Digital Pixel Circuit for Organic EL Brightness Consistency

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Solution Overview

Problem

Existing organic EL devices face issues with variations in current-voltage characteristics and threshold voltage of driving transistors, leading to inconsistencies in pixel brightness and gray scale deviation, which degrade image quality and require increased power consumption for analog driving methods.

Innovation Solution

The implementation of a digital driving method using a pixel circuit with a memory circuit including a first and second inverter, where the light emitting element is driven based on two values for emission and non-emission states, and the use of a scan line drive circuit to manage selection and maintain signals for efficient pixel control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If analog driving method is used to control current through driving transistor, then gray scale display is achieved, but variation in transistor characteristics leads to brightness inconsistency and gray scale deviation

Engineering Contradiction:

Improvebrightness consistencyVSAvoidtransistor characteristic variation

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The patent replaces the analog voltage control mechanism with a digital control mechanism using a memory circuit. Instead of relying on continuous voltage adjustment through the driving transistor gate, the invention uses a memory circuit (first and second inverters) to store digital signal states that directly control the light emitting element, eliminating the influence of transistor characteristic variations on brightness consistency.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the control parameter from analog voltage (continuous) to digital signal states (discrete). By using a memory circuit to store binary states representing different gray levels, the system transforms the continuous brightness control into discrete state control, making the display immune to transistor parameter variations.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If digital driving method with memory circuit is implemented, then transistor variation impact is reduced, but circuit complexity increases

Engineering Contradiction:

Improvebrightness consistencyVSAvoidpixel circuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the pixel circuit into distinct functional blocks: a memory circuit portion (first inverter, second inverter) and a light emitting element portion. This segmentation allows the memory circuit to independently store signal states without affecting the light emitting element structure, managing complexity through functional separation while achieving reliable digital control.

Inventive Principle:

Principle #1Segmentation

3Area of stationary object

If analog driving with capacitive element is used, then signal storage is achieved, but large capacitive elements increase pixel area

Engineering Contradiction:

Improvepixel areaVSAvoidsignal storage capability

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent replaces the physical capacitive storage mechanism with a digital memory circuit consisting of inverters. Instead of using large capacitors to hold analog voltage levels, the invention uses the bistable states of the inverter memory circuit to store digital signal representations of gray levels, dramatically reducing the area required for signal storage within each pixel.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Productivity

If scan line drive circuit outputs selection and non-maintain signals during identical period, then pixel control efficiency is improved, but signal timing coordination becomes challenging

Engineering Contradiction:

Improvepixel control efficiencyVSAvoidsignal timing coordination

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent implements feedback mechanisms in the scan line drive circuit to coordinate signal timing. The circuit monitors the output signals and adjusts the timing of selection and non-maintain signals to ensure they are properly synchronized, even when output during identical periods. This feedback control prevents timing conflicts and ensures efficient pixel control without signal interference.

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 reduces the impact of transistor variations on pixel brightness and gray scale accuracy, eliminates the need for large capacitive elements, and allows for higher resolution and lower power consumption, enabling high-quality image display with reduced power usage.

Implementation Method 1

an organic EL device including an organic EL element that is a light emitting element

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS10861390B2Electro-optical device, electronic device, and electronic apparatus

Publication Date: 2020.12.08 SEIKO EPSON CORP

AI summary

An electro-optical device includes a first scan line, a second scan line, a data line, a pixel circuit located at a position corresponding to an intersection of the data line and each of the first scan line and the second scan line, and a scan line drive circuit supplying one of a selection signal and a non-selection signal to the first scan line and supplying one of a maintain signal and a non-maintain signal to the second scan line. The scan line drive circuit is capable of output the selection signal and the non-maintain signal during an identical period.