OLED Pixel Circuit Compensating Threshold Voltage Variations
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Solution Overview
Problem
Organic light emitting diode display panels face issues with image quality due to variations in electrical characteristics of current control switches and organic light emitting diodes, affecting brightness control.
Innovation Solution
A pixel structure comprising specific transistors, capacitors, and a driving method that compensates for these variations by using a scanning period with sub-periods to reset, write, and compensate voltage signals, decoupling current flow from threshold voltages and voltage across the light emitting diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a current control switch is used to control the amount of current flowing through the organic light emitting diode, then the brightness of the organic light emitting diode can be controlled according to display voltage, but the threshold voltage differences of the current control switch and voltage variations due to aging affect the brightness control and worsen image quality
Solution Approach 1:
The patent applies preliminary action by introducing a compensation transistor and capacitor that pre-compensate for threshold voltage differences and aging effects before the main display voltage is applied. The compensation circuit is activated in advance during a compensation period to store compensation charges that counteract the electrical characteristic variations, ensuring accurate brightness control despite device variations and aging.
2Device complexity
If the organic light emitting diode display panel uses conventional current control, then the structure is simple, but the electrical characteristic differences of components directly affect brightness and degrade image quality
Solution Approach 1:
The patent uses an intermediary approach by introducing a compensation transistor and capacitor as mediator elements between the data line and the organic light emitting diode. These intermediary components capture and store voltage variation information and threshold difference information, then use this stored information to compensate for brightness deviations, thereby improving manufacturing precision and brightness uniformity without significantly increasing overall device complexity.
Data Source
AI summary
A pixel of a display panel includes a first transistor with a first end coupled to a data line, a control end coupled to a scan line; a second transistor with a first end coupled to a first voltage source, a control end coupled to a second end of the first transistor; a third transistor with a first end coupled to a second end of the second transistor, a control end for receiving a control signal; a light emitting unit with a first end coupled to the second end of the second transistor, a second end coupled to a second voltage source; a first capacitor with a first end coupled to the second end of the first transistor, a second end coupled to a second end of the third transistor; and a second capacitor coupled between the second end of the first capacitor and the second voltage source.