Organic Light Emitting Display Threshold Voltage Compensation
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Solution Overview
Problem
Organic light emitting display devices face issues with non-uniform image luminance due to variations in threshold voltage of driving transistors and voltage drops in power supplies, leading to reliability concerns and inability to display desired luminance.
Innovation Solution
The solution involves a driving method for organic light emitting display devices that includes a pixel circuit with four transistors and one capacitor, using a demultiplexer and common circuit units to control voltages, compensating for threshold voltage and voltage drops by supplying reference and initial voltages, and adjusting the gate voltage of the driving transistor to achieve consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional circuits such as multiple transistors are included in the pixel to compensate for threshold voltage variation, then threshold voltage compensation is improved, but device complexity increases and reliability deteriorates
Solution Approach 1:
The invention changes the voltage parameters by introducing a first voltage different from the second voltage to the gate electrode of the driving transistor. This parameter change enables threshold voltage compensation without requiring additional transistors, as the different voltage levels allow the existing transistor to operate in modes that compensate for threshold variations.
Solution Approach 2:
The driving transistor serves multiple functions: it acts as both a switching transistor and a compensation transistor. By applying different voltages to the gate electrode at different times, the same transistor performs both signal switching and threshold voltage compensation, eliminating the need for separate compensation circuits.
2Device complexity
If a simple pixel structure with few transistors is used, then device complexity is reduced and reliability is improved, but threshold voltage compensation capability is insufficient
Solution Approach 1:
The invention makes the gate electrode voltage dynamic by sequentially applying different first voltages and second voltages during different time periods. This dynamic voltage application allows the simple pixel structure to achieve threshold voltage compensation through time-multiplexed operation rather than through additional hardware components.
Solution Approach 2:
The gate electrode receives periodic voltage applications with different levels (first voltage and second voltage) during different time periods within each frame cycle. This periodic action enables the transistor to perform alternating functions of signal transmission and threshold compensation, achieving uniform luminance output despite device variations.
3Device complexity
If conventional driving methods are used without voltage compensation, then device complexity is low, but luminance uniformity and image quality deteriorate due to voltage drops and threshold variations
Solution Approach 1:
The invention applies preliminary voltage compensation by setting the gate electrode voltage to a specific first voltage before data signal input, and then adjusting to a second voltage during the data writing period. This preliminary action prepares the driving transistor to operate despite threshold voltage variations and power supply drops, ensuring accurate luminance reproduction.
Solution Approach 2:
The invention implements implicit feedback by using the relationship between the driving transistor's threshold voltage and the applied gate voltages to automatically compensate for variations. The different voltage levels create operating conditions where the transistor's inherent characteristics are compensated, resulting in uniform luminance output across all pixels regardless of individual device variations.
Data Source
AI summary
An organic light emitting display device includes: a scan driver for driving one or more scan lines and emission control lines; a data driver for sequentially providing j data signals to each of a plurality of output lines in each horizontal period; a demultiplexer for transmitting the j data signals to j first data lines, the demultiplexer being coupled to the output lines; a plurality of pixels at crossing regions of the scan lines and second data lines extending in a direction crossing the scan lines; and a common circuit unit for controlling voltages of the second data lines coupled to the pixels by using a reference voltage and an initial voltage and the data signals, the common circuit unit being coupled between the first data lines and the second data lines.