CMOS Image Sensor Pixel Noise Suppression Circuit

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Solution Overview

Problem

Miniaturization of CMOS image sensors leads to increased pixel power supply noise, which affects signal-to-noise ratio and image quality, as existing noise suppression methods like Low Dropout Regulators (LDOs) are inefficient and consume significant power, limiting the performance of image sensor chips.

Innovation Solution

A power supply noise suppression circuit that uses a mirror power supply noise circuit and a gain amplifier to cancel out noise interference at the source follower transistor, effectively reducing image noise by matching and amplifying the noise signal to counteract power supply noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If LDO is used to reduce power supply noise impact, then power supply noise is reduced, but layout area increases, power consumption increases, and power supply voltage stability slows down

Engineering Contradiction:

Improvepower supply noiseVSAvoidlayout area

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The invention extracts and separates the noise suppression function from the main pixel circuit by introducing a dedicated noise suppression circuit that mirrors the power supply noise. This extracted noise component is then subtracted from the pixel output signal, achieving noise reduction without requiring a large LDO circuit in the pixel layout.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces an intermediary noise suppression circuit that acts as a mediator between the power supply noise source and the pixel output. This circuit mirrors the power supply noise and subtracts it from the pixel signal, serving as an intermediate step to eliminate noise without directly modifying the power supply or pixel structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If LDO is used to reduce power supply noise impact, then power supply noise is reduced, but power consumption increases

Engineering Contradiction:

Improvepower supply noiseVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If LDO is used to reduce power supply noise impact, then power supply noise is reduced, but power supply voltage stability speed decreases

Engineering Contradiction:

Improvepower supply noiseVSAvoidpower supply voltage stability speed

Core Design Contradiction:

Object-affected harmful factorsVSSpeed

Solution Approach 1:

The invention performs preliminary action by proactively mirroring the power supply noise in advance and making it available for subtraction from the pixel output signal. This preliminary preparation of the noise component allows for immediate noise cancellation without waiting for LDO stabilization, thus maintaining fast response speed while reducing noise.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Inventive Principle:

Principle #24Intermediary (Mediator)

4Quantity of substance

If pixel array is miniaturized to increase pixel count, then pixel density increases, but pixel power supply noise increases

Engineering Contradiction:

Improvepixel countVSAvoidpixel power supply noise

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The invention segments the noise suppression function from the main pixel circuitry by introducing a separate noise suppression circuit. This segmentation allows each miniaturized pixel to use a simplified circuit structure while the dedicated noise suppression circuit handles the noise cancellation, enabling high pixel density without proportionally increasing noise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11381765B2CMOS image sensor with pixel power supply noise suppression circuit

Publication Date: 2022.07.05 SMARTSENS TECH (HK) CO LTD

AI summary

An image sensor pixel noise suppression circuit having a source follower transistor based pixel circuit, a power supply voltage and noise mirror circuit, a power supply voltage and noise gain circuit, and a comparator circuit. An output of the comparator circuit provides an image related output signal wherein the noise component of the source follower signal has been suppressed. The invention further includes a CMOS image sensor containing the image sensor pixel noise suppression circuit.