OELD Pixel Circuit Voltage Compensation Driving
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Solution Overview
Problem
Existing organic electroluminescent display (OELD) devices face limitations in displaying images due to a short row line drive period, which is insufficient for normal operation of the voltage compensation driving method, especially at Full HD resolution and 120 Hz frequency.
Innovation Solution
The OELD device employs a configuration with a switching transistor, a driving transistor, a sampling transistor, and an initializing transistor, where pixels at odd and even row lines are alternately driven in alternating frames, allowing for a longer row line drive period and eliminating the need for additional initialization control lines, thereby enabling stable voltage compensation driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage compensation driving method is used to compensate for transistor threshold voltage variation, then display stability and image quality are improved, but the row line drive period becomes insufficient for normal operation
Solution Approach 1:
The pixel circuit is divided into multiple functional transistors (switching transistor, driving transistor, sampling transistor, initializing transistor) that perform operations in sequential time segments. The sampling transistor samples the threshold voltage in one time segment and reflects it to the driving transistor in a subsequent segment, enabling voltage compensation without requiring the entire row line drive period for a single operation.
Solution Approach 2:
The sampling transistor performs preliminary sampling of the threshold voltage before the driving transistor needs to operate. By sampling the threshold voltage in advance and storing it in a capacitor, the system prepares the compensation data beforehand, allowing the driving transistor to use this pre-sampled information for stable operation without extending the overall drive period.
2Manufacturing precision
If additional initialization control lines are added to improve initialization accuracy, then manufacturing precision is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The gate line serves multiple functions: it acts as both the data input line for the switching transistor and the control signal line for the initializing transistor. By using the same physical line for multiple purposes with different timing controls, the system achieves accurate initialization without adding separate initialization control lines, thus reducing device complexity.
Solution Approach 2:
The initialization operation is performed periodically at specific timing intervals within the row line drive period, rather than requiring continuous or separate initialization control signals. The initializing transistor is activated at a predetermined timing when the gate line voltage is in a specific state, allowing accurate initialization through timing-based control rather than additional dedicated control lines.
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 approach extends the row line drive period to 15.4 microseconds, allowing for stable voltage compensation driving and normal image display, while reducing manufacturing complexity and costs by eliminating the need for additional initialization control lines.
Implementation Method 1
the third transistor Tr3 adjusts the driving current IOLED, which flows through the third transistor Tr3, and light is emitted from the organic light emitting diode OLED according to an amount of the driving current IOLED
Data Source
AI summary
An organic electroluminescent display device includes a plurality of pixels, each one of the plurality of pixels including: a switching transistor that is connected to a gate line and a data line; a driving transistor, wherein a data voltage of the data line passing through the switching transistor is reflected into a gate of the driving transistor; a sampling transistor that samples a threshold voltage of the driving transistor, wherein a gate of the sampling transistor is connected to a control line, and the sampled threshold voltage is reflected into the gate of the driving transistor; an initializing transistor, wherein a gate of the initializing transistor is connected to a previous or next gate line, and an initialization voltage passing through the initializing transistor is reflected into the gate of the driving transistor; and an organic light emitting diode that is connected to the driving transistor, wherein a driving current of the organic light emitting diode is adjusted according to a voltage of the gate of the driving transistor.