Imaging Device Charge Overflow Detection

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Solution Overview

Problem

Existing imaging devices face challenges in accurately capturing a wide range of light levels due to charge overflow and saturation issues, leading to reduced dynamic range and increased noise in pixel readouts.

Innovation Solution

The implementation of a charge overflow detection mechanism that sets the transfer gate to an intermediate state to overflow charge from the accumulation site to the readout node when the charge level exceeds a threshold, allowing for non-destructive sampling and minimizing the effect on ongoing integration, while using correlated double sampling to correct for charge loss and reduce noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the transfer gate is set to an intermediate state to overflow charge when charge level exceeds a threshold, then charge overflow and saturation issues are reduced, but device complexity increases

Engineering Contradiction:

Improvedynamic rangeVSAvoidcomplexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs preliminary non-destructive sampling of the charge level at the readout node before the integration period ends. This preliminary action allows the system to detect charge levels and select appropriate integration periods in advance, preventing saturation while maintaining simple pixel structures without requiring complex real-time intervention circuits.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses the readout node as an intermediary element to temporarily hold and sample charge from the accumulation site without permanently removing it. This intermediary approach enables non-destructive measurement of charge levels, allowing the system to detect when charge exceeds thresholds and adjust integration periods accordingly, thereby extending dynamic range without adding complex control circuits to each pixel.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If charge is overflowed from the accumulation site to the readout node, then charge level detection accuracy is improved, but charge loss increases

Engineering Contradiction:

Improvecharge level detection accuracyVSAvoidcharge loss

Core Design Contradiction:

Measurement precisionVSLoss of substance

Solution Approach 1:

The patent employs correlated double sampling where the readout node itself provides the reference level for comparison. By sampling the readout node voltage at two different times (before and after charge transfer) and using the first sample as a reference for the second, the system achieves accurate charge level measurement without losing charge, as the reference information is preserved and used to compensate for any minor charge loss.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent changes the operational parameters of the readout node by applying different voltages at different times during the sampling process. By controlling the transfer gate voltage and readout node voltage in a coordinated manner, the system enables charge to be transferred for measurement while maintaining the ability to recover and preserve the charge information, thereby achieving accurate detection without permanent charge loss.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If non-destructive sampling is performed, then integration process stability is maintained, but measurement precision may be reduced

Engineering Contradiction:

Improveintegration process stabilityVSAvoidmeasurement precision

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the result of the preliminary non-destructive sampling is used to control subsequent charge transfer operations. The sampled charge level information feeds back to the integration period selection logic, which then determines whether to extend or terminate the integration period. This feedback loop maintains integration stability while achieving high measurement precision through correlated double sampling that compensates for noise and drift.

Inventive Principle:

Principle #23Feedback

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 enables high dynamic range imaging with improved accuracy and reduced noise, allowing for consistent and reliable light level detection across a wide range of light levels without significantly altering the ongoing integration process.

Implementation Method 1

the charge transfer mechanism for a pixel is set to an intermediate state to cause charge to overflow from the light sensing charge accumulation site to the readout node when the sampled light induced charge in the accumulation site of the pixel exceeds a threshold level

Methodology Applied

Scientific EffectCharge overflow:

Implementation Method 2

using correlated double sampling to correct for charge loss and reduce noise

Methodology Applied

Scientific EffectCorrelated double sampling:

Implementation Method 3

a site to accumulate light induced charge during an integration period

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS8144223B2Imaging device

Publication Date: 2012.03.27 HL KLEMOVE CORP

AI summary

The present invention relates to improved imaging devices having high dynamic range and to monitoring and automatic control systems incorporating the improved imaging devices.