OLED Pixel Circuit Bias Writing for Threshold Drift Control
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Solution Overview
Problem
The threshold voltage drifting of the driving transistor in OLED display panels affects display uniformity due to prolonged operation in a forward bias state.
Innovation Solution
A display panel design that includes a data writing transistor to write a bias voltage to the driving transistor in a writing frame, adjusting its bias state and reducing space occupancy, thereby improving display uniformity and meeting high PPI wiring requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate transistor is added to write bias voltage to the driving transistor, then display uniformity is improved, but pixel circuit area increases
Solution Approach 1:
The data writing transistor is designed to perform multiple functions: writing data voltage to the driving transistor during the data writing stage, and writing bias voltage to the first electrode of the driving transistor during the bias stage. This multi-functionality eliminates the need for a separate transistor dedicated solely to bias writing, thereby reducing pixel circuit area while maintaining display uniformity
Solution Approach 2:
The patent merges the data writing function and bias writing function into a single data writing transistor. By combining these two functions that were previously performed by separate transistors, the pixel circuit area is reduced while still achieving the goal of improving display uniformity through proper bias voltage application
2Duration of action of stationary object
If the driving transistor operates in forward bias state for long time, then continuous operation is maintained, but threshold voltage drift occurs affecting display uniformity
Solution Approach 1:
The patent implements periodic bias stage operations within the writing frame to periodically adjust the bias state of the driving transistor. This periodic action prevents continuous forward bias operation, thereby reducing threshold voltage drift and maintaining display uniformity over extended operation periods
Solution Approach 2:
The bias stage is introduced as a preliminary action before the light emitting stage to pre-adjust the bias state of the driving transistor. This preliminary adjustment prevents threshold voltage drift from accumulating during continuous operation, thereby maintaining display uniformity
3Area of stationary object
If pixel circuit area is reduced to meet high PPI requirements, then wiring density increases, but circuit design complexity increases
Solution Approach 1:
By designing the data writing transistor to perform both data writing and bias writing functions, the patent reduces the total transistor count in the pixel circuit. This reduction in component count simplifies the overall circuit design while still meeting the area requirements for high PPI displays
Solution Approach 2:
The patent employs dynamic control of the data writing transistor through different scanning signals (first scanning signal for data writing stage, second scanning signal for bias stage). This dynamic operation allows a single transistor to perform multiple functions at different time periods, reducing circuit complexity while achieving compact pixel design
Data Source
AI summary
Provided are a display panel and a display apparatus. The display panel includes a plurality of pixel circuits and a plurality of light-emitting devices, wherein the pixel circuits are electrically connected to the light-emitting devices, each pixel circuit includes a driving transistor and a data writing transistor, the driving transistor is configured to generate a driving current, and the data writing transistor is electrically connected to a first electrode of the driving transistor; an operation of the pixel circuit includes a data writing stage and a bias stage; and the display panel further includes a writing frame, and in the writing frame: the data writing transistor is turned on in the data writing stage to write a data voltage to the driving transistor; and the data writing transistor is turned on in the bias stage to write a first bias voltage to the first electrode of the driving transistor.