Pixel Circuit Threshold Compensation for OLED Luminance Uniformity
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Solution Overview
Problem
Organic light-emitting display devices experience luminance unevenness due to process deviations and device characteristic deviations, leading to differences in electrical characteristics of driving elements across pixels, which are exacerbated over time.
Innovation Solution
A pixel circuit with an internal compensation circuit that compensates for the threshold voltage of the driving element in real time by separating the sensing of threshold voltage and writing pixel data, using multiple switch elements and capacitors to ensure accurate luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an internal compensation circuit is added to compensate for threshold voltage differences, then luminance uniformity is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is divided into distinct functional modules: a driving element for current control, a sensing circuit for threshold voltage measurement, and a compensation circuit for gate voltage adjustment. This segmentation allows each module to perform its specific function efficiently while maintaining overall luminance uniformity across the display panel.
Solution Approach 2:
The internal compensation circuit enables each pixel to automatically sense and compensate for its own threshold voltage variations without requiring external calibration or adjustment. The circuit samples the threshold voltage of the driving element and adjusts the gate voltage accordingly, allowing the pixel to self-correct for manufacturing deviations and maintain consistent luminance output.
2Illumination intensity
If threshold voltage compensation is performed in real time, then luminance uniformity is improved, but power consumption increases
Solution Approach 1:
The threshold voltage sensing and compensation operation is performed periodically at specific timing intervals rather than continuously. The sensing circuit activates during designated sensing periods to sample the threshold voltage, then the compensation is applied during subsequent driving periods. This periodic operation reduces power consumption compared to continuous monitoring while still maintaining real-time compensation effectiveness.
3Manufacturing precision
If multiple switch elements and capacitors are added for accurate threshold voltage sensing, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Capacitors are introduced as intermediary elements to store and transfer voltage signals during the threshold voltage sensing process. The capacitors hold the sensed threshold voltage and the compensated gate voltage, enabling accurate voltage transfer between different circuit stages. This use of capacitive intermediaries improves sensing accuracy without requiring complex active circuitry.
Solution Approach 2:
The switch elements and capacitors in the compensation circuit are designed to serve multiple functions: they control signal routing during different operating phases, store voltage information, and enable both sensing and compensation operations. This multi-functionality reduces the need for separate dedicated components for each function, thereby limiting the increase in overall device complexity.
Data Source
AI summary
A pixel circuit and a display device including the same are discussed. The pixel circuit in one example includes a driving element having 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 capacitor connected between the second node and a fourth node, a second capacitor connected between the third node and the fourth node, a light emitting element including an anode electrode connected to a fifth node and a cathode electrode to which a cathode voltage is applied, a first switch element configured to connect a data voltage to the second node, and a switch circuit configured to selectively apply a reference voltage to the second node and the fourth node.