AMOLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing pixel circuits for AMOLED displays suffer from uneven brightness due to variations in threshold voltages of TFTs across the array substrate, leading to reduced brightness uniformity.
Innovation Solution
A pixel circuit with a controlling sub-circuit and a compensating sub-circuit that sets a constant potential for the gate electrode of the driving transistor and pre-stores its threshold voltage, independent of the transistor's threshold voltage, using capacitors to ensure consistent driving current for the light-emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional pixel circuit with a driving TFT is used, then the display device can achieve high resolution and large size, but the brightness uniformity deteriorates due to threshold voltage variations of TFTs across the array substrate
Solution Approach 1:
The patent applies preliminary action by pre-storing the threshold voltage of the driving TFT in a capacitor during a charging phase before the actual display operation. The compensating sub-circuit charges the capacitor with the threshold voltage value in advance, so that during the light-emitting phase, the driving current calculation can use this pre-stored value to compensate for threshold voltage variations, thereby achieving uniform brightness across the display panel without requiring real-time threshold voltage measurement or adjustment
Solution Approach 2:
The patent introduces a compensating sub-circuit as an intermediary between the driving TFT and the light-emitting element. This compensating sub-circuit includes a capacitor that stores the threshold voltage and participates in the driving current calculation. By adding this intermediary component, the system can compensate for the harmful effect of threshold voltage variations, allowing the driving current to be calculated as I=K(Vdata−Vth+Vref)2, where Vref is the pre-stored threshold voltage, thus achieving uniform brightness while maintaining the existing TFT manufacturing process
2Productivity
If LTPS TFTs are used to provide high electron mobility, then the driving current increases to achieve optimal display effect, but the threshold voltage varies significantly across the array substrate
Solution Approach 1:
The patent implements feedback by measuring or estimating the threshold voltage of each driving TFT and using this information to adjust the driving current calculation. The compensating sub-circuit captures the threshold voltage (either through direct measurement or indirect estimation during the charging phase) and feeds this information back into the driving current formula. This feedback mechanism allows the system to compensate for threshold voltage variations caused by LTPS manufacturing variations, ensuring that high electron mobility LTPS TFTs can be used while maintaining uniform brightness across the display panel
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution improves display uniformity by making the driving current for the light-emitting element independent of the driving transistor's threshold voltage, resulting in consistent brightness across the display panel.
Implementation Method 1
a compensating sub-circuit, a driving transistor and a light-emitting element. The compensating sub-circuit is configured to, under the control of the controlling sub-circuit, set a constant potential for a gate electrode of the driving transistor, and pre-store a threshold voltage of the driving transistor
Data Source
AI summary
The present disclosure provides an array substrate, comprising a plurality of pixel circuits arranged in a matrix form. Each pixel circuit comprises a controlling sub-circuit, a compensating sub-circuit, a driving transistor and a light-emitting element. The controlling sub-circuit is configured to, under the control of a scanning voltage signal and a charging signal, charge the compensating sub-circuit, and under the control of a light-emitting controlling signal, control the driving transistor so as to drive the light-emitting element to emit light, and the compensating sub-circuit is configured to, under the control of the controlling sob-circuit, set a constant potential for a gate electrode of the driving transistor, and pre-store a threshold voltage of the driving transistor, so as to compensate for the threshold voltage of the driving transistor when the driving transistor drives the light-emitting element to emit light.