CMOS Image Sensor Comparator Initialization for Low-Noise Readout
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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 in comparator non-operating states.
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 P-phase variation and column fixed pattern noise increase
Solution Approach 1:
The patent applies preliminary action by initializing the comparator before intermittent operation. The initialization circuit resets the comparator state and clears any accumulated charge or voltage offsets before the comparator enters standby mode. This preliminary initialization prevents P-phase variation and column fixed pattern noise from accumulating during intermittent operation, allowing the comparator to maintain reliability while reducing power consumption during non-active periods.
2Stability of the object's composition
If initialization signals are applied to all comparators, then operating point stability is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the initialization control into two independent parts: a global initialization signal that controls all comparators simultaneously, and a column-specific initialization signal that controls each column's comparator independently. This segmentation allows the system to initialize all comparators when needed while also providing the flexibility to initialize individual columns selectively, reducing the overall control complexity compared to managing each comparator individually.
Solution Approach 2:
The patent applies universality by designing the initialization circuit to serve multiple functions: it can initialize all comparators globally, initialize individual columns selectively, and maintain comparators in a stable state during intermittent operation. The dual-signal initialization system provides a universal solution that handles various operational modes (continuous operation, intermittent operation, column-selective operation) with a single integrated initialization mechanism, avoiding the need for separate control circuits for each mode.
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.