Pixel Circuit Threshold Voltage Compensation for Display Uniformity
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Solution Overview
Problem
Differences in threshold voltage and mobility of driving transistors in pixels can lead to luminance deviations, causing stains on display panels due to varying driving currents.
Innovation Solution
A pixel configuration that includes multiple transistors and a storage capacitor to compensate for threshold voltage differences, with specific signal control during anode initialization, threshold voltage compensation, and light emitting periods to ensure uniform luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional pixel structures are used without threshold voltage compensation, then device complexity is low, but luminance uniformity deteriorates due to threshold voltage differences causing driving current variations
Solution Approach 1:
The pixel circuit performs threshold voltage compensation in advance during the initialization period before the light emitting period. The fourth transistor applies a reference voltage to the gate electrode of the first transistor, and the third transistor diode-connects the first transistor, allowing the storage capacitor to store a voltage that compensates for the threshold voltage difference. This preliminary compensation action ensures that subsequent driving currents are uniform across pixels despite process variations.
2Stability of the object's composition
If multiple transistors and capacitors are added for threshold voltage compensation, then luminance uniformity improves, but manufacturing precision requirements increase
Solution Approach 1:
The pixel circuit uses itself to compensate for its own threshold voltage differences. The first transistor's threshold voltage difference is compensated by utilizing the transistor's own characteristics in a diode connection configuration during the compensation period. The storage capacitor stores the compensated voltage, and this self-compensation mechanism reduces reliance on high manufacturing precision for additional compensation components.
3Stability of the object's composition
If threshold voltage compensation circuitry is implemented, then driving current uniformity improves, but ease of manufacture deteriorates due to increased transistor count
Solution Approach 1:
The first transistor serves multiple functions: it acts as the driving transistor during the light emitting period and as part of the compensation circuit during the initialization period. By diode-connecting the first transistor using the third transistor, the circuit achieves threshold voltage compensation without requiring entirely separate compensation transistors, thereby reducing the overall transistor count and improving ease of manufacture while maintaining driving current uniformity.
Data Source
AI summary
In a pixel of a display device, a back gate control voltage is applied to a back gate electrode of a first transistor that operates as a driving transistor in an anode initialization period, and the back gate electrode of the first transistor is connected to an anode of a light emitting element in a light emitting period. A first transfer line is disposed apart from the first transistor in a first direction. A capacitor pattern is disposed apart from the first transistor in a second direction opposite to the first direction. A second transmission line is disposed between the first transistor and the capacitor pattern.