Pixel Circuit Bias Control for Low-Frequency Screen Drag
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Solution Overview
Problem
Display devices experience screen drag (ghost phenomenon) due to hysteresis differences in threshold voltage shifts of adjacent pixels when driven at low frequencies, leading to severe grayscale differences.
Innovation Solution
Pixels are designed to operate at various driving frequencies with a bias voltage applied to the source electrode of the driving transistor, using a specific transistor configuration and capacitors to stabilize voltage and control current direction, preventing unintended light emission during initialization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the display device is driven at a low frequency to improve driving efficiency and minimize power consumption, then power consumption is reduced, but hysteresis difference due to grayscale difference between adjacent pixels becomes severe, causing screen drag
Solution Approach 1:
The patent applies preliminary action by initializing the driving transistor before normal operation to prevent hysteresis effects. The initialization voltage is applied in advance to reset the threshold voltage of the driving transistor, ensuring that when low-frequency driving occurs, the transistor starts from a known state without accumulated hysteresis from previous operations, thereby preventing screen drag while maintaining power efficiency
Solution Approach 2:
The patent changes the voltage parameter by applying a specific initialization voltage (Vint) to the gate of the driving transistor. This parameter change resets the threshold voltage of the transistor to a predetermined value, compensating for hysteresis effects that occur during low-frequency driving. By dynamically adjusting the voltage state of the transistor through initialization, the display maintains quality without increasing power consumption
2Reliability
If the initialization voltage is applied to both the gate electrode of the driving transistor and the anode of the light emitting element separately, then the light emitting element is properly initialized, but the light emitting element may unintentionally emit light during initialization
Solution Approach 1:
The patent segments the initialization process into two distinct phases: first initializing the driving transistor gate electrode, then initializing the light emitting element anode. By separating these initialization actions in time rather than applying voltages simultaneously, the patent ensures that the light emitting element is properly initialized while preventing unintended light emission that would occur if both were initialized at the same time
Solution Approach 2:
The patent employs periodic action by applying initialization voltages in a specific sequence and timing. The gate electrode is initialized first, followed by the anode initialization after a controlled time interval. This periodic, sequential approach ensures proper initialization of both components while preventing the harmful effect of unintended light emission during the initialization process
Data Source
AI summary
A pixel of display device includes a light emitting element, a first transistor coupled between first power source and a second node and having a gate electrode connected to a first node N1, and the first transistor being configured to control a driving current supplied to the light emitting element in response to a voltage of the first node, a first capacitor including one electrode connected to the first node and another electrode connected to a third node, a second transistor coupled between the third node and a data line, a third transistor coupled between the first node and the second node, a fourth transistor coupled between the first node and an initialization power source, a fifth transistor coupled between a reference power source and the third node, and an eighth transistor coupled between a fourth node and an anode initialization power source.