Pixel Circuit Self-Scan for Display Flicker Reduction
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Solution Overview
Problem
Display devices face issues with flicker phenomena due to hysteresis characteristics of driving transistors and luminance non-uniformity when operating at low driving frequencies, caused by inconsistent frame rates and fixed transistor states, leading to suboptimal image quality.
Innovation Solution
A pixel circuit design that includes specific transistors and a storage capacitor, allowing for one display-scan operation at minimum driving time and one or more self-scan operations at non-minimum driving times, along with an initializing operation to compensate for transistor characteristics and provide compensation signals from both sides of the panel, preventing flicker and luminance non-uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sync technology is adopted to change the frame rate of the panel driving frame, then the frame rate consistency between image frame and panel driving frame is improved, but the driving time of the panel driving frame is increased causing flicker effect due to hysteresis characteristics of driving transistor
Solution Approach 1:
The pixel circuit is divided into multiple transistors (first through eighth transistors) with distinct functions: driving transistor for current control, switching transistor for signal input, compensation transistor for threshold voltage compensation, initialization transistor for reset, and emission transistor for light output control. This segmentation allows independent optimization of each function to prevent flicker while maintaining frame rate consistency.
Solution Approach 2:
The pixel circuit dynamically adjusts transistor characteristics through multiple scan operations (display-scan and self-scan) and initialization operations. The driving transistor characteristics are changed during self-scan operations to adapt to varying frame rates, preventing hysteresis-induced flicker while maintaining image quality.
2Object-affected harmful factors
If the number of control signals is increased to reduce flicker, then the flicker effect is reduced, but luminance non-uniformity occurs between regions near and far from the driver
Solution Approach 1:
Different control signals are applied to different regions of the display panel through separate drivers positioned at opposite sides. The first and second compensation control signals, bias control signals, and emission control signals are locally optimized for their respective regions, ensuring uniform luminance compensation across the entire panel while reducing flicker.
Solution Approach 2:
Compensation control signals act as intermediaries between the drivers and the pixel circuits. These signals compensate for threshold voltage variations and timing differences in control signals, ensuring uniform luminance output across regions near and far from the drivers while maintaining the necessary control signal complexity to reduce flicker.
3Use of energy by stationary object
If the panel driving frame operates at low driving frequency, then power consumption is reduced, but image quality is degraded due to fixed transistor characteristics and hysteresis effects
Solution Approach 1:
The pixel circuit performs periodic initialization operations and self-scan operations in addition to display-scan operations. These periodic actions reset and adjust transistor characteristics before each frame display, preventing hysteresis accumulation and maintaining image quality even at low driving frequencies where power consumption is reduced.
Solution Approach 2:
Initialization operations are performed before each display frame to preset the transistor characteristics in optimal states. Compensation control signals are applied in advance to pre-compensate for threshold voltage variations, ensuring that when the frame is displayed at low frequency, the transistor characteristics remain stable and image quality is maintained.
Data Source
AI summary
A pixel circuit includes a first transistor, a second transistor operating based on a gate control signal, a third transistor operating based on a compensation control signal, a fourth transistor operating based on a previous gate control signal, fifth and sixth transistors operating based on an emission control signal, a seventh transistor operating based on a bias control signal, an eighth transistor operating based on the bias control signal, a storage capacitor, and a light emitting element connected to the first transistor. The pixel circuit performs one display-scan operation when a driving time of a panel driving frame is a minimum driving time and performs one display-scan operation and at least one self-scan operation when the driving time is not the minimum driving time.