Pixel Circuit Transistor Configuration for OLED Uniformity

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Solution Overview

Problem

Existing active matrix organic EL display devices face challenges in achieving uniformity due to variations in threshold voltage and mobility of thin-film transistors, requiring additional transistors for correction functions, which increases the complexity and layout area of the power supply scanner, affecting reliability and screen size.

Innovation Solution

Incorporating a P-channel type drive transistor and a switching transistor into each pixel circuit, eliminating the need for a power supply scanner by fixing the power supply voltage and using a switching transistor for line-sequential driving, reducing the number of transistors and buffer size, and improving reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If additional transistors are added to each pixel circuit for threshold voltage and mobility correction, then uniformity is improved, but device complexity and layout area increase

Engineering Contradiction:

ImproveuniformityVSAvoidnumber of transistors

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The switching transistor is designed to perform multiple functions: it acts as a correction transistor for mobility compensation during the correction period, and as a driving transistor during the emission period. This multi-functionality eliminates the need for separate correction transistors, reducing the total number of transistors in the pixel circuit while maintaining uniformity correction capability

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The switching transistor dynamically changes its function based on the operating period. During the correction period, it enables correction current flow for mobility compensation. During the emission period, it serves as the driving transistor for light emission. This dynamic role switching allows one transistor to replace multiple static components

Inventive Principle:

Principle #15Dynamics

2Manufacturing precision

If a power supply scanner is used to supply variable power supply voltage for correction, then mobility correction is achieved, but the layout area and complexity of the driving unit increase

Engineering Contradiction:

Improvemobility correctionVSAvoidlayout area of driving unit

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

The patent extracts and eliminates the power supply scanner component from the display device. Instead of using a dedicated power supply scanner to provide variable power supply voltage for mobility correction, the invention uses a fixed power supply voltage combined with a switching transistor that can be controlled to achieve the same mobility correction effect, thereby removing the need for the power supply scanner and its associated layout area

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The switching transistor acts as an intermediary component that replaces the need for variable power supply voltage. By controlling the switching transistor's on/off state and using it in conjunction with the fixed power supply voltage, the system achieves mobility correction without requiring a power supply scanner to generate variable voltage

Inventive Principle:

Principle #24Intermediary (Mediator)

3Area of stationary object

If the number of transistors in each pixel circuit is reduced, then layout area for pixel array increases, but uniformity correction capability may be compromised

Engineering Contradiction:

Improvelayout area for pixel arrayVSAvoiduniformity correction

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The display device operates with periodic timing control, dividing operation into correction periods and emission periods. During correction periods, the switching transistor enables mobility compensation current flow. During emission periods, it serves as the driving transistor. This periodic role switching allows one transistor to provide both correction and driving functions

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS8988320B2Display device, driving method thereof, and electronic device

Publication Date: 2015.03.24 MAGNOLIA BLUE CORP

AI summary

Disclosed herein is a display device including: a pixel array unit; and a driving unit; wherein said pixel array unit includes first scanning lines and second scanning lines in a form of rows, signal lines in a form of columns, and pixels in a form of a matrix, each pixel includes a drive transistor, a sampling transistor, a switching transistor, a retaining capacitance, and a light emitting element, said driving unit includes a write scanner for sequentially supplying a control signal to each first scanning line, a drive scanner for sequentially supplying a control signal to each second scanning line, and a signal selector for alternately supplying a signal potential as a video signal and a predetermined reference potential to each signal line.