circuit complexity increase significantly
Solution Approach 1:
The patent implements a shared tracking voltage generator that serves multiple column lines simultaneously. Instead of dedicating separate DACs to each column, a single tracking voltage generator is time-multiplexed across multiple columns, allowing one component to perform multiple functions and serve multiple purposes, thereby reducing overall circuit complexity while maintaining conversion performance
Solution Approach 2:
The patent combines multiple DAC functions into a single integrated tracking voltage generator. By merging the voltage generation functionality that would otherwise be distributed across multiple separate DACs into one shared component, the design reduces the total number of devices while maintaining the necessary conversion capabilities across all column lines
2Productivity
If a separate digital-to-analog converter (DAC) is employed for each column line of the CIS, then the SAR analog-to-digital converter can achieve shorter converting times, but the power consumption increases
Solution Approach 1:
The shared tracking voltage generator is designed to be time-multiplexed across multiple column lines, allowing a single power-consuming component to serve multiple functions. By universally utilizing one generator for multiple columns through time-division multiplexing, the overall power consumption is reduced compared to having dedicated generators for each column, while maintaining the fast conversion capability
3Measurement precision
If a separate digital-to-analog converter (DAC) is employed for each column line of the CIS, then the SAR analog-to-digital converter can achieve higher resolution, but the size of peripheral circuits increases
Solution Approach 1:
The tracking voltage generator is designed as a universal component that can be shared across multiple column lines through time-multiplexing. This single component replaces what would otherwise require multiple separate DAC circuits, dramatically reducing the peripheral circuit area while maintaining the high-resolution conversion capability across all columns
Solution Approach 2:
The patent merges multiple distributed DAC functions into one centralized tracking voltage generator, combining what would be spatially distributed components into a single location. This consolidation reduces the total area occupied by peripheral circuits while preserving the resolution performance through shared resource utilization
Data Source
AI summary
A complementary metal oxide semiconductor (CMOS) image sensor includes a pixel array suitable for outputting a pixel signal corresponding to incident light; a row decoder suitable for selecting and controlling pixels in the pixel array by row lines; a tracking voltage generator suitable for generating a tracking voltage; a plurality of successive approximation register (SAR) analog-to-digital converters suitable for analog-to-digital converting a pixel signal by repeatedly performing N times (where N is a natural number representing desired resolution) a process of comparing the pixel signal generated by the pixel array with the tracking voltage generated by the tracking voltage generator and modulating the pixel signal; and a control unit suitable for controlling operations of the row decoder, the tracking voltage generator, and the plurality of SAR analog-to-digital converters.