OLED Pixel Circuit with Four Transistors for Brightness Uniformity
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Solution Overview
Problem
Conventional OLED display pixel circuits suffer from non-uniformity issues due to impedance in metal wires and variations in transistor threshold voltages, leading to inconsistent brightness across organic light-emitting diodes.
Innovation Solution
A pixel circuit design incorporating four transistors, two capacitors, and a light-emitting element, where the current through the light-emitting element is solely dependent on the capacitors and display data, eliminating the impact of IR-drop and threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pixel circuit with two transistors and one capacitor is used, then device complexity is reduced, but non-uniformity occurs due to impedance and threshold voltage variations
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks with four transistors (T1-T4) and two capacitors (C1, C2), each performing specific functions. This segmentation allows independent optimization of different circuit functions to achieve uniform brightness while managing complexity through modular design.
Solution Approach 2:
The invention changes the circuit parameters by adding additional transistors and capacitors to create a more complex circuit topology. This parameter change enables compensation for impedance effects and threshold voltage variations, thereby improving brightness uniformity across the display panel.
2Ease of manufacture
If simple pixel circuit design is used, then ease of manufacture is improved, but IR-drop causes non-uniform pixel currents
Solution Approach 1:
The pixel circuit implements feedback mechanisms where capacitors C1 and C2 store voltage information and transistors T2 and T3 regulate current flow based on stored charges. This feedback system compensates for IR-drop effects by adjusting pixel current dynamically, ensuring consistent brightness despite impedance variations in metal wires.
Solution Approach 2:
The circuit uses additional components to change the electrical parameters of the pixel circuit, creating multiple charge storage nodes that can compensate for voltage drops. This parameter enhancement improves reliability by maintaining consistent pixel currents across different locations on the display panel.
3Device complexity
If transistor threshold voltage variations are not compensated, then device complexity is reduced, but brightness uniformity deteriorates
Solution Approach 1:
The invention changes the circuit configuration by adding transistors T2 and T3 along with capacitors C1 and C2 to create a more complex circuit topology. This parameter change enables the circuit to compensate for threshold voltage variations in the driving transistor, thereby improving brightness uniformity across all pixels.
Solution Approach 2:
The circuit employs feedback through the capacitor network that stores voltage information and uses additional transistors to regulate current flow. This feedback mechanism compensates for threshold voltage variations, ensuring uniform illumination intensity across the display panel despite manufacturing variations.
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
This design effectively addresses non-uniformity and light-emitting element degradation, enhancing display quality by ensuring consistent pixel currents and improved brightness uniformity across the display panel.
Implementation Method 1
an organic light emitting diode
Implementation Method 2
light emitting element includes an anode and a cathode
Data Source
AI summary
A pixel circuit includes four transistors, two capacitors and a light emitting element. A gate of first transistor receives a scan signal and a source/drain thereof receives a display data. A terminal of first capacitor couples to another source/drain of first transistor. A gate and a source/drain of second transistor couple to another terminal of first capacitor; and another source/drain thereof receives a switch signal. A terminal of second capacitor receives a reset signal; and another terminal thereof couples to another terminal of first capacitor. A gate of third transistor couples to a terminal of first capacitor. A gate of fourth transistor receives an enable signal; a source/drain thereof couples to a first power supply voltage; and another source/drain thereof couples to one source/drain of third transistor. The anode and cathode of the light emitting element couple to one source/drain of third transistor and a second power supply voltage, respectively.