Display Pixel Circuit With Threshold-Compensated MOSFET Current Control
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Solution Overview
Problem
Existing display devices, particularly high-resolution panels used in Head Mounted Displays (HMDs), face challenges in achieving stable and efficient pixel operation due to variations in transistor threshold voltages, which affect luminance and image quality.
Innovation Solution
A pixel design incorporating a diode-connected transistor and a storage capacitor, along with a specific transistor configuration, including P-type MOSFETs, to minimize threshold voltage variations and stabilize current flow, allowing for wider data signal voltage ranges and improved luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transistor configurations are used in high-resolution panels, then manufacturing is simpler, but threshold voltage variations cause unstable current flow and poor luminance consistency
Solution Approach 1:
The patent implements a feedback mechanism where the third transistor's gate electrode is connected to its drain electrode (diode connection), creating a self-regulating circuit that compensates for threshold voltage variations. This feedback loop stabilizes the current flowing through the light emitting element by automatically adjusting the third transistor's conductivity based on voltage fluctuations, thereby resolving the contradiction between reliability and complexity.
Solution Approach 2:
The pixel circuit is designed to compensate for its own threshold voltage variations using internal components rather than external control. The storage capacitor maintains the gate voltage of the first transistor, while the diode-connected third transistor automatically adjusts to counteract threshold voltage drift, enabling the circuit to self-correct and maintain stable current flow without additional control circuits.
2Illumination intensity
If transistor threshold voltage variations are not compensated, then device structure is simpler, but luminance consistency deteriorates
Solution Approach 1:
The storage capacitor is charged beforehand to a voltage that compensates for the threshold voltage of the first transistor. This preliminary action ensures that when the pixel operates, the gate voltage of the first transistor already accounts for threshold variations, resulting in stable current flow and consistent luminance output without requiring real-time complex adjustments.
Solution Approach 2:
The patent changes the electrical parameters of the circuit by using a diode-connected transistor configuration, which alters the voltage-current relationship. This parameter change enables the third transistor to dynamically adjust its effective resistance, compensating for threshold voltage variations and maintaining consistent luminance across different pixels and operating conditions.
3Reliability
If more transistors are added to compensate for threshold voltage, then current stability improves, but pixel area increases
Solution Approach 1:
The patent merges the function of the third transistor with the pixel's output node by connecting its gate to its drain (diode connection). This merging allows the third transistor to serve dual purposes: as a current regulation element and as part of the pixel's output structure. By combining functions into fewer components, the design achieves stable current flow without proportionally increasing the pixel area.
Solution Approach 2:
The third transistor is designed with multi-functionality, serving as both a current regulation device and a voltage compensation element. Its diode connection enables it to participate in both the current mirror configuration and the threshold voltage compensation mechanism, reducing the need for separate compensation components and thereby minimizing pixel area while maintaining operational stability.
Data Source
AI summary
A pixel includes: a light emitting element; a first transistor including a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to an anode electrode of the light emitting element; a second transistor connected between a data line and the first node, the second transistor including a gate electrode connected to a first scan line; and a third transistor connected between a first power line and the second node, the third transistor including a gate electrode connected to the second node.