Per-Column 1-Bit ADC Using Current Comparison for Stable Image Sensing
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Solution Overview
Problem
Conventional analog-to-digital converters in image sensors face performance issues due to power supply variations, noise, and precision challenges, leading to inefficiencies in power consumption and signal conversion.
Innovation Solution
A per column one-bit analog-to-digital converter that utilizes the difference between a reference signal current and a pixel signal current to produce a digital output, eliminating the need for reference voltage, digital-to-analog converters, and precision elements, and employing switched capacitor resistors to adjust resistance dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ramp analog-to-digital converters are used, then conversion function is achieved, but power consumption is high and performance is adversely affected by power supply variations and noise
Solution Approach 1:
The patent extracts and removes the reference voltage source and digital-to-analog converter from the conventional ADC architecture. By eliminating these components that are sensitive to power supply variations and consume significant power, the invention achieves more stable conversion performance with reduced power consumption, directly resolving the technical contradiction between reliability and energy use.
Solution Approach 2:
The patent uses a current mirror circuit to create a copy of the pixel signal current, allowing the ADC to operate with current signals rather than voltage signals. This copying approach eliminates the need for precision voltage references and reduces sensitivity to power supply variations, thereby improving conversion stability while reducing power consumption.
2Measurement precision
If conventional analog-to-digital converters with reference voltage and digital-to-analog converters are used, then precise conversion is achieved, but circuit complexity increases and precision variations occur
Solution Approach 1:
The patent removes the reference voltage source and digital-to-analog converter from the conventional ADC architecture. By eliminating these precision-critical components, the invention reduces circuit complexity and eliminates the precision variations that arise from power supply fluctuations and noise, while maintaining conversion precision through alternative current-based measurement techniques.
Solution Approach 2:
The patent substitutes the voltage-based conversion mechanism with a current-based mechanism. By using current mirrors and transimpedance amplifiers instead of voltage references and DACs, the invention simplifies the circuit architecture while maintaining measurement precision, directly addressing the contradiction between precision and complexity.
3Reliability
If conventional analog-to-digital converters are used, then conversion function is achieved, but noise and precision variations adversely impact performance
Solution Approach 1:
The patent employs current mirror circuits to copy the pixel signal current, creating a precise replica that is insensitive to power supply variations and noise. This copying mechanism eliminates the precision variations affecting conventional voltage-based ADCs, thereby improving performance stability while rejecting harmful noise factors.
Solution Approach 2:
The patent substitutes the voltage-based conversion mechanism with a current-based mechanism. By using transimpedance amplifiers and current mirrors instead of voltage references and comparators, the invention achieves better noise immunity and precision stability, directly resolving the contradiction between reliability and susceptibility to harmful factors.
Data Source
AI summary
A per column one-bit analog-to-digital converter for an image sensor. The analog-to-digital converter utilizes the difference between a reference signal current and a pixel signal current to obtain a digital output representative of the analog pixel signal in an efficient and simple manner. The output of the one-bit analog-to-digital converter is fed to a counter to give a representation of the brightness of the light-to-charge conversion in the associated pixel. The analog-to-digital converter does not use a reference voltage and precision elements and thus, does not suffer from power supply, noise and precision variations.