DisplayPort is the new interface standard for the Video Electronic Standards Association (VESA), which simplifies display design and its associated connectivity. It also supports higher resolutions with powerful electrical characteristics. Although the DisplayPort interface is mainly used in notebooks and displays from the current application, it is also suitable for many embedded and internal applications such as digital TV.
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DisplayPort is a high-bandwidth, bi-directional display interconnect that enables a universal next-generation interface standard for both internal and external display connections. With scalable SerDes technology and varying channel counts and speeds, the display system can support various resolutions using the DisplayPort interface standard, making it ideal for digital TV. Table 1 shows some examples of resolutions for DisplayPort supported by different speeds and channel counts.
There are many interfaces in today's digital TV applications, such as HDMI, VGA, RS-232, RGB, etc. Multiple interfaces increase the weight and thickness of the panel and increase the number of cables connected to the TV, making it difficult to hang on the wall. A new way to solve this problem is to place all the interfaces in a set-top box with only one cable in the set-top box and panel (see Figure 1), ensuring that the panel is light and thin, making it easy to hang on the wall.
Figure 1 TV to set-top box configuration
The system cable is an external audio and video interface that brings new demands to the TV display interface. It needs to support long-distance data transfer and data bandwidth of 120Hz refresh rate. The data of this interface needs to be protected by protocols such as high-definition content protection (HDCP).
For external interfaces, most word TVs also use Low-Voltage Differential Signaling (LVDS) interfaces between system chips or between boards. Because it is easy to use, it has been around for many years, and it has been expanding, far exceeding the original expectations in terms of speed and distance. Despite this, LVDS limits its support for higher resolution, faster refresh rates, and long-distance application technology due to its high voltage and swing. Dual channel LVDS up to 135MHz can support 120Hz 1080p resolution, but the bit error rate is too high, so it can't support higher resolution. If you use a half-speed four-channel LVDS, the number of connected cables will become so large that the board layout becomes a problem. Each LVDS link operates at 7 times the specified frequency, that is, the 135 MHz frequency corresponds to a link speed of 945 MHz. In addition, increased link count, high common-mode voltage (3.3V) and swing, and decrypted data on LVDS links can cause severe electromagnetic interference (EMI) problems.
The next-generation TV display interface not only faces the challenge of replacing the internal interface, but also meets the needs of the external interface. Due to its higher resolution and lower electromagnetic interference, DisplayPort is a viable and powerful alternative to LVDS. The embedded clock and 8B10B code can achieve lower electromagnetic interference than LVDS. DisplayPort is also an ideal external interface because it can be as high as 15 to 30m and can also support HDCP. Figure 2 is a block diagram of a TV panel with a DisplayPort interface.
Figure 2 TV panel with DisplayPort interface
As shown in Figure 2, DisplayPort can also implement direct drive of the TV panel, allowing the scaler or video processor to be integrated into the timing controller (TCON) or directly into the set-top box.
DisplayPort is also a smart display interface with a dedicated bidirectional command channel (AUX). The advantages of AUX are much more than that, because it can transform the TV design paradigm, can replace the existing slower command interface, such as I2C, and achieve better consistency between the system software and the display signal, which will help Image processing of large amounts of data on these devices. The AUX channel also facilitates debugging during the design phase of the TV system. The processor on the set-top box can be programmed to run preset debug or test software for runtime check or error status recovery.
The AUX channel communicates control information between the panel and the set-top box during operation. This control information can be used to manage new algorithms such as LED backlight control, gamma meters or other image based display adjustments.
Compared to HDMI, DisplayPort is a better choice for next-generation interfaces because DisplayPort is an open interface standard supported by many companies, from original equipment manufacturers (OEMs) to cable manufacturers. It is suitable for internal and external interfaces and has better immunity to electromagnetic interference because its link speed comes from the pixel clock and enables lower electromagnetic interference.
in conclusion
DisplayPort is a powerful interface standard that meets the internal and external interface requirements of next-generation TV platforms. The flexibility to implement content protection, speed for SerDes, or increased link count makes it suitable for TV applications with a variety of screen sizes, resolutions, and refresh rates.
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