OLED Pixel Driving Circuit Coupling Capacitor Flicker Suppression
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Solution Overview
Problem
Organic Light Emitting Diode (OLED) devices experience flicker due to differences in threshold voltage and mobility of driving TFTs and voltage drops, leading to luminance variations between pixels.
Innovation Solution
Incorporating a coupling capacitor in each pixel driving circuit to rapidly increase the voltage of the gate and source nodes of the driving TFT, minimizing current delay and reducing flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conventional pixel driving circuit without coupling capacitor is used, then the device complexity is low, but luminance uniformity deteriorates due to flicker caused by threshold voltage differences and mobility variations
Solution Approach 1:
A coupling capacitor is introduced as an intermediary component between the data line and the gate of the driving TFT. This capacitor couples the data voltage to the gate, providing a bootstrapping effect that compensates for threshold voltage variations and mobility differences, thereby eliminating flicker and improving luminance uniformity without requiring fundamental changes to the pixel structure
Solution Approach 2:
The invention changes the voltage parameter at the gate of the driving TFT by using the coupling capacitor to provide a boosted voltage during the emission period. This voltage enhancement compensates for the voltage drops and threshold variations, maintaining stable current flow through the OLED and achieving uniform luminance across all pixels
2Speed
If the voltage of gate and source nodes is increased rapidly using coupling capacitor, then current delay is reduced, but the device complexity increases
Solution Approach 1:
The coupling capacitor serves as an intermediary that rapidly transfers charge to the gate node when the data line voltage changes. This capacitive coupling provides a fast voltage transition at the gate, reducing the delay in current response through the OLED while adding only a single capacitor component to the circuit
Solution Approach 2:
The coupling capacitor is charged in advance during the programming period when the data voltage is applied to the data line. This preliminary charging action ensures that when the emission period begins, the capacitor can immediately discharge and rapidly increase the gate voltage, thereby reducing current delay without requiring complex active control circuits
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
The solution effectively suppresses flicker by ensuring consistent current flow to the organic light emitting diode, enhancing display stability and reducing luminance differences between pixels.
Implementation Method 1
a coupling capacitor connected to a gate node of a third switching TFT so as to increase a voltage to be applied to the gate node of the driving TFT
Data Source
AI summary
According to an aspect of the present disclosure, an organic light emitting display device includes a plurality of pixels each including a pixel driving circuit. The plurality of pixels includes an organic light emitting diode and a driving TFT configured to control driving of the organic light emitting diode and including a gate node as a first node, a source node as a second node, and a drain node. Also, the plurality of pixels includes first to third switching TFTs electrically connected to the driving TFT and first and second storage capacitors configured to store a voltage to be applied to the driving TFT DT. Further, the plurality of pixels includes a coupling capacitor connected to a gate node of the third switching TFT so as to increase a voltage to be applied to the gate node of the driving TFT.