What is a Matrix Switcher

What is a Matrix Switcher

The application of matrix switchers is becoming increasingly popular in the broadcasting and television industry and display control industry. This article mainly discusses some issues of analog signal (video, audio, VGA signal) matrix switchers, because the signal format, circuit form, main indicators and main issues of analog signals are basically the same. Of course, there will be some differences for different bandwidths, impedances, etc., but they can be classified into one category of problems. The digital matrix is ​​quite different from the analog method in terms of circuit form, etc., so it is discussed separately.

The concept of matrix refers to the concept of linear algebra in advanced mathematics. It generally refers to multiple output options in the case of multiple inputs, forming the matrix structure shown in the figure below. That is, each output can be "short-circuited" with different input signals, and each output can only be connected to a certain input, but a certain input can be connected to different outputs (simultaneously), as shown in the figure below.

Output 1 = input 1, output 2 = input 2, and output 3 = output 4 = input 3, or in other words, each output can be "independently" selected from the input without having to care about the output of other channels, that is, it can be different from other outputs or the same. For example, 8 to 4 means there are 4 independent outputs, each of which can be selected from 8 inputs, or there are 4 independent 8 to 1, but the 8 inputs are the same. What is often confused with this is the concept of allocation, such as 8 to 1 to 4, which means selecting 1 output from 8 inputs and allocating it to 4 identical outputs. Although there are 4 outputs in appearance, these 4 outputs are the same, not independent. In general, the structure that forms M×N is called a matrix, and the structure that forms M×1 is called a switch or selector. In fact, N=1, and we treat them as matrices when discussing.

The function of the matrix switcher is to independently select multiple (including 1) signals for output as needed when multiple signals are input, thus completing signal selection.

1. Circuit principle:

Switching is selection in principle. There are many ways to select. The simplest way is to connect the signal lines directly together, such as a wiring board. You can also manually jump the output signal line to the input signal line to complete the selection, or use a piano key switch to complete the connection and disconnection. Of course, this is manually operated and mechanical. There are no technical problems such as indicators, so it is not discussed as a matrix switch. The second way is to use relays to complete the selection. The on and off of the relay can be controlled by level to complete the disconnection and connection between the output line and the input signal, and the signal selection can also be completed. The third way is to use the conduction and closure of the internal circuit of the chip to connect and shut down according to the circuit principle, and the signal selection can be completed by level control.

The relay method and the chip method each have their own advantages and disadvantages.

Relay method: If the circuit parts of input matching and output drive are not considered, it is consistent with the wiring method, which relies on physical contact for connection and disconnection. From this perspective, there is no concept of indicators (at most there are contact resistance and reaction time). Therefore, the technical indicators are good and the price is low. Its disadvantage is that the stability is poor. After all, it relies on physical contact. The relay has a certain lifespan. In principle, it has an average trouble-free operation of 80,000 times and there is sound during operation. Due to the wiring of the circuit board, it cannot be made on a large scale and it appears not high-end enough.

Chip method: Since it relies on circuits for connection and shutdown, the chip itself has technical indicators (when the input matching and output drive are the same). Therefore, in order to ensure the technical indicators, it is necessary to choose a dedicated switching chip. Therefore, the price is higher, but the stability is good, and the matrix scale that can be formed is larger.

2. Technical indicators that matrix switching should ensure

The matrix switcher has different technical indicators according to different application fields. Taking the radio and television industry as an example, in order to ensure the display quality of the terminal, the radio and television industry has allocated technical indicators for the entire signal transmission process, from the camera to the TV. For analog matrix switching and allocation, the technical indicators are as follows: GB/T14236-93 and our company's KT-128*32 example indicators:

3. The most important indicators used in daily life in the national standard are as follows:

1) Random signal-to-noise ratio: When a signal passes through any device, the quality will deteriorate due to the introduction of "noise". The signal-to-noise ratio refers to the ratio of the signal to the noise generated. The larger the value, the smaller the introduced noise. For video signals (within 6MHZ), the signal-to-noise ratio is required to be at least 65dB.

2) Amplitude-frequency characteristics: When the signal passes through the device, signals of various frequencies will have different attenuation. Generally, the higher the frequency, the greater the attenuation. For video signals, the concept of bandwidth (the frequency at which the attenuation is 3dB) is generally not used. Instead, the maximum attenuation within the 6MHZ spectrum (the spectrum of the video signal is within 6MHZ) is used. The standard requires that it should not exceed 0.2dB. If audio modulation is taken into account, it should not exceed 0.5dB within 8MHZ.

3) Crosstalk: Multiple signals in the same device will interfere with each other due to radiation in space and power supply fluctuations, which is called crosstalk. The crosstalk cannot be greater than -55dB.

4. Depending on the application, the requirements for indicators are different.

1) Monitoring industry: In the monitoring industry, since the signal only passes through the camera, transmission (generally baseband transmission), control and display, and the quality requirements for the image during display are relatively low, as long as it can be seen clearly, no broadcasting or other work is required. Therefore, the monitoring industry requires the matrix to have multiple functions (with PTZ control, alarm, etc.) and low indicators. This industry has no clear mandatory requirements for the matrix indicators.

2) Radio and television and video conferencing. There is no need to say much about radio and television. They must comply with national standards and broadcast-level standards. It is worth mentioning that in the field of video conferencing, video signals must be transmitted, recorded and broadcasted, and the audience also has high requirements for image quality. Therefore, broadcast-level indicators should be selected instead of simply using monitoring products.

3) VGA signal application: Since VGA signal has a wide bandwidth and five signals (R, G, B, H, V) are transmitted simultaneously, the indicators of each channel are required to be as high as possible (within 6MHZ, it should meet the requirements of radio and television) and must be consistent. It should be in accordance with the technical requirements of component equipment at the broadcast level. However, since VGA signal switching is not as widely used as in radio and television, involving a large number of users, there is no mandatory indicator standard at present.

1) Type selection

For radio, television and video conferencing applications, broadcast-grade products should be selected. For monitoring applications, monitoring products can be used. VGA signals (some people also regard them as videos) should use VGA signal matrix.

2) Size selection

In a project, audio signals, video signals and VGA signals should be considered as three different media. Generally, there are more audio signals, such as microphones, CDs and audio from disc players, but considering that there is usually only one set of power amplifiers and speakers, at most one mixer is added before the power amplifier for mixing, and several signals may be needed, so the output of the audio matrix will not be very large, such as 32×8 or 64×8, but there is no need to choose 32×32 or 64×64, unless it is for broadcasting and video conferencing transmission, each video channel must have audio synchronous transmission.

When designing a plan, the number of signal sources is relatively easy to determine. By looking at the number of signal sources, the number of matrix inputs can be determined. However, the number of independent output channels must be considered. This depends on the system's operating mode. Sometimes there may be only a distribution relationship between several display devices (they are always consistent with each other and not independent). In this case, you can consider occupying one output port and then adding a distributor. If these devices are likely to be independent, it is better for each to occupy an independent output port.

In many cases, the number of inputs and outputs is large. If a large matrix is ​​used, the cost will be high (the larger the matrix, the more difficult it is to make and the higher the cost). You can consider whether it can be used in groups. For example, when monitoring, some display devices in the display wall can only display the signal of a certain area, while other devices each display the signal of other specific areas. In this way, the large-scale matrix can be divided into small-scale matrices (such as 128×64 divided into 4 32×16). If there is a need to transmit signals between the zones, the structure shown in the following figure can also be used:

This allows the output of matrix 2 to include part of the input signal of matrix 1. Although the effect is not as good as the full matrix structure, the cost will be reduced.

As a part of the transmission system, the matrix switcher has the main problems that can be found in my work "Common Problems and Solutions in Engineering". The principles are the same, and there are only a few mechanisms of occurrence. As long as the phenomena can be distinguished, there should be no big problem in the direction of solution. A more special problem is the problem of using a small-scale matrix to form a large-scale one. For example, when using 64×32 to form 128×32, two 64×32s cannot be used to form 128×64. This is still the concept of group use, and three 64×32s are used to form 128×32, as shown in the figure below. This is the concept of full matrix. Therefore, when using in combination, the difference between group use and full matrix should be distinguished (full matrix means that each output port can be selected from all inputs, and they are independent of each other).

3) Manufacturer selection

There are many manufacturers of production matrices, and the nominal indicators are different. Since this type of equipment is not a laboratory prototype, but an engineering application product, the applicability and reliability issues in the project are very important. The conditions on the project site are different. In the process of product maturity, it needs to undergo continuous engineering inspections, and problems need to be improved in a timely manner. Therefore, the product maturity process is relatively long. A common situation is: on site, using certain brands of products, some technical problems will arise in the project, and after using other brands of products, the problems can be solved. It is not that the former brand product has a big mistake, but its applicability is not as good as the latter brand product. In layman's terms, the tuition fee has not been paid enough, the problems encountered are not enough, and there are inconsiderate aspects in the product design. Therefore, choose the products of professional production companies because their products are relatively mature.

The manufacturer's nominal indicators, especially for VGA signal products, the matrix device is the core device for display. If there is a problem, it will be a global problem that will paralyze the entire system. Therefore, stability and reliability are paralyzing. We would rather have a higher price or even lower indicators to ensure stability and reliability.

In terms of technical support, there are many strange problems encountered on the engineering site. The manufacturer's technical support capability is a very important indicator. It is necessary to cooperate with manufacturers with independent research and development capabilities, a correct understanding of the mechanism of problem generation, strong applicability of products, stability and reliability, and strong on-site problem-solving capabilities.