Pixel Circuit Layout for Stable Brightness in Variable Refresh Displays
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Solution Overview
Problem
Variable refresh rate modes in display devices cause brightness differences between pixels due to varying refresh rates, leading to image warpage and flicker.
Innovation Solution
A pixel circuit design with a gate electrode receiving an inverted emission signal, a capacitor between the inverted emission signal line and a node, and separate reference and initialization voltages to minimize charging/discharging delays and reduce on-bias stress of the driving transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If variable refresh rate mode is applied to drive pixels at various refresh rates, then power consumption is reduced and device lifetime is extended, but brightness difference occurs between pixels causing image warpage or flicker
Solution Approach 1:
The initialization transistor applies initialization voltage to the anode of the light emitting element in advance during the anode initialization period, before the emission period begins. This preliminary action ensures that the light emitting element is properly initialized at different refresh rates, preventing brightness differences and flicker while maintaining power savings from variable refresh rate operation
Solution Approach 2:
The pixel circuit dynamically adjusts its operation based on the refresh rate by using the initialization transistor to conditionally apply initialization voltage during the anode initialization period. This dynamic adjustment ensures consistent display quality across different refresh rates while maintaining the power benefits of variable refresh rate mode
2Speed
If initialization voltage is applied continuously to the anode of the light emitting element, then charging/discharging delays are minimized, but on-bias stress of the driving transistor increases
Solution Approach 1:
The initialization transistor applies initialization voltage periodically during the anode initialization period rather than continuously. This periodic action is synchronized with the refresh rate, providing necessary charging/discharging speed while reducing continuous stress on the driving transistor by allowing it to rest during other periods
Data Source
AI summary
A pixel circuit includes a light emitting element having an anode, a driving transistor having a first electrode connected to a high potential driving voltage line, a second electrode connected to the light emitting element, the driving transistor controlling a magnitude of driving current supplied to the light emitting element in response to a voltage applied to a gate electrode, a first switching transistor connected between a data line and the gate electrode of the driving transistor and receiving a first scan signal through a gate electrode, a light emitting transistor connected between the driving transistor and the light emitting element and receiving an emission signal through a gate electrode, and an initialization transistor connected between an initialization voltage line and the anode and receiving an inverted emission signal through a gate electrode, the inverted emission signal having a phase opposite to a phase of the emission signal.