OLED Pixel Circuit with Boosting Capacitor for Transistor Degradation
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Solution Overview
Problem
In organic light emitting displays, the operational characteristics of pixel elements change over time, leading to difficulties in maintaining uniform operation, particularly due to deterioration of drive transistors, which affects the display's ability to show desired grey levels.
Innovation Solution
The implementation of a pixel structure that includes a boosting capacitor to increase the voltage of the gate electrode of a drive transistor, using a scan driver and data driver configuration, and specific transistor control signals to compensate for transistor deterioration and ensure accurate grey level display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel structure without boosting capacitor is used, then the device complexity is lower, but the drive transistor deteriorates over time causing non-uniform operation and inability to maintain desired grey levels
Solution Approach 1:
The boosting capacitor is charged in advance during the scan signal high period before the light emitting control signal is applied. This preliminary charging action stores energy that will be used to compensate for transistor deterioration during the subsequent light emission period, allowing the system to anticipate and counteract future degradation effects.
Solution Approach 2:
The voltage of the gate electrode is dynamically changed by applying a high voltage through the boosting capacitor during specific time periods. This parameter change in gate voltage compensates for the threshold voltage shift caused by transistor deterioration, restoring the transistor's drive capability and maintaining uniform pixel operation across different grey levels.
2Manufacturing precision
If the voltage of gate electrode is increased using boosting capacitor, then the drive transistor deterioration is compensated and desired grey level is displayed, but the device complexity increases due to additional capacitor and transistor control circuits
Solution Approach 1:
The boosting capacitor serves multiple functions: it acts as a voltage compensation element for transistor deterioration, a timing control element for gate voltage application, and an energy storage element for maintaining grey levels. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall device complexity.
Solution Approach 2:
The gate voltage boosting is applied periodically during specific time windows defined by the scan and light emitting control signals. By restricting the boosting action to specific periodic intervals rather than continuously, the circuit complexity is minimized while still achieving effective compensation for transistor deterioration over time.
3Reliability
If additional transistors and capacitors are added to compensate for transistor deterioration, then the reliability improves, but the ease of manufacture decreases
Solution Approach 1:
The boosting capacitor is nested within the existing pixel circuit structure, sharing space and control signals with the drive transistor and scan/data lines. The additional components are integrated into the existing layout rather than requiring separate dedicated regions, reducing the overall manufacturing complexity despite the increased component count.
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 effectively compensates for drive transistor deterioration and enables the display to show images with desired grey levels by applying a high voltage to the gate electrode, improving image quality and maintaining uniform pixel operation.
Implementation Method 1
a boosting capacitor coupled between the gate electrode of the second transistor and the ith scan line
Implementation Method 2
Each of the pixels may include an organic light emitting diode
Data Source
AI summary
An organic light emitting display includes a scan driver configured to sequentially supply a scan signal to scan lines and sequentially supply a light emitting control signal to light emitting control lines, a data driver configured to supply a data signal to data lines, and pixels arranged coupled to the scan lines, the data lines and the light emitting control lines. Each of the pixels includes an organic light emitting diode, a second transistor, a storage capacitor coupled between an i−1th light emitting control line and a gate electrode of the second transistor, a first transistor coupled between an ith scan line, a data line and a first electrode of the second transistor, and a third transistor coupled between the gate electrode and a second electrode of the second transistor.