Pixel Circuit Topology for Stable Luminance During Skip Driving
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Solution Overview
Problem
Display devices experience poor image quality due to increased node voltage in gate drivers caused by current leakage and noise during skip periods when driven at low speeds for extended periods, reducing the driving force and affecting pixel performance.
Innovation Solution
A pixel design that reduces the number of switching transistors connected to the driving transistor by removing a switching transistor and utilizing a simplified control circuit with fewer emission signals, including a driving transistor, transistors for reference and data voltage transmission, and capacitors for voltage storage, with a method of driving that involves specific signal phases to stabilize node voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the display panel is driven at a low speed for a long time, then power consumption is reduced, but the voltage at a specific node in the gate driver increases due to current leakage and noise, reducing the driving force and causing poor image quality
Solution Approach 1:
The patent applies preliminary action by initializing the pixel circuit to a known state before the display panel enters a skip period (low-speed driving mode). Specifically, during the skip period, the pixel circuit performs an initialization operation that resets the voltage at the gate electrode of the driving transistor to a predetermined level. This preliminary initialization prevents the accumulation of voltage errors caused by current leakage and noise during extended low-speed operation, thereby maintaining image quality while enabling power-saving skip periods.
2Device complexity
If the number of switching transistors connected to the driving transistor is reduced, then the complexity of the pixel circuit is reduced and emission signals are minimized, but the ability to control and stabilize node voltages during skip periods becomes more challenging
Solution Approach 1:
The patent applies universality by designing the pixel circuit with a reduced set of transistors where each transistor performs multiple functions. Specifically, the driving transistor serves both as the main current control element for the light emitting element and as part of the initialization circuitry during skip periods. The gate electrode of the driving transistor is reused as a control node that can be initialized to a predetermined voltage level, eliminating the need for separate initialization transistors while maintaining voltage stability through multi-functional operation.
3Device complexity
If a simplified control circuit with fewer emission signals is used, then the number of emission signals required for driving the pixel is reduced, but the precision of voltage control and luminance consistency becomes more difficult to maintain
Solution Approach 1:
The patent applies self-service by enabling the pixel circuit to automatically initialize itself during skip periods without requiring external intervention or additional control signals. The pixel circuit uses its existing nodes and transistors to perform self-initialization, where the gate electrode of the driving transistor is reset to a predetermined voltage level using the same transistor and capacitor resources already present in the simplified circuit. This self-service capability maintains voltage control precision despite the reduced number of emission signals.
Data Source
AI summary
A pixel comprises a driving transistor having a gate electrode at a first node, a first electrode connected to a high potential driving voltage, a second electrode connected to the light emitting element, and the driving transistor controlling the amount of driving current supplied to the light emitting element; a first transistor configured to transmit a reference voltage to the gate electrode of the driving transistor in response to a first gate signal; a second transistor configured to transmit a data voltage to the gate electrode of the driving transistor in response to a second gate signal; a third transistor electrically connecting the gate electrode of the driving transistor to the second electrode of the driving transistor in response to the first gate signal; and a fourth transistor electrically connecting the driving transistor with the light emitting element in response to an emission signal.