CMOS Detection Cells Correct Dark Current Errors

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Solution Overview

Problem

Semiconductor imaging devices suffer from dark current errors due to substrate and optical leakage, which cause inaccuracies in image signals by aggregating dark charge, leading to vertical shading in images captured by CMOS image pixel cells.

Innovation Solution

A system and method involving a CMOS imaging device with detection cells that accumulate dark charge without photocharge, allowing for the generation of dark charge signals to correct image signals by subtracting dark charge components, thereby mitigating the effects of dark current errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If detection cells accumulate dark charge without photocharge to generate correction signals, then dark current error correction is achieved, but device complexity increases due to additional cell structures and signal processing circuits

Engineering Contradiction:

Improveimage signal accuracyVSAvoidpixel cell array structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The pixel cell array is segmented into two functional types: image pixel cells that accumulate both photocharge and dark charge, and detection cells that accumulate only dark charge. This segmentation allows separate measurement of the desired signal (photocharge) and the error component (dark charge), enabling correction while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Detection cells serve as intermediary elements that measure dark charge independently. By introducing these specialized detection cells as mediators between the light source and the image pixel cells, the system can obtain dark charge measurements without interfering with the primary image capture function, thus correcting errors without substantially increasing complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If dark charge is accumulated in floating diffusion regions during integration, then dark current error occurs, but integration time must be extended to capture sufficient light signal

Engineering Contradiction:

Improvelight signal accumulationVSAvoiddark charge aggregation

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The system implements feedback by using detection cells to continuously measure dark charge levels and feeding this information back to correct image pixel cell readings. This feedback mechanism allows the system to compensate for dark charge accumulation in real-time, enabling longer integration times without proportionally increasing dark current errors.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The invention converts the harmful effect of dark charge accumulation into a useful measurement signal. By designing detection cells that deliberately accumulate dark charge, the system transforms this previously problematic phenomenon into a valuable source of correction data that improves overall image signal accuracy.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If substrate leakage and optical leakage are present, then dark charge is generated continuously, but longer exposure times are needed to improve signal-to-noise ratio

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidsignal accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The system performs preliminary measurement of dark charge using detection cells before final image signal readout. By measuring and correcting for dark charge components in advance, the system can extend exposure times to improve signal-to-noise ratio without allowing dark charge to compromise the final measurement accuracy.

Inventive Principle:

Principle #10Preliminary action

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

The solution effectively reduces dark current errors, improving image accuracy by uniformly correcting for dark charge contributions across the image array, reducing vertical shading and enhancing the representation of light detection in images.

Implementation Method 1

photocharge is generated by the photosensor 101 in response to impinging light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

photocharge is generated by the photosensor 101 in response to impinging light and collected in the accumulation region 101A

Methodology Applied

Scientific EffectElectrical charge accumulation: Capacitance

Data Source

PatentUS8130289B2System, method, and apparatus for correction of dark current error in semiconductor imaging devices

Publication Date: 2012.03.06 APTINA IMAGING CORP

AI summary

Detection cells configured to output signals for dark current error correction. Various embodiments of detection cells accumulate dark charge supplied by dark current sources, and output dark charge signals indicating the amount of accumulated dark charge. The dark charge signals may be used to approximate the amount of dark charge read out by pixel cells of an imaging array and/or to offset portions of pixel cell signals attributable to dark charge accumulation.