OLED Pixel Circuit Layout for Leakage and Kickback Control
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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 that includes a driving p-channel MOS 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, and a second capacitor to manage parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If n-channel MOS switching transistors are used in the pixel circuit, then leakage current is reduced and display quality is improved, but kickback effect and parasitic capacitance cause voltage instability
Solution Approach 1:
A compensation transistor is introduced as an intermediary element between the switching transistor and the OLED. This compensation transistor actively counteracts the kickback effect by providing a compensating current that offsets the voltage instability caused by the switching transistor's parasitic capacitance, thereby maintaining stable OLED operation without changing the beneficial low-leakage characteristics of the n-channel MOS switching transistor.
Solution Approach 2:
The invention changes the electrical parameters of the pixel circuit by adding the compensation transistor, which modifies the current distribution and voltage levels in the circuit. This parameter change allows the system to maintain the low leakage current advantage of n-channel MOS transistors while compensating for the harmful kickback effect through active parameter adjustment during operation.
2Device complexity
If the pixel circuit uses conventional transistor configuration, then device complexity is low, but leakage current degrades display quality
Solution Approach 1:
The pixel circuit is segmented into distinct functional blocks: a driving transistor for current control, switching transistors for signal routing, and a compensation transistor for kickback effect mitigation. This segmentation allows each transistor to perform its specific function optimally, with the compensation transistor dedicated to addressing leakage and kickback issues without interfering with the primary switching and driving functions.
Solution Approach 2:
Different regions of the pixel circuit are assigned different transistor types with optimized characteristics. The compensation transistor is specifically positioned and configured to address the local issue of kickback effect near the OLED, while n-channel MOS switching transistors are used in switching positions where low leakage is critical. This local optimization ensures that each part of the circuit has the quality needed for its specific function.
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.