EL Display Pixel Circuit for Low-Power Charge Retention
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Solution Overview
Problem
Existing self-luminous display devices face challenges in reducing power consumption and circuit size while maintaining image quality, particularly in EL display devices where increased power consumption is a concern.
Innovation Solution
The display device incorporates a specific transistor configuration and capacitive element arrangement that includes first and second transistors controlled by different control signals, along with a capacitive element to manage voltage and current flow efficiently, utilizing metal oxide semiconductor properties to minimize leakage and enhance charge retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional transistor configurations are used in EL display devices, then circuit functionality is maintained, but power consumption increases and circuit size expands
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks with distinct transistors (first through fourth transistors) each performing specific functions: data writing, threshold correction, initialization, and light emission control. This segmentation allows optimized current paths and reduced leakage in each segment, lowering overall power consumption while maintaining necessary circuit functions.
Solution Approach 2:
The capacitive element stores voltage information in advance during the data writing period, and the initialization transistor pre-charges or pre-discharges nodes before the light emission phase. This preliminary action ensures that the correct current flows through the EL element during emission without requiring continuous power supply adjustments, reducing power consumption.
2Area of stationary object
If conventional transistor configurations are used in EL display devices, then circuit functionality is maintained, but circuit size increases
Solution Approach 1:
The capacitive element serves dual purposes: it stores the data voltage for the current frame and also functions as part of the threshold correction mechanism by maintaining voltage levels across the drive transistor. This merging of functions reduces the need for separate dedicated components, thereby reducing overall circuit area.
Solution Approach 2:
The drive transistor serves multiple functions: it acts as the primary current regulator for the EL element, participates in threshold voltage correction through its gate connection to the capacitive element, and enables initialization through the initialization transistor. This multi-functionality reduces the total transistor count and circuit size compared to dedicated separate circuits for each function.
3Use of energy by moving object
If charge retention is improved in the capacitive element, then power consumption decreases, but leakage current management becomes more challenging
Solution Approach 1:
The capacitive element is connected to the gate of the drive transistor, creating a feedback mechanism where the stored voltage directly controls the transistor's gate-source voltage. This feedback ensures that the voltage stored in the capacitive element is maintained at the correct level throughout the light emission period, improving charge retention reliability while the controlled current flow reduces power consumption.
Solution Approach 2:
The initialization transistor changes the voltage state of the capacitive element and associated nodes between frames by connecting them to initialization voltage lines. This parameter change (voltage level adjustment) resets the system to a known state, ensuring reliable charge retention for the next frame while allowing the capacitive element to hold charge at optimal levels during emission, reducing leakage.
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 reduces power consumption by effectively managing charge retention and current flow, thereby improving the efficiency and longevity of the display device.
Implementation Method 1
a capacitive element electrically connected between the first node and the third node
Implementation Method 2
utilizing metal oxide semiconductor properties to minimize leakage and enhance charge retention
Data Source
AI summary
A display device includes a first transistor whose switching is controlled by a first control signal and connected between an image data signal line to which a data voltage is supplied and a first node, a third transistor whose switching is controlled by the first control signal and connected between the first node and a second node, a second transistor having a gate electrode connected to the second node and connected between a power line to which a constant voltage is supplied and the third node, a fourth transistor whose switching is controlled by the first control signal and connected between a reference voltage power line to which a reference voltage is supplied and the second node, and a fifth transistor whose switching is controlled by a second control signal and connected between an initialization voltage power line to which an initialization voltage is supplied and the third node.