OLED Pixel Compensation Circuit for Washed-Out Black Prevention
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Solution Overview
Problem
OLED display devices with internal compensation suffer from washed-out black and low contrast due to parasitic capacitance effects when using transistors of different conductivity types, leading to increased power consumption when trying to prevent this issue.
Innovation Solution
A display device with a drive transistor and two compensation transistors of different conductivity types, connected in series between the control and conduction terminals of the drive transistor, where both compensation transistors are controlled to prevent parasitic capacitance-induced luminance changes, allowing for stable black display without increasing data potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single compensation transistor of different conductivity type is used, then gate potential fluctuation is restrained, but parasitic capacitance causes washed-out black and low contrast
Solution Approach 1:
The single compensation transistor is divided into two series-connected compensation transistors with different conductivity types. This segmentation allows each transistor to compensate for parasitic capacitance effects of the other, preventing washed-out black while maintaining gate potential stability.
Solution Approach 2:
Different regions of the compensation circuit use transistors with different conductivity types (N-channel and P-channel) positioned strategically in series. This local quality differentiation enables targeted compensation of parasitic capacitance effects that would otherwise degrade black display quality.
2Illumination intensity
If data potential is increased to prevent washed-out black, then black display quality improves, but power consumption increases
Solution Approach 1:
The problem of washed-out black caused by parasitic capacitance is extracted and addressed by the dual compensation transistor circuit, eliminating the need to increase data potential for compensation. This removes the harmful side effect of increased power consumption while maintaining black display quality.
3Reliability
If oxide semiconductor-based transistor is used for compensation, then leak current is restrained and gate potential stability improves, but device complexity increases
Solution Approach 1:
The conductivity type parameter of compensation transistors is changed from uniform to varied (N-channel and P-channel combination). This parameter change enables the transistors to compensate for each other's parasitic capacitance, improving black display quality while maintaining the low leak current characteristics of oxide semiconductor materials.
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 effectively prevents washed-out black and maintains contrast by controlling the conduction states of the compensation transistors, reducing power consumption and eliminating the need for increased data potential, while using oxide semiconductor-based transistors for low-frequency drive.
Implementation Method 1
The OLED is a current-driven light-emitting element that emits light at a luminance that matches the magnitude of the electric current flowing through the OLED
Implementation Method 2
There exists a parasitic capacitance Cp between the gate terminal of the TFT T2 and one of the conduction terminals of the TFT T2 that is connected to the gate terminal of the TFT T4
Data Source
AI summary
A display device includes: a display unit including a plurality of first scan lines, a plurality of second scan lines, a plurality of data lines, and a plurality of pixel circuits; and a drive circuit configured to drive the first scan lines, the second scan lines, and the data lines. Each of the pixel circuits includes: a light-emitting element; a drive transistor configured to control a magnitude of an electric current that flows through the light-emitting element, a first compensation transistor having a control terminal connected to an associated one of the first scan lines; and a second compensation transistor having a control terminal connected to an associated one of the second scan lines. The first and second compensation transistors are connected in series and disposed between a control terminal and a conduction terminal of the drive transistor, the conduction terminal leading to the light-emitting element.