Pixel Circuit Boost Capacitor for Oxide TFT Voltage Stability
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Solution Overview
Problem
Display apparatuses experience tearing phenomena due to mismatched frame frequencies between host processors and display panels, and oxide thin film transistors unintentionally lower control electrode voltages, requiring higher data voltages for black grayscale images.
Innovation Solution
A pixel circuit with a boost capacitor that applies previous or next initialization gate signals to boost the control electrode of a driving transistor, including compensation transistors to manage threshold voltage and data voltage, enhancing hysteresis characteristics and reducing luminance differences between pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an oxide thin film transistor is used to control the driving transistor, then the pixel circuit can be manufactured with lower temperature processes, but the oxide thin film transistor unintentionally lowers the control electrode voltage (kickback voltage)
Solution Approach 1:
A boost capacitor is introduced as an intermediary component between the oxide thin film transistor and the driving transistor. The boost capacitor stores charge during the initialization period and releases it during the emission period to compensate for the voltage drop caused by the oxide thin film transistor, thereby maintaining stable control electrode voltage without changing the manufacturing process
Solution Approach 2:
The boost capacitor is charged in advance during the initialization period before the emission period begins. This preliminary charging action ensures that when the emission period starts, the boost capacitor can immediately provide the necessary voltage boost to compensate for the kickback effect, maintaining proper driving voltage levels
2Illumination intensity
If a higher data voltage is used to compensate for the lowered control electrode voltage, then the display can maintain proper luminance, but the power consumption increases and the contrast ratio deteriorates
Solution Approach 1:
The invention converts the harmful kickback voltage drop into a beneficial effect by using it to charge the boost capacitor during the initialization period. This stored charge is then used during emission to maintain proper voltage levels, eliminating the need for higher data voltages and thus reducing power consumption while maintaining luminance
3Illumination intensity
If a higher data voltage is used to compensate for the lowered control electrode voltage, then the display can maintain proper luminance, but the contrast ratio and black grayscale display quality deteriorate
Solution Approach 1:
The boost capacitor acts as a voltage regulation intermediary that decouples the data voltage from the control electrode voltage. By providing independent voltage compensation through the boost capacitor, the system can maintain precise grayscale levels without being forced to use higher data voltages, thus preserving black grayscale display quality and contrast ratio
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
The pixel circuit effectively compensates for voltage decreases, secures threshold voltage compensation time, and lowers data voltage for black grayscale images, improving display quality by reducing luminance differences and enhancing hysteresis characteristics.
Implementation Method 1
a boost capacitor including a first electrode to which a previous initialization gate signal applied to a previous pixel row is applied and a second electrode connected to the control electrode of the driving transistor
Data Source
AI summary
A pixel circuit includes a light emitting element, a write transistor configured to apply a data voltage to an input node in response to a write gate signal, a storage capacitor configured to store the data voltage, a driving transistor configured to apply a driving current to the light emitting element based on the data voltage, a first compensation transistor configured to compensate for a threshold voltage of the driving transistor in response to a compensation gate signal, a first initialization transistor configured to apply a first initialization voltage to a control electrode of the driving transistor in response to an initialization gate signal, and a boost capacitor including a first electrode to which a previous initialization gate signal applied to a previous pixel row is applied and a second electrode connected to the control electrode of the driving transistor.