Current-Controlled Organic EL Display Driving Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional active matrix driving type organic EL displays face challenges in maintaining consistent luminance due to changes in transistor channel resistance with temperature and time, leading to variations in luminance across pixels.
Innovation Solution
A display device and method that includes a selection scan driver, data driving circuit, and pixel circuits, where a reset voltage is applied to current lines in a selection period to discharge parasitic capacitance, allowing for precise control of a designating current to ensure consistent luminance across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If voltage-controlled active matrix driving is used to control luminance, then the display can achieve high luminance and high contrast, but transistor channel resistance changes with temperature and time cause luminance variations across pixels
Solution Approach 1:
The patent replaces the voltage-controlled system with a current-controlled system. Specifically, current lines are used to supply current to pixel circuits, and the luminance of organic EL elements is controlled by the current value rather than voltage level. This substitution of control mechanism (from voltage to current) resolves the luminance consistency issue because current control is less sensitive to transistor parameter variations.
Solution Approach 2:
The patent changes the control parameter from voltage to current. By controlling the current value supplied to each pixel circuit through dedicated current lines, the system achieves more stable luminance control. The current value becomes the primary control parameter that directly determines organic EL element luminance, making the system less susceptible to temperature and aging effects.
2Reliability
If additional switching transistors are added to compensate for transistor variations, then luminance consistency can be improved, but the aperture ratio decreases
Solution Approach 1:
Instead of adding more transistors to the pixel circuit, the patent substitutes the control approach by introducing separate current lines that carry compensation information. This allows luminance consistency to be achieved through current control rather than through additional switching transistors, thereby preserving the aperture ratio.
Solution Approach 2:
The patent introduces a new dimension of control by separating the voltage control function and current control function. Current lines provide an additional control pathway that operates independently from the existing voltage-controlled transistor switching mechanism, enabling compensation without increasing the number of transistors in the pixel circuit.
3Measurement precision
If reset voltage is applied to current lines during selection period, then parasitic capacitance is discharged and current control precision is improved, but the selection period time increases
Solution Approach 1:
The reset voltage is applied at the beginning of the selection period as a preliminary action to discharge parasitic capacitance before the actual current control operation. This preliminary reset ensures that subsequent current measurements and controls are performed on a known baseline, improving precision without significantly impacting the overall selection period duration.
Solution Approach 2:
The reset voltage application is implemented as a periodic action within each selection period. By systematically resetting the parasitic capacitance at regular intervals (at the start of each selection period), the system maintains current control precision throughout operation while managing the time overhead through efficient periodic execution rather than continuous resetting.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high-quality image display by maintaining consistent luminance across pixels, reducing variations caused by transistor aging and temperature changes, and eliminating the need for additional switching transistors, thus preserving the aperture ratio.
Implementation Method 1
a reset voltage is applied to current lines in a selection period to discharge parasitic capacitance
Implementation Method 2
organic EL (ElecctroLuminescent) elements as self-light-emitting elements
Data Source
AI summary
A display device includes a plurality of selection scan lines, a plurality of current lines, a selection scan driver which sequentially selects the plurality of selection scan lines in each selection period, a data driving circuit which applies a reset voltage to the plurality of current lines in the selection period and supplies a designating current having a current value corresponding to an image signal to the plurality of current lines after applying the reset voltage, and a plurality of pixel circuits which are connected to the plurality of selection scan lines and the plurality of current lines, and supply a driving current having a current value corresponding to the current value of the designating current which flows through the plurality of current lines.