Pixel Driving Circuit Threshold Voltage Drift Compensation
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Solution Overview
Problem
Conventional pixel driving circuits fail to compensate for threshold voltage drift in transistors and organic light-emitting diodes (OLEDs), leading to luminance non-uniformity and shortened OLED lifetime due to directional motion of ionic impurities under bias voltage.
Innovation Solution
A pixel driving circuit with a 5T1C structure, including an input sub-circuit, adjust sub-circuit, charge sub-circuit, drive sub-circuit, and storage sub-circuit, which sets and adjusts voltage levels to maintain a voltage difference, charge the drive sub-circuit to latch voltages above a first threshold but below a second, and generate a driving current independent of these thresholds, while also inverting the polarity of the OLED to reduce electrical field-induced degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional pixel driving circuits are used with thin-film transistors, then the display panel can be manufactured with uniform electric properties, but threshold voltage drift occurs during long-time operation causing luminance decay
Solution Approach 1:
The circuit performs preliminary threshold voltage measurement and compensation before the display operation begins. The compensation voltage is pre-calculated and stored, then applied to offset the threshold voltage drift, ensuring luminance stability without requiring complex real-time adjustments during operation.
Solution Approach 2:
The circuit incorporates a feedback mechanism that continuously monitors the actual luminance output and adjusts the driving voltage accordingly. The compensation voltage is dynamically updated based on the detected threshold voltage drift, creating a closed-loop system that maintains luminance stability over time.
2Reliability
If low-temperature-poly-silicon thin-film transistors are used, then electric property stability is improved, but manufacturing uniformity across large display panels deteriorates
Solution Approach 1:
The circuit introduces an intermediary compensation mechanism that decouples the transistor performance requirements from the final display uniformity. By measuring and compensating for individual transistor threshold voltage variations, the system achieves uniform display output even with variations in transistor manufacturing characteristics.
3Illumination intensity
If OLED is driven by positive DC current, then light emission is achieved, but ionic impurities move directionally inducing internal electrical field that reduces effective electrical field for carrier injection
Solution Approach 1:
The circuit applies periodic polarity reversal to the OLED driving voltage. During normal display operation, positive voltage drives light emission. Periodically, the polarity is reversed to negative voltage, which causes ionic impurities to move back toward their original positions, neutralizing the accumulated internal electrical field and preventing threshold voltage shift.
Solution Approach 2:
The circuit applies a preliminary counteracting voltage of opposite polarity to neutralize the harmful effects of ionic impurity accumulation before they significantly degrade OLED performance. This preventive approach reverses the internal electrical field buildup, maintaining effective carrier injection and extending OLED lifetime.
4Device complexity
If conventional pixel driving circuits without compensation functions are used, then circuit simplicity is maintained, but luminance uniformity deteriorates due to uncorrected threshold voltage drift
Solution Approach 1:
The pixel driving circuit is segmented into distinct functional modules: a normal driving transistor for light emission control, a separate compensation transistor for threshold voltage measurement, and a storage capacitor for holding compensation voltage. This modular segmentation allows the compensation function to be added without significantly complicating the overall circuit structure.
Data Source
AI summary
The present application discloses a pixel driving circuit. The circuit includes an input sub-circuit configured to set a voltage level at a first node; a storage sub-circuit coupled between the first node and a second node; and a drive sub-circuit coupled to the first node and the second node and configured to drive light emission of a light-emitting device. Additionally, the circuit includes a charge sub-circuit coupled to the drive sub-circuit, and configured to charge the drive sub-circuit to latch a voltage level at the second node to be larger than a first threshold but smaller than a second threshold. Furthermore, the circuit includes an adjust sub-circuit coupled to a second node and coupled to the input sub-circuit at least via the first node, and configured to at least adjust voltage level at the second node to make the light-emitting device with an inverted polarity in one partial period.