LED Pixel Circuit Threshold Compensation for Brightness Uniformity
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Solution Overview
Problem
AMOLED display panels experience brightness non-uniformity due to varying threshold voltages of Thin Film Transistors (TFTs) across different positions, leading to inconsistent driving currents and display brightness.
Innovation Solution
A LED pixel unit circuit is designed with a driving module and a matching TFT to compensate for threshold voltage differences by charging and discharging a capacitor, and a reference voltage is introduced to eliminate the influence of internal resistance, ensuring consistent driving currents across the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2T1C pixel driving circuit is used, then the circuit structure is simple, but the brightness uniformity deteriorates due to threshold voltage variations of TFTs at different positions
Solution Approach 1:
The patent introduces a compensation circuit that dynamically adjusts the gate-source voltage of the driving TFT by changing the voltage stored in the storage capacitor. This parameter change compensates for threshold voltage variations, ensuring consistent driving currents and brightness uniformity across different positions of the display panel.
Solution Approach 2:
The patent introduces a storage capacitor and compensation transistor as intermediary elements between the data line and the driving TFT. These intermediaries store and adjust the voltage signals to compensate for threshold voltage differences, thereby improving brightness uniformity without significantly increasing overall circuit complexity.
2Ease of manufacture
If TFTs are manufactured with the same process parameters, then the manufacturing process is consistent, but the threshold voltages at different positions vary significantly
Solution Approach 1:
The patent implements a feedback mechanism where the compensation transistor and storage capacitor form a circuit that automatically adjusts for threshold voltage variations. The circuit measures the actual threshold voltage effect and compensates for it by adjusting the stored voltage, thereby achieving precise threshold voltage uniformity despite variations in manufacturing processes.
3Ease of operation
If the same gray-scale voltage is applied to all pixels, then the voltage control is simple, but the driving currents differ due to threshold voltage variations
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage capacitor to a specific voltage level before the actual display operation. This preliminary voltage storage is calculated to compensate for the threshold voltage of the driving TFT, so that when the same gray-scale voltage is applied to all pixels, the effective gate-source voltage accounts for threshold variations, ensuring consistent driving currents.
Data Source
AI summary
A LED pixel unit circuit and a display panel. The circuit comprises a driving module (31) which is provided with a driving control unit (311). The driving control unit (311) comprises a matching TFT (T4) whose threshold voltage is matched with the threshold voltage of the driving TFT (DTFT), is located between the first switching element (T1) and the first capacitor (C1), and is configured to control charging and discharging of the first capacitor (C1) so as to write the threshold voltage of the matching TFT (T4) and a new data voltage into the first capacitor (C1) while eliminating the original data voltage in the first capacitor (C1) and thereby compensate for the threshold voltage of the driving TFT (DTFT). The circuit can solve the problem of brightness non-uniformity of the display panel due to different threshold voltages of the TFTs, and also integrate a touch screen circuit into the pixel unit circuit to realize a touch function of the LED display panel.