Digital EL Display Driver Circuit Segmentation for Power and Speed
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Solution Overview
Problem
Existing digital display devices, particularly active matrix electroluminescence (EL) displays, face challenges in achieving high-speed operation and increasing the number of display gradations due to large parasitic capacitance loads on data lines, which require high-amplitude digital signals for adequate switching of driver transistors, leading to limited gradation display capabilities.
Innovation Solution
A digital light emitting device with a driver transistor, a control transistor, and a control capacitor that allows for the control of the gate potential of the driver transistor using a digital data signal, reducing the need for high-amplitude signals and enabling efficient power supply operation, thereby simplifying the driver circuit and reducing power consumption while allowing for high-speed data transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-amplitude digital signals are used to switch driver transistors in existing digital EL display devices, then switching reliability is improved, but power consumption increases and the ability to represent multiple gradations is limited
Solution Approach 1:
The patent segments the single driver transistor function into two separate transistors: a driver transistor for current control and a control transistor for gate potential control. This segmentation allows the control transistor to use low-amplitude digital signals for switching the driver transistor gate, reducing power consumption while maintaining reliable switching through the driver transistor's optimized structure and control mechanism
Solution Approach 2:
The control transistor acts as an intermediary between the digital signal source and the driver transistor. It translates low-amplitude digital signals into effective gate control for the driver transistor, enabling reliable switching without requiring high-amplitude signals directly from the data line, thus reducing power consumption
2Reliability
If high-amplitude digital signals are used to switch driver transistors, then switching reliability is improved, but the number of displayable gradations is limited
Solution Approach 1:
By separating the driver transistor control from the gate potential control into two independent transistor functions, the system can use simple digital signals for the control transistor while the driver transistor handles current modulation. This enables easier implementation of multiple gradations through digital signal combinations without compromising switching reliability
Solution Approach 2:
The patent changes the control parameter from direct high-amplitude voltage control of the driver transistor gate to low-amplitude digital control of a separate control transistor. This parameter change enables the use of standard digital logic levels, facilitating higher gradation representation through digital signal processing while maintaining reliable switching through the driver transistor's optimized characteristics
3Use of energy by moving object
If simple driver circuits are used to reduce power consumption, then power efficiency is improved, but the ability to achieve high-speed operation is reduced due to parasitic capacitance
Solution Approach 1:
The segmentation of driver and control functions into separate transistors allows the control transistor to be optimized for low-power digital switching while the driver transistor is optimized for high-speed current control. This functional separation enables the simple, low-power control circuit to drive the high-speed driver transistor effectively, achieving both power efficiency and high-speed operation
Solution Approach 2:
The patent adds a control dimension by introducing the control transistor between the digital signal and the driver transistor. This additional control layer enables independent optimization of the control path for low power and the driver path for high speed, resolving the contradiction between power efficiency and operation speed
4Productivity
If digital signals with multiple bits are used to represent gradations by controlling light emission period, then the number of displayable gradations is improved, but the complexity of timing control increases
Solution Approach 1:
The control transistor and driver transistor work together in a self-coordinating manner where the digital signal to the control transistor automatically determines the driver transistor's operation. The inherent characteristics of the transistors and their interconnection provide automatic timing coordination, reducing the need for complex external timing control circuits while enabling multiple gradations through digital signal combinations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables easy representation of multiple gradations by controlling the light emission period of emissive elements, reduces power consumption, and increases the number of displayable gradations by using a simple driver circuit and lower parasitic capacitance, facilitating high-speed operation.
Implementation Method 1
a control capacitor connected between a gate of the driver transistor and a control line to which a control pulse signal for controlling a light emission period of the emissive element is supplied
Implementation Method 2
an organic EL element, a selection TFT, a driver TFT, and a storage capacitor... supply operation of power through the driver transistor to the emissive element
Data Source
AI summary
Each pixel in a display device includes an emissive element, a driver transistor, a control transistor, and a control capacitor. The driver transistor is provided between the emissive element and a power supply and controls supply of power from the power supply to the emissive element. The control transistor is connected between a constant voltage power supply and a gate of the driver transistor, receives a digital data signal on a gate, and controls whether or not to fix a gate voltage of the driver transistor. The control capacitor is connected between a control line and the gate of the driver transistor. The gate voltage of the driver transistor is shifted to a voltage corresponding to a control pulse signal when the control transistor is off and is non-fixed during a light emission period defined by the control pulse signal applied to the control line.