OLED Driving Circuit Voltage Stability
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Solution Overview
Problem
In OLED devices, the power supply voltage is reduced during the writing process due to wiring line resistance, leading to incorrect brightness emission when the driving current flows, as the voltage maintained in the capacitor changes, affecting the conduction state of the driving transistor and the brightness of the electro-optical device.
Innovation Solution
An electronic circuit is designed with a driving transistor, a capacitor, and switching devices to control the conduction state and intercept the driving current, ensuring the power supply voltage remains stable during data voltage writing, using switching devices to manage the flow of current and prevent voltage reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving current flows during data voltage writing, then the OLED device can emit light with correct brightness, but the power supply voltage is reduced due to wiring line resistance causing incorrect brightness emission
Solution Approach 1:
The patent applies preliminary action by turning off the second switching device before writing the data voltage to the capacitor. This preemptive action prevents driving current from flowing during the writing process, thereby avoiding power supply voltage reduction before the actual writing occurs. The timing sequence ensures that the current path is blocked in advance, protecting the voltage stability during the critical writing operation.
Solution Approach 2:
The patent employs dynamics by using switching devices to dynamically control the conduction state of the driving transistor and the flow of driving current. The first switching device controls the data voltage writing path, while the second switching device controls the driving current path. By dynamically switching these devices on and off at different times, the system adapts its current flow characteristics to match the operational phase (writing vs. emission), resolving the contradiction between needing current for brightness and needing voltage stability for accurate writing.
2Loss of information
If the data voltage is written while driving current flows, then the capacitor can store the data voltage, but the voltage maintained in the capacitor changes due to power supply voltage reduction
Solution Approach 1:
The patent applies preliminary action by turning off the second switching device before the data voltage writing operation begins. This ensures that the driving current path is blocked in advance, preventing any power supply voltage reduction during the writing process. The capacitor then charges to the correct data voltage without interference from voltage fluctuations, ensuring accurate data storage.
Solution Approach 2:
The patent uses the second switching device as an intermediary element that mediates between the driving current source and the OLED device during the writing phase. By controlling this switching device to be off during writing, it acts as a barrier that prevents the driving current from affecting the power supply voltage, thereby protecting the data voltage writing accuracy from voltage fluctuation stress.
3Use of energy by moving object
If the second switching device is turned on to supply driving current, then the OLED device emits light, but the power supply voltage is reduced during data writing
Solution Approach 1:
The patent applies periodic action by dividing the operation into distinct time periods: a writing period when the second switching device is off and data voltage is written to the capacitor, and an emission period when the second switching device is on and driving current flows to the OLED device. This periodic switching ensures that data writing and current supply do not occur simultaneously, eliminating the conflict between energy supply and writing precision.
Solution Approach 2:
The patent employs dynamics by making the second switching device dynamically switch between on and off states based on the operational phase. During the writing phase, it is off to protect writing precision; during the emission phase, it is on to supply driving current. This dynamic control allows the system to optimize for the current priority objective, resolving the contradiction between energy supply and writing precision.
Data Source
AI summary
At a writing time, a first transistor 412 is turned on so that a data signal Xj is supplied to one end of a capacitor 420. At this time, since a second transistor 414 is turned off, driving current does not flow to an organic light emitting diode (OLED) device 430. A power supply voltage Vdd is supplied to the other end of a capacitor through a power supply line L. However, since the driving current does not flow at the writing time, the power supply voltage Vdd is not reduced by the wiring line resistance of the power supply line L. On the other hand, at an emission time, the first transistor 412 is turned off and the second transistor 414 is turned on. Therefore, the driving current is supplied to the OLED device 430.