Pixel Circuit Threshold Voltage Compensation for Display Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Display devices face challenges in maintaining image quality due to variations in hysteresis characteristics of driving transistors, current leakage, and luminance unevenness caused by resistance drops, especially when operating at different frame frequencies.
Innovation Solution
A pixel design incorporating multiple N-type oxide semiconductor transistors and capacitors, with a light emitting element in an inverted structure, that includes specific transistor configurations and timing control to manage threshold voltage compensation and emission control, minimizing current leakage and resistance drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the frame frequency is reduced to lower power consumption, then energy efficiency is improved, but the threshold voltage compensation time becomes insufficient and image quality deteriorates
Solution Approach 1:
The pixel circuit performs threshold voltage compensation in advance during the non-emission period before the emission period begins. The compensation is completed before the actual display emission, ensuring that the driving transistor is properly compensated even at low frame frequencies. This preliminary action allows the system to maintain image quality without requiring higher frame rates.
2Reliability
If the frame frequency is increased to 120 Hz or more to achieve high resolution and stereoscopic images, then image quality is improved, but power consumption increases
Solution Approach 1:
The pixel circuit dynamically adapts to different frame frequencies (60 Hz, 120 Hz, or higher) by adjusting its operation mode. The circuit can operate in normal mode for high frame frequencies or in extended mode for low frame frequencies, allowing the display to maintain high image quality across various power consumption levels and driving conditions.
3Use of energy by moving object
If conventional pixel circuits are used at low frame frequencies, then power consumption is reduced, but current leakage causes image quality deterioration
Solution Approach 1:
The invention converts the harmful effect of current leakage into a beneficial outcome by using the leakage current path to charge the compensation capacitor during the non-emission period. The leakage that would normally degrade image quality is instead utilized to maintain the compensation voltage, thereby improving image quality while operating at low frame frequencies with reduced power consumption.
4Reliability
If conventional pixel circuits are used at high frame frequencies, then high resolution and stereoscopic images are achieved, but threshold voltage compensation time becomes insufficient
Solution Approach 1:
The pixel circuit utilizes the periodic non-emission period between consecutive frame emissions to perform threshold voltage compensation. By concentrating the compensation action during this dedicated time window before each emission period, the circuit ensures sufficient compensation time is allocated even when operating at high frame frequencies like 120 Hz or higher, preventing time shortage for proper compensation.
Data Source
AI summary
A pixel and a display device including the same are disclosed. The pixel includes a light emitting element, first through seventh transistors, and a first capacitor. The first transistor is connected between first and second nodes. The second transistor is connected between a data line and a fourth node and configured to be turned on by a first scan signal. The third transistor is connected between the first node and a third node and configured to be turned on by a second scan signal. The fourth transistor is connected between the fourth node and a third power line and configured to be turned on by a third scan signal. The fifth transistor is connected between the third node and the third power line and configured to be turned on by a fourth scan signal. The sixth transistor is connected between the first node and a fifth node and configured to be turned off by an emission control signal. The seventh transistor is connected between the second node and the second power line and configured to be turned off in response to the emission control signal. The first capacitor is connected between the third and fourth nodes.