OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Organic light emitting display devices face issues with inconsistent image luminance due to variations in the threshold voltage of driving transistors, leading to leakage currents and image quality deterioration, particularly when using compensation circuits with multiple capacitors.
Innovation Solution
A pixel design that includes specific transistors and a storage capacitor, where the gate electrode of the driving transistor is not coupled to a separate initialization power source, and only one capacitor is used, minimizing leakage current and maintaining image quality by compensating for threshold voltage variations using the storage capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a compensation circuit with multiple capacitors is used to compensate for threshold voltage variation, then the threshold voltage compensation is improved, but image quality deteriorates due to leakage current and capacitance ratio sensitivity
Solution Approach 1:
The patent removes the initialization power source and one of the two capacitors from the conventional compensation circuit, extracting only the necessary storage capacitor to maintain threshold voltage compensation while eliminating the leakage current path and reducing sensitivity to capacitance ratio variations
Solution Approach 2:
Instead of using an initialization power source to set the gate voltage, the patent inverts the approach by using the data signal directly to charge the storage capacitor, which then maintains the gate voltage without requiring a separate initialization power source, thereby eliminating the leakage current path
2Reliability
If two capacitors are included in the compensation circuit, then threshold voltage compensation is achieved, but image quality deteriorates due to sensitivity to capacitance ratio changes
Solution Approach 1:
The patent extracts only one storage capacitor from the conventional two-capacitor compensation circuit, eliminating the need to maintain a specific capacitance ratio while still achieving effective threshold voltage compensation through the single capacitor's ability to store and maintain the gate voltage
Solution Approach 2:
The patent segments the compensation function into a single capacitor that performs both the storage and compensation functions, separating the capacitance ratio control requirement from the compensation mechanism itself, thereby making the circuit less sensitive to manufacturing 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 design ensures consistent image luminance and prevents image quality deterioration by eliminating leakage current and maintaining capacitance ratios, thereby improving overall image quality in organic light emitting display devices.
Implementation Method 1
a storage capacitor coupled between the first and second nodes
Implementation Method 2
The organic light emitting display device displays images using organic light emitting diodes that emit light through recombination of electrons and holes
Data Source
AI summary
A structure of a pixel and an organic light emitting display device using the same are provided. The pixel includes an organic light emitting diode; a first transistor controlling the amount of current supplied from a first power source to the organic light emitting diode depending on a voltage applied to a second node; a second transistor coupled between a data line and a first node, and turned on when a scan signal is supplied to a first scan line; a third transistor coupled between the first power source and the first node, and turned on when the scan signal is supplied to a second scan line; a fourth transistor coupled between the first power source and the second node, and turned on when the scan signal is supplied to the second scan line; and a storage capacitor coupled between the first and second nodes.