Dual-Gate Pixel Circuit for Low-Gray Gamma Stability
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Solution Overview
Problem
The electrical characteristics of driving elements in organic light-emitting display devices deteriorate over time, leading to variations in gate-source voltage (Vgs) that affect gamma curve and increase power consumption or hinder low gray scale expression.
Innovation Solution
A pixel circuit design incorporating a dual gate structure with two capacitors and additional switch elements for selectively connecting capacitors to the gate and source electrodes of the driving element, enhancing threshold voltage sensing speed and reducing data voltage for high luminance output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If internal compensation technology is used to sense threshold voltage of driving element, then gate-source voltage can be compensated for deterioration, but gamma curve characteristics deteriorate and power consumption increases
Solution Approach 1:
The patent implements a dual-gate structure where the first gate controls the main current flow and the second gate controls the threshold voltage sensing operation. This dynamic separation allows the circuit to switch between compensation mode and normal operation mode, enabling threshold voltage sensing without continuously affecting the gamma curve characteristics or increasing power consumption during display operation.
Solution Approach 2:
The driving element is divided into two independent gate control systems: a first gate for main driving control and a second gate for threshold voltage sensing. This segmentation allows independent optimization of each function, where the sensing operation through the second gate does not interfere with the gamma characteristics controlled by the first gate, thus avoiding power consumption increase while maintaining compensation capability.
2Reliability
If threshold voltage sensing is performed for each sub-pixel, then driving element deterioration is compensated, but sensing time increases and productivity decreases
Solution Approach 1:
The patent uses a dual-gate structure that enables parallel threshold voltage sensing across multiple pixels simultaneously. The second gate can be activated to perform sensing operations without sequentially processing each pixel, as the dual-gate design allows for simultaneous sensing and driving operations across the display panel, significantly improving sensing speed while maintaining compensation accuracy.
3Device complexity
If conventional pixel circuit design is used, then device complexity is low, but gamma characteristics in low gray scales are poor and data voltage for high luminance is excessive
Solution Approach 1:
The pixel circuit is segmented into two independent gate control paths: one for main driving signals and another for threshold voltage sensing and compensation. This segmentation allows precise control of the driving element's threshold voltage without affecting the overall circuit complexity significantly, as each gate can be controlled by existing pixel circuit components working in coordinated phases.
Solution Approach 2:
The patent changes the control parameter from single-gate voltage control to dual-gate independent control, where the second gate specifically controls the threshold voltage parameter. This parameter separation enables precise adjustment of threshold voltage to improve gamma characteristics in low gray scales, while the first gate maintains control over the main driving voltage for high luminance output, avoiding excessive data voltage requirements.
Data Source
AI summary
A pixel circuit includes a driving element including a first electrode connected to a first node, a gate electrode connected to a second node, and a second electrode connected to a third node; a first switch element supplying a pixel driving voltage to the first node; a second switch element connecting a fourth node to the second node; a third switch element supplying a data voltage to the second node; a fourth switch element supplying a reference voltage to the second node; a fifth switch element connecting the fourth node to the third node; a first capacitor connected to the second node and the third node; a second capacitor connected to a first power line and the fourth node; and a light-emitting element connected to the third node and a second power line.