OLED Drive Circuit Compensation for Voltage Drop and Brightness Uniformity
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Solution Overview
Problem
Existing organic electro-luminescence devices face challenges in achieving uniform brightness across pixels due to variations in drive voltage and threshold voltage, leading to inconsistencies in gray scale representation.
Innovation Solution
The implementation of a drive unit comprising first to fourth transistors and a capacitor, which allows for precise control of drive current and voltage by charging a voltage corresponding to a data current and adjusting it with a signal, enabling proportional drive current emission from the OLED, thereby improving gray scale expression and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a current drive transistor supplies drive current to the OLED based on data voltage, then the OLED emits light with brightness determined by drive current intensity, but voltage drops in the power voltage supply line cause different drive voltages at different pixel locations, resulting in non-uniform brightness across the display
Solution Approach 1:
The patent introduces a compensation transistor connected in parallel with the drive transistor, where the gate of the compensation transistor is connected to a compensation voltage line. By adjusting the width-to-length ratio of the compensation transistor relative to the drive transistor, the circuit compensates for voltage drops in the power supply line, ensuring uniform drive voltage across different pixel locations and achieving uniform brightness.
2Power
If the drive voltage is supplied through power voltage supply lines with original line resistance, then voltage can be delivered to all pixels, but a drop voltage is generated as the drive voltage flows through the power voltage supply line, causing brightness differences between pixels
Solution Approach 1:
The patent introduces a compensation transistor as an intermediary element that counteracts the voltage drop caused by line resistance. The compensation transistor is controlled by a compensation voltage signal that is adjusted based on the distance from the power supply, effectively mediating the voltage distribution across the display to compensate for resistive losses in the power supply lines.
3Ease of manufacture
If there is a non-uniformity of manufacturing processes, then there is a deviation in the threshold voltage of the current drive transistor, but a unit pixel with the same structure is formed on the entire region of the panel, causing characteristics of the current drive transistor to fluctuate according to pixel positions
Solution Approach 1:
The patent introduces a compensation transistor with an adjustable width-to-length ratio that is specifically designed to compensate for manufacturing variations. By optimizing the dimensions of the compensation transistor relative to the drive transistor, the circuit achieves compensation for threshold voltage deviations caused by manufacturing non-uniformity, ensuring consistent performance across all pixels despite process variations.
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 solution enables accurate control of drive voltage and current, allowing for enhanced expression of low gray scales and improved image quality by compensating for voltage drops and transistor characteristic fluctuations, resulting in more uniform pixel brightness.
Implementation Method 1
the organic electro-luminescence device emits light by itself. The organic electro-luminescence device displays a predetermined image by recombining electrons and holes
Data Source
AI summary
An organic electro-luminescence device includes a drive unit having first to fourth transistors and a capacitor, and an organic light emitting diode (OLED) controlled by the drive unit, wherein the first transistor has its gate, drain and source connected to a first node, a second node and a power voltage supply line, respectively; the second transistor has its drain and source connected to the OLED and the second node, respectively; the third transistor has its gate, drain and source connected to a first select signal line, the second node and the first node, respectively; the fourth transistor has its gate, drain and source connected to the first select signal line, a data line, and the second node, respectively; and the capacitor is connected to the first node and a predetermined signal line.