Pixel Circuit Transistor Segmentation for Mura Reduction
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Solution Overview
Problem
Display devices experience unintended stains such as mura due to voltage drops at the source node of driving transistors caused by kick-back at the falling edge of emission control signals, leading to suboptimal display performance.
Innovation Solution
A pixel configuration that includes specific transistors and capacitors to compensate for threshold voltage and control current flow, with separate transistors handling compensation and emission operations, reducing voltage drops and improving display clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single transistor is used for both threshold voltage compensation and light emission control, then device complexity is reduced, but voltage drops occur at the source node causing mura phenomenon
Solution Approach 1:
The patent divides the single transistor function into two separate transistors: a first transistor dedicated to threshold voltage compensation and a second transistor dedicated to light emission control. This segmentation eliminates the kick-back effect that occurs when a single transistor performs both functions, as the compensation operation is isolated from the emission control operation, preventing voltage drops at the source node during emission.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element that stores the compensated threshold voltage. The capacitor acts as a mediator between the compensation phase and the emission phase, maintaining the compensated voltage level throughout the emission period and preventing voltage fluctuations that would cause mura.
2Device complexity
If threshold voltage compensation is performed during emission control, then device structure is simplified, but voltage stability deteriorates causing kick-back effect
Solution Approach 1:
The patent separates the compensation function and emission control function into distinct time periods and distinct transistor operations. The first transistor operates during a compensation period to establish the threshold voltage, while the second transistor operates during the emission period to control light output. This temporal and functional segmentation ensures voltage stability by preventing the kick-back effect that occurs when both operations share the same transistor.
Solution Approach 2:
The patent performs threshold voltage compensation in advance during a dedicated compensation period before the emission period begins. This preliminary action ensures that the threshold voltage is established and stabilized before emission control starts, preventing voltage fluctuations during the actual light emission process.
Data Source
AI summary
A pixel includes a light emitting element, a driving transistor having an electrode electrically connected to an anode electrode of the light emitting element and another electrode electrically connected to a first power source, and controlling a current flowing from the first power source to a second power source, a first transistor electrically connected between a gate electrode of the driving transistor and a reference power source, a second transistor electrically connected between the anode electrode and an initialization power source, a third transistor electrically connected between the gate electrode and a data line, and a fourth transistor and a fifth transistor electrically connected in parallel between the first power source and the another electrode. The fourth transistor compensates a threshold voltage of the driving transistor during a compensation period, and the fifth transistor is turned so that the current is controlled during an emission period.