Organic Light Emitting Display Driving Transistor Hysteresis Control
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Solution Overview
Problem
Organic light emitting display devices face issues with hysteresis characteristics in driving transistors, leading to inconsistent luminance and afterimages due to shifting threshold voltages and current changes, especially when transitioning from black to white grayscale.
Innovation Solution
The implementation of an organic light emitting display device that alternates initialization voltage levels between a first and a second voltage level during specific periods, synchronized with scan pulses, to maintain a consistent operational characteristic of the driving transistor, thereby minimizing hysteresis effects and ensuring desired luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed initialization voltage is supplied to the driving transistor, then the circuit operation is simplified, but hysteresis effects cause luminance inconsistency and afterimages
Solution Approach 1:
The patent applies periodic action by alternating the initialization voltage between a first voltage level and a second voltage level at regular intervals (e.g., every horizontal period or every other horizontal period). This periodic switching prevents the driving transistor from remaining in a fixed state, thereby reducing hysteresis effects and improving luminance consistency without significantly increasing circuit complexity
Solution Approach 2:
The patent changes the voltage level parameter of the initialization signal dynamically. Instead of using a fixed voltage level, the initialization voltage alternates between a first voltage level (e.g., 0V or negative voltage) and a second voltage level (e.g., positive voltage), allowing the system to adapt to different operational states and minimize hysteresis-induced display defects
2Reliability
If the initialization voltage level is switched frequently, then hysteresis effects are minimized, but power consumption increases
Solution Approach 1:
The patent optimizes the switching frequency of the initialization voltage to balance hysteresis reduction and power consumption. By switching the voltage level at specific periodic intervals (e.g., every horizontal period or every other horizontal period) rather than continuously, the system achieves sufficient hysteresis mitigation while avoiding excessive power consumption associated with frequent switching
Solution Approach 2:
The patent applies preliminary action by supplying the initialization voltage during specific periods (e.g., during the bias period or initialization period before the emission period) to pre-condition the driving transistor. This preliminary initialization ensures the transistor is properly biased before data writing and emission, reducing the need for continuous voltage switching during active display periods
Data Source
AI summary
An organic light emitting display device includes: a display unit including a plurality of pixels each coupled to a first scan line, a second scan line, and a data line; a scan driver configured to supply, to the display unit, a plurality of first scan pulses corresponding to a bias period and a second scan pulse corresponding to a data write period after the bias period through the respective first and second scan lines; an emission driver configured to supply an emission control signal to the display unit through emission control lines; a data driver configured to supply a data voltage to the display unit through the data lines; and a power supply configured to commonly supply, to the pixels, an initialization voltage, the initialization voltage having a voltage level switching between a first voltage level and a second voltage level in a preset period.