OLED Pixel Circuit With PMOS/NMOS Layout for Low Gray Accuracy
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Solution Overview
Problem
Existing organic light-emitting display apparatuses face challenges in reducing power consumption without compromising display quality, particularly in accurately displaying low gray-scale images due to transistor mobility and reliability issues and leakage currents.
Innovation Solution
The configuration of transistors within the organic light-emitting display apparatus includes PMOS transistors with polycrystalline silicon for high mobility and reliability, and NMOS transistors with oxide semiconductors for low leakage current, along with specific layer structures and signal control mechanisms to manage driving and light emission control signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transistors are used in the pixel circuit, then the device complexity is reduced, but the power consumption increases and display quality deteriorates due to leakage current and low mobility
Solution Approach 1:
The pixel circuit is divided into multiple transistor components with specific functions: switching transistor (T1) for signal routing, driving transistor (T2) for current control, first light emission control transistor (T3) for emission timing, and second light emission control transistor (T4) for complementary control. Each transistor is optimized for its specific function to achieve high mobility and low leakage current collectively
Solution Approach 2:
Different transistor types are strategically assigned to different circuit positions based on their characteristics: NMOS switching transistor for high-speed switching, PMOS driving transistor for low leakage, and PMOS light emission control transistors for precise emission timing. This local optimization ensures each transistor contributes maximally to overall performance
2Manufacturing precision
If transistors with high mobility are used, then display quality improves, but power consumption increases due to higher current flow
Solution Approach 1:
The light emission control transistors (T3 and T4) are configured to operate periodically based on emission control signals, enabling light emission only during specific time periods. This periodic operation allows high-mobility transistors to deliver precise current control during emission while minimizing power consumption during non-emission periods through controlled cutoff
Solution Approach 2:
The circuit incorporates feedback mechanisms where the driving transistor current is controlled based on stored voltage from the storage capacitor, which reflects previous emission states. This feedback loop enables the high-mobility transistors to maintain precise display quality while automatically adjusting current levels to optimize power consumption
3Measurement precision
If conventional transistor configuration is used, then the device structure is simple, but leakage current increases and low gray-scale image accuracy deteriorates
Solution Approach 1:
The circuit employs asymmetric transistor configuration where PMOS transistors (T2, T3, T4) are used for positions requiring low leakage current, while NMOS transistor (T1) is used for switching applications. The complementary PMOS pair (T3 and T4) provides asymmetric control for precise gray-scale management, ensuring low leakage current while maintaining accurate low gray-scale image display
Solution Approach 2:
The storage capacitor is pre-charged to store voltage corresponding to the desired gray-scale level before emission. The light emission control transistors are pre-configured in their off-state to prevent leakage current during non-emission periods. This preliminary preparation ensures that when emission occurs, the precise gray-scale level is maintained without interference from leakage current
Data Source
AI summary
An organic light-emitting display apparatus includes an organic light-emitting diode, a switching transistor, a first light emission control transistor, and a driving transistor. The organic light-emitting diode includes an anode and a cathode for receiving a reference voltage. The switching transistor includes a gate electrode for receiving an nth scan signal and a source electrode for receiving a data signal, and is an NMOS transistor. The first light emission control transistor includes a gate electrode for receiving a light emission control signal, and is configured to turn on upon receiving the light emission control signal to determine a timing of flow of a driving current to the organic light-emitting diode, and is a PMOS transistor. The driving transistor is connected to the switching transistor and the first light emission control transistor and provides the driving current to the organic light-emitting diode.