Organic EL Emission Driver Circuit Size Reduction
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Solution Overview
Problem
Conventional organic EL display devices require a large number of transistors for the emission driver circuit, increasing the circuit size and power consumption due to the use of CMOS circuits, which generates shoot-through currents during input transitions.
Innovation Solution
The proposed solution involves an active matrix display device with a reduced circuit size emission driver, utilizing OFF-control and ON-control switching elements to control the electric potential of emission control lines, eliminating the need for additional power supply lines and reducing shoot-through currents by using two transistors per emission line, specifically designed for organic EL display devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMOS circuits are used for the emission driver, then the emission driver can be implemented, but the circuit size increases and power consumption increases due to shoot-through currents
Solution Approach 1:
The patent extracts and eliminates the shoot-through current problem by removing the need for complementary transistor pairs. Instead of using CMOS circuits with both n-channel and p-channel transistors, the invention uses only n-channel transistors configured as switching elements, thereby extracting the harmful shoot-through current path from the circuit design.
Solution Approach 2:
The patent employs simple n-channel transistor switching elements that are easier to manufacture and consume less power compared to complex CMOS circuits. These switching elements are designed to be turned on and off sequentially to control emission lines, replacing the need for expensive and power-consuming complementary transistor structures.
2Reliability
If CMOS circuits are used for the emission driver, then the emission driver can be implemented, but power consumption increases due to shoot-through currents
Solution Approach 1:
The patent converts the potential harm of shoot-through currents into a benefit by designing a circuit that intentionally uses sequential switching of n-channel transistors to control emission lines. The switching elements are designed to be turned on and off in a specific sequence, thereby preventing shoot-through currents while maintaining efficient power consumption.
3Device complexity
If two transistors per emission line are used, then the circuit size is reduced, but the electron mobility requirements become more stringent
Solution Approach 1:
The patent applies preliminary charging to the drive capacitance element before the actual emission control operation. This preliminary action ensures that the capacitance element is pre-charged to the required voltage level, compensating for the lower electron mobility of the transistors and ensuring reliable display quality even with reduced transistor count.
Data Source
AI summary
An organic EL display device includes an emission driver that has an ON-control transistor (T1e) and an OFF-control transistor (T2e) for each emission line. The ON-control transistor (T1e) in the i-th row has its gate terminal and drain terminal connected to the scanning line (Si+1) in the (i+1)th row whereas its source terminal is connected to the emission line (EMi) in the i-th row. The OFF-control transistor (T2e) in the i-th row has its gate terminal connected to the scanning line (Si−1) in the (i−1)th row, whereas its drain terminal is connected to the emission line (EMi) in the i-th row, and its source terminal is connected to a LOW level logic power supply line (VSS).