Display Pixel Circuit Using Diode-Connected NMOS for Uniform Luminance
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Solution Overview
Problem
Driving transistors of display devices, such as OLEDs, exhibit varying threshold voltages due to process variation and degradation, leading to non-uniform luminance in pixels.
Innovation Solution
A pixel design incorporating N-type metal oxide semiconductor (NMOS) transistors performs threshold voltage compensation in a diode connection method, using a diode-connected driving transistor to store the threshold voltage in a storage capacitor, allowing for faster and more accurate luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the source follower method is used for threshold voltage compensation, then the driving transistor threshold voltage can be stored in the storage capacitor, but a long time is required for accurate threshold voltage storage
Solution Approach 1:
The patent inverts the conventional source follower method by using a diode connection configuration where the gate and drain of the driving transistor are connected together. This inversion allows the threshold voltage to be directly transferred to the storage capacitor during the write period without requiring extended compensation time, thereby achieving both high accuracy and fast operation.
Solution Approach 2:
The patent changes the operational parameters of the transistor by switching from source follower mode to diode connection mode. This parameter change enables the threshold voltage compensation to occur rapidly during the write period when the write signal is active, eliminating the time delay inherent in the source follower method while maintaining accurate threshold voltage storage.
2Reliability
If traditional threshold voltage compensation methods are used, then luminance non-uniformity can be addressed, but the compensation process requires a long time
Solution Approach 1:
The patent inverts the conventional approach by implementing threshold voltage compensation during the write period through diode connection rather than during the emission period through source follower action. This inversion enables luminance uniformity to be achieved without compromising display refresh efficiency, as the compensation occurs in parallel with data writing.
Solution Approach 2:
The patent performs threshold voltage compensation as a preliminary action during the write period before the emission period begins. By using the diode connection method to store the threshold voltage in advance, the display device ensures luminance uniformity is established beforehand, allowing the emission period to proceed without time-consuming compensation delays.
3Productivity
If the diode connection method is used for threshold voltage compensation, then rapid and accurate compensation can be achieved, but specific transistor configurations are required
Solution Approach 1:
The patent applies multi-functionality to the driving transistor by enabling it to operate in diode connection mode for threshold voltage compensation while maintaining its primary function of driving the light emitting element. The same transistor structure serves dual purposes: rapid threshold voltage storage during the write period and current driving during the emission period, thereby achieving fast compensation without adding extra transistors or complex configurations.
Solution Approach 2:
The patent merges the threshold voltage compensation function with the data writing operation by using the diode connection method. The compensation process is combined with the normal write operation, allowing threshold voltage to be stored in the capacitor during the same time window used for data input, thus achieving rapid compensation without increasing device complexity or requiring separate compensation circuits.
Data Source
AI summary
A pixel of a display device includes a first transistor including a gate connected to a gate node, a first terminal connected to a drain node, and a second terminal connected to a source node, a second transistor configured to transfer a first power supply voltage to the gate node in response to an initialization signal, a third transistor configured to diode-connect the first transistor in response to a write signal, a fourth transistor configured to transfer a second power supply voltage to the source node in response to the write signal, a fifth transistor configured to transfer the first power supply voltage to the drain node in response to an emission signal, a capacitor including a first electrode connected to a data line, and a second electrode connected to the gate node, and a light emitting element including an anode connected to the source node, and a cathode which receives the second power supply voltage.