Pixel Circuit Biasing for Low-Frequency Display Hysteresis
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Solution Overview
Problem
Existing display devices face challenges in maintaining display quality and reducing power consumption when driven at low frequencies, particularly due to issues with hysteresis deviation and motion blur caused by grayscale differences between pixels.
Innovation Solution
A pixel design that periodically applies a bias voltage to the driving transistor using a fourth transistor, which is turned on at a specific frequency, while the second and third transistors are turned on at a lower frequency, to synchronize the emission control signal and initialization processes, thereby reducing hysteresis deviation and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the display device is driven at low frequency to improve driving efficiency and minimize power consumption, then power consumption is reduced, but hysteresis deviation and motion blur increase causing degraded display quality
Solution Approach 1:
The patent applies periodic bias voltage to the driving transistor at a frequency higher than the image refresh rate (e.g., twice the refresh rate) to counteract hysteresis effects. This periodic action ensures that the transistor operates in a more stable region during low-frequency driving, reducing hysteresis deviation and motion blur while maintaining power efficiency benefits of low-frequency operation.
2Reliability
If the fourth transistor is turned on at high frequency to apply bias voltage and reduce hysteresis deviation, then display quality is improved, but device complexity increases
Solution Approach 1:
The fourth transistor serves multiple functions: it applies bias voltage to reduce hysteresis, synchronizes with the emission control signal, and operates at a frequency that is an aliquot of the refresh rate. This multi-functionality reduces the need for separate circuits for each function, thereby managing device complexity while achieving improved display quality.
Solution Approach 2:
The patent dynamically adjusts the operating frequency of the fourth transistor based on the image refresh rate. The bias application frequency is set to an aliquot of the refresh rate (e.g., 2x, 3x, or 4x the refresh rate), allowing the system to adapt to different driving conditions and maintain optimal performance across various operating scenarios.
Data Source
AI summary
A pixel for a display device includes a light-emitting element, a first transistor including a first electrode electrically connected to a first node and controlling a driving current, a second transistor electrically connected between a data line and the first node and being turned on in response to a first scan signal supplied through a first scan line, a third transistor electrically connected between the second node and a third node electrically connected to a second electrode of the first transistor and being turned on in response to the first scan signal, and a fourth transistor being turned on in response to a second scan signal supplied through a second scan line, and applying a bias voltage to the first transistor. The fourth transistor is turned on at a first frequency. The second and third transistors are turned on at a second frequency different from the first frequency.