Display Device Initialization Circuit for High-Luminance OLEDs
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Solution Overview
Problem
In organic EL display devices, increasing the channel width of TFTs to enhance current flow through them poses a challenge in initializing the gate terminal of the drive transistor effectively, especially when high luminance is required, leading to potential image quality deterioration due to insufficient initialization.
Innovation Solution
A display device configuration with additional initialization control lines and transistors allows for a longer initialization period compared to the data writing period, ensuring the gate terminal of the drive transistor is adequately initialized, even with increased capacitance for high-luminance displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the channel width of TFT is increased to increase current flow for high luminance display, then luminance is improved, but the initialization of gate terminal becomes insufficient leading to image quality deterioration
Solution Approach 1:
The patent applies preliminary action by extending the initialization period to occur before the data writing period. The initialization transistor is turned on earlier and remains on for a longer duration, ensuring the gate terminal is fully initialized to the reference potential before data voltage is written. This preliminary initialization action resolves the contradiction by guaranteeing proper gate terminal preparation even when large capacitor currents are present during high-luminance operation.
2Stability of the object's composition
If the capacitance of capacitor is increased to maintain gate voltage stability for high luminance, then gate voltage stability is improved, but the initialization time required increases beyond available initialization period
Solution Approach 1:
The patent extends the initialization period to occur before the data writing period, performing preliminary initialization action. The initialization transistor is turned on at the start of the initialization period and remains on throughout the entire initialization period, ensuring the gate terminal reaches reference potential before data writing begins. This resolves the time conflict by providing sufficient initialization duration independent of capacitor size.
Solution Approach 2:
The patent dynamically controls the initialization transistor gate voltage to be at a low level (turning on the transistor) during the initialization period, and then changes the gate voltage to a high level (turning off the transistor) before the data writing period. This dynamic control allows the system to adapt to different capacitor values and initialization requirements, resolving the contradiction between capacitance size and initialization time availability.
3Manufacturing precision
If the initialization period is extended to adequately initialize gate terminal, then initialization quality is improved, but the overall pixel circuit operation time increases
Solution Approach 1:
The patent performs initialization as a preliminary action before data writing by controlling the initialization transistor to be on during the initialization period and off before the data writing period. This preliminary initialization ensures high initialization quality without extending the critical data writing and display time, thus maintaining pixel circuit operation speed while improving initialization quality.
Data Source
AI summary
A pixel circuit of a display device Includes: an electro-optical element; a drive transistor; a write control transistor; a threshold compensation transistor; two light emission control transistors; a first initialization transistor having a first conduction terminal connected to a gate terminal of the drive transistor, a second conduction terminal to which an initialization voltage is applied, and a gate terminal connected to a first initialization control line; and a capacitor provided between a first conductive member and the gate terminal of the drive transistor. In a non-light emission period, time during which a voltage of the first initialization control line is at an on-level is longer than a period during which a voltage of a scanning line is at the on-level. As a result, a display device capable of sufficiently initializing the gate terminal of the drive transistor is provided.