OLED Driving Circuit Voltage Writing Speed via Segmented Switching
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Solution Overview
Problem
In OLED-driven electronic circuits, the non-uniform threshold voltage characteristic of driving transistors leads to varying brightness across pixels, making it difficult to rapidly write target voltages, especially for P-channel-type transistors due to parasitic capacitance issues.
Innovation Solution
An electronic circuit design that includes a driving transistor, switching elements, and a voltage storage element, allowing for distinct periods to apply initial and target voltages, reducing the time required for voltage writing by utilizing diode-connected and diode-canceled states, and independent control of switching elements to manage current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the driving transistor is diode-connected to write target voltage in the gate, then the threshold voltage non-uniformity is compensated, but the writing time becomes too long for P-channel-type transistors due to parasitic capacitance of data lines
Solution Approach 1:
The patent divides the voltage writing process into two distinct phases: (1) writing initial voltage to the drain while the transistor is diode-connected, and (2) writing target voltage to the gate after canceling the diode connection. This segmentation allows each voltage to be written independently through optimized pathways, resolving the time conflict between compensation and speed.
Solution Approach 2:
The patent applies preliminary action by first writing the initial voltage to the drain in advance (while diode-connected) before the target voltage writing phase. This preliminary voltage establishment reduces the parasitic capacitance burden during subsequent target voltage writing, enabling faster operation for P-channel transistors.
2Manufacturing precision
If the driving transistor is diode-connected during target voltage writing, then current compensation is achieved, but the parasitic capacitance of data lines prevents rapid voltage increase
Solution Approach 1:
The patent dynamically changes the circuit configuration by switching the diode connection state. The switching element connects the drain to the gate during initial voltage writing (diode-connected state), then disconnects them during target voltage writing (non-diode-connected state). This dynamic reconfiguration optimizes both current control precision and voltage writing speed at different phases.
Solution Approach 2:
The switching element acts as an intermediary that controls the diode connection between drain and gate. By mediating this connection state, it enables the circuit to transition between compensation mode (diode-connected for precision) and speed mode (disconnected for fast writing), resolving the contradiction between precision and speed.
3Device complexity
If a single voltage writing process is used, then the circuit structure is simple, but both initial and target voltages cannot be written rapidly
Solution Approach 1:
The patent makes the switching element multi-functional by having it serve dual purposes: (1) controlling the diode connection for compensation, and (2) enabling/disabling the initial voltage writing pathway. This universal element adds minimal complexity while achieving both rapid initial voltage writing and target voltage writing with compensation.
Solution Approach 2:
The patent employs periodic action by sequentially executing distinct voltage writing periods: first the initial voltage writing period with diode connection, then the target voltage writing period without diode connection. This periodic sequence optimizes writing efficiency for both voltages while maintaining relatively simple circuit structure through time-division multiplexing.
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 reduces the time needed to write target voltages, improving the uniformity of pixel brightness and overall image quality by allowing rapid voltage writing and efficient current control, thus enhancing the resolution and size of electro-optical devices.
Implementation Method 1
a voltage storage element, its one end being connected to the gate of the driving transistor
Implementation Method 2
a first switching element switched on or off between the gate and drain of the driving transistor
Data Source
AI summary
To reduce time for writing a target voltage in the gate of a driving transistor. In a first period, a transistor 211 is switched on to allow a driving transistor 210 to function as a diode and transistors 212 and 213 are switched on to electrically connect the drain of the driving transistor 210 to a data line 112, to which an initial voltage is applied, such that the initial voltage is applied to the gate of the driving transistor 210. In a second period, a transistor 212 is switched off such that the gate of the driving transistor 210 is maintained to have an off voltage corresponding to the power source. In a third period, the transistor 211 is switched off such that the voltage of the data line 112 is converted into a grayscale voltage to maintain the gate of the driving transistor at the target voltage. In a fourth period, the driving transistor 210 flows the current corresponding to the maintained gate voltage to an OLED element 230.