OLED Pixel Circuit Reducing Transistor Count for Threshold Compensation
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Solution Overview
Problem
Organic light emitting display devices face issues with non-uniform luminance due to manufacturing variations in driving transistors, leading to differences in threshold voltages, which complicate the pixel structure and reduce yield.
Innovation Solution
A pixel structure is introduced with a reduced number of transistors, including an organic light emitting diode, a first transistor, a second transistor, a third transistor, a first capacitor, and a second capacitor, where the second and third transistors are concurrently turned on for one frame period, and the second transistor is turned on for a longer time during the scan period, along with a power driver configuration that supplies power at different levels during various periods to compensate for threshold voltage differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a six-transistor structure is used to compensate for threshold voltage variations, then luminance uniformity is improved, but device complexity increases and yield decreases
Solution Approach 1:
The patent extracts and eliminates the need for a sixth transistor by using the existing fifth transistor (switching transistor) to perform the threshold voltage compensation function. This is achieved by configuring the fifth transistor to conduct during the emission period, allowing it to compensate for threshold voltage variations without requiring an additional sixth transistor, thus reducing device complexity while maintaining luminance uniformity.
Solution Approach 2:
The patent makes the fifth transistor multi-functional by having it serve both as a switching transistor for controlling the organic light emitting diode and as a compensation transistor for threshold voltage variations. This universal use of the fifth transistor eliminates the need for a dedicated sixth transistor, reducing the overall number of transistors while maintaining compensation capability.
2Manufacturing precision
If a six-transistor structure is used to compensate for threshold voltage variations, then luminance uniformity is improved, but manufacturing yield decreases
Solution Approach 1:
The patent removes the sixth transistor from the pixel structure, reducing the number of components that could potentially malfunction. This extraction of the unnecessary sixth transistor directly reduces the complexity-related yield loss while maintaining the compensation function through the optimized five-transistor configuration.
Solution Approach 2:
By making the fifth transistor multi-functional for both switching and compensation purposes, the patent eliminates the need for an additional sixth transistor. This reduces the total transistor count and associated manufacturing complexity, thereby improving manufacturing yield while still achieving luminance uniformity through the compensation mechanism.
3Device complexity
If the number of transistors is reduced, then device complexity decreases and yield improves, but threshold voltage compensation capability may be compromised
Solution Approach 1:
The patent achieves threshold voltage compensation with only five transistors by making the fifth transistor multi-functional. The fifth transistor is configured to conduct during the emission period and compensate for threshold voltage variations, while also serving as the switching transistor. This universal use maintains compensation capability without requiring a sixth transistor.
Solution Approach 2:
The patent employs dynamic control of the fifth transistor's conduction state during different periods (initialization, scan, emission) to achieve compensation. By controlling when the fifth transistor conducts (specifically during the emission period), the system dynamically adjusts the compensation effect to maintain uniform luminance while using fewer transistors.
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 configuration effectively compensates for threshold voltage variations, reducing the number of transistors and improving the display's ability to maintain uniform luminance, thereby enhancing the yield and simplifying the pixel structure.
Implementation Method 1
an organic light emitting diode that produces light by recombining electrons and holes
Data Source
AI summary
A pixel includes: an organic light emitting diode; a first transistor having a second electrode coupled with the organic light emitting diode and a first electrode coupled with a data line; a second transistor coupled between a gate electrode and the second electrode of the first transistor and turned on when a first scan signal is supplied to a first scan line; a third transistor coupled between the first electrode of the first transistor and the data line and turned on when a second scan signal is supplied to the second scan line; a first capacitor coupled between the first electrode of the first transistor and a first power supply; and a second capacitor coupled between the gate electrode of the first transistor and the first power supply.