Mixed Compensation Pixel Circuit for OLED Stability
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Solution Overview
Problem
N-type thin film transistors (NTFTs) used in mixed compensation pixel circuits face reliability anomalies due to prolonged operation under high electrical potential, leading to instability and circuit failure, especially in OLED devices where a current is constantly flowing.
Innovation Solution
A mixed compensation pixel circuit is designed with an internal and external compensation circuit, including specific thin film transistors, capacitors, and a diode, which optimizes the pixel circuit architecture to maintain thin film transistors at reduced relative voltage, improving stability and simplifying the compensation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the gate of thin film transistor T4 is maintained at high electrical potential during light-emitting step, then the OLED can emit light properly, but the stability and reliability of thin film transistor T4 deteriorates due to prolonged exposure to high voltage
Solution Approach 1:
The pixel circuit is divided into two separate compensation circuits: an internal compensation circuit (comprising transistors T1-T4 and capacitors C1-C2) and an external compensation circuit (comprising transistor T5 and capacitor C3). This segmentation allows the internal circuit to handle light emission while the external circuit manages threshold voltage compensation, reducing the burden on T4 and improving its reliability during light-emitting operation.
Solution Approach 2:
The invention changes the operating parameters of thin film transistor T4 by using the external compensation circuit to adjust and compensate for threshold voltage variations. This parameter adjustment allows T4 to operate at optimized voltage levels during light emission, reducing stress and improving long-term stability while maintaining proper light emission function.
2Productivity
If internal compensation circuit is used to control pixel operation, then the circuit can drive OLED to emit light, but the thin film transistor T4 suffers from reliability anomalies due to long-term operation under large Vgs voltage
Solution Approach 1:
The external compensation circuit acts as an intermediary that compensates for threshold voltage changes in the internal compensation circuit. By introducing this intermediate compensation mechanism, the internal circuit can maintain proper operation for light emission while the external circuit absorbs the stress and reliability concerns, preventing direct degradation of transistor T4.
3Measurement precision
If external compensation circuit is used with gate at high electrical potential, then compensation can be performed, but the thin film transistor T4 still experiences stability issues under prolonged high voltage operation
Solution Approach 1:
The compensation function is segmented between internal and external circuits. The external compensation circuit (T5, C3) specifically handles threshold voltage measurement and compensation with high precision, while the internal circuit (T1-T4, C1-C2) focuses on light emission control. This functional segmentation allows precise compensation without requiring T4 to sustain high voltage continuously, improving both accuracy and reliability.
Data Source
AI summary
The present disclosure provides a mixed compensation pixel circuit, control method, and display device, the mixed compensation pixel circuit includes an internal compensation circuit and an external compensation circuit. The internal compensation circuit includes a first thin film transistor, a second thin film transistor, a third thin transistor, and a fourth thin transistor, the external compensation circuit includes a fifth thin transistor. By optimizing the pixel circuit architecture, the present disclosure does not have an NTFT with a positive long-term relative voltage, improves the stability of the circuit, simplifies the compensation process, and improves the accuracy of compensation.