Organic EL Pixel Circuit With Threshold Voltage Compensation
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Solution Overview
Problem
Current display technologies using liquid crystals are inefficient in terms of power consumption and manufacturing complexity, particularly when using transistors of different polarities in organic electroluminescent (EL) devices, which also face issues with threshold voltage shifts in amorphous silicon transistors.
Innovation Solution
A pixel circuit design that utilizes only same-type transistors, specifically n-type transistors, with a characteristic-adjustment circuit and voltage clamp circuit to control current as a data signal, allowing for precise control of organic EL devices and addressing manufacturing and operational challenges such as threshold voltage shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transistors of different polarities (n-type and p-type) are combined to constitute a pixel circuit, then the control precision of organic EL device is improved, but the manufacturing process becomes more complicated
Solution Approach 1:
The patent applies homogeneity by using only n-type transistors throughout the pixel circuit, eliminating the need for both n-type and p-type transistors. This uniform transistor type simplifies the manufacturing process while maintaining the circuit's functionality through a carefully designed configuration with five n-type transistors and two capacitors that achieves precise control of the organic EL device using current as the data signal.
2Ease of manufacture
If only n-type transistors are used in the pixel circuit, then the manufacturing process is simplified, but the control capability may be limited
Solution Approach 1:
The patent employs dynamics by implementing a time-multiplexed control scheme where the five n-type transistors are switched at different times during the frame period. The first through fourth transistors are turned on sequentially during the data input period, and the fifth transistor is turned on during the light emission period. This dynamic switching strategy enables the circuit to perform multiple functions with only n-type transistors, maintaining full control capability while simplifying manufacturing.
3Ease of manufacture
If amorphous silicon transistors are used in the pixel circuit, then the manufacturing cost is reduced, but threshold voltage shifts occur affecting display quality
Solution Approach 1:
The patent applies preliminary action by implementing a threshold voltage compensation mechanism that operates before the light emission phase. During the data input period, the circuit writes not only the data signal but also compensation signals that anticipate and counteract the threshold voltage shifts. This preliminary compensation ensures that even if threshold voltage drifts occur in the amorphous silicon transistors, the display quality remains stable.
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 simplifies the manufacturing process, improves production yield, reduces manufacturing costs, and enhances the control and efficiency of organic EL devices by using current as a data signal, while maintaining low power consumption and high display performance.
Implementation Method 1
current-driven light-emitting devices, instead of liquid crystal devices. Since current-driven light-emitting devices are self luminous devices, which emit light in response to a supplied current
Data Source
AI summary
The invention provides an electro-optical apparatus that can prevent a shift in a threshold voltage of an amorphous silicon transistor while driving an organic EL device in a pixel circuit including the amorphous silicon transistor. A characteristic-adjustment circuit can be provided, which has a function of returning a shift in the threshold voltage of the amorphous silicon transistor included in the pixel circuit to the original state.