OLED Pixel Circuit Variable Frequency Flicker
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Solution Overview
Problem
OLED display devices experience flicker and luminance differences when operating in variable frequency modes due to mismatched driving frequencies, leading to suboptimal image rendering and potential tearing phenomena.
Innovation Solution
The OLED display device incorporates a pixel configuration with specific transistors and capacitors that allow for both normal and variable frequency modes, including a diode initialization transistor and a drain initialization transistor, to maintain uniform luminance across different frame frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the OLED display device operates in variable frequency mode to prevent tearing phenomena, then image synchronization with host processor is improved, but luminance uniformity deteriorates causing flicker
Solution Approach 1:
The patent applies preliminary action by initializing the organic light emitting diode at the beginning of each frame period through a dedicated diode initialization transistor. This pre-initialization ensures that regardless of when the emission period starts within the frame period, the OLED starts from a consistent state, eliminating luminance variations caused by different driving frequencies in variable frequency mode.
Solution Approach 2:
The patent changes the timing parameter of OLED initialization from being tied to the emission period start to being tied to the frame period start. By using a diode initialization transistor that activates at the frame period beginning rather than at the emission period beginning, the system maintains consistent luminance across variable frame frequencies while still preventing tearing phenomena.
2Reliability
If the driving frequency of the display panel is changed to match variable frame frequency, then tearing phenomenon is reduced, but luminance difference between different frequencies increases causing flicker
Solution Approach 1:
The patent performs preliminary initialization of the OLED at the frame period start through the diode initialization transistor, ensuring that the OLED is always in a known state before emission begins. This preliminary action decouples the initialization timing from the emission timing, allowing the display to operate at variable frequencies without luminance flicker.
Solution Approach 2:
The patent segments the frame period into distinct phases: a diode initialization phase at the frame period start, and an emission phase that may start at variable times within the frame period. This segmentation allows the OLED to be initialized once per frame regardless of when emission occurs, maintaining luminance consistency across different frame frequencies.
Data Source
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AI summary
A pixel of an OLED display device includes a first capacitor, a second capacitor, a first transistor configured to generate a driving current, a second transistor configured to transfer a data voltage to a first node, a third transistor configured to diode-connect the first transistor, a fourth transistor configured to transfer an initialization voltage to the second node, a fifth transistor configured to transfer a reference voltage to the first node, a sixth transistor configured to couple a drain of the first transistor and an anode of an organic light emitting diode, a seventh transistor configured to transfer the initialization voltage to the anode of the organic light emitting diode, an eighth transistor configured to transfer the initialization voltage to the drain of the first transistor, and the organic light emitting diode.