Periodic Transistor Off-Control for Persistent Image Reduction
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Solution Overview
Problem
Persistent images occur in active matrix display devices using organic electroluminescence elements due to hysteresis in p-channel element driving transistors, leading to degraded display quality, especially when displaying animated images with large voltage variations.
Innovation Solution
A display device with a vertical driver that generates capacitor control signals to periodically switch off the element driving transistor, using a storage capacitor to store data voltage and control the element driving transistor's operation, thereby preventing persistent images by ensuring the element driving transistor is switched off before the next frame period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the element driving transistor is continuously turned on during one frame period, then the display can maintain image brightness, but persistent images occur due to hysteresis in the p-channel transistor
Solution Approach 1:
The patent applies periodic action by turning off the element driving transistor after a predetermined time period (first time period) following data voltage input, and then turning it back on for the second time period. This periodic switching prevents persistent images by interrupting the continuous current flow that causes hysteresis effects, while still maintaining image brightness during the active display period.
Solution Approach 2:
The patent implements preliminary action by introducing a first time period delay before turning off the element driving transistor. This preliminary delay ensures that the transistor remains on long enough to maintain proper image brightness, while the subsequent turning off after the first time period prevents the harmful persistent image effect from developing.
2Object-affected harmful factors
If the element driving transistor is turned off immediately after data voltage input, then persistent images are prevented, but the transistor cannot maintain proper drive current for the entire frame period
Solution Approach 1:
The patent uses periodic action by implementing a two-phase timing control: the element driving transistor is turned on during the first time period to maintain proper drive current, then turned off during the second time period to prevent persistent images. This periodic switching pattern resolves the contradiction between maintaining conduction duration and preventing persistent images.
3Illumination intensity
If a capacitor control signal is continuously applied to keep the element driving transistor on, then image brightness is maintained, but trapped carriers in the gate insulating film cause hysteresis and persistent images
Solution Approach 1:
The patent applies periodic action by controlling the capacitor control signal to switch the element driving transistor on and off in specific time periods. The transistor is turned on during the first time period to maintain image brightness, then turned off during the second time period to allow trapped carriers to be released from the gate insulating film, preventing hysteresis and persistent images in subsequent frames.
Data Source
AI summary
An element driving transistor controls an amount of power supplied from a power supply PVDD to an element to be driven (display element) provided in a pixel of each row. A storage capacitor has a first electrode connected to a gate electrode of an element driving transistor and a second electrode connected to a capacitor line. A voltage level of a capacitor control signal SCn to be output to the capacitor line is set to a voltage level which controls the element driving transistor via the storage capacitor Cs to be periodically switched off. A V driver formed at a periphery of a display portion of a panel has a generator which generates a capacitor control signal SCn using outputs of registers which sequentially transfer and output a signal according to a V start signal STV so that the off-control period of the element driving transistor is determined according to the H level period of the V start signal STV. The voltage level of the capacitor control signal allows, for each row, the element driving transistor to be controlled to be switched off for a period according to the signal STV and persistent images can be improved.