Pixel Circuit Classification for Overcompensation Prevention in OLED Displays

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Solution Overview

Problem

Organic electroluminescent display devices face luminance reduction due to deteriorating drive transistor characteristics, leading to overcorrection of video signals when display is restarted, resulting in an overcompensated image.

Innovation Solution

A display device with a classification system for pixel circuits, where specific and general pixel circuits are distinguished, and a recovery ratio is calculated based on current measurements to correct video signals, ensuring suitable compensation upon restart.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If external compensation is performed based on currents measured before display stop, then drive transistor characteristic deterioration is compensated, but drive transistor characteristics recover during stop causing overcorrection and overcompensated image

Engineering Contradiction:

Improvecompensation accuracyVSAvoidcurrent measurement timing

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent measures currents for specific pixel circuits before display stops so that compensation can be performed based on the most recent characteristic state. This preliminary measurement ensures that the compensation is accurate when display restarts, avoiding overcorrection that would occur if measurements were taken much earlier.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where compensation values are calculated based on measured currents and then applied to correct video signals. The system continuously monitors and adjusts compensation based on actual drive transistor characteristics, creating a closed-loop control that adapts to characteristic changes and recovery.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If real-time monitoring measures currents for all pixel circuits, then accurate compensation is achieved, but measurement time exceeds one frame period causing display restart delay

Engineering Contradiction:

Improvecurrent measurement completenessVSAvoiddisplay restart speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent divides pixel circuits into two groups: specific pixel circuits (measured before display stop) and other pixel circuits (measured after restart). This segmentation allows the system to prioritize measurement of critical circuits while reducing overall measurement time, enabling display restart within one frame period.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs partial measurement by measuring currents for only specific pixel circuits before display stops, rather than measuring all pixel circuits. This partial action is sufficient to achieve accurate compensation for the most critical circuits while maintaining fast restart capability.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS11430387B2Display device and driving method therefor

Publication Date: 2022.08.30 SHARP KK

AI summary

In a display device that performs external compensation, pixel circuits are classified into specific and general pixel circuits. When display is restarted, a current measurement circuit, along with a drive circuit, measures a current flowing through a drive transistor in the specific pixel circuit as a first current. A correction circuit obtains a recovery ratio for a characteristic of the drive transistor on the basis of an amount of the first current and corrects a video signal for each of the specific and general pixel circuits using the recovery ratio. Thus, when display is restarted, a suitably compensated image is displayed.