6T1C AMOLED Pixel Driver Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing AMOLED pixel driver circuits face issues with threshold voltage drift in driving TFTs, leading to unstable current flow and non-uniform light emission due to factors like light and voltage stress, which cannot be effectively compensated in known 2T1C structures.
Innovation Solution
The proposed solution involves a 6T1C AMOLED pixel driver circuit with a double-gate TFT as the driving TFT, utilizing a pre-charging phase, threshold voltage programming design phase, and driving light-emitting phase to stabilize the threshold voltage, ensuring the current flowing through the OLED is independent of the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-gate TFT is used as the driving TFT to simplify the circuit structure, then the device complexity is reduced, but the threshold voltage drift cannot be effectively compensated, leading to unstable current flow
Solution Approach 1:
The patent divides the gate into two separate gates (first gate and second gate) in the double-gate TFT structure. The first gate controls the main current flow while the second gate provides additional control for threshold voltage compensation. This segmentation allows independent optimization of each gate's function, enabling both circuit simplicity and reliable threshold voltage compensation.
2Reliability
If the data signal is increased to compensate for positive threshold voltage drift, then the current stability is improved, but the voltage stress on the driving TFT increases, accelerating the threshold voltage drift
Solution Approach 1:
The patent implements a feedback mechanism where the threshold voltage of the driving TFT is detected and used to adjust the data signal value. The second gate voltage is dynamically adjusted based on the detected threshold voltage drift, creating a closed-loop control system that compensates for threshold voltage changes without requiring excessive data signal increases, thereby reducing voltage stress on the TFT.
Solution Approach 2:
The patent changes the control parameter from solely data signal voltage to a combination of first gate voltage, second gate voltage, and detected threshold voltage. By adjusting the second gate voltage based on threshold voltage drift detection, the system compensates for parameter changes in the TFT characteristics without increasing the harmful voltage stress on the device.
3Reliability
If multiple TFTs and capacitors are added to provide threshold voltage compensation functionality, then the threshold voltage drift is compensated, but the device complexity increases
Solution Approach 1:
The double-gate TFT structure performs multiple functions: the first gate provides main switching control, the second gate provides threshold voltage compensation control, and the same device structure also serves as the driving element for the OLED. This multi-functionality reduces the need for separate compensation circuits, maintaining circuit simplicity while achieving reliable threshold voltage compensation.
Data Source
AI summary
The invention provides an AMOLED pixel driver circuit and pixel driving method. The AMOLED pixel driver circuit has a 6T2C structure, comprising a first thin film transistor (TFT) (T1), a second TFT (T2) forming mirror relation with the first TFT (T1), a third TFT (T3), a fourth TFT (T4), a fifth TFT (T5), a sixth TFT (T6), a first capacitor (C1), a second capacitor (C2) and an organic light-emitting diode (OLED) (D1), and receiving a first scan signal (Scant), a second scan signal (Scan2), a third scan signal (Scan3), a data signal (Data), and a predefined voltage (Vpre). The circuit can effectively compensate the threshold voltages of the driving TFT and the OLED, simplify the data signal, stabilize the current flowing through the OLED to ensure uniform light-emission of the OLED and improve display quality.