GOA Shift Register Pull-Down Circuit Stability

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Solution Overview

Problem

In shift register units of Gate Driver on Array (GOA) display panels, the pull-down TFTs are often in an on state, leading to long-time forward bias, causing threshold voltage shift and reduced on-state current due to defects in the back channel, resulting in stability issues like multi-output or jitter in long-time operation.

Innovation Solution

A shift register unit design with alternating first and second pull-down circuits, controlled by opposing phase control signals, to correct threshold voltage shifts and improve current leakage characteristics of TFTs by alternating their on/off states.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If pull-down TFTs are kept in on state to maintain display panel operation, then the display panel can function continuously, but threshold voltage shift occurs and on-state current decreases due to long-time forward bias

Engineering Contradiction:

Improvecontinuous operation timeVSAvoidthreshold voltage stability

Core Design Contradiction:

Duration of action of stationary objectVSReliability

Solution Approach 1:

The patent implements periodic switching between first and second pull-down circuits using alternating control signals. The first pull-down circuit operates during first time periods while the second pull-down circuit operates during second time periods, creating a periodic action pattern that prevents continuous forward bias on any single TFT, thereby mitigating threshold voltage shift while maintaining continuous display operation

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent divides the pull-down function into two separate pull-down circuits (first pull-down circuit and second pull-down circuit) that operate alternately. This segmentation allows the display panel to maintain continuous operation while distributing the stress on different TFTs, preventing any single TFT from experiencing continuous forward bias and threshold voltage degradation

Inventive Principle:

Principle #1Segmentation

2Reliability

If alternating pull-down circuits are implemented to correct threshold voltage shift, then TFT stability improves, but circuit complexity increases

Engineering Contradiction:

ImproveTFT operation stabilityVSAvoidpull-down circuit structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the alternating operation of first and second pull-down circuits with the existing gate driver structure, where control signals are generated using existing circuit elements. The first and second pull-down circuits share common connections to the display panel and are controlled by phase-shifted versions of the same clock signal, merging the redundancy into a unified system that improves reliability without proportionally increasing complexity

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS10872551B2Shift register unit and control method thereof, gate drive circuit and display device

Publication Date: 2020.12.22 HEFEI BOE OPTOELECTRONIC TECH CO LTD

AI summary

This disclosure provides a shift register unit that includes an input circuit, a reset circuit, an output circuit, a first pull-down control circuit, a second pull-down control circuit, a first pull-down circuit and a second pull-down circuit. This disclosure also provides a control method for the shift register unit, a gate drive circuit, a display substrate and a display device.