Pixel Circuit Back Gate Electrode Threshold Voltage Compensation
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Solution Overview
Problem
Display devices face issues with luminance changes due to deviations in threshold voltages of driving transistors, leading to reduced driving current range and mura (image defects) in pixel circuits.
Innovation Solution
The pixel circuit design includes a first driving transistor with a back gate electrode connected to a second node, a second driving transistor with a back gate electrode connected to a first node, and additional transistors and capacitors to manage gate and back gate voltages, increasing the driving range and reducing current changes with voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit with a single driving transistor is used, then the circuit structure is simple, but the driving range is limited and luminance changes occur due to threshold voltage deviations
Solution Approach 1:
The pixel circuit is divided into multiple driving transistors (first driving transistor and second driving transistor) with separate gate electrodes and back gate electrodes. This segmentation allows independent control of channel formation and threshold voltage compensation, enabling the circuit to maintain stable luminance output while reducing the impact of threshold voltage deviations. Each transistor segment performs a specific function: one segment forms the conduction channel while another segment compensates for threshold voltage variations.
Solution Approach 2:
The invention introduces back gate electrodes in addition to the conventional gate electrodes, adding a new control dimension to the transistor operation. By applying voltages to the back gate electrodes, the threshold voltages of the driving transistors can be dynamically adjusted and compensated. This additional dimensional control (back gate voltage) enables precise luminance stability without increasing the basic transistor count excessively.
2Reliability
If multiple driving transistors with back gate electrodes are added, then the driving range increases and luminance stability improves, but the device complexity increases
Solution Approach 1:
The back gate electrodes serve multiple functions: they compensate for threshold voltage deviations, extend the driving range, and maintain luminance stability across different operating conditions. By making the back gate electrode structure multi-functional, the invention reduces the need for additional separate compensation circuits or transistors, thereby limiting the increase in overall device complexity while achieving improved luminance stability.
Solution Approach 2:
The invention merges the threshold voltage compensation function with the driving function by integrating back gate electrodes directly into the driving transistor structure. Instead of using separate compensation transistors or circuits, the back gate electrodes are combined with the gate electrodes to form an unified control system that simultaneously drives the light emitting element and compensates for threshold voltage variations.
3Ease of operation
If threshold voltage deviations are not compensated, then the circuit operation is straightforward, but luminance changes occur and mura defects appear
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the back gate electrodes receive compensation voltages based on the threshold voltage deviations of the driving transistors. This feedback loop continuously adjusts the back gate voltages to counteract threshold voltage variations, thereby maintaining stable luminance output and preventing mura defects. The feedback is achieved through the interconnected gate and back gate electrode structures that sense and compensate for voltage deviations in real-time.
Solution Approach 2:
The back gate electrodes apply preliminary compensatory voltages to counteract threshold voltage deviations before they cause significant luminance variations or mura defects. By proactively adjusting the back gate voltages in response to detected threshold voltage changes, the circuit prevents harmful luminance variations from occurring in the first place, rather than merely correcting them after they manifest.
Data Source
AI summary
A pixel circuit includes a first driving transistor including a gate electrode connected to a first node, a first electrode to receive a first power voltage, and a second electrode connected to a second node, a second driving transistor including a gate electrode and a second electrode connected to the second node, a first electrode to receive the first power voltage, and a back gate electrode connected to the first node, a write transistor including a first electrode to receive a data voltage and a second electrode connected to the first node, an initialization transistor including a gate electrode to receive an initialization gate signal, a first electrode to receive an initialization voltage, and a second electrode connected to the second node, a storage capacitor connected to the first and second nodes, and a light emitting element connected to the second node and configured to receive a second power voltage.