OLED Pixel Circuit Layout for Low-Frequency Leakage Compensation
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Solution Overview
Problem
Organic light emitting display devices face display quality degradation due to leakage currents in switching transistors, which are exacerbated at low frequencies.
Innovation Solution
The implementation of a pixel structure with a p-channel MOS driving transistor and n-channel MOS switching transistors, along with a first capacitor formed by overlapping a second gate pattern and a third gate pattern to reduce the kickback effect, enhances reliability and prevents display quality degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If switching transistors are used in the pixel circuit, then the pixel can be driven and controlled, but leakage current occurs in the transistors which degrades display quality
Solution Approach 1:
The patent introduces a compensation transistor as an intermediary element that mediates between the switching transistor and the OLED. This compensation transistor actively compensates for the leakage current effects by adjusting its own current to counterbalance the leakage, thereby maintaining display quality without compromising the switching control functionality
Solution Approach 2:
The pixel circuit implements a feedback mechanism where the compensation transistor continuously monitors and compensates for leakage current in real-time. The circuit uses the leakage current information to adjust the compensation transistor's operation, creating a closed-loop system that maintains stable display performance despite transistor leakage
2Loss of energy
If low frequency driving is used, then power consumption is reduced, but leakage current impact increases and degrades display quality
Solution Approach 1:
The compensation transistor is designed to preemptively counteract the leakage current effects before they can significantly degrade display quality. By continuously compensating during low-frequency operation, the circuit prevents the accumulation of leakage effects that would otherwise occur during extended between-frame intervals
Solution Approach 2:
The feedback mechanism remains active during low-frequency driving, continuously monitoring and compensating for leakage current. This ensures that even when power consumption is reduced through low-frequency operation, the display quality is maintained through real-time leakage compensation
3Reliability
If multiple transistors are added to compensate for leakage, then display quality is improved, but device complexity increases
Solution Approach 1:
The compensation mechanism is applied locally and selectively only where leakage current significantly impacts display quality, rather than uniformly across all transistors. The compensation transistor is strategically positioned to compensate for the most critical leakage paths in the pixel circuit, optimizing the balance between complexity and performance
Data Source
AI summary
An organic light emitting display device includes a plurality of pixels. Each of the pixels includes an organic light emitting diode, first to third transistors, a storage capacitor, and a first capacitor. The second transistor includes a gate electrode receiving a first scan signal, a first electrode receiving a data signal, and a second electrode connected to a first electrode of the first transistor. The third transistor includes a gate electrode receiving a second scan signal, a first electrode connected to a second electrode of the first transistor, and a second electrode connected to a gate electrode of the first transistor. The storage capacitor includes a first electrode receiving a power voltage and a second electrode connected to the gate electrode of the first transistor. The first capacitor includes a first electrode connected to the gate electrode of the third transistor and a second electrode receiving the power voltage.