Design of USB transmission of high-definition video for mobile phone

In order to meet the challenge of mobile phones transmitting high-definition cameras, a USB audio and video class needs to be defined in the USB standard to regulate the USB-over-USB technology.

The camera function of mobile phones has evolved from a new thing to a mainstream configuration, and mobile vendors strategically regard high-definition video as their high-end products. The integration of high-definition video in mobile phones will further reflect its practical value, because it is not only a digital camera, but also a digital video camera.

Putting high-definition video on the phone will bring a new problem: how to make high-definition video playback. It is very common to directly play back videos on mobile phones, but the limitations of screen size and resolution prevent high-definition video from delivering its moving high-definition experience to users. Similar to sharing mobile documents and photos, the challenge facing developers is how to share high-definition video without restricting it to the inside of the phone.

Use high-definition video output interface on mobile phones

The current development of mobile phone video output interface can not keep up with the demand of mobile phone high-definition video transmission. USB data transfer speed is sufficient to transfer photos, but high-definition video connected to high-definition TVs, monitors, and other display devices requires real-time streaming. At the same time, current high-definition video phones are either equipped with standard-definition analog video output or adopt the high-definition video standard used by high-definition televisions. These are not optimized specifically for mobile phones.

Traditional HD video standard

HDMI is one of the best standards for high-definition video today. By the second quarter of 2009, more than 850 companies had obtained HDMI authorization.

In-Stat once predicted that in 2010, more than one billion HDMI-enabled devices were on the market. These devices include HDTVs, projectors, and handheld devices such as media players and mobile phones. HDMI (below Figure 1) uses three TMDS (Minimized Transmission Differential Signaling) data channels and a separate clock channel to transmit uncompressed audiovisual signals up to 10.2 Gbps (3.4 Gbps per channel). With this bandwidth, HDMI supports more than 1080p data streams, which has created a digital three-dimensional experience.

(Electronic Engineering Album)

Figure 1: Block diagram of HDMI structure.

At the same time, DisplayPort, another high-definition standard, is rapidly penetrating the market. It has strong support from manufacturers such as HP, Dell, and Apple. In the DisplayPort core, audio, video and embedded clock signals can be transmitted through the scalable 1, 2 or 4 channels under the micro-packet architecture.

As shown in Figure 2, the original data stream is well packed and transmitted via the data channel through pixel control and addressing. DisplayPort1.2a supports a bandwidth of 17.28 Gbps.

(Electronic Engineering Album)

Figure 2: Block diagram of DisplayPort structure.

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