Pixel Unit Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In AMOLED displays, the variation in threshold voltage of drive TFTs leads to inconsistent driving currents across pixels, resulting in uneven brightness and image quality due to process and aging factors, which existing technologies have not adequately addressed.
Innovation Solution
A pixel unit driving circuit with a specific configuration that includes scanning signal lines, power supply lines, a data line, a driving unit, a charging unit, a storage unit, and a lighting control unit, where the driving current is made independent of the threshold voltage of the driving unit by using a fourth switching transistor and a capacitor to rapidly reach saturation state, ensuring uniform brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2T1C pixel unit driving circuit is used, then the circuit structure is simple, but the threshold voltage drift of drive TFT causes inconsistent driving current and uneven brightness
Solution Approach 1:
The pixel unit is divided into multiple functional modules: drive TFT for current generation, switching TFTs for signal control, storage capacitance for voltage holding, and compensation circuitry for threshold voltage correction. This segmentation allows each component to perform its specific function optimally while addressing the brightness uniformity issue through dedicated compensation mechanisms.
Solution Approach 2:
The circuit dynamically adjusts the gate-source voltage of the drive TFT by using storage capacitance to maintain stable voltage levels and employing compensation transistors to correct threshold voltage drift. This parameter stabilization ensures that driving current remains consistent despite process variations and aging effects.
2Ease of operation
If identical grey scale voltages are input to different pixels, then the voltage input is consistent, but different threshold voltages generate different driving currents leading to brightness inconsistency
Solution Approach 1:
The compensation circuitry monitors the actual driving current and adjusts the gate voltage of the drive TFT accordingly. By using feedback mechanisms through compensation transistors and storage capacitance, the circuit corrects for threshold voltage variations, ensuring that each pixel receives the appropriate adjusted voltage to produce consistent brightness despite manufacturing variations.
Solution Approach 2:
The storage capacitance is pre-charged to the required voltage level during the programming phase, and compensation transistors are configured in advance to counteract expected threshold voltage drift. This preliminary setup ensures that when the pixel operates, the driving current is already optimized for consistent brightness without requiring real-time adjustment.
3Manufacturing precision
If the storage unit charging time is extended to ensure stable voltage, then the brightness uniformity improves, but the response speed of the pixel unit decreases
Solution Approach 1:
The pixel unit operates in periodic cycles: during the programming phase, the storage capacitance is quickly charged to the required voltage level; during the display phase, the stored voltage is maintained with minimal additional charging. This periodic charging strategy ensures both fast response and stable voltage without requiring continuous extended charging.
Solution Approach 2:
The storage capacitance is pre-charged to the exact voltage level needed during the programming phase before the display phase begins. This preliminary charging action ensures that the voltage is stable and ready for immediate display operation, eliminating the need for extended charging during the response-critical display phase and thus maintaining fast response speed while ensuring brightness uniformity.
Data Source
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Figure 3
AI summary
The embodiment of the present disclosure provides a pixel unit driving circuit comprising: a driving unit; a charging unit; a storage unit configured to be charged during the charging stage of the pixel unit driving circuit, and provide a control voltage to the driving unit during a driving stage of the pixel unit driving circuit; a lighting control unit configured to make that a driving current provided from the driving unit to the lighting element during the driving stage of the pixel unit driving circuit is independent on a threshold voltage of the driving unit; and the driving control unit connected to the lighting control unit, the storage unit and the driving unit and configured to control the supply of the control voltage of the driving unit. According the embodiments of the present disclosure, the influence of the threshold voltage of the driving unit on the operating current is eliminated by providing the lighting control unit and the driving control unit, so as to moderate the drift of the threshold voltage caused by process procedure and a long term operation and to ensure the uniformity of the displayed brightness of the lighting element.