OLED Pixel Driving Circuit Flicker Reduction
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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, which affect the emission delay and overall display quality.
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 during the emission section, minimizing current delay and flicker phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel driving circuit is used, then the device structure is simple, but luminance uniformity deteriorates due to threshold voltage differences and mobility variations in driving TFTs
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 node, enabling rapid voltage increase during the emission period and compensating for threshold voltage differences and mobility variations, thereby improving luminance uniformity without significantly complicating the overall device structure
Solution Approach 2:
The invention changes the voltage parameter dynamics by using the coupling capacitor to rapidly increase the gate voltage during emission. This dynamic parameter adjustment compensates for TFT variations and ensures consistent current flow to the OLED, resolving the luminance uniformity issue
2Reliability
If the emission control signal is applied normally, then the emission timing is controlled, but current delay occurs due to parasitic capacitance and voltage changes, causing flicker
Solution Approach 1:
The coupling capacitor is pre-charged during the programming period with the data voltage. When the emission control signal is applied, this pre-charged capacitor rapidly discharges to increase the gate voltage, eliminating the delay that would otherwise occur due to parasitic capacitance and ensuring timely current flow to the OLED
Solution Approach 2:
The coupling capacitor enables the gate voltage to rapidly increase during the emission period, effectively 'rushing through' the delay that would normally occur due to parasitic capacitance and voltage changes, thereby maintaining accurate emission timing and preventing flicker
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 reduces flicker by ensuring consistent current flow to the organic light emitting diode, enhancing display stability and minimizing luminance differences between pixels.
Implementation Method 1
a coupling capacitor electrically connected in series to the storage capacitor and configured to cause capacitive coupling so as to supply a bootstrapped voltage to the gate node of the driving TFT
Data Source
AI summary
An organic light emitting display device includes a plurality of pixels each having a pixel driving circuit. Each of the pixels includes an organic light emitting diode and a driving TFT that controls driving of the organic light emitting diode and includes an active layer of low temperature poly-silicon, a gate node, a source node, and a drain node. The pixels include first to fifth switching TFTs electrically connected to the driving TFT and each including an active layer of an oxide semiconductor, a gate node, a source node, and a drain node. Further, the pixels include a storage capacitor connected between the gate node of the driving TFT and the source node of the fifth switching TFT and a coupling capacitor electrically connected in series to the storage capacitor and configured to cause capacitive coupling to supply a bootstrapped voltage to the gate node of the driving TFT.