OLED Pixel Control Circuit Compensates Threshold Voltage Variations
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Solution Overview
Problem
Active-matrix OLED display devices suffer from the mura phenomenon due to variations in threshold voltages of transistors and driving voltages of light-emitting diodes over time, affecting image quality.
Innovation Solution
The display device incorporates a control unit that stores and compensates for threshold and driving voltages, allowing the driving transistor to generate a current independent of these voltages, thereby maintaining consistent image quality by interlacing data and scan signals and using a series connection of transistors and light-emitting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional active-matrix OLED display devices are used, then the display device can be manufactured with simple process and low cost, but threshold voltages of TFTs and driving voltages of OLEDs vary over time causing mura phenomenon
Solution Approach 1:
The patent implements feedback by measuring the actual threshold voltage of the TFT and actual driving voltage of the OLED, then using these measured values to compensate and adjust the driving parameters. The control unit stores the measured threshold voltage and driving voltage, and uses them to calculate compensated values that eliminate the mura phenomenon, thereby maintaining image quality consistency over time.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the driving voltage and current based on the measured threshold voltage and driving voltage of the OLED. The control unit changes the voltage level of the control terminal according to the stored threshold voltage, driving voltage, and data signal, thereby compensating for parameter variations and maintaining consistent display quality.
2Reliability
If threshold voltage and driving voltage variations are compensated, then image quality consistency is improved, but device complexity increases due to additional control units and measurement circuits
Solution Approach 1:
The patent implements self-service by having the control unit automatically measure, store, and compensate for threshold voltage and driving voltage variations without external intervention. The system performs self-diagnosis and self-adjustment by continuously monitoring the actual voltages and automatically calculating compensated values, thereby maintaining image quality consistency while minimizing the need for complex external control systems.
Solution Approach 2:
The control unit performs multiple functions including measuring threshold voltage, measuring driving voltage, storing these values, calculating compensated values, and controlling the driving transistor. By consolidating these functions into a single multi-functional control unit, the patent reduces overall device complexity while maintaining effective compensation capabilities.
Data Source
AI summary
A display device includes pixel units. Each pixel unit includes a driving transistor, a switch transistor, a reset transistor, a light-emitting element, and a control unit. The driving transistor has a control terminal, a first terminal coupled to a first operation voltage source and a second terminal. The reset transistor is coupled to the control terminal of the driving transistor. The light-emitting element is coupled to the switch transistor in series between the second terminal of the driving transistor and a second operation voltage source. The control unit stores a threshold voltage of the driving transistor and a driving voltage of the light-emitting element according to a voltage level of the second terminal of the driving transistor. The control unit changes a voltage level of the control terminal of the driving transistor according to the stored threshold voltage, the stored driving voltage, and a corresponding data signal.