Subway HDMI interface technology for spring
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Now that the HDTV format is starting to catch on, you can see the download of various movies in HDTV high-definition format everywhere on the Internet. You can also see a variety of color TVs in the electrical industry everywhere to start supporting the HDTV format. But with HDTV sources alone, is it enough to have a TV that can play HDTV? What kind of link should they use? I will introduce a new multimedia interface that has become popular, HDMI.
What is the HDMI interface?
HDMI (High-Definition Multimedia InteRFace) is a new type of digital audio and video interface that will replace the signal interfaces of various digital devices such as DVD players, TV sets, set-top boxes and displays in the future. This means that consumers can use just one signal line instead of the previous signal lines. You can use it to connect to a DVD player and connect it to a TV. The connection of this heart
The biggest benefit of this new digital interface is the ability to simultaneously transmit audio and video data, giving consumers the highest quality and picture quality experience. Today's digital audio can use light to transmit digital signals, but digital video devices such as DVD players use the S-Video. It is a very popular analog signal interface. Of course, digital video interfaces already exist, its name is DVI, usually you can see this interface on the LCD.
The latest HDMI interface has three distinct differences compared to the DVI interface. First, HDMI supports higher resolution than DVI. About HDMI can support twice the resolution of HDTV now. Second, DVI only supports the transmission of video signals, but the audio signals are transmitted using additional cables. HDMI can transmit audio and video digital signals simultaneously. Third, the size of the HDMI interface is much smaller than the DVI interface. What makes consumers happy is that HDMI is backward compatible with the DVI interface, which means that you can connect to a DVI device using an HDMI device, using only a small patch cord. When the user is fully upgraded to the new HDMI system, the previous DVI device can still be used.
Another big difference is the difference in object orientation. The traditional DVI interface standard is for general PC users, while the HDMI interface standard is for people using consumer electronics, such as DVD players, home theater equipment, and more.
The most important concern for users is the performance of the new interface, and for content publishers they are more concerned with copyright protection measures. The new HDMI interface features advanced HDCP copyright protection technology. (High-Bandwidth Digital Copy Protection, high-bandwidth digital copy copyright protection) This technology was developed by the famous Intel.
How the HDMI interface works
This picture is a schematic diagram of the architecture of the HDMI interface. As you can see from the source on the left, the HDMI interface can be any device that supports HDMI output, and the access can be any device with an HDMI input. Whether they are audio, video or control devices, the HDMI interface can be used.
The data signal in the HDMI interface uses the TMDS Minimized Transmission Differential Signaling Protocol. This data transmission protocol has been widely used on the DVI interface. The data signal on the HDMI interface also follows this protocol. This protocol converts standard 8-bit data to a 10-bit signal and uses differential transmission during the conversion process. Differential transmission technology has also been widely used in Gigabit Ethernet data transmission.
Three TMDS data channels can be used for the transmission of audio and video data in the HDMI interface. The video information is converted into continuous 24-bit pixel data during transmission, and 10 bits of data can be transmitted per clock cycle. The pixel clock cycle transfer ratio is approximately between 25MHz and 165MHz. In general, the standard NTSC 480i interlaced signal has a pixel clock transfer ratio of approximately 13.5 MHz. If the ratio of the transmitted signal is less than 25MHz, HDMI will use automatic loop technology to fill the code rate and raise the signal rate to 25MHz. The HDMI interface can transmit up to 165M pixels per second, and this data throughput is quite amazing. In the future, it will be sufficient to cope with the signal transmission tasks of high-rate, high-data stream household appliances.
The highest standard for HDTV is 1080p, which has a resolution of 1920×1080 per screen. If 60 frames per second (1080p@60) is transmitted, the final pixel clock transmission ratio is 124.4MHz. From this point of view, the HDMI interface can fully handle the various applications of today's consumer electronics products. Of course, HDMI also supports dual-interface parallel mode, which can provide an amazing 330MHz transmission ratio. However, this dual parallel HDMI interface is currently not used for the general consumer class.
The video signals used in HDMI are encoded in RGB format, such as YCbCr 4:4:4 or YCbCr 4:2:2 format, which are 24 bits per pixel. YCbCr is a format for digital video signals similar to the YPbPr format. (The current component output of DVD players is in YCbCr/YPbPr format.) This video signal standard is what we often call "YUY". Y means brightness, it does not carry information about the color of the image. Just responsible for recording black in the image
With white information. Cb is the difference value (BY) between blue and luminance in the image, and Cr is the difference value (RY) between red and luminance.
Then the three values ​​of Y, Cb, and Cr define the sampling rate at the time of video encoding. The "4" in the above represents the sampling rate when using the NTSC or PAL system, that is, 13.5 MHz. Then we see 4:4:4, which means that the encoding sampling rates of Y, Cb, and Cr are each 13.5MHz. The sampling rate of Cb and Cr in the 4:2:2 format we see is 6.75MHz. So now you can clearly distinguish which of the above two YCbCr formats is better.
In the HDMI interface, the audio signal can use 2 to 8 channels, and the sampling rate of each channel is 192KHz. In addition, the HDMI interface also provides a DDC display data channel, which sends configuration information and data format information to the video receiving device. The receiving device can read the information of these E-EDID enhanced extended display identification data. Finally, the HDMI interface also provides a CEC consumer electronics control channel through which the operation of the audiovisual equipment can be controlled.
HDMI interface connector
There are two types of HDMI interfaces, one is A-type with 19 pins, and the other is B-type with 29-pin. The Type B interface is larger than the Type A interface and can support two-way connections. This means that the amount of data transferred will double as you use the Type B interface. The Type A interface can transmit information for 165MHz pixels per clock cycle, while the Type B interface can transmit up to 330MHz pixel information per clock cycle.
As indicated in the TMDS standard, the length of the cable must not exceed 15 meters. Therefore, the length of the HDMI interface cable using the TMDS standard is also limited to 15 meters. This length is sufficient for the general home and office areas.
The signal transmitting device with the A-type HDMI interface can be connected to the receiving device using the B-type interface. In this case, a B to A type conversion interface is required to be successfully connected. However, it should be noted that it is impossible to connect a signal receiving device with a type B interface to a signal transmitting device with a type B interface. At present, the HDMI interface can be backward compatible with the DVI interface, and only need to use a dedicated adapter cable to convert each other.
Patent license fee
Unfortunately, the HDMI interface is not an open standard. Manufacturers must pay royalties to the HDMI Standards Development Association in exchange for a production license. But this royalty is not cheap, it costs $15,000 a year in licensing fees, and the darker is that it costs $0.15 per license to produce an HDMI interface. Only in this way can the manufacturer identify the logo that supports HDMI in its own product and manual. If the manufacturer is already a member of the HDCP HD Digital Content Protection Agreement, each product with an HDMI interface will only be subject to a license fee of $0.04. If a manufacturer uses HDCP HD digital content protection in their products, they must pay an annual fee of $15,000 plus a purchase key fee of $0.005 per product.
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