Pixel Circuit Phase Segmentation for Threshold Voltage Sampling
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Solution Overview
Problem
Diode connection circuits in organic light-emitting display devices face challenges in securing sufficient sampling time for threshold voltage due to reduced horizontal periods when driving high-resolution or high-speed display panels, leading to insufficient compensation performance.
Innovation Solution
A pixel circuit design that separates the steps of sensing threshold voltage and writing pixel data temporally within the driving period, using multiple switch elements and capacitors to ensure adequate sampling time, particularly for diode connection circuits, and includes an anode reset voltage separate from the reference voltage to prevent luminance fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diode connection circuit is used for threshold voltage sampling, then compensation performance is improved, but sampling time becomes insufficient due to reduced horizontal period
Solution Approach 1:
The pixel circuit is divided into multiple operational phases (first period, second period, third period, fourth period) with distinct functions. Threshold voltage sampling is performed in the second period when the second switch element connects the first and second nodes, separating this operation from data writing which occurs in the third period. This temporal segmentation allows sufficient sampling time without compromising compensation performance.
Solution Approach 2:
The circuit employs dynamic switching of the second switch element based on gate signals that change over time. The switch element is turned on during the second period to enable threshold voltage sampling, and turned off during the third period for data writing. This dynamic control adapts the circuit configuration to different operational requirements within the same pixel circuit.
2Productivity
If threshold voltage sampling and data writing are performed simultaneously, then horizontal period is reduced, but sampling time becomes insufficient
Solution Approach 1:
The pixel circuit operates through periodic cycles divided into four distinct periods. The second period is dedicated to threshold voltage sampling with the second switch element turned on, while the third period handles data writing. This periodic separation ensures that both sampling and writing operations receive adequate time allocation within each complete driving cycle, maintaining both productivity and sampling accuracy.
3Device complexity
If reference voltage is applied to anode electrode, then circuit complexity is reduced, but luminance fluctuations occur
Solution Approach 1:
Different voltage nodes are assigned to different circuit locations based on their specific functional requirements. The third node (anode electrode) is specifically assigned a separate pixel driving voltage from the reference voltage applied to other nodes. This localized voltage assignment ensures that the anode electrode receives the appropriate voltage for stable luminance output, while other nodes receive reference voltage to maintain overall circuit simplicity.
Data Source
AI summary
A pixel circuit and a display device including the same are disclosed. The pixel circuit includes a driving element connected to a first node, a second node, and a third node; a capacitor connected between the second node and the third node; a first switch element connected between a data line to which a data voltage of pixel data is applied and the second node; a second switch element connected between the first node and the second node; a third switch element; a fourth switch element; and a light emitting element. When the third switch element is turned on, a reference voltage is applied to the third node or an anode electrode of the light emitting element.