Pixel Driving Circuit for OLED Luminance Uniformity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In light-emitting devices, variations in threshold voltage of driving transistors cause uneven luminance across pixels, and the deterioration of the EL layer leads to decreased luminance, as the potential of the driving transistor's source is affected by the voltage between the anode and cathode of the light-emitting element.
Innovation Solution
A light-emitting device configuration that includes transistors, switches, and a capacitor, allowing for the application of a potential higher than the threshold voltage of the driving transistor but lower than the sum of the threshold voltage and the source-drain voltage, enabling the compensation of threshold voltage variations and maintaining image quality by controlling the current supplied to the light-emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an n-channel driving transistor is used with the light-emitting element configuration (anode-EL layer-cathode stacked in order), then the device can be fabricated through a simple process and achieve high emission efficiency, but when the voltage between anode and cathode increases due to deterioration of light-emitting material, the potential of the source of the driving transistor increases, causing the gate voltage to decrease and the drain current to decrease, resulting in a decrease in luminance
Solution Approach 1:
The patent applies preliminary action by introducing a capacitor that stores charge in advance to compensate for threshold voltage variations. The capacitor is charged during a first period and then maintains the gate voltage during a second period, proactively counteracting the luminance decrease that would occur due to source potential increase from EL layer deterioration. This preliminary charge storage action prevents the harmful effect before it fully manifests.
Solution Approach 2:
The capacitor acts as an intermediary element between the driving transistor and the light-emitting element. It mediates the voltage relationship by storing and releasing charge to maintain stable gate voltage despite changes in source potential caused by EL layer deterioration. This intermediary component isolates the driving transistor from the direct impact of light-emitting material degradation.
2Power
If the voltage between anode and cathode of the light-emitting element is increased, then the emission efficiency is improved, but the potential of the source of the driving transistor is increased, whereby the gate voltage is decreased and the drain current is decreased
Solution Approach 1:
The patent implements feedback through the capacitor that continuously monitors and compensates for voltage changes. As the source potential increases due to higher anode-cathode voltage, the capacitor releases stored charge to maintain the gate voltage, creating a negative feedback loop that counteracts the unwanted decrease in drain current. This feedback mechanism ensures that luminance remains stable even when emission efficiency increases.
Data Source
AI summary
A light-emitting device in which variation in luminance of pixels is suppressed. A light-emitting device includes at least a transistor, a first wiring, a second wiring, a first switch, a second switch, a third switch, a fourth switch, a capacitor, and a light-emitting element. The first wiring and a first electrode of the capacitor are electrically connected to each other through the first switch. A second electrode of the capacitor is connected to a first terminal of the transistor. The second wiring and a gate of the transistor are electrically connected to each other through the second switch. The first electrode of the capacitor and the gate of the transistor are electrically connected to each other through the third switch. The first terminal of the transistor and an anode of the light-emitting element are electrically connected to each other through the fourth switch.