A matrix system should usually include the following basic functions: character signal superposition; decoder interface to control the pan/tilt and camera; alarm interface; control host, as well as audio control box, alarm interface box, control keyboard and other accessories. For domestic users, the character overlay should be in full Chinese to facilitate the use of operators who do not understand English. The matrix system also needs to support cascading to achieve higher capacity. In order to adapt to different users' requirements for matrix system capacity, the matrix system should support modularization and plug-and-play (PnP). Different capacity combinations can be achieved by adding or reducing video input and output cards.
The development direction of matrix systems is multi-function, large capacity, networkable and remote switching. Generally speaking, a matrix system with a capacity of 64×16 is a large-capacity matrix. If a larger capacity matrix system is required, it can also be achieved by cascading multiple matrix systems. The larger the matrix capacity, the higher the technical level required, and the more difficult it is to design and implement.
Classification of matrices
With the development of image signal technology and the improvement of human vision for audio and video; the transmission of image signals has gone through several stages of development, from AV video to color difference component (YPbPr), then to VGA signal, and now to DVI, HDMI, DISPLAYPORT, etc.; in this process, signal matrix switching was formed due to the need for convenient application, so there are corresponding matrix switchers at each signal stage; now with the development of IP technology and image compression technology, the It has become a virtual matrix switch for multimedia stream (based on MPEG-4, H2.64);
According to the transmission signal form, it is divided into: analog matrix switcher and digital matrix switcher; That is, the type of matrix switcher is determined based on the signals you want to split. Matrix switchers can be divided into VGA, AV, V, YPbPr matrix switchers according to the type of signal source. For example: a VGA matrix switcher is a matrix switcher whose input and output signals are []VGA signals. Other types can be deduced by analogy and will not be described again here. The following will focus on the types of signal sources.
VGA matrix
The components of VGA signals are divided into five types: RGBHV, which are the three primary colors of red, green and blue and horizontal and vertical synchronization signals. The VGA transmission distance is very short. In order to transmit longer distances in actual projects, people disassemble the VGA cable, separate the five RGBHV signals, and transmit them with five coaxial cables respectively. This transmission method is called RGB transmission. It is customary to call this signal RGB signal. In fact, there is essentially no difference between RGB and VGA.
VGA interface, also called D-Sub interface. The VGA interface is a D-type interface with a total of 15 empty pins, divided into three rows of five in each row. The VGA interface is the most widely used interface type on graphics cards, and most graphics cards have this interface. At present, most computers and external display devices are connected through an analog VGA interface. The display image information generated digitally inside the computer is converted into R, G, and B primary color signals and horizontal and field synchronization signals by the digital/analog converter in the graphics card. The signals are transmitted to the display device through cables.
RGB matrix
There are five components of VGA signals: RGBHV, which are the three primary colors of red, green and blue and horizontal and vertical synchronization signals. The VGA transmission distance is very short. In order to transmit longer distances in actual projects, people disassemble the VGA cable, separate the five RGBHV signals, and use five coaxial cables to transmit them respectively. This transmission method is called RGB transmission. It is customary to call this signal RGB signal. In fact, there is no difference between RGB and VGA signals in essence.
RGB transmission uses BNC plus coaxial cable transmission. The RGB cable has 5 connectors for receiving red, green, blue, horizontal sync and vertical sync signals. The BNC connector can isolate video input signals, reduce mutual interference between signals, and have a larger signal bandwidth than ordinary D-SUB, achieving the best signal response effect.
AV matrix
AV port (also known as composite port) is originally called Composite video connector. It is a common port used by home audio and video appliances to transmit analog video such as NTSC, PAL, and SECAM. The AV port is usually a yellow RCA port, and two red and white RCA ports are used to transmit audio. European TVs usually use SCART ports instead of RCA ports. However, SCART is designed to carry RGB signals with better image quality than YUV, so it is also used to connect monitors, video game consoles or DVD players. In professional applications, BNC ports are also used to obtain better signal quality.
What is transmitted in the AV port are the three source elements of the analog TV signal: Y, U, V, and the pulse signal as the synchronization reference. Y represents the brightness of the image (luminance, also known as brightness), and contains synchronization pulses. As long as the Y signal exists, you can see black and white TV images. The U signal and V signal carry color data. U and V are first mixed into two sets of orthogonal phases in one signal (the mixed signal is called chrominance), and then summed with the Y signal. Because Y is the fundamental frequency signal and UV is mixed with the carrier, this summing action is equivalent to frequency division multiplexing.
DVI matrix
The DVI interface is based on Silicon Image's Panallink interface technology and is based on the TMDS (Transition Minimized Differential Signaling, minimized transmission of differential signals) electronic protocol as the basic electrical connection. TMDS is a differential signaling mechanism that encodes pixel data and transmits it over a serial connection. The digital signal generated by the graphics card is encoded by the transmitter according to the TMDS protocol and sent to the receiver through the TMDS channel. After decoding, it is sent to the digital display device.
A DVI display system includes a transmitter and a receiver. The transmitter is the source of the signal, which can be built into the graphics card chip, or can appear as an additional chip on the graphics card PCB; while the receiver is a circuit on the display that can accept digital signals, decode them and pass them to the digital display circuit. Through these two, the signal sent by the graphics card becomes an image on the display.
DVI has two standards: DVI1.0 and DVI2.0. DVI1.0 only uses one set of signal transmission channels. The highest pixel clock for image transmission is 165M, and the highest signal transmission code stream in the channel is 1.65GHz. DVI2.0 uses all two sets of signal transmission channels. The highest pixel clock for image transmission is 330M, and the highest signal transmission code stream in each set of channels is also 1.65GHz. In display equipment, there is currently no application of DVI2.0, so the DVI discussed in this article refers to the DVI1.0 standard.
HDMI Matrix
HDMI, also known as the high-definition multimedia interface, is the first digital interface to support the transmission of uncompressed all-digital high-definition, multi-channel audio and intelligent format and control command data on a single cable.
HDMI originates from DVI interface technology, which is mainly based on TMDS signal transmission technology. This is why HDMI interface and DVI interface can be converted to each other through adapters. TMDS (Transition Minimized Differential Signaling), also known as Minimized Transmission Differential Signaling, refers to converting the original signal data into 10 bits through logical algorithms such as XOR and XNOR. The first 8 are data obtained from the original signal after operation. The 9th bit indicates the operation method, and the 10th bit is used to correspond to the DC level. (DC-balanced means ensuring that the DC offset in the channel is zero during the encoding process, and level conversion achieves matching between different logical interfaces). The converted data is transmitted in a differential transmission manner. This algorithm reduces the overshoot and undershoot in the transition process of the transmitted signal, and the transmitted data tends to DC level, which reduces the electromagnetic interference of the signal on the transmission line and improves the speed and reliability of signal transmission.
Generally, an HDMI connection consists of a pair of signal sources and receivers. Sometimes a system can also contain multiple HDMI input or output devices. Each HDMI signal input interface can receive connector information according to the standard, and the signal output interface will also carry all signal information. HDMI data lines and receivers include three different TMDS data channels and a clock channel. These channels support video, audio data and additional information. Video, audio data and additional information are transmitted to the receiver through three channels, while the pixel clock of the video is transmitted through the TMDS clock channel. After the receiver accepts this frequency parameter, it restores the information transmitted by the other three data channels.
Packet switching virtual matrix
Packet switching virtual matrix implements the transmission and switching of image data through packet switching (usually IP packets). Packet-switched matrices are now relatively popular, such as remote monitoring centers that have been widely used. That is, the image is compressed at the local recording end, and then the compressed code stream is sent to the remote end through the network (which can be a high-speed private network, the Internet, a local area network, etc.). After being decoded at the remote end, it is displayed on a large screen. The packet-switched digital matrix currently has two major limitations: large delay and poor image quality. Since it is transmitted through the network, delays are inevitable. At the same time, in order to reduce bandwidth usage, images often need to be compressed at the sending end and then decompressed at the receiving end. It is difficult to ensure good image quality for images that have been lossyly compressed. At the same time, the encoding and decoding process will also increase the delay. Therefore, the current packet-switched matrix cannot be applied to situations that require high real-time performance and image quality. It is more suitable for monitoring use and cannot meet the requirements of television and conferencing.
Video matrix related products
Splitter: Divide a single signal into multiple identical signals without signal loss and output them to multiple display devices.
Long-line driver: Integrate VGA signal tailing ghosting and other problems that occur during long-distance transmission.
Selector: Select one of the multiple input signals to output to the display device.
Switching matrix: Select two or more types of signal sources to output to different display devices. In addition, there are switches; scalers, etc. The matrix switcher can independently become an audio switching matrix, or it can use dedicated cascade cables to achieve synchronous switching with VIDEVGA and RGB matrices. The device has a power outage on-site protection function, which can save the working status of the device before it is shut down. It has an RS-232 communication interface for online use with a computer, and provides communication protocols and demonstration programs for easy online use.
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