AMOLED Pixel Driver Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing AMOLED pixel driver circuits face significant brightness unevenness due to threshold voltage drift in driving TFTs, particularly those made from low temperature polysilicon or oxide semiconductors, which affects panel brightness uniformity.
Innovation Solution
The proposed AMOLED pixel driver circuit incorporates a dual-gate structure with specific TFT configurations and capacitors to sense and compensate the threshold voltage of driving TFTs, ensuring uniformity by generating and storing compensation data for each pixel, thereby adjusting the threshold voltage to maintain consistent brightness across the panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 2T1C voltage/current conversion circuit is used to drive OLED, then the circuit can convert voltage signal to current signal, but the brightness uniformity deteriorates due to threshold voltage drift of driving TFT
Solution Approach 1:
The patent measures and stores the threshold voltage of the driving TFT in advance during an initialization phase, then uses this pre-acquired data to compensate for threshold voltage drift during subsequent display operation. This preliminary measurement and storage of threshold voltage information enables the circuit to maintain brightness uniformity without requiring complex real-time compensation mechanisms.
2Reliability
If LTPS or oxide semiconductor TFTs are used for driving TFT, then the transistor performance is improved, but threshold voltage drift occurs during use affecting brightness uniformity
Solution Approach 1:
The patent implements a feedback mechanism where the threshold voltage of the driving TFT is measured and stored in a storage element (such as a capacitor or register). During display operation, this stored threshold voltage information is used to adjust the gate voltage of the driving TFT, creating a closed-loop feedback system that compensates for threshold voltage drift and maintains stable transistor performance over time.
3Manufacturing precision
If compensation circuit is added to each pixel, then the brightness unevenness is reduced, but the device complexity increases
Solution Approach 1:
The patent performs threshold voltage measurement and compensation data generation during an initialization phase before normal display operation begins. By completing the complex measurement and compensation setup in advance, the actual display phase only requires simple data retrieval and application, thereby reducing brightness unevenness without significantly increasing the complexity of the operational circuit structure.
Data Source
AI summary
The invention provides an AMOLED pixel driver circuit, comprising: first TFT (T1), with top gate connected to first node (G), bottom gate connected to second node (B), source and drain connected respectively to high voltage power source (VDD) and third node (S); second TFT (T2), with gate connected to scan line (Scan), source and drain connected respectively to first node (G) and first data line (Data1); third TFT (T3), with gate connected to scan line (Scan), source and drain connected respectively to sense signal line (Sense) and third node (S); fourth TFT (T4), with gate connected to scan line (Scan), source and drain connected respectively to second node (B) and second data line (Data2); first capacitor (C), connected to second node (B) and high voltage power source (VDD); second capacitor Cst, connected to first node (G) and third node (S); OLED (D1), with anode connected to third node (S).