Pixel Driving Circuit for Electroluminescent Displays
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Solution Overview
Problem
Electroluminescent display devices face issues with non-uniform luminance and luminance deterioration during variable frequency driving, particularly at low speeds, due to leakage currents and hysteresis in the driving transistors, which affect image quality and power consumption.
Innovation Solution
The implementation of a pixel driving circuit with a light emitting diode, a driving transistor, and a capacitor, where the transistor is initialized during an initialization period, threshold voltage compensation and data voltage charging occur during a sampling period, and the light emitting diode emits light during a light emission period, with a fixed voltage applied to the source of the driving transistor to reduce luminance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the driving frequency is lowered to reduce power consumption, then power consumption is reduced, but luminance uniformity deteriorates due to leakage current and hysteresis
Solution Approach 1:
The patent applies preliminary action by initializing the gate voltage of the driving transistor before the light emission period at each frame. This initialization step proactively compensates for leakage current accumulation and hysteresis effects that would otherwise occur during low-speed driving, thereby maintaining luminance uniformity while enabling reduced power consumption through lower driving frequencies
Solution Approach 2:
The patent changes the gate voltage parameter dynamically by applying different voltages during different periods: a first voltage during the light emission period and a second voltage (initialization voltage) during the initialization period. This parameter change compensates for transistor hysteresis and leakage effects, maintaining luminance stability across variable frame rates while allowing power consumption to be reduced through frequency variation
2Device complexity
If P-type polysilicon transistors are used in the pixel driving circuit, then device complexity is reduced, but leakage current increases during low-speed driving
Solution Approach 1:
The patent converts the harmful leakage current effect into a beneficial compensation mechanism. By intentionally applying initialization voltages and designing the pixel circuit to account for leakage current accumulation over frames, the system transforms the previously harmful effect into a predictable and compensatable phenomenon, maintaining display quality while using simpler P-type polysilicon transistors
3Use of energy by moving object
If frame rate is reduced for power saving, then power consumption is reduced, but luminance deterioration occurs due to hysteresis during screen switching
Solution Approach 1:
The patent applies preliminary action by performing gate voltage initialization before each light emission period. This proactive measure prevents hysteresis-induced luminance deterioration from occurring in the first frame during screen switching events, ensuring consistent luminance quality even when operating at reduced frame rates for power saving
Solution Approach 2:
The patent implements periodic initialization of the gate voltage at each frame cycle. This periodic action systematically addresses hysteresis effects that accumulate during low-speed driving and screen switching, maintaining luminance quality across variable frame rates while enabling power consumption reduction through frequency variation
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 luminance deterioration and leakage currents, maintaining consistent luminance across frames and reducing power consumption by optimizing the driving circuit's operation during variable frequency driving.
Implementation Method 1
the light emitting diode emits light during a light emission period
Data Source
AI summary
An electroluminescent display device comprises subpixels each including a pixel driving circuit driven in accordance with an initialization period, a sampling period and a light emission period. The pixel driving circuit includes a light emitting diode, a driving transistor including a gate connected to a first node, a drain connected to a second node, and a source connected to a third node, a first switching circuit turned on for the initialization period, providing an initialization voltage to the first node and providing a fixed voltage to the third node, a second switching circuit turned on for the sampling period, applying a data voltage to the third node and providing the initialization voltage to an anode of the light emitting diode, and a light emitting control circuit controlled by an emission signal and turned on for the light emission period to provide a high potential voltage to the third node.