Dynamic Bias Current for CMOS Image Sensor Comparators
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Solution Overview
Problem
CMOS image sensors face challenges in reducing power consumption while maintaining image quality, particularly due to the trade-off between bias current and noise levels, where constant bias current schemes lead to excessive power usage and noise variations with signal strength.
Innovation Solution
Implementing a dynamic bias current profile for column ramp comparators in CMOS image sensors, which adjusts bias current over time to maintain a consistent noise margin across varying signal levels, reducing power consumption without compromising image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If constant bias current is used in column ramp comparators, then noise margin is maintained, but power consumption increases
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant bias current scheme to a dynamic bias current scheme. The bias current is adjusted over time based on the integration phase and signal characteristics, allowing the system to maintain adequate noise margin during critical operations while reducing power consumption during less demanding periods. This is achieved through time-varying bias current profiles that adapt to different operational phases of the image sensor.
Solution Approach 2:
The patent changes the bias current parameter from a fixed constant value to a dynamically adjustable parameter. By modifying the bias current level based on operational requirements and signal strength, the system optimizes the trade-off between noise margin and power consumption. Different bias current levels are applied during different phases of operation to achieve both reliability and energy efficiency.
2Use of energy by moving object
If bias current is reduced to lower power consumption, then power consumption decreases, but noise margin becomes inconsistent with signal strength
Solution Approach 1:
The patent implements feedback mechanisms that monitor signal characteristics and adjust the bias current accordingly. This feedback loop ensures that the bias current is optimized based on actual signal conditions, maintaining consistent noise margin across varying signal strengths while minimizing power consumption. The system responds to changing operational requirements by dynamically adjusting the bias current level.
Solution Approach 2:
The dynamic bias current scheme adapts to varying signal conditions by continuously adjusting the bias current level. This dynamic adjustment ensures that the noise margin remains consistent across different signal strengths, preventing the inconsistency that would occur with simple bias current reduction. The system transitions from static to dynamic operation to maintain performance while reducing power consumption.
3Measurement precision
If miniaturization and integration are increased to meet higher resolution demands, then resolution improves, but power consumption management becomes more challenging
Solution Approach 1:
The patent applies local quality by implementing selective bias current adjustment in different regions or phases of the image sensor operation. Rather than uniformly reducing bias current across the entire system, the invention applies optimized bias current profiles to specific column ramp comparators based on their operational requirements. This localized approach maintains resolution performance while managing power consumption effectively in the miniaturized, high-resolution sensor architecture.
Data Source
AI summary
Embodiments of an image sensor including a pixel array with a plurality of pixels arranged into rows and columns. Control circuitry coupled to the pixels in each row, and an analog-to-digital converter is coupled to the pixels in each column of the pixel array. Each analog-to-digital converter includes a ramp comparator, and a variable current source coupled to the ramp comparator to provide a variable bias current to the ramp comparator. The bias current can adjusted during reading of a row of pixels according to a dynamic bias current profile that maintains at least a specified margin between the random noise of the pixels and an acceptable noise level. Other embodiments are disclosed and claimed.