Pixel Circuit Threshold Voltage Compensation for Display Devices
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Solution Overview
Problem
Display devices face challenges in maintaining high image quality at high driving frequencies due to issues with threshold voltage compensation and data signal writing, leading to potential image flicker and increased power consumption.
Innovation Solution
A pixel structure incorporating specific transistors and capacitors, along with a controlled timing scheme for emission and control signals, allows for efficient threshold voltage compensation and data writing, separate from the emission period, using PMOS and NMOS transistors to minimize leakage current and secure sufficient compensation time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the display device is driven at a high frequency (e.g., 120 Hz) to realize high-resolution image or stereoscopic image, then the image quality is improved, but the time available for threshold voltage compensation is reduced
Solution Approach 1:
The patent performs threshold voltage compensation in advance during a dedicated compensation period before the emission period. The compensation transistor adjusts the gate voltage of the driving transistor to compensate for threshold voltage shifts, ensuring accurate current control is already in place before high-speed emission begins, thus resolving the time conflict between compensation and high-frequency driving
Solution Approach 2:
The patent divides the driving cycle into distinct segments: a compensation period for threshold voltage adjustment and an emission period for light output. By separating these functions into non-overlapping time segments, the system can perform thorough compensation without interfering with the high-speed emission required for 120Hz driving, thus resolving the time resource conflict
2Productivity
If the data signal writing and threshold voltage compensation are performed in overlapping periods, then the productivity is improved, but the image defects like motion blur increase
Solution Approach 1:
The patent segments the operation into distinct compensation and emission periods, preventing overlap between data writing and threshold voltage compensation. This temporal separation ensures that compensation is completed before emission begins, eliminating motion blur while still achieving high driving speeds through efficient period management
Solution Approach 2:
The patent performs threshold voltage compensation as a preliminary action before the emission period starts. By completing the compensation process in advance during a dedicated compensation period, the system ensures accurate voltage control is established before high-speed data writing and emission begin, preventing image defects while maintaining high productivity
3Use of energy by moving object
If the display device is driven at a low frequency (e.g., 1 Hz) to minimize power consumption, then the energy consumption is reduced, but the displayed image flickers
Solution Approach 1:
The patent performs threshold voltage compensation in advance during a dedicated compensation period before emission. This preliminary compensation ensures that the driving transistor is properly calibrated to maintain stable current control throughout the emission period, preventing flicker even when operating at low frequencies for power savings
Data Source
AI summary
A pixel including: a light-emitting element; a first transistor including a first electrode coupled to a power source and a second electrode coupled to the light-emitting element; a first capacitor between a second and a third node; a second transistor between the third node and a data line and turned on by a scan signal; a third transistor between a first node and the second node and turned on by a first control signal; a fourth transistor between the power source and the third node and turned on by a second control signal; a fifth transistor between the power source and the first electrode of the first transistor and turned on by an emission control signal; a sixth transistor between the second node and the light-emitting element and turned on by a previous emission control signal; and a second capacitor between the power source and the first node.