Pixel Circuit Bootstrap Stabilization for AMOLED Luminance Uniformity
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Solution Overview
Problem
In large-sized AMOLED displays, the drifting of threshold voltage in TFTs leads to luminance uniformity and constancy issues, affecting image quality due to fluctuations in electrical parameters during the manufacturing process.
Innovation Solution
A pixel circuit comprising multiple transistors and a storage capacitor is designed to maintain constant voltage between the storage capacitor terminals, independent of the threshold voltage, using a bootstrap function to stabilize the current flowing through the light emitting diode, thereby preventing luminance unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If polysilicon is adopted to constitute TFTs to increase carrier mobility and reduce resistivity, then power consumption is reduced, but threshold voltage drifting occurs causing luminance uniformity and constancy deterioration
Solution Approach 1:
The pixel circuit performs preliminary compensation actions during the reset phase and write phase before the light emission phase. The reset transistor resets the gate voltage of the driving transistor to a reference voltage, and the write transistor writes the data voltage to the gate of the driving transistor. These preliminary actions ensure that the driving voltage is established before threshold voltage drifting can affect luminance, thereby maintaining luminance uniformity and constancy while using polysilicon TFTs.
Solution Approach 2:
The pixel circuit incorporates a storage capacitor that stores the gate voltage of the driving transistor, providing a feedback mechanism to maintain stable driving voltage. The storage capacitor holds the compensated voltage level, compensating for threshold voltage variations that occur during operation. This feedback mechanism ensures that luminance remains consistent despite polysilicon TFT threshold voltage drifting.
2Power
If polysilicon TFTs are used to reduce resistivity, then current flow efficiency is improved, but electrical parameter fluctuations occur affecting display quality
Solution Approach 1:
The pixel circuit changes the voltage parameters dynamically through different operating phases. During the reset phase, the gate voltage is set to a reference voltage (first voltage level). During the write phase, the data voltage is applied (second voltage level). During the light emission phase, the stored voltage maintains the driving current. These parameter changes compensate for electrical parameter fluctuations in polysilicon TFTs, ensuring stable current flow efficiency while maintaining manufacturing feasibility.
3Device complexity
If a simple pixel circuit is used, then device complexity is reduced, but threshold voltage drifting cannot be compensated affecting luminance uniformity
Solution Approach 1:
The pixel circuit is segmented into distinct functional units: a reset transistor for resetting the gate voltage, a write transistor for writing data voltage, a driving transistor for controlling light emission, a storage capacitor for maintaining voltage, and a light emitting diode. This segmentation allows each component to perform its specific function in compensating for threshold voltage drifting, achieving luminance uniformity without excessive complexity.
Solution Approach 2:
The storage capacitor acts as an intermediary element between the write transistor and the driving transistor. It stores the gate voltage and provides a stable voltage reference during the light emission phase, mediating the effect of threshold voltage variations. This intermediary component enables the circuit to maintain luminance uniformity with a relatively simple structure by isolating the driving transistor from direct threshold voltage fluctuations.
Data Source
AI summary
A pixel circuit, a driving method therefor, and a display device. The pixel circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, a storage capacitor, and a light-emitting device. The pixel circuit can avoid the influence of drifting of a threshold voltage on brightness uniformity and constancy of a display.