Development of HDMI
Hitachi, Panasonic, Philips, siliconimage, Sony, Thomson and Toshiba jointly established the hdmihd Multimedia Interface Organization in 2002 and began to develop a new high-definition digital video / audio interface technology. It has been nearly 20 years.
So is this technology effective? Because of one line, the problem of audio and video transmission is certainly solved. Looking back on the hard scene when I connected the VCR and VCD in my childhood, I was even more impressed by the progress of science and technology.
HDMI Type-A, the most common HDMI plug, has been used since version 1.0, while type C (minihdmi) is version 1.3 and type D (microhdmi) is version 1.4. Obviously, the latter two applications are not common. Some can be seen on some tablets in the early days, but they are basically not available later.
1、 HDMI Pin definition
HMDI The emergence of is to serve audio and video transmission. Then, on the premise of gradually improving the image resolution, HDMI also continues to upgrade, mainly to increase the transmission bandwidth, in short, to improve the transmission speed of TMDs groups of differential lines.
2、 HDMI rate
Let's first understand what is the relationship between image resolution and transmission bandwidth? For the popular 4K movies, the resolution is 3840 * 2160, and a frame of image is 3840 * 2160 = 8294400 pixels in total. The HDMI image also needs to reserve 20% of blank pixels, so the pixels of a real image are: 8294400 * 1.2 = 9953280 pixels. Each pixel is represented by 3 8bit, that is, 24 bit color, so the total number of bits required is 9953280 * 3 * (8 + 2) = 298598400 bits (note that 2 control bits should be added every 8bit). Refresh 60 times per second, i.e. 60Hz, then the number of bits transmitted per second is: 298598400 * 60 ≈ 1.8e + 010, which is converted into Gbps, then the rate is 18gbps, which is the total rate of three TMDs channels, so the rate of each channel is 18 / 3 = 6gbps. Did you find that only 2.0 HDMI can barely watch 4K movies, so it is inevitable to upgrade.
Although high speed alone is not a problem, with distance, the problem comes. High speed signal transmission in cable has loss. The longer the distance, the greater the loss. There are other problems, such as electromagnetic interference. How can we ensure the transmission of signals over long distances? At this point, there is an optical fiber HDMI cable, which uses light to transmit signals.
3. Advantages of light:
Zero impedance, no signal compression, no signal loss;
Long distance, high bandwidth;
No electromagnetic interference
4. Optical fiber HDMI Cable
In fact, the optical fiber only works as four groups of photoelectric conversion modules of HDMI high frequency R, G, B and clock. The advantage of optical fiber is that one fiber tube is used to do three tasks: tmds0 +, ground wire and tmds0 -. Therefore, the four groups of fiber tubes are on the photoelectric conversion module. Through the calculation and adjustment of the chip, the skew of RGB three primary colors is perfectly adjusted to no delay or advanced working state. In addition, the difference and clock synchronization functions in the clock state are also completed in the chip module.
Whether it's cable or optical fiber,HDMI As a new digital multimedia transmission interface, it has experienced more than ten years of development and successfully replaced the traditional VGA and DVI interfaces. Although some people say that HDMI may be gradually replaced by the emerging type-C, it is estimated that this day will not come too early. In addition, when using type-C interface cable, HDMI Communication Protocol shall be used.
