OLED Pixel Circuit Leakage Current Compensation via Segmented Transistor Control
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Solution Overview
Problem
OLED pixel circuits face challenges with leakage currents due to complex waveforms and thin film transistor (TFT) issues, affecting the stability and efficiency of display devices.
Innovation Solution
A pixel circuit design incorporating a compensation circuit, writing circuit, and power supplying circuit, which uses a first node to provide a driving current based on voltage and system high voltage, with control and emission signals opposing each other to reset and stabilize the voltage, thereby reducing leakage currents and ensuring stable light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If OLED pixel circuits use transistors operated in saturation region as current sources, then power consumption is reduced and response speed is improved, but leakage currents occur through thin film transistors
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a first transistor (T1) for current source operation, a second transistor (T2) for voltage storage, a third transistor (T3) for compensation, and a fourth transistor (T4) for control. This segmentation allows each transistor to perform a specific function, with T1 operating in saturation region for low power consumption while T2, T3, and T4 manage leakage currents through coordinated switching and compensation operations.
2Ease of manufacture
If thin film transistors are used in OLED pixel circuits, then manufacturing is simplified, but leakage currents affect circuit stability
Solution Approach 1:
The third transistor (T3) functions as a compensation transistor that detects and corrects threshold voltage variations in the first transistor (T1). During the compensation phase, T3 adjusts the voltage at the gate of T1 to compensate for leakage-induced threshold shifts, providing negative feedback that maintains circuit stability despite the inherent leakage characteristics of thin film transistors.
Solution Approach 2:
The second transistor (T2) stores a reference voltage during the initialization phase before the actual operation begins. This preliminary voltage storage establishes a stable baseline that compensates for subsequent leakage effects, allowing the circuit to maintain stability throughout the emission and compensation phases without requiring continuous active correction.
3Ease of operation
If complex waveforms are used to control OLED pixel circuits, then light emission control is improved, but leakage currents increase
Solution Approach 1:
The pixel circuit operates through distinct periodic phases: initialization phase where T2 stores reference voltage, emission phase where the OLED emits light controlled by the stored voltage, and compensation phase where T3 corrects threshold variations. This periodic operation allows complex light emission control to be achieved through simple voltage storage and periodic compensation, rather than requiring complex continuous waveforms that would increase leakage.
Data Source
AI summary
A pixel circuit including a compensation circuit, a writing circuit, a light emitting element, and a power supplying circuit is provided. The compensation circuit comprises a first node, and provides a driving current to the light emitting element according to a voltage of the first node and a system high voltage. The writing circuit provides a data voltage to the compensation circuit according to a first control signal so that the compensation circuit sets the voltage of the first node. The power supplying circuit selectively couples the compensation circuit to the light emitting element, and provides the system high voltage and a system low voltage to the compensation circuit, in which the system low voltage is configured to reset the voltage of the first node. The first control signal and the second control signal are opposite to the first emission signal and the second emission signal, respectively.