CMOS Image Sensor Readout Circuit for Intermittent Column Noise
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Solution Overview
Problem
CMOS image sensors experience increased P-phase variation and column fixed pattern noise during intermittent column operation, affecting image quality due to initialization failures and AC coupling issues with non-operating comparators.
Innovation Solution
The implementation of a pixel signal readout circuit with comparators that include initializing switches, allowing independent control of initialization signals for each column, and additional switches to manage capacitive coupling, ensuring proper operating points and reducing noise during intermittent operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If comparators are operated intermittently to reduce power consumption, then energy efficiency is improved, but initialization failures and AC coupling issues cause increased P-phase variation and column fixed pattern noise
Solution Approach 1:
The patent applies preliminary action by initializing non-operating comparators before they are needed. Specifically, the initialization circuit proactively sets the operating points of comparators that will not be used in the current frame, ensuring they are properly prepared for future intermittent operation. This prevents initialization failures when these comparators are activated later, resolving the reliability issue while maintaining energy efficiency benefits.
2Use of energy by moving object
If comparators are operated intermittently, then power consumption is reduced, but feed-through and charge injection increase causing degraded image quality
Solution Approach 1:
The patent converts the harmful feed-through and charge injection effects into beneficial outcomes. By intentionally controlling the initialization of non-operating comparators, the circuit uses the inherent charge transfer mechanisms to establish proper operating points rather than allowing uncontrolled charge injection. This transforms what would be harmful noise sources into useful initialization actions, reducing image quality degradation while maintaining power savings.
3Reliability
If all comparators are initialized for each row operation, then initialization reliability is improved, but power consumption increases
Solution Approach 1:
The patent applies local quality by differentiating the initialization treatment between operating and non-operating comparators. Instead of uniformly initializing all comparators, the circuit selectively initializes only the non-operating comparators using a dedicated initialization circuit, while operating comparators follow their normal initialization path. This localized approach ensures reliability for the specific comparators that need it while avoiding unnecessary power consumption from initializing all comparators.
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 configuration reduces P-phase variation and column fixed pattern noise, thereby enhancing image quality by minimizing feed-through and charge injection during intermittent operations.
Implementation Method 1
a photodiode 11 as a photoelectric conversion element, and four transistors as active elements for one photodiode 11. The photodiode 11 photoelectrically converts an incident light into an amount of electric charge (here, it is an electron) corresponding to the amount of the incident light.
Data Source
AI summary
A solid-state imaging device and a camera system are provided. The solid-state imaging device capable of performing an intermittent operation includes a pixel unit and a pixel signal readout unit for reading out a pixel signal from the pixel unit in units of a plurality of pixels for each column. The pixel signal readout circuit includes a plurality of comparators and a plurality of counters whose operations are controlled by outputs of the comparators. Each of the comparators includes an initializing switch for determining an operating point for each column at a start of row operation, and is configured so that an initialization signal to be applied to the initializing switch is controlled independently in parallel only a basic unit of the initialization signal used for a horizontal intermittent operation, and the initializing switch is held in an off-state at a start of non-operating row.