OLED Driving Circuit Voltage Writing Speed
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Solution Overview
Problem
In OLED element driving circuits, the threshold voltage characteristic deviation of driving transistors leads to varying brightness across pixels, deteriorating display quality, especially when using N-channel transistors, where it's difficult to write the required voltage onto the gate during the writing period due to low current flow.
Innovation Solution
An electronic circuit with a driving transistor and switching elements that allows for quick voltage writing onto the gate by using a capacitive element to hold and adjust the voltage, independent of the threshold voltage characteristics, enabling efficient current flow into the OLED element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the driving transistor is brought into diode connection to compensate threshold voltage deviation, then the brightness uniformity is improved, but the writing time is extended and the required voltage cannot be written in time
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitive element before the writing operation. The capacitive element is charged to an initial voltage in advance, so when the writing signal is applied, the voltage can be immediately written to the gate of the driving transistor without waiting for the diode connection charging process, thus reducing the writing time while maintaining threshold voltage compensation
Solution Approach 2:
The patent segments the voltage writing process into two independent parts: the capacitive element provides the initial voltage charge, and the diode-connected transistor provides threshold voltage compensation. This segmentation allows the capacitive element to supply voltage immediately while the transistor compensates for threshold deviations, resolving the time conflict
2Use of energy by moving object
If the current flowing into the OLED element is set to become small, then the power consumption is reduced, but the gate voltage becomes low and it is difficult to flow current between source and drain
Solution Approach 1:
The patent uses the capacitive element as an intermediary to provide the necessary gate voltage. The capacitive element stores and supplies voltage to the gate of the driving transistor, enabling the transistor to maintain proper gate voltage even when the current flowing into the OLED element is small, thus allowing low power consumption without sacrificing current flow capability
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 reduces the time required to write the voltage and ensures uniform current flow into the OLED element, improving display quality by compensating for threshold voltage deviations and maintaining brightness consistency across pixels.
Implementation Method 1
a capacitive element, one end of which is connected to the gate of the driving transistor
Data Source
AI summary
To reduce the time for writing a voltage onto a gate of a driving transistor. In an initialization period, a node B is fixed to an initial voltage VINI, transistors are turned on, and a current flows into an OLED element, such that a voltage according to the current is held at the node A. Thereafter, the transistors are sequentially turned off, such that a threshold voltage of a driving transistor is held at the node A. In a writing period, a transistor is turned on and a data signal X-j is supplied, such that a voltage of the node B varies by the amount according to the current flowing into the OLED element. The voltage of the node A varies from the threshold voltage by the amount which is obtained by dividing the voltage variation by a capacitance ratio. In a light-emitting period, the transistor is turned on, such that a current according to the voltage of the node A flows into the OLED element.