Pixel Circuit Dual Capacitor Threshold Voltage Compensation
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Solution Overview
Problem
In organic light emitting display devices, a loss in data voltage occurs due to parasitic capacitance in circuit wirings, leading to a decrease in data transfer rate and image quality due to reduced threshold voltage compensation.
Innovation Solution
A pixel circuit design that includes a driving element with a gate connected to a first node, a first electrode connected to a high-potential voltage line, and a second electrode connected to a second node, along with switch elements and capacitors to sense and compensate for the threshold voltage twice, thereby improving compensation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If internal compensation scheme is used to compensate for driving element deterioration, then compensation performance is improved, but data voltage loss occurs due to parasitic capacitance in circuit wirings
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a driving element (transistor), a first capacitor connected between the gate and source nodes for storing gate-source voltage, and a second capacitor connected between the source node and reference voltage. This segmentation allows independent optimization of each component's function, enabling the first capacitor to handle compensation while the second capacitor addresses voltage loss due to parasitic capacitance.
Solution Approach 2:
The source node acts as an intermediary between the gate node and the reference voltage, with the second capacitor connecting these nodes. This intermediary structure enables the circuit to sense and compensate for threshold voltage shifts while simultaneously correcting voltage losses caused by parasitic capacitance in the wirings.
2Productivity
If data voltage is applied to drive the OLED, then image display is achieved, but data transfer rate decreases due to parasitic capacitance
Solution Approach 1:
The first capacitor is charged in advance during the programming phase before the data voltage needs to be fully transferred. This preliminary charging action stores the gate-source voltage required for driving the OLED, allowing the data transfer to proceed at higher speed without being limited by parasitic capacitance effects.
Solution Approach 2:
The circuit incorporates feedback through the second capacitor connected between the source node and reference voltage. This feedback mechanism continuously monitors and corrects voltage deviations caused by parasitic capacitance, maintaining stable data transfer rates while enabling proper image display.
3Manufacturing precision
If threshold voltage compensation is performed, then pixel uniformity is improved, but threshold voltage deviation between pixels increases due to parasitic capacitance
Solution Approach 1:
Each pixel is equipped with dedicated first and second capacitors tailored to its specific requirements. The first capacitor provides local compensation for threshold voltage shifts, while the second capacitor addresses local voltage losses due to parasitic capacitance. This localized approach ensures uniform compensation across all pixels while minimizing the impact of parasitic capacitance on measurement precision.
Data Source
AI summary
A pixel circuit and a display panel including the same may include a driving element including a gate connected to a first node to which a data voltage is configured to be applied, a first electrode connected to a high-potential voltage line, and a second electrode connected to a second node; a first switch element connected between the second node and a third node; a second switch element connected between the second node and a fourth node; a third switch element connected between the fourth node and a reference voltage line; a first capacitor connected between the first node and the third node; and a second capacitor connected between the third node and the fourth node.