Dual Transistor Pixel Circuit for Luminance Control
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Solution Overview
Problem
Display apparatuses using light-emitting devices face issues with luminance control due to variations in cathode potential, especially in high grayscale displays, and silicon-based transistors have high off-state current and limited layout flexibility, affecting display quality and power consumption.
Innovation Solution
A display apparatus is designed with a combination of p-channel and n-channel transistors, where the p-channel transistor is used for high grayscale levels and the n-channel transistor with metal oxide in the channel formation region is used for low grayscale levels, along with a signal generator circuit to manage binary signal potentials, reducing gate-source voltage variations and improving display characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If an n-channel transistor is used as the driving transistor, then the display can achieve high grayscale levels with high luminance, but the cathode potential varies or shows position dependence due to electrode resistance, causing Vgs variation and luminance discrepancy
Solution Approach 1:
The driving transistor is segmented into two separate transistors: a first n-channel transistor connected to the light-emitting device and a second n-channel transistor receiving the image signal. This segmentation isolates the Vgs control function from the high-current driving function, preventing cathode potential variations from affecting the gate-source voltage control accuracy while maintaining high luminance capability.
2Reliability
If a p-channel transistor is used as the driving transistor, then the cathode potential variation problem is avoided, but the off-state current is high and transfer characteristics for low grayscale levels are insufficient
Solution Approach 1:
Different transistor types are used in different locations within the pixel circuit based on functional requirements. The first transistor uses n-channel structure optimized for low off-state current and low grayscale control, while the second transistor handles high grayscale driving. This local optimization allows each transistor to operate in its optimal performance regime without compromising overall system reliability or energy efficiency.
3Reliability
If the channel length is lengthened to improve saturation characteristics and current control, then the transistor performance is improved, but the layout flexibility is reduced
Solution Approach 1:
The pixel circuit is segmented into multiple functional blocks with dedicated transistors for different purposes. This segmentation allows each transistor to have optimized dimensions for its specific function without constraining the overall layout. The separate signal processing and driving functions enable independent optimization of channel lengths while maintaining layout flexibility through modular circuit architecture.
Data Source
AI summary
A display apparatus suitable for wide-grayscale display is provided. The display apparatus includes, in a pixel, two driving transistors and a light-emitting device that are connected in series. One of the transistors is a p-channel transistor and the other of the transistors is an n-channel transistor, and switching therebetween is performed for driving. Such a configuration can inhibit the change in a gate-source voltage in display with a high grayscale level. In addition, the use of a transistor containing a metal oxide in a channel formation region as the n-channel transistor enables an increase in display characteristics in display with a low grayscale level.