CMOS Image Sensor Comparator Switch Circuit for CDS

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Solution Overview

Problem

Existing CMOS image sensors face challenges in performing correlated double sampling (CDS) without analog-to-digital conversion of the reset signal, which limits their efficiency and speed in image processing.

Innovation Solution

The implementation of a comparator with a switch circuit that compares reset and image signals with a ramp signal, allowing for separate phases of operation and control signals to manage switch arrangements, enabling CDS without converting the reset signal into a digital format, thus facilitating high-speed operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If a single-slope analog-to-digital conversion method is used, then area of layout and power consumption are reduced, but the ability to perform CDS without analog-to-digital conversion of reset signal is limited

Engineering Contradiction:

Improvearea of layoutVSAvoidability to perform CDS without ADC of reset signal

Core Design Contradiction:

Area of stationary objectVSAdaptability or versatility

Solution Approach 1:

The conversion process is segmented into distinct phases: a reset phase where the reset signal is compared with the ramp signal to generate a first comparison signal, and an image phase where the image signal is compared with the ramp signal to generate a second comparison signal. This segmentation allows CDS to be performed using only the comparison circuits without requiring ADC conversion of the reset signal, thereby maintaining area efficiency while enabling the desired functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The switch circuit dynamically changes its connection configuration between the reset phase and the image phase. During the reset phase, the switch circuit connects the reset signal to the comparator; during the image phase, it connects the image signal to the comparator. This dynamic reconfiguration enables the same hardware to perform different functions at different times, achieving CDS capability without additional ADC circuitry for the reset signal.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If the comparator transitions between reset phase and image phase, then CDS operation is enabled, but control complexity increases

Engineering Contradiction:

ImproveCDS operation capabilityVSAvoidcontrol complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The comparator operates in periodic alternating phases between the reset phase and the image phase. A control circuit generates periodic control signals that systematically switch the comparator between these two phases. This periodic operation simplifies the control logic compared to arbitrary phase switching, as the phases follow a regular alternating pattern that can be generated with simple timing circuits.

Inventive Principle:

Principle #19Periodic action

3Speed

If analog-to-digital conversion of reset signal is avoided, then processing speed is enhanced, but conversion accuracy may be affected

Engineering Contradiction:

Improveprocessing speedVSAvoidconversion accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The ramp signal serves as an intermediary reference that mediates the comparison between the reset signal and the image signal. By comparing both signals against this common ramp reference, the system achieves accurate differential measurement (CDS) without requiring separate ADC conversions. The ramp signal acts as a time-based intermediary that preserves signal integrity while enabling high-speed comparison operations.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach allows for efficient correlated double sampling without the need for analog-to-digital conversion of the reset signal, enhancing the speed and efficiency of image processing in CMOS image sensors.

Implementation Method 1

The comparator may be configured to compare the reset signal with the ramp signal and output a first comparison signal through the output terminal according to a first arrangement of the switches in a reset phase and the comparator may be configured to compare the image signal with the ramp signal and output a second comparison signal through the output terminal according to a second arrangement of the switches in an image phase

Methodology Applied

Scientific EffectElectrical signal comparison:

Data Source

PatentUS9509932B2Image sensors, methods of operating the same, and image processing systems including the same

Publication Date: 2016.11.29 SAMSUNG ELECTRONICS CO LTD

AI summary

An image sensor may include a comparator including a first input terminal configured to receive a reset signal, a second input terminal configured to receive an image signal, a third input terminal configured to receive a ramp signal configured to ramp in one direction, and an output terminal. The comparator may further include a switch circuit including a plurality of switches. The comparator may be configured to compare the reset signal with the ramp signal and output a first comparison signal through the output terminal according to a first arrangement of the switches in a reset phase and the comparator may be configured to compare the image signal with the ramp signal and output a second comparison signal through the output terminal according to a second arrangement of the switches in an image phase.