Pixel Circuit High-Frequency Driving Threshold Compensation
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Solution Overview
Problem
Display devices face challenges in maintaining image quality at high driving frequencies due to flicker issues and the need for sufficient threshold voltage compensation, which is difficult to achieve with existing pixel structures.
Innovation Solution
A pixel structure with multiple transistors and capacitors that perform specific operations during non-emission periods, including threshold voltage compensation and initialization, using emission control signals and control signals to manage transistor states and voltage levels, allowing for efficient high-speed driving without image flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a display device is driven at a high frequency (e.g., 120 Hz) to realize high resolution or three-dimensional image, then image quality and resolution are improved, but it becomes difficult to secure sufficient time for threshold voltage compensation of the driving transistor
Solution Approach 1:
The pixel performs threshold voltage compensation during the non-emission period (when the light emitting element is not emitting light) before the emission period begins. This preliminary action allows the compensation to be completed in advance, ensuring that sufficient time is allocated for compensation without reducing the overall driving frequency. The compensation is performed during periods when the emission control signal is at the first level, utilizing otherwise unused time resources.
Solution Approach 2:
The pixel dynamically adjusts its operation between emission and non-emission periods, utilizing the non-emission period for compensation tasks. This dynamic time management allows the system to maintain high driving frequencies while still performing necessary compensation operations, as the compensation is integrated into the dynamic cycle rather than being a separate static process.
2Productivity
If a display device is driven at a high frequency, then productivity is improved, but image flicker occurs and image quality deteriorates
Solution Approach 1:
The pixel performs preliminary initialization of voltages during the non-emission period, setting the gate voltage of the driving transistor and the voltage at the light emitting element to predetermined levels before emission begins. This preliminary initialization ensures that the pixel is properly prepared for high-frequency operation, preventing flicker and maintaining image quality even at driving frequencies of 120 Hz or higher.
Solution Approach 2:
The pixel employs periodic emission control signals that alternate between a first level (non-emission period) and a second level (emission period). This periodic action creates regular cycles of initialization/compensation followed by emission, ensuring that voltage levels are continuously maintained within appropriate ranges. The periodic nature of this control prevents accumulation of voltage errors that would cause flicker, while maintaining the high driving frequency needed for productivity.
Data Source
AI summary
A pixel including: a light emitter; a first transistor including first and second electrodes respectively connected to power and the light emitter, the first transistor controlling driving current; a first capacitor between a second and third node; a second transistor between the third node and data line and turned on by a scan signal; a third transistor between a first and second node, and turned on by a control signal; a fourth transistor between power and the third node, and turned on by a emission control signal; a fifth transistor between power and the first electrode, and turned on by the emission control signal; a sixth transistor between the second node and the light emitter, and turned on by another emission control signal; and a second capacitor between power and the first node, wherein the fourth, fifth and sixth transistors turn-on/off at least four times in a non-emission period.