There are two major problems to be solved in the engineering application of DVI signal, because the signal source and display device already have DVI interface, so transmission and switching have become the main problems. Regarding DVI transmission, a previous article has been specifically discussed, now Mainly discuss the matrix switching problem of DVI.
The DVI signal is a four-channel digital signal with a maximum code stream of 1.65G (at 1600 × 1200 × 60). When performing matrix switching, there are many problems different from the analog matrix. If it is a general DVI switch, it can be completed by using DVI decoding / encoding chips (even it can also be solved by a relay method, which is not desirable in practical use because there is no driving capability and the transmission distance is too short). For example, the DVI signal is decoded into parallel data. Because the code stream is low at this time (maximum is 165MHZ), it can be switched using a general-purpose digital circuit and then encoded. However, due to the wiring structure problem, the switch that can be formed in this way is small. In the range of 1, 2, and 4, it is difficult to complete it. Therefore, a special high-speed chip is used to complete the moment switching. For example, the existing 3.3G switching chip can constitute 8-select 8-DVI matrix switching.
In contrast, the switching chip itself is not the main problem of the matrix switcher. The main problem lies in the technical process. The most typical problems are the driving ability and the routing process.
The normal transmission distance of the DVI signal is about 7 meters. As the input / output port of the matrix switcher, because it is not known how far the signal is "walked", and how much drive capacity is left, the switch itself must have Connectors and internal wiring (connector loss of driving capacity is much larger than we expected), it is impossible to take risks in the project to use only the driving power of the original signal, so Repeater will be performed on the input port first to complete the switcher and distance "Isolation" to form "a standard length". Similarly, do not dare not do drive processing on the output port, otherwise the output line may (very likely) fail to reach "a standard length" (the experimental result is to retain at most half), so the matrix requires too much external conditions. High, cannot be applied in engineering. This "isolation" approach is equivalent to adding 16 sets of Repeaters, which has a significant increase in cost, and brings many technical problems in terms of internal connections and routing. The complete isolation of the input and output ports also has the benefit of being flexible. In actual engineering, if the routing distance and signal interface can be considered in advance, the input and output interface boards can be replaced to complete multiple function combinations. For example, the input interface board can be a simple Repeater; it can also be a fiber optic receiver that directly obtains DVI signals from the fiber; it can also be a cable equalizer (Cable Equalizer) to complete long-line reception; Convert a small amount of VGA signals into DVI signals to form a fully digital system. An interface board for digitally converting Video and Audio signals is also being considered to complete the functions of the multimedia digital matrix described below. The same is true for the output port. A simple Repeater can complete "a standard length" output; a fiber optic transmitter directly converts DVI signals into optical signals and enters the optical fiber transmission system; it can also convert DVI to VGA signals for some special applications; Can output analog or digital Video and Audio signals. The combined application is very flexible.
At present, a digital switching chip with a 34 × 34, 3.3G code stream is used. It is calculated based on 4 groups of DVI signals, which can form an 8 × 8 DVI matrix (in fact, there are 2 channels each for input and output). If DVI There are not so many signals, for example, there are only 5 × 4 DVI signals, so the input and output ports only occupy 20 × 16, and there is 14 × 18 surplus, and these surplus channels can be formed completely, such as 8 × 8 or 8 × 16. Digital video, digital audio matrix. Because the chip only cares about the digital stream that does not exceed 3.3G code stream, it does not matter DVI or video or audio signals. With the development of digital applications, digital video (SDI, D1, MPEG2, MPEG4, etc.) and digital audio have many applications. After the completion of the HDMI (1.95G) or HDCP standard and the application starts, this DVI matrix will cooperate with HDMI The interface board is fully applicable to the matrix switching with HDMI, because in fact, the matrix is a high-speed digital matrix. At present, this DVI matrix can be combined with various input and output interface boards to form a multimedia digital matrix. With flexible control interfaces, this matrix will be a field-programmable (field-determined DVI, digital video , Digital audio in / out) multi-functional media matrix, its benefits are self-evident.