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Know and use DVI, HDMI interface

Know and use DVI, HDMI interface

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As the DVI/HDMI interface is used in the projector, we need to know both interfaces and understand the conditions and concerns in using them.

In the coming months, many manufacturers will release consumer electronics products with DVI and HDMI connectors. DVI (Digital Visual Interface) refers to digital video interfaces, and HDMI (High Definition Multimedia Interface) refers to high definition. Degree multimedia interface.

These two interfaces will be widely used in DVD players, cable TV/satellite TV set-top boxes, HDTV and other devices, which can effectively improve the quality of digital images without the need for analog-to-digital conversion. Especially in HDTV products, DVI and HDMI interfaces are often used, which is also related to HDCP (High-Bandwidth Digital Content Protection).

DVI and HDMI interfaces support HDCP, but as of now, HDCP has not been widely used. use. As more and more content is protected by copyright, it will become increasingly important for your device to comply with HDCP standards. In addition to the control signals, the HDMI connector also includes high-quality digital audio capabilities. The digital signals transmitted by the DVI and HDMI cables are different from the current analog signals, which cause problems when transmitting signals. Under what conditions will DVI/HDMI devices work? When a DVI or HDMI device transmits video signals from a source device to a display, its capabilities will be reflected in the following aspects:

1. the transmitter can correctly transmit signals

2. The cable can transmit signals with minimal interference and attenuation.

3. The receiver can correctly recover the received signal and verify the HDCP signal. These three links are complementary and indispensable. The compatibility of the source device and the receiving device is the root cause of the problem. Improving the performance and circuit design of HDMI and DVI backplane outputs will also improve the ability of source and sink devices to provide and recover signals.

The cable itself is usually not the source of the problem unless the cable is too long. When the DVI and HDMI cables are well-made and connected to the RPTV, the Plasma and LCD cables are usually not a problem when they are short.

This is common because devices such as projectors require longer cables and this can cause problems.

Currently, some DVI connector cables for set-top boxes and DVD players are limited to a length of 5 meters (approximately 15 feet). In a typical home theater, the distance between sources such as signal sources may be much larger than the 5 meters recommended by DVI applications. The projector is usually 14 to 20 feet away from the source, and it requires a slap in the face of 0 to 30 feet.

This brings severe challenges to cable manufacturers. In the case where the receiving end can completely recover the signal, some small-sized twisted-pair TMDS lines bring a lot of accumulated attenuation when transmitting signals. Under this condition, the receiver can also Normal recovery.

Many companies are now proposing copper-based solutions because they are more affordable than fiber or other cable methods. HDMI is designed based on long-distance cable transmission, but its actual performance constraints are similar to DVI.

Currently, the application of long-distance DVI cables requires booster amplifiers or fiber optic extenders, which increases the cost of use by hundreds of dollars. Other factors that may affect transmission In addition to cable specifications or their insulation properties, there are many quality factors, including the cable itself, which is related to signal amplitude attenuation and transmission delay.

When these cables are squeezed or bent, they have a serious impact on the transmission performance. The design of the cable itself is also important, and it has a lot to do with the degree to which the cable changes its performance when it is bent or entangled or squeezed.

There is a PE foamed insulated cable with internal nitrogen injection that does not have much attenuation even when the signal frequency is high. This is the main reason why people used it for cable TV applications. However, unfortunately, compared with a non-foamed insulated cable or an HCF (hard cell foam) type insulated cable, the uniform impedance is low, and the return loss is large during transmission reflection. These characteristics can get worse when the cable is bent or squeezed.

As you can see, trying to improve one aspect of the cable performance will have a detrimental effect on other performance. easy to say, hard to do For manufacturers, the pressure still exists.

It is necessary to find a solution to the possible problems of DVI and HDMI cables in long-distance transmission. The principle is to try to ensure the most important performance characteristics are optimized, and it does not mind that it may affect other minors. Performance characteristics.

It's easier said than done, just like the famous "Murphy's Law", it thinks that anything that can go wrong will eventually go wrong (if something can go wrong, it will), and in a set of AV equipment The cable is the weakest and vulnerable part of the attack.

When the connection cable is an analog audio, video or digital audio cable, the problems encountered are easy to solve, but when the connection cable is a DVI/HDMI interface cable, the problem becomes tricky.

Some people have always wanted to solve this problem with one or two unnecessary adapters, such as connecting several cables through adapters to form a long cable or cutting and soldering them through the same pipe at the same time. These practices can easily improve the performance characteristics of digital video cables, but they can create a range of image quality problems.

The bandwidth of these cables is relatively high. In practice, DVI/HDMI interface cables are susceptible to skin effects, delays, impedance changes, and other factors that are common in other types of cables. Insignificant. A very interesting question about HDMI is that many companies boast that HDMI's superior performance makes it perform well under extreme cable lengths.

But most of these companies are chip makers, and many of the famous high-quality cable manufacturers have neglected the market capacity in this field, which is simply giving the long-distance communication market to optical network manufacturers and other solution providers, although They can come up with a good solution, but for consumers, the cost is too high.

The result is that the low-cost copper DVI/HDMI solution market has always been dominated by people, just like the "high-end" AV market, it does not consider the overall long-distance endurance cable. This pattern will not change in the short term. why? However, for a cable manufacturer, it is unlikely that he will know which components the user will use with the cable.

So why not let us take a look at the full specification of the DVI/HDMI cable? A) First of all, no manufacturer will be willing to let others easily copy the excellent design and performance of their products. B) It is too difficult to decide which factors will affect the performance of the cable. C) There are many other factors to consider.

Some factors are more or less related to the level of chip manufacturing, signal source and receiver performance. In a typical HDTV application, a single single link cable may be sufficient for 99% of the time.

Most computer graphics cards still have a single link output, only with a dual link on their analog output. Get higher performance. Some new high-performance displays and video cards are equipped with dual TMDS links, which require a dual link DVI cable.

The HDMI standard is backward compatible, so if there is only a DVI connector on the display, you can connect it with an "HDMI to DVI" conversion cable.

However, DVI does not transmit digital audio signals like HDMI, so a separate audio connector is required for audio output. If you are using digital audio, you will need to use a coaxial cable or fiber optic cable connector for the audio portion.

Suggest - Use DVI/HDMI cable connectors when the two connected devices need the best image quality.

- Minimize the length of the cable and try to use the shortest connection.

- A "quiet length" cable connected directly to the device is the optimal configuration.

- If multiple signals are connected to a single display device, a quality switch that supports HDCP is required.

- When purchasing cables and switches, be sure to choose a manufacturer with quality assurance and allow you enough time to try it out. Before the installation project begins, be sure to connect the signal source to the monitor cable for some tests. During the installation process, properly transport the cables.