Dual Switching Transistor Pixel Circuit for Leakage Current Control
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Solution Overview
Problem
Active matrix organic electroluminescence (EL) displays suffer from leakage current issues in their pixel circuits, leading to erroneous operations and reduced efficiency.
Innovation Solution
The implementation of a pixel circuit design that utilizes dual switching transistors and capacitors to manage data signal transmission with minimal leakage current, employing a series configuration of switches and storage elements to ensure accurate data signal delivery to the light-emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit with single switching transistor is used, then the device complexity is low, but leakage current occurs leading to erroneous operation
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks with dual switching transistors (first switching transistor and second switching transistor) that operate at different times. The first switching transistor transmits data signal during a first period, while the second switching transistor transmits data signal during a second period. This segmentation prevents leakage current by ensuring that switching transistors are not simultaneously active, thereby resolving the contradiction between operational reliability and device complexity.
Solution Approach 2:
The pixel circuit incorporates a storage element (capacitor) that pre-stores the data signal before it is transmitted to the light-emitting element. The storage element holds the data voltage during the period when the switching transistor is not active, preventing leakage current from affecting the displayed image. This preliminary action ensures accurate data signal delivery while maintaining circuit reliability without excessive complexity.
2Reliability
If dual switching transistors are used in pixel circuit, then leakage current is prevented, but device complexity increases
Solution Approach 1:
The dual switching transistors operate in a periodic manner with distinct time periods. The first switching transistor is activated during a first period to transmit the data signal, while the second switching transistor is activated during a second period. This periodic operation ensures that only one switching transistor is active at any given time, preventing leakage current while maintaining manageable device complexity through time-division multiplexing.
Solution Approach 2:
The storage element (capacitor) acts as an intermediary between the data line and the light-emitting element. It temporarily stores the data voltage and releases it at the appropriate time, mediating the signal transmission between the switching transistors and the display element. This intermediary function reduces the direct complexity of the switching network while maintaining reliable leakage-free operation.
3Illumination intensity
If data signal is transmitted through switching transistors, then pixel control is achieved, but threshold voltage deviations cause luminance non-uniformity
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the storage element continuously monitors and adjusts the data voltage level to compensate for threshold voltage variations in the switching transistors. By storing the adjusted voltage level and using it for light emission control, the system achieves luminance uniformity across pixels despite manufacturing variations in transistor characteristics.
Solution Approach 2:
The circuit dynamically adjusts the voltage parameter stored in the storage element to compensate for threshold voltage deviations. By changing the stored voltage level based on the actual switching transistor characteristics, the system maintains consistent luminance output across all pixels, effectively addressing manufacturing precision issues through parameter adaptation.
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 design effectively prevents leakage current, enhances luminance uniformity across pixels, reduces power consumption, and ensures accurate representation of black levels by compensating for threshold voltage deviations among transistors.
Implementation Method 1
The light-emitting element emits light corresponding to a current supplied thereto through the first transistor
Implementation Method 2
The storage element charges a voltage corresponding to a data signal transmitted from the corresponding data line through the first and second switches
Data Source
AI summary
A light-emitting display device includes a pixel circuit that transmits a data signal using switches responding to control signals. The pixel circuit of the light-emitting display device includes first and second switching transistors serially coupled to a data line. A capacitor is charged with charges in response to a data signal from the data line through the first and second switching transistors. A driving transistor outputs a current corresponding to the charges in the capacitor. A light-emitting diode emits light corresponding to the current. One of the first and second switching transistors is turned on in response to a select signal from a first scan line and the other one is turned on in response to a control signal for controlling an operation of a second pixel circuit.