Pixel Circuit Compensation for AMOLED Threshold Voltage Variations
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Solution Overview
Problem
Active Matrix Organic Light Emitting Diode (AMOLED) display devices face challenges due to threshold voltage variations in thin film transistors, leading to display defects like mura and off-state leaking currents, which existing pixel circuits fail to adequately compensate for.
Innovation Solution
A pixel circuit comprising a driver circuit, switch circuit, compensation circuit, and reset circuit, which includes a storage capacitor and multiple transistors to control the driving current and compensate for threshold voltage variations, reducing leakage currents by providing two leakage paths with opposite polarities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit without compensation is used, then the device complexity is low, but threshold voltage variations cause display defects like mura and leakage currents
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: driver circuit, switch circuit, compensation circuit, and reset circuit. Each module performs a specific function, allowing the compensation of threshold voltage variations without requiring a complete redesign of the entire circuit.
Solution Approach 2:
The compensation circuit performs preliminary compensation for threshold voltage variations before the light emitting stage. By pre-compensating the voltage signal and providing two leakage paths with opposite polarities, the circuit prevents display defects before they occur.
2Reliability
If the pixel circuit includes compensation circuits and multiple transistors, then threshold voltage variations are compensated, but the device complexity increases
Solution Approach 1:
The compensation circuit is designed to perform multiple functions: compensating for threshold voltage variations, providing leakage current paths with opposite polarities, and maintaining driving current stability. This multi-functionality reduces the need for separate circuits for each function.
Solution Approach 2:
The compensation circuit is integrated with the driver circuit and switch circuit, sharing common transistors and nodes. This merging of functions reduces the overall number of discrete components while maintaining the compensation capability.
3Manufacturing precision
If existing pixel circuits are used, then the manufacturing process is simple, but they fail to adequately compensate for threshold voltage variations leading to mura defects
Solution Approach 1:
The compensation circuit changes the electrical parameters by providing two leakage paths with opposite polarities. This parameter change approach compensates for threshold voltage variations without requiring complex manufacturing processes or additional material layers.
4Reliability
If the pixel circuit uses a single leakage path, then the circuit is simpler, but it cannot effectively reduce off-state leaking currents
Solution Approach 1:
The compensation circuit creates two leakage paths with opposite polarities that act as counterweights to each other. The opposite polarity paths balance out the leakage currents, effectively reducing the net off-state leakage without requiring complex additional structures.
Data Source
AI summary
A pixel circuit and a driving method thereof and a display device are disclosed. The pixel circuit includes a switch circuit, a driver circuit, a compensation circuit, a reset circuit and a light emitting element. The driver circuit includes a control terminal, a first terminal and a second terminal and is configured to control a driving current, which runs through the first terminal and the second terminal; the switch circuit is configured to write a data signal to the control terminal in response to a scan signal; the compensation circuit is configured to store the data signal that is written in and electrically connect the control terminal and the second terminal in response to the scan signal; the reset circuit is configured to apply a reset voltage to the compensation circuit in response to a reset signal and electrically connect the control terminal and the first terminal.