OLED Pixel Circuit Voltage Division Compensation for Mura
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Solution Overview
Problem
In large-sized displays, traditional OLEDs face issues with power consumption, voltage drop, and non-uniform brightness due to internal resistance and threshold voltage variations, leading to defects like mura and ghosting.
Innovation Solution
A pixel circuit design featuring a control thin film transistor, a drive thin film transistor, a storage capacitor, and a voltage division control module, which charges the storage capacitor to a reference voltage and outputs a low level in the compensation phase, ensuring current through the light-emitting device is independent of the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional passive matrix OLED is used for large-sized display, then display size can be increased, but power consumption increases and voltage drop occurs
Solution Approach 1:
The patent transitions from static passive matrix driving to dynamic active matrix driving with switching transistors that progressively scan and control current to each pixel, enabling large displays to be driven efficiently with reduced power consumption and voltage drop
2Speed
If large current is applied to drive pixels in large-sized display, then driving speed improves, but voltage drop on ITO line increases and operation voltage becomes too high
Solution Approach 1:
The patent segments the display into independently controllable pixel units, each with its own switching transistor that progressively scans and controls current, allowing fast response without requiring excessive current or voltage across the entire display
3Device complexity
If power supply lines with resistance are used to supply drive currents to all pixels, then power distribution is simplified, but internal resistance drop causes voltage difference and mura defect
Solution Approach 1:
The patent segments the power distribution by providing independent power supply terminals to each pixel unit, isolating the electrical characteristics of each pixel and eliminating the internal resistance drop effects that cause mura defects
Solution Approach 2:
Each pixel unit is equipped with its own power supply terminal and control circuitry, allowing local adjustment and independent operation, ensuring that voltage variations in one region do not affect other regions
4Device complexity
If storage capacitor is connected between drive thin film transistor and anode of light-emitting diode, then circuit structure is simplified, but threshold voltage differences and drift cause current variation and ghosting
Solution Approach 1:
The patent introduces a compensation capacitor as an intermediary element that decouples the drive transistor from direct dependence on threshold voltage, storing compensation charges that stabilize the drive current against threshold voltage variations and drift
Solution Approach 2:
The compensation capacitor creates a feedback mechanism that automatically adjusts to threshold voltage changes, maintaining stable drive current and preventing ghosting defects without requiring complex external control
Data Source
AI summary
The present invention provides a pixel circuit, a display substrate and a display panel. The pixel circuit comprises a power supply terminal; a control thin film transistor; a drive thin film transistor; a storage capacitor; a light-emitting device, the pixel circuit further comprises a voltage division control module and a voltage division capacitor, the voltage division control module is used for charging the storage capacitor in the pre-charging phase of the pixel circuit, so that voltage of the gate of the drive thin film transistor becomes a reference voltage, and the voltage division control module is capable of outputting a low level to the second end of the storage capacitor in the compensation phase of the pixel circuit. A first end of the voltage division capacitor is connected to the first end of the storage capacitor, a second end thereof is connected to the cathode of the light-emitting device.