Stage Circuit Leakage Current Reduction in OLED Displays

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Solution Overview

Problem

Existing OLED display devices face challenges in reliability due to incomplete transistor turn-off in stage circuits, leading to leakage current and instability in voltage control, which affects the driving efficiency and accuracy of scan signals.

Innovation Solution

A stage circuit design incorporating N-type transistors with specific power source configurations and transistor architectures, including a controller to ensure complete turn-off of transistors during carry signal supply, reduces leakage current and stabilizes voltage, enhancing the reliability of OLED display device driving.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional stage circuits are used in OLED display devices, then the device can operate with basic functionality, but leakage current occurs due to incomplete transistor turn-off, reducing reliability

Engineering Contradiction:

Improvereliability of drivingVSAvoidleakage current

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The stage circuit is divided into multiple independent driver blocks (first driver, second driver, third driver) that can be individually controlled. Each driver manages specific transistor groups, allowing selective turn-off of transistors to minimize leakage current while maintaining necessary circuit functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The controller pre-charges specific nodes (such as node N3) to appropriate voltage levels before the carry signal is output. This preliminary voltage setting ensures that transistors are in the correct state for complete turn-off, preventing leakage current from affecting the carry signal integrity.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If transistors are turned off to reduce leakage current, then reliability improves, but voltage control stability may be affected

Engineering Contradiction:

Improvetransistor turn-off completenessVSAvoidvoltage control stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

Capacitors are introduced as intermediary elements to store charge and maintain voltage levels at critical nodes. These capacitors act as buffers that stabilize voltage during transistor switching transitions, ensuring stable voltage control even when transistors are turned off to reduce leakage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The controller monitors the states of various nodes and transistors, dynamically adjusting control signals to maintain proper voltage levels. This feedback mechanism ensures that voltage stability is maintained while achieving complete transistor turn-off for leakage reduction.

Inventive Principle:

Principle #23Feedback

3Stability of the object's composition

If multiple power sources are used to control transistor states, then voltage stability improves, but circuit complexity increases

Engineering Contradiction:

Improvevoltage stabilityVSAvoidpower source configuration

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

Multiple power sources (first power source, second power source, third power source) are designed to serve multiple functions simultaneously. Each power source not only provides voltage levels for transistor control but also contributes to node charging, leakage prevention, and signal level stabilization, reducing the need for additional dedicated components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Object-generated harmful factors

If N-type transistors are used for complete turn-off, then leakage current is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

Improveleakage current reductionVSAvoidtransistor fabrication accuracy

Core Design Contradiction:

Object-generated harmful factorsVSManufacturing precision

Solution Approach 1:

The invention optimizes transistor parameters such as channel length and width ratios, threshold voltages, and gate oxide thickness to enhance the turn-off characteristics of N-type transistors. By carefully selecting and adjusting these parameters, the circuit achieves complete transistor turn-off with reduced leakage current while maintaining feasibility within standard manufacturing tolerances.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9830856B2Stage circuit including a controller, drivers, and output units and scan driver using the same

Publication Date: 2017.11.28 SAMSUNG DISPLAY CO LTD

AI summary

A stage circuit includes a first driver, a second driver, a first output unit, a second output unit and a controller. The first driver controls voltages of first and second nodes, according to a first power source, a third power source, a start signal or a carry signal of a previous stage input to a first input terminal, and a clock signal supplied to a second input terminal. The second driver controls voltages of third and fourth nodes, according to voltages of the first power source, the third power source, the first input terminal and the first and second nodes. The first output unit outputs a carry signal to a first output terminal, according to voltages of the first power source, the second input terminal and the third and fourth nodes. The second output unit outputs a scan signal to a second output terminal, according to voltages of the second power source, the second input terminal and the third and fourth nodes. The controller is electrically coupled to the first output terminal and the second driver.