D sub vga dvi hdmi connector. Types of computer ports: types of connectors and adapters

Besides the fact that LCD monitors require digital data to display images, they differ from classic CRT displays in several other ways. For example, depending on the capabilities of the monitor, almost any resolution can be displayed on a CRT, since the tube does not have a clearly defined number of pixels.

And LCD monitors, due to the principle of their operation, always have a fixed (“native”) resolution, at which the monitor will provide optimal picture quality. This limitation has nothing to do with DVI, since its main reason lies in the architecture of the LCD monitor.

An LCD monitor uses an array of tiny pixels, each made up of three diodes, one for each primary color (RGB: red, green, blue). The LCD screen, which has a native resolution of 1600x1200 (UXGA), consists of 1.92 million pixels!

Of course, LCD monitors are capable of displaying other resolutions. But in such cases, the image will have to be scaled or interpolated. If, for example, an LCD monitor has a native resolution of 1280x1024, then the lower resolution of 800x600 will be stretched to 1280x1024. The quality of interpolation depends on the monitor model. An alternative is to display the reduced image in the “native” resolution of 800x600, but in this case you will have to be content with a black frame.

Both frames show the image from the LCD monitor screen. On the left is an image in “native resolution” 1280x1024 (Eizo L885). On the right is an interpolated image at 800x600 resolution. As a result of increasing the pixels, the picture appears blocky. Such problems do not exist on CRT monitors.

To display a 1600x1200 (UXGA) resolution with 1.92 million pixels and a 60Hz vertical refresh rate, the monitor requires high bandwidth. If you do the math, you need a frequency of 115 MHz. But the frequency is also affected by other factors, such as the passage of the blanking region, so the required bandwidth increases even more.

About 25% of all transmitted information relates to blanking time. It is needed to change the position of the electron gun to the next line in the CRT monitor. At the same time, LCD monitors require virtually no blanking time.

For each frame, not only image information is transmitted, but also the boundaries and the blanking area are taken into account. CRT monitors require a blanking time to turn off the electron gun when it finishes printing a line on the screen and move it to the next line to continue printing. The same thing happens at the end of the picture, that is, in the lower right corner - the electron beam turns off and changes position to the upper left corner of the screen.

About 25% of all pixel data relates to blanking time. Since LCD monitors do not use an electron gun, the blanking time is completely useless here. But it had to be taken into account in the DVI 1.0 standard, since it allows you to connect not only digital LCDs, but also digital CRT monitors (where the DAC is built into the monitor).

Blanking time turns out to be a very important factor when connecting an LCD display via a DVI interface, since each resolution requires a certain bandwidth from the transmitter (video card). The higher the required resolution, the higher the pixel frequency of the TMDS transmitter must be. The DVI standard specifies a maximum pixel frequency of 165 MHz (one channel). Thanks to the 10x frequency multiplication described above, we get a peak data throughput of 1.65 GB/s, which will be enough for a resolution of 1600x1200 at 60 Hz. If higher resolution is required, the display should be connected via Dual Link DVI, then the two DVI transmitters will work together, which will double the throughput. This option is described in more detail in the next section.

However, a simpler and cheaper solution would be to reduce the blanking data. As a result, graphics cards will be given more bandwidth, and even a 165 MHz DVI transmitter will be able to handle higher resolutions. Another option is to reduce the horizontal refresh rate of the screen.

The top of the table shows the resolutions supported by a single 165 MHz DVI transmitter. Reducing the blanking data (middle) or refresh rate (Hz) allows higher resolutions to be achieved.

This illustration shows what pixel clock is required for a specific resolution. The top line shows the operation of the LCD monitor with reduced blanking data. The second row (60Hz CRT GTF Blanking) shows the required LCD monitor bandwidth if the blanking data cannot be reduced.

The limitation of the TMDS transmitter to a pixel frequency of 165 MHz also affects the maximum possible resolution of the LCD display. Even if we reduce the damping data, we still hit a certain limit. And reducing the horizontal refresh rate may not give very good results in some applications.

To solve this problem, the DVI specification provides an additional operating mode called Dual Link. In this case, a combination of two TMDS transmitters is used, which transmit data to one monitor through one connector. The available bandwidth doubles to 330 MHz, which is enough to output almost any existing resolution. Important note: a video card with two DVI outputs is not a Dual Link card, which has two TMDS transmitters running through one DVI port!

The illustration shows dual-link DVI operation when two TMDS transmitters are used.

However, a video card with good DVI support and reduced blanking information will be quite enough to display information on one of the new 20" and 23" Apple Cinema displays in the "native" resolution of 1680x1050 or 1920x1200, respectively. At the same time, to support a 30" display with a resolution of 2560x1600, there is no escape from the Dual Link interface.

Due to the high "native" resolution of the 30" Apple Cinema display, it requires a Dual Link DVI connection!

Although dual DVI connectors have already become standard on high-end 3D workstation cards, not all consumer-grade graphics cards can boast this. Thanks to two DVI connectors, we can still use an interesting alternative.

In this example, two single-link ports are used to connect a nine-megapixel (3840x2400) display. The picture is simply divided into two parts. But both the monitor and the video card must support this mode.

Currently, you can find six different DVI connectors. Among them: DVI-D for a completely digital connection in single-link and dual-link versions; DVI-I for analog and digital connections in two versions; DVI-A for analog connection and a new VESA DMS-59 connector. Most often, graphics card manufacturers equip their products with a dual-link DVI-I connector, even if the card has one port. Using an adapter, the DVI-I port can be converted into an analog VGA output.

Overview of various DVI connectors.

DVI connector layout.

The DVI 1.0 specification does not specify the new dual-link DMS-59 connector. It was introduced by the VESA Working Group in 2003 and allows dual DVI outputs to be output on small form factor cards. It is also intended to simplify the layout of connectors on cards that support four displays.

Finally, we come to the core of our article: the quality of TMDS transmitters of different graphics cards. Although the DVI 1.0 specification stipulates a maximum pixel frequency of 165 MHz, not all video cards produce an acceptable signal at it. Many allow you to achieve 1600x1200 only at reduced pixel frequencies and with reduced blanking times. If you try to connect a 1920x1080 HDTV device to such a card (even with reduced blanking time), you'll be in for an unpleasant surprise.

All GPUs shipped today from ATi and nVidia already have an on-chip TMDS transmitter for DVI. Manufacturers of ATi GPU cards most often use an integrated transmitter for the standard 1xVGA and 1xDVI combination. By comparison, many nVidia GPU cards use an external TMDS module (for example, from Silicon Image), even though there is a TMDS transmitter on the chip itself. To provide two DVI outputs, the card manufacturer always installs a second TMDS chip, regardless of which GPU the card is based on.

The following illustrations show common designs.

Typical configuration: one VGA and one DVI output. The TMDS transmitter can be either integrated into the graphics chip or placed on a separate chip.

Possible DVI configurations: 1x VGA and 1x Single Link DVI (A), 2x Single Link DVI (B), 1x Single Link and 1x Dual Link DVI, 2x Dual Link DVI (D). Note: if the card has two DVI outputs, this does not mean that they are dual-link! Figures E and F show the configuration of the new DMS-59 VESA ports with high density, where four or two single-link DVI outputs are provided.

As further testing in our article will show, the quality of DVI output on ATi or nVidia cards varies greatly. Even if the individual TMDS chip on a card is known for its quality, this does not mean that every card with that chip will provide a high-quality DVI signal. Even its location on the graphics card greatly affects the final result.

DVI compatible

To test the DVI quality of modern graphics cards on ATi and nVidia processors, we sent six sample cards to the Silicon Image test labs to check compatibility with the DVI standard.

Interestingly, to obtain a DVI license it is not at all necessary to conduct compatibility tests with the standard. As a result, products are entering the market that claim to support DVI but do not meet the specifications. One of the reasons for this state of affairs is the complex and therefore expensive testing procedure.

In response to this problem, Silicon Image founded a test center in December 2003. DVI Compliance Test Center (CTC). Manufacturers of DVI-enabled devices may submit their products for DVI compatibility testing. In fact, that's what we did with our six graphics cards.

The tests are divided into three categories: transmitter (usually a video card), cable, and receiver (monitor). To evaluate DVI compatibility, so-called eye diagrams are created to represent the DVI signal. If the signal does not go beyond certain limits, then the test is considered passed. Otherwise, the device is not compatible with the DVI standard.

The illustration shows the eye diagram of a TMDS transmitter at 162 MHz (UXGA) transmitting billions of bits of data.

The eye diagram test is the most important test to evaluate signal quality. The diagram shows signal fluctuations (phase jitter), amplitude distortion and the “ringing” effect. These tests also allow you to clearly see the quality of DVI.

DVI compatibility tests include the following checks.

1. Transmitter: Eye diagram with specified boundaries.
2. Cables: Eye diagrams are created before and after signal transmission, then compared. Once again, the signal deviation limits are strictly defined. But here large discrepancies with the ideal signal are already allowed.
3. Receiver: The eye diagram is again created, but again, even greater discrepancies are allowed.

The biggest problems with serial high-speed transmission are signal phase jitter. If there is no such effect, then you can always clearly highlight the signal on the chart. Most signal fluctuations are created by the clock signal graphics chip, which leads to the appearance of low-frequency frequency fluctuations in the ranges from 100 kHz to 10 MHz. In an eye diagram, signal fluctuation is noticeable by changes in frequency, data, data relative to frequency, amplitude, too much or too little rise. Additionally, DVI measurements vary at different frequencies, which must be taken into account when checking the eye diagram. But thanks to the eye diagram, you can clearly evaluate the quality of the DVI signal.

For measurements, one million overlapping areas are analyzed using an oscilloscope. This is sufficient to evaluate the overall performance of a DVI connection since the signal will not change significantly over a long period of time. Graphical representation of the data is produced using special software that Silicon Image created in collaboration with Tektronix. A signal that complies with the DVI specification must not interfere with the boundaries (blue areas) that are automatically drawn by the software. If the signal falls into the blue area, the test is considered failed and the device does not comply with the DVI specification. The program immediately shows the result.

The video card did not pass the DVI compatibility test.

The software immediately shows whether the card passed the test or not.

Different boundaries (eyes) are used for the cable, transmitter and receiver. The signal should not interfere with these areas.

To understand how DVI compatibility is determined and what needs to be considered, we need to dive into more detail.

Since DVI transmission is completely digital, the question arises where the signal phase jitter comes from. Two reasons can be put forward here. The first is that jitter is caused by the data itself, that is, the 24 parallel bits of data that the graphics chip produces. However, the data is automatically corrected in the TMDS chip when necessary, ensuring that there is no jitter in the data. Therefore, the remaining cause of jitter is the clock signal.

At first glance, the data signal appears to be free of interference. This is guaranteed thanks to the latch register built into the TMDS. But the main problem still remains the clock signal, which spoils the data flow through the 10x PLL multiplication.

Since the frequency is multiplied by a factor of 10 by the PLL, the impact of even small amounts of distortion is magnified. As a result, the data reaches the receiver no longer in its original state.

Above is an ideal clock signal, below is a signal where one of the edges began to be transmitted too early. Thanks to the PLL, this directly affects the data signal. In general, every disturbance in the clock signal results in errors in data transmission.

When the receiver samples the corrupted data signal using the "ideal" hypothetical PLL clock, it receives erroneous data (yellow bar).

How it actually works: If the receiver uses a corrupted transmitter clock signal, it will still be able to read the corrupted data (red bar). That is why the clock signal is also transmitted via DVI cable! The receiver requires the same (damaged) clock signal.

The DVI standard includes jitter management. If both components use the same corrupted clock signal, then information can be read from the corrupted data signal without errors. Thus, DVI-compatible devices can operate even in environments with low-frequency jitter. The error in the clock signal can then be bypassed.

As we explained above, DVI works optimally if the transmitter and receiver use the same clock signal and their architecture is the same. But this doesn't always happen. This is why using DVI can cause problems despite sophisticated anti-jitter measures.

The illustration shows the optimal scenario for DVI transmission. Multiplying the clock signal in the PLL introduces a delay. And the data flow will no longer be consistent. But everything is corrected by taking into account the same delay in the receiver's PLL, so the data is received correctly.

The DVI 1.0 standard clearly defines PLL latency. This architecture is called non-coherent. If the PLL does not meet these latency specifications, problems may occur. There is heated debate in the industry today about whether such a decoupled architecture should be used. Moreover, a number of companies are in favor of a complete revision of the standard.

This example uses the PLL clock signal instead of the graphics chip signal. Therefore, the data signals and clock signals are consistent. However, due to the delay in the receiver's PLL, the data is not processed correctly, and jitter removal no longer works!

You should now understand why using long cables can be problematic, even without taking into account external interference. A long cable can introduce delay into the clock signal (remember that data signals and clock signals have different frequency ranges), additional delay can affect the quality of signal reception.

The DVI connector is used in modern televisions (plasma, liquid crystal), LCD monitors and video cards of personal computers. The name "DVI" comes from the English abbreviation Digital VisualInterface, which translates as "digital video interface". The DVI connector was developed and first introduced back in 1999 by the Digital Display Working Group. It includes global giants in the production of computer equipment and monitors, such as Intel, Compaq, Fujitsu, Silicon Image, Hewlett Packard and NEC. The DVI connector replaced the VGA interface and today has almost completely replaced it.

Description of DVI technology

The method used in this interface was developed by Silicon Image. It is a type of serial communication device. The DVI cable is built on the twisted pair principle. Three pairs of wires carry colors (red, green and blue), and the fourth carries clock signals. The DVI connector allows you to transmit both analog and There are three subtypes of the interface in question:

• DVI-A - used for transmission exclusively;
• DVI-I is a universal connector, used for transmitting both analog and digital signals;
• DVI-D - for transmitting digital signals only.

In addition, DVI technology is equipped with a special HDCP digital information protection system developed by Intel.

Disadvantages of the DVI interface

The main disadvantage of transmitting information through this connector is the limitation of the cable length, as well as the dependence of the mentioned parameter on the type of signal being transmitted. For example, an image with an extension of 1920x1200 pixels at a frequency of 60 Hz can be transmitted over a cable whose length is 5 meters, and through a fifteen-meter cable it is possible to transmit a signal whose maximum quality is only 1280x1024 pixels at the same frequency. Therefore, if it is necessary to use long cables, it is necessary to use additional equipment - special signal amplifiers (repeaters), which are installed at certain distances. This disadvantage is associated with the appearance of dots on the monitor when using a low-quality cable. To eliminate this effect, you must either change the cord or reduce the quality of the input signal.

DVI-HDMI connector

This digital connector is used to transmit HDTV signals. Designed to connect TVs to various signal sources. A special feature of this connector is that it can transmit not only a video signal, but also digital audio. It allows you to broadcast 8 audio channels with a bit depth of 24 bits. There are various specifications for the designated interface, as well as adapters, thanks to which you can connect different types connectors. The HDMI connector can also be used to connect a personal computer and a TV. It should be remembered that the HDMI-DVI interface supports a special protocol designed to protect licensed content from unauthorized rewriting.

Conclusion

Despite the fact that DVI technology has almost completely replaced VGA interfaces, today this type is quite widely used on older PCs. If your video card does not have a DVI connector, but you still need to connect a monitor that supports this technology, then you can use a special adapter - a DVI-VGA connector.

The choice of video card can also be influenced by the monitor you have or are planning to purchase. Or even monitors (plural). So, for modern LCD monitors with digital inputs, it is very desirable that the video card have a DVI, HDMI or DisplayPort connector. Fortunately, for everyone modern solutions Now there are such ports, and often all together. Another subtlety is that if you require a resolution higher than 1920x1200 via the digital DVI output, then you must connect the video card to the monitor using a connector and cable that supports Dual-Link DVI. However, now there are no problems with this anymore. Let's look at the main connectors used to connect information display devices.

Analog D-Sub connector (also known as VGA-exit or DB-15F)

This is a long-known and familiar 15-pin connector for connecting analog monitors. The abbreviation VGA stands for video graphics array (pixel array) or video graphics adapter (video adapter). The connector is designed to output an analog signal, the quality of which can be influenced by many different factors, such as the quality of RAMDAC and analog circuits, so the quality of the resulting image may vary on different video cards. In addition, in modern video cards less attention is paid to the quality of the analog output, and to obtain clear picture It is better to use at high resolutions digital connection.

D-Sub connectors were actually the only standard until the widespread use of LCD monitors. Such outputs are still often used to connect LCD monitors, but only budget models that are not well suited for gaming. To connect modern monitors and projectors, it is recommended to use digital interfaces, one of the most common of which is DVI.

Connector DVI(variations: DVI-I And DVI-D)

DVI is standard interface, most commonly used to output digital video to all but the cheapest LCD monitors. The photo shows a rather old video card with three connectors: D-Sub, S-Video and DVI. There are three types of DVI connectors: DVI-D (digital), DVI-A (analog) and DVI-I (integrated - combined or universal):

DVI-D- an exclusively digital connection, which avoids losses in quality due to double conversion of the digital signal to analog and from analog to digital. This type of connection provides the highest quality picture, it outputs the signal only in digital form, digital LCD monitors with DVI inputs or professional CRT monitors with built-in RAMDAC and a DVI input can be connected to it (very rare copies, especially now). This connector differs from DVI-I in the physical absence of some contacts, and the DVI-to-D-Sub adapter, which will be discussed later, cannot be plugged into it. Most often this DVI type used in motherboards with an integrated video core; it is less common on video cards.

DVI-A- This is a rather rare type of analog connection via DVI, designed to output analog images to CRT receivers. In this case, the signal is degraded due to dual digital-to-analog and analog-to-digital conversion, its quality is equal to that of a standard VGA connection. Almost never found in nature.

DVI-I is a combination of the two options described above, capable of transmitting both analog and digital signals. This type is used most often in video cards; it is universal and, using special adapters that come with most video cards, you can also connect a regular analog CRT monitor with a DB-15F input to it. This is what these adapters look like:

All modern video cards have at least one DVI output, or even two universal DVI-I connectors. D-Subs are most often absent (but they can be connected using adapters, see above), except, again, for budget models. To transmit digital data, either a single-channel DVI Single-Link solution or a two-channel Dual-Link solution is used. The Single-Link transmission format uses one TMDS transmitter (165 MHz) and Dual-Link uses two, it doubles the bandwidth and allows screen resolutions higher than 1920x1080 and 1920x1200 at 60Hz, supporting very high resolution, like 2560x1600. Therefore, for the largest LCD monitors with high resolution, such as 30-inch models, as well as monitors designed to output stereo images, you will definitely need a video card with dual-channel DVI output Dual-Link or HDMI version 1.3.

Connector HDMI

IN lately a new consumer interface has become widespread - High Definition Multimedia Interface. This standard provides simultaneous transmission of visual and audio information over a single cable, it is designed for television and cinema, but PC users can also use it to output video data using the HDMI connector.

In the photo on the left is HDMI, on the right is DVI-I. HDMI outputs on video cards are now quite common, and there are more and more such models, especially in the case of video cards intended for creating media centers. Viewing high-definition video on a computer requires a video card and monitor that support HDCP content protection, connected by an HDMI or DVI cable. Video cards do not necessarily have to have an HDMI connector on board; in other cases, the HDMI cable can also be connected via an adapter to DVI:

HDMI is the latest attempt to standardize a universal connection for digital audio and video applications. It immediately received strong support from the giants of the electronics industry (the group of companies involved in developing the standard includes companies such as Sony, Toshiba, Hitachi, Panasonic, Thomson, Philips and Silicon Image), and most modern high-resolution output devices have although There would be one such connector. HDMI allows you to transmit copy-protected audio and video in digital format over a single cable; the first version of the standard was based on a bandwidth of 5 Gbps, and HDMI 1.3 expanded this limit to 10.2 Gbps.

HDMI 1.3 is an updated standard specification with increased interface bandwidth, increased clock frequency to 340 MHz, which allows you to connect high-resolution displays that support more colors (formats with color depths up to 48 bits). The new version of the specification also defines support for new Dolby standards for transmitting compressed audio without loss in quality. In addition, other innovations appeared; specification 1.3 described a new mini-HDMI connector, smaller in size compared to the original. Such connectors are also used on video cards.

HDMI 1.4b is the latest new version of this standard, released not so long ago. HDMI 1.4 introduced the following major innovations: support for stereo display format (also called "3D") with frame-by-frame transmission and active viewing glasses, support for Fast Ethernet connection HDMI Ethernet Channel for data transmission, audio return channel, which allows digital audio to be transmitted in the reverse direction , support for resolution formats 3840x2160 up to 30 Hz and 4096x2160 up to 24 Hz, support for new color spaces and the smallest micro-HDMI connector.

In HDMI 1.4a, stereo display support has been significantly improved, with new Side-by-Side and Top-and-Bottom modes in addition to the 1.4 specification modes. And finally, a very recent update to the HDMI 1.4b standard occurred just a few weeks ago, and the innovations of this version are still unknown to the general public, and there are no devices supporting it yet on the market.

Actually, the presence of an HDMI connector on the video card is not necessary; in many cases it can be replaced by an adapter from DVI to HDMI. It is simple and therefore included with most modern video cards. Moreover, modern GPUs have a built-in audio chip necessary to support audio transmission over HDMI. On all modern AMD and NVIDIA video cards, there is no need for an external audio solution and corresponding connecting cables, and transmit the audio signal from an external sound card no need.

Transmission of video and audio signals via one HDMI connector is in demand primarily on mid-range and lower levels, which are installed in small and quiet barebones used as media centers, although HDMI is often used in gaming solutions, largely due to the proliferation of household appliances with such connectors.

Connector

Gradually, in addition to the common DVI and HDMI video interfaces, solutions with DisplayPort interface. Single-Link DVI transmits a video signal with a resolution of up to 1920x1080 pixels, a frequency of 60 Hz and 8 bits per color component, Dual-Link allows transmission of 2560x1600 at a frequency of 60 Hz, but already 3840x2400 pixels under the same conditions for Dual-Link Link DVI not available. HDMI has almost the same limitations; version 1.3 supports signal transmission with a resolution of up to 2560x1600 pixels at a frequency of 60 Hz and 8 bits per color component (at lower resolutions - 16 bits). Although the maximum capabilities of DisplayPort are slightly higher than those of Dual-Link DVI, only 2560x2048 pixels at 60 Hz and 8 bits per color channel, but it has support for 10-bit color per channel at 2560x1600 resolution, as well as 12-bit for 1080p.

The first version of the DisplayPort digital video interface was adopted by VESA (Video Electronics Standards Association) in the spring of 2006. It defines a new universal digital interface, license-free and royalty-free, designed to connect computers and monitors, as well as other multimedia equipment. The VESA DisplayPort group that promotes the standard includes large electronics manufacturers: AMD, NVIDIA, Dell, HP, Intel, Lenovo, Molex, Philips, Samsung.

DisplayPort's main competitor is HDMI, which supports HDCP write protection, although it is intended more for connecting household devices. digital devices, like players and HDTV panels. Another competitor could previously be called Unified Display Interface - less expensive alternative HDMI and DVI connectors, but its main developer, Intel, refused to promote the standard in favor of DisplayPort.

The absence of licensing fees is important for manufacturers, because in order to use the HDMI interface in their products, they are required to pay license fees to HDMI Licensing, which then divides the funds between the holders of rights to the standard: Panasonic, Philips, Hitachi, Silicon Image, Sony, Thomson and Toshiba. Abandoning HDMI in favor of a similar “free” universal interface will save manufacturers of video cards and monitors a lot of money - it’s clear why they liked DisplayPort.

Technically, the DisplayPort connector supports up to four data lines, each of which can transmit 1.3, 2.2 or 4.3 gigabits/s, for a total of up to 17.28 gigabits/s. Modes with color depth from 6 to 16 bits per color channel are supported. An additional bidirectional channel, designed to transmit commands and control information, operates at a speed of 1 megabit/s or 720 megabit/s and is used to service the operation of the main channel, as well as the transmission of VESA EDID and VESA MCCS signals. Also, unlike DVI, the clock signal is transmitted along signal lines, rather than separately, and is decoded by the receiver.

DisplayPort has optional DPCP (DisplayPort Content Protection) copy protection capability developed by AMD and using 128-bit AES encoding. The transmitted video signal is not compatible with DVI and HDMI, but according to the specification their transmission is allowed. Currently, DisplayPort supports a maximum data transfer rate of 17.28 gigabits/s and a resolution of 3840x2160 at 60 Hz.

Basic distinctive features DisplayPort: an open and extensible standard; support for RGB and YCbCr formats; color depth support: 6, 8, 10, 12 and 16 bits per color component; full signal transmission at 3 meters, and 1080p at 15 meters; support for 128-bit AES encoding DisplayPort Content Protection, as well as 40-bit High-bandwidth Digital Content Protection (HDCP 1.3); greater bandwidth compared to Dual-Link DVI and HDMI; transmission of multiple streams over one connection; compatibility with DVI, HDMI and VGA using adapters; simple expansion of the standard to meet changing market needs; external and internal connections (connecting an LCD panel in a laptop, replacing internal LVDS connections).

The updated version of the standard, 1.1, appeared a year after 1.0. Its innovations include support for HDCP copy protection, important when viewing protected content from Blu-ray discs and HD DVDs, and support for fiber optic cables in addition to conventional copper cables. The latter allows you to transmit a signal over even greater distances without loss of quality.

DisplayPort 1.2, approved in 2009, doubled the interface's bandwidth to 17.28 gigabits/s, allowing it to support higher resolutions, screen refresh rates, and color depths. Also, it was in 1.2 that support for transmitting multiple streams over one connection for connecting multiple monitors, support for stereo display formats and xvYCC, scRGB and Adobe RGB color spaces appeared. A smaller Mini-DisplayPort connector for portable devices has also appeared.

The full-size external DisplayPort connector has 20 pins, its physical size can be compared to all known USB connectors. A new type of connector can already be seen on many modern video cards and monitors; it looks similar to both HDMI and USB, but can also be equipped with latches on the connectors, similar to those provided in Serial ATA.

Before AMD bought ATI, the latter announced the supply of video cards with DisplayPort connectors at the beginning of 2007, but the merger of companies pushed back this appearance for some time. Subsequently, AMD announced DisplayPort as a standard connector within the Fusion platform, implying a unified architecture of central and graphic processors in one chip, as well as future mobile platforms. NVIDIA is keeping up with its rivals by releasing a wide range of DisplayPort-enabled graphics cards.

Among the monitor manufacturers that announced support and announced DisplayPort products, Samsung and Dell were the first. Naturally, such support was first received by new monitors with a large screen diagonal size and high resolution. There are DisplayPort-to-HDMI and DisplayPort-to-DVI adapters, as well as DisplayPort-to-VGA, which converts digital signal to analog. That is, even if the video card contains only DisplayPort connectors, they can be connected to any type of monitor.

In addition to the connectors listed above, older video cards also sometimes have a composite connector and S-Video (S-VHS) with four or seven pins. Most often they are used to output a signal to outdated analog television receivers, and even on S-Video the composite signal is often mixed, which negatively affects the picture quality. S-Video is better quality than composite tulip, but both are inferior to YPbPr component output. This connector is found on some monitors and high-definition TVs; the signal is transmitted through it to analogue form and is comparable in quality to the D-Sub interface. However, in the case of modern video cards and monitors, paying attention to all analog connectors simply does not make any sense.

Technological progress in the field of high-tech is gaining speed like an interceptor fighter. Until recently, digital electronics was associated exclusively with bulky computers in computing centers, and today cell phones, laptops and plasma displays no one is surprised anymore. True, the ways of improving radio-electronic equipment are sometimes quite strange, and at the beginning of the 21st century Hi-End audio amplifiers appear on sale, on the casings of which, like on pre-war radios, samovar radio tubes are proudly lined up. But this is so - toys for the rich, and in fact, after prices for powerful microprocessors fell to the level of $20 apiece, the transition to digital methods of creating, processing, storing and transmitting video and audio information became inevitable. From a circuit design point of view, digital equipment is more complex than analog equipment, but its functionality is much wider, and some of them are fundamentally unattainable with analog signal processing.

The transition to digital audio and video formats is due to their technical and user advantages over analogue ones.

TO technical advantages include:

From a circuit design point of view, digital equipment is more complex than analog equipment, but its functionality is much wider, and some of them are fundamentally unattainable with analog signal processing

• fundamental exclusion of loss of signal quality during transmission, rewriting and storage of the signal;
• the ability to accurately time synchronize video material;
• more advanced control systems and signal quality monitoring;
• simplification of technology for receiving, processing, storing and transmitting high-quality signals;
• expanding the creative capabilities of television studio staff;
• the ability to encrypt video data (using cryptography).

User properties of the digital format include:

• the ability to obtain high-quality, interference- and noise-free pictures with multi-channel stereo sound;
• wide service capabilities of digital equipment.

It is clear that analog interfaces are not suitable for working with a digital signal or are poorly suited, so special digital interfaces were created for it.

These include the serial digital interface SDI/SDTI, used in professional and studio equipment, as well as digital video interfaces DVI And HDMI.

The last two interfaces are discussed below. The HDMI interface is a development of the DVI interface, it uses the same basic technologies, that’s why they are discussed within the same brochure.

DVI DIGITAL VIDEO INTERFACE

The problem of signal quality deterioration during repeated analog-to-digital and digital-to-analog conversion was solved with the advent of the new DVI standard, which can now be confidently considered as generally accepted. The group that developed the standard, the Digital Display Working Group (DDWG), was created at the initiative of Intel and included Compaq, Fujitsu, Hewlett-Packard, IBM, NEC and Silicon Image. The DVI specification was presented in April 1999, at which time working solutions using the standard were demonstrated - plasma monitors from Fujitsu and Phillips, LCD monitors from IBM and Compaq, and other products.

The transition from composite and S-Video to component and RGB channels allowed for a sharp increase in image quality, but unnecessary analog-to-digital-to-analog conversions significantly deteriorated the picture quality

The creators of the DVI standard expected that its scope would be much wider than digital connection computer with monitor. In the late 90s of the twentieth century, the rapid development of video technology continued. Fully digital DLP projectors have firmly come into use, and LCD and CRT monitors, even if they remained analog in the principle of image formation, had digital circuits signal processing. The image scaling and scan conversion necessary to correctly convert the number of lines, pixels and fields was carried out digitally. Functions for adjusting color, brightness, contrast and other video parameters were also implemented digitally. After Fujitsu began licensing plasma technology to other manufacturers, it became clear that bringing another type of high-quality digital display to the market was a matter of the near future.

The introduction of high-definition television has moved into practice. Screen sizes grew and their resolution increased. There was only one thing missing - a digital video interface that would meet the current and future demands of the market. The transition from composite and S-Video to component and RGB paths made it possible to sharply increase image quality, however, unnecessary analog-to-digital-to-analog conversions significantly worsened the picture quality, which was especially offensive due to the absolute uselessness of the ADC and DAC in the path consisting from digital source(DVD, computer), digital display and digital processor between them. It turned out that the ADC and DAC only worked on the “wires” between the source and the monitor.

The need to create a digital interface that meets the needs of HDTV and has a solid future reserve has become quite obvious.

Interface DVI- Digital Visual Interface - can, with certain tolerances, be called a digital RGB interface. In the single-channel modification of the Single Link DVI format, there are four data transmission channels: three of them are designed to transmit information about the primary colors: blue, green and red, and the fourth transmits the “Clock” clock signal. This achieves a maximum data rate of 1.65 Gbps, or 165 megapixels per second, with 10-bit encoding (that's an effective 8 bits of data), which corresponds to a resolution of 1600 x 1200 pixels (UXGA) at a 60-field refresh rate. Hz (or 1920 x 1080 and even 1920 x 1200). Today, this more than covers the needs of modern HDTV formats.

The modification of the Dual Link DVI interface has even greater throughput. Everything is the same here, but in double size (except for the clock frequency signal, which does not need to be transmitted twice). Dual Link DVI is capable of transmitting QXGA signals (2048 x 1536 pixels) at a frame rate of 60 Hz.

DVI transmits resolutions up to 1600 x 1200 (UXGA) at 60 Hz (or 1920 x 1080 and even 1920 x 1200). This more than covers the needs of HDTV

Despite the obvious redundancy of Dual Link DVI in terms of modern displays devices supporting this interface are being produced (for example, large displays for workstations).

Thanks to DVI technology, it has become possible to remove the analog part from the video adapter boards and transfer it to the monitor, which should improve the image quality much more than eliminating the influence of interference in the video card-monitor connecting cable. Since image information is transferred from the video card to the monitor digitally, the influence of external noise is significantly reduced.

VARIETIES OF DVI

There are two more types of DVI interface: DVI-D and DVI-I, the difference between which is that to ensure wider compatibility of equipment of different generations in DVI connector, in addition to three rows of “digital” contacts, analogue ones can also be provided, to which a regular analog RGBHV signal is supplied (the same as VGA, in Fig. 1 - contacts C1 - C5). Thus, a version of the DVI interface, including analog and digital parts, is called DVI-I (Integrated), i.e. combined. Thus, in total you can find 4 types of interface:

• DVI-I Dual Link (digital + analog, up to 2048 x 1536)
• DVI-I Single Link (digital + analog, up to 1920 x 1200)
• DVI-D Dual Link (digital, up to 2048 x 1536)
• DVI-D Single Link (digital, up to 1920 x 1200)

DVI CABLE

Single Link versions may not have pins 4, 5, 12, 13, 20, 21 on the connector. DVI-D versions may not have C1, C2, C3, C4, C5 pins on the connector.

The DVI connector layout (for the “full” Dual Link DVI-I interface) is shown in Fig. 1, and the assignment of contacts is summarized in Table 1.

Table 1. DVI-I Dual Link connector pinout

Rice. 1. DVI-D and DVI-I connectors

INTERNAL: VIDEO DATA DATA (TMDS)

The high speed characteristics of the DVI interface are achieved through the use of a signal encoding algorithm specially developed for it, which is called Transition Minimized Differential Signaling (T.M.D.S) - differential signal transmission with minimization of level differences.

Rice. 2. TMDS communication line

Differential (or balanced, symmetrical) transmission method, when the same direct and inverted signal passes through each conductor of a twisted pair, provides effective protection data from common mode interference.

Rice. 3. Balanced communication line with differential receiver

Rice. 4. Balanced communication line suppresses interference

On the transmit side of the DVI interface there is a T.M.D.S transmitter. in which the digitized RGB signal is converted and a sequential data stream is formed in each of the channels. On the receiving side, on the contrary, it happens full recovery digital streams on channels R, G, B, as well as the Clock signal.

The transmission format is always the same: RGB color space, color depth 24 bits (8 bits per component). For high resolutions, frame rates up to 60 Hz (progressive scan) are supported.

When restoring, automatic compensation of cable losses and reclocking are used (reclocking, elimination of jitter, i.e. phase jitter of a digital signal).

Rice. 5. Signal before and after recovery

Recovery is effective only if the signal degradation does not exceed a certain threshold value. In this case, the digital signal is restored almost completely, without losses or errors. However, as soon as the situation gets a little worse (for example, we take a slightly longer cable), the signal cannot be restored, and the picture is riddled with interference, “falls apart,” or even disappears completely. This phenomenon is called the “clipping effect” and is characteristic of digital signals.

Rice. 6. “Cliff Effect”

As a result, when using cables of a reasonable length and repeaters (receivers-transmitters of the signal with its intermediate restoration), it is possible to broadcast a digital signal over almost unlimited distances - without loss!

Rice. 7. Use of repeaters

The higher the signal resolution (and, therefore, the data transfer rate in TMDS channels), the greater the losses in the cable and (all other things being equal) the shorter the cable used can be. The DVI standard does not specify the possible cable length and the signal resolution at which such a length will work. Real quality DVI cables usually work well at lengths and resolutions no greater than those shown in the graph below (shown for the Single Link interface):

Rice. 8. Permissions vs cable lengths

In some cases, longer cables will work, but this requires experimental confirmation in each specific equipment combination.

To overcome cable length restrictions, you can:

• purchase ultra-high quality (and price) DVI electrical cables. In some cases, manufacturers of such cables guarantee their operation with maximum resolutions for lengths up to 15 meters
• use a scheme with repeaters (see Fig. 7)
• use fiber optic extension cords or other special solutions. Usually this is cheaper than repeaters (if the latter number is more than 2), extenders work at distances from tens to hundreds of meters.

Rice. 9. Integrated fiber optic cable (left, up to 100m length), transmitter and receiver for use with separate optical cable (right, up to 500m cable length)

INTERIOR: SERVICE CHANNEL (DDC)

If the DDC service channel is down, video data on TMDS channels may be blocked

The DVI-D and DVI-I interfaces, in addition to the digital channels described above, contain another one designed for exchanging information between a source equipped with a video processor (for example, a PC with a video card) and a display. Channel DDC(Display Data Channel) is designed to transmit a detailed “dossier” of the display to the processor, which, having familiarized itself with it, produces an optimal signal for this display with the required resolution and screen proportions. This dossier, called EDID(Extended Display Identification Data, or detailed display identification data), is a block of data with the following sections: manufacturer brand, identification number models, serial number, release date, screen size, supported resolutions and native screen resolution.

When a DVI-compatible source is started, the HPD (Hot Plug Detect) process is activated. The source then reads the EDID data block. If the monitor refuses to provide information about itself, the T.M.D.S channel is blocked.

When using equipment that complies with the standard and standard cables, for a simple connection circuit (source-cable-monitor), this circuit works normally. However, in more difficult cases the DDC channel may not work - for example, if switches, distribution amplifiers, and other elements of complex AV systems are installed between the output and the display. In this case, a problem arises: how to make the output, for example, of a laptop video card, work in the absence of a service channel.

Rice. 10. Device - EDID emulator and its application
(Click on photo to enlarge)

You can “deceive” the video output using a special device. Such a device stores the EDID data block in its internal memory and issues it from there upon request of the video card. In this case, video data passes through the device “transparently”. If the emulator is pre-trained (by reading the real EDID from a real display), the signal source will “think” that it is permanently connected to the display and output data.

Many switches and distribution amplifiers for DVI and HDMI signals already have similar emulators built-in, which makes the installer’s work easier. Note that the presence of an emulator in no way ensures the operation of the HDCP video data encryption system, for which the presence of a “live” DDC channel is mandatory.

INTERNAL: HDCP DATA ENCRYPTION

Intel's HDCP (Highbandwidth Digital Content Protection) cryptographic system is a method for protecting high-resolution digital data. It provides the opportunity, depending on specific case establish different levels of protection, so that it does not limit the freedom of handling video data within the framework approved by current legislation. For example, HDCP does not provide copy protection and does not artificially degrade the quality of copies. The following actions are strictly prohibited: copying programs with the protection removed, receiving an unprotected high-resolution digital stream. Repeaters and signal splitters are allowed, but they must "exchange passwords" with each other and obtain mutual approval, which is only possible if all devices are HDCP compliant.

A Blu-Ray disc or DVB stream contains a special mark, in the presence of which the player or receiver must enable data encryption on its digital output

Note that HDCP is not tied, for example, to encryption of data on a Blu-Ray disc or stream in a DVB receiver. These are different technologies. A special mark is simply written on the disc itself or in the DVB stream, in the presence of which the device (player or receiver) must enable data encryption on its digital output.

The HDCP system can work with both the DVI and HDMI interfaces. True, for the (mostly) computer DVI interface, HDCP is used extremely rarely, while for the consumer HDMI interface, HDCP encoding is used everywhere (and for most video programs - without fail).

HDCP protects the rights of the consumer by protecting him from the flow of low-grade
video production

It should be especially noted that HDCP works not only for the rights holders of film materials, but also protects the rights of the consumer, protecting him from the flow of low-quality video products (for example, received via the Internet), the quality of which is incompatible with modern high-definition television formats.

HDCP works according to a complex scheme, which primarily requires the presence of its own “secret” code combinations in each DVI/HDMI transmitter and receiver. In a single system, up to 127 pairs of transmitters and receivers and up to 7 levels of branching (or relaying) are allowed. In order for the DVI/HDMI link to be activated, each pair of transmitters and receivers must successfully pass the mutual authentication process. For this task, the same DDC service channel is used.

When using HDCP, analog outputs can produce a high-resolution image, or a low-resolution image, or not produce an image at all - at the discretion of the manufacturer

The first stage of the authentication process is the exchange of code combinations, which are “hardwired” into the equipment chips and are inaccessible to the user. Code combinations must have plausibility, which is verified by calculating the mathematical sum R0. The transmitter generates a pseudo-random sequence AN, which, together with the so-called. the "code selection vector" (KSV) is sent to the receiver. Similarly, a similar message is sent from the receiver to the transmitter. If the KSV check is positive (their structure, among other things, must contain 20 zeros and 20 ones), code generators are launched on both sides, generating 24-bit encryption codes corresponding to certain values ​​of the “secret” parameter Ks. The values ​​of R0 and Ks synthesized in the transmitter and receiver are compared.

KSV values ​​are individual for each separate device. There is also a “black list” of hacked codes, which is stored in the device’s memory and is updated when new BluRay releases are played (one of the methods). If the individual data of a specific device matches the data from this list, the initialization process is immediately blocked. Thus, once noticed in an attempt to circumvent the prohibitions, a DVD/BluRay player will become persona non grata in any system, provided that someone notices this attempt and reports it where it should be.

The entire process of “starting” the operation of the DVI/HDMI interface (reading EDID, setting the output) and the HDCP system (authentication) can take up to several seconds. At this time there is no image on the display.

When a video stream with HDCP encoding is on the digital output of a player or satellite receiver, its analog outputs can produce a high-resolution image, or a low-resolution image, or not produce an image at all - at the discretion of the device manufacturer. Unfortunately, descriptions of this behavior are extremely rare in documentation.

The conceptual complexity of the entire system (DVI/HDMI, DDC/EDID, HDCP) turns out to be orders of magnitude higher than all previously used analog interfaces. Although in mass production this practically does not lead to an increase in the cost of equipment (and theoretically should even make it cheaper), problems of compatibility and even simple operability of equipment, especially from different manufacturers, are now extremely relevant. Features of the “firmware” of the equipment and errors in the implementation of interfaces can negate all the advantages of the most expensive and advanced modern technology.

Before purchasing a set of equipment with a DVI/HDMI interface and HDCP support, be sure to turn it on and check it in all modes, including when playing content with HDCP protection enabled

We recommend that before purchasing equipment with a DVI/HDMI interface and HDCP support, be sure to turn it on (the entire complex - signal sources, intermediate switches, distributors, AV receivers, displays and all connecting cables) and check it in all modes, including when playing content with HDCP protection enabled.

THE FUTURE OF DVI AND HDMI

According to optimistic forecasts from Intel, the DVI and HDMI standard will be relevant for at least the next ten years.

The displacement of old interfaces is gaining momentum. In the not too distant future, things will most likely come to the point of the extinction of the analog part of video equipment. For the HDMI interface, which is replacing DVI, this has already happened (there is no analog part there).

HDMI INTERFACE

A development of the DVI interface is the high-definition multimedia interface HDMI (High Definition Multimedia Interface). The HDMI video part, as well as the DDC service channel, are fully compatible with DVI, but its appearance is completely different, because a different connector is used. HDMI is a more advanced interface than DVI, primarily due to its ability to transmit multi-channel audio. Additionally, HDMI is equipped with a CEC control interface (it is not found in DVI).

HDMI is a more advanced interface than DVI, primarily due to the ability to transmit multi-channel audio

Just like DVI, the HDMI interface can be single-channel (Single Link) and two-channel (Dual Link) (for these versions, different connectors). TMDS links and DDC overhead operate exactly the same as in DVI.

The bandwidth of HDMI (like DVI) reaches 5 Gbit/s. This is enough for a 1080p video signal and two channels of uncompressed digital audio in PCM up to 48 kHz or 5.1 channels in Dolby Digital or DTS. Audio transmission is carried out in a mixture with video, the same TMDS lines are used (there are no additional conductors for audio in the cable).

Rice. 11. Comparison of HDMI and DVI cable plugs (right)

The HDMI connector is more compact, but does not have latches, and (when using any long and heavy cables) is prone to falling out of its socket.

HDMI CABLE

The latest version of the HDMI 1.3a standard at the time of publication of the brochure describes 3 types of connectors:

• Standard Single Link (Type A)
• Standard Dual Link (Type B)
• Miniature Single Link (for compact devices) (Type C)

The most common type is the standard Single Link (Type A). Other types of connectors are still rare. The layout of such a connector is shown in Fig. 12, and the assignment of contacts is summarized in Table 2.

Table 2. HDMI connector pinout (Type A, Single Link)

Rice. 12. Cable part of the HDMI Type A connector

INTERIOR: TMDS, DDC, HDCP

Video data transmission technologies (TMDS), service channel (DDC), encryption system (HDCP) are similar to those described for the DVI interface.

Cable lengths and maximum resolutions are similar to those for DVI - see fig. 8. To overcome length limitations, you can use the same methods as for DVI (Fig. 13).

Rice. 13. Optical cable for HDMI extension (Type A) up to 100 meters

In addition to all video modes DVI interface HDMI supports:

• from version 1.2 - YUV color space (i.e. Y/Pb/Pr)
• from version 1.3 - xvYCC color space (IEC 61966-2-4, has a 1.8 times wider color gamut)
• from version 1.3 - double the data transfer rate (x2) via TMDS. The mode requires application special cables(“category 2”) with improved parameters. Cables for everyone previous versions in this case they fall into “category 1”. In addition to x2 mode, x1.25 and x1.5 modes are supported.

When using the transfer rate doubling mode, starting from version 1.3 the following is possible:

• increase color depth up to 48 bits
• increase frame rate for standard maximum resolutions to 120 Hz
• increase maximum resolution

INTRINS: AUDIO TRANSMISSION

Audio data is transmitted along with video over the same TMDS communication lines. The audio stream is “cut” into packets and transmitted in unused sections of the video (during horizontal and vertical blanking intervals).

Rice. 14. The audio stream is transmitted in packets in video blanking intervals

• from version 1.0 PCM stereo up to 48k, Dolby Digital, DTS are supported
• DVD-audio is also supported from version 1.1
• SACD is also supported from version 1.2
• from version 1.3 Dolby®TrueHD and DTS-HD Master Audio™ are also supported (with bitrates up to 8 Mbit/s)

INTERIOR: CONTROL CHANNEL (CEC)

Many electronics manufacturers have announced support for the CEC control channel

An additional communication line CEC (Consumer Electronics Control) can be used to control consumer electronics. Thanks to it, all devices connected via the HDMI interface (up to 10 pieces) are combined into a control network. There are standard control commands (Start, Stop, Rewind, commands for menus, tuners, TV, etc.) that devices can transmit to each other. This allows you to control one device (say, a Blu-Ray player) from the remote control of another (say, a TV), automate some processes, etc. With the exit HDMI versions 1.3, many electronics manufacturers have announced support for this control channel.

INTERFACE COMPATIBILITY

The HDMI standard stipulates full compatibility of all versions of interfaces (top-down and bottom-up):

• DVI (version 1.0) must be compatible with HDMI (any version). Of course, there is no audio support. Video modes will be limited to those specified for DVI. The connection can be made using an adapter cable (or through an adapter adapter)
• HDMI (any version) must be compatible with HDMI (any version). Moreover, the capabilities of such a system are determined by the capabilities of its “junior” component.
• Any combination of versions of the signal source, display and intermediate devices (repeaters, switches, etc.) is acceptable, with the same caveat regarding capabilities.

Rice. 15. DVI-HDMI adapter cable and adapter

Unfortunately, not all devices on the market demonstrate such excellent compatibility. For example, some widescreen home theater displays do not support the RGB color space (required by DVI and HDMI 1.0) and only understand a limited number of video modes (versus the minimum required by the standard). At the same time, such displays display the “HDMI” logo and proclaim support for version 1.3.

Note also that the advanced features of HDMI 1.3a are largely optional, making it easy to "comply" with this newest version of the standard - you just need to meet the minimum requirements (in fact, the requirements for version 1.0). Therefore, when purchasing equipment, be sure to make sure that it really has the extensions that you need - the number 1.3a in the specification, unfortunately, does not mean anything...

Internet links:

Currently, there are a huge number of different video standards and interfaces. Some have been in use for more than a decade, others are just entering our everyday life, and it’s quite easy to get confused in this variety. This is as difficult as for a non-specialist to understand a template for a forum. In this article, we have made a small selection of various interfaces for transmitting video signals, as well as common video connectors.

We hope you find this information useful.

Composite video output

Composite video output is designed to transmit all components of a video signal in a mixed form over one wire.

Typically the composite connector is a yellow RCA jack, or a generic SCART jack. To transmit a composite video signal, a coaxial cable with RCA ("tulip") connectors at the ends is used.

Composite video signal ( composite video) has been used since the reign of video cassettes, but is not capable of transmitting a high-quality signal. For this reason, it is currently used only in inexpensive video equipment, for example, in televisions with a small screen diagonal (14"-21").

Component video output

Component video is also called color difference video. It contains a luminance signal (Y) and two chrominance signals (U and V), which are determined by the formula:

Y = 0.299R + 0.587G + 0.114B

To display the image, interlace ( interlaced) or progressive ( progressive) sweep. Interlace scanning is used in all existing television broadcasting systems. Progressive scan is used in modern television standard HDTV and in modern DVD players, as it allows you to get higher image quality.

To transmit such a video signal, three separate coaxial cables are used, at the ends of which there are RCA ("tulip") connectors or BNC connectors.

Video output S-Video

The S-Video connector is commonly used to output video signals from camcorders, PCs, and game consoles to household televisions and other consumer video equipment. The S-Video interface uses two signal lines - a chrominance (C) signal and a luminance (Y) signal. When used as a signal source from a DVD player or a satellite receiver and a TV with a diagonal of 25" or more, this interface allows you to obtain a higher quality image than a composite video signal.

The cable for transmitting this video signal contains different types of connectors: 2 BNC connectors, 2 RCA connectors, 4-pin Mini DIN connector or a universal SCART connector.

RGB video output

To transmit a color image to a CRT monitor, intensity signals for each RGB color are used, as well as horizontal (H) and vertical (V) scan signals. A total of five signals are obtained - RGBHV.

To transmit the RGB signal, 5 coaxial cables equipped with BNC connectors are used.

VGA video output

In addition to RGB and synchronization signals, the VGA connector also contains so-called DDC signals for transmitting information between the video card and the monitor. The VGA cable connects using a 15-pin D-Sub connector (also called D-Sub 15 pin).

DVI video output

DVI digital video output is used mainly in video adapters of personal computers. It provides digital signal transmission directly from the video adapter of a computer or laptop to the projector. This does not use an intermediate digital-analog image (as in the S-Video standard or in a composite video signal), which allows you to obtain a higher quality picture.

Today there are two types of DVI connectors:

• universal combination connector DVI-I. It allows you to connect both digital and analog monitors (with an adapter from DVI-I to 15-pin VGA D-Sub);
• fully digital connector DVI-D, to which only digital monitors can be connected. This connector differs from the DVD-I connector in that it does not have four holes (pins) around the horizontal slot. As a rule, such an interface is used only in cheap video cards.

In addition, DVI connectors (DVI-I and DVI-D) have two types of connector: Single Link And Dual Link, differing in the number of contacts. At the same time, Dual Link uses all 24 digital contacts, while Single Link uses only 18. Single Link is used in devices with a resolution of up to 1920x1080 (the so-called HDTV). For higher resolutions, Dual Link is used, which allows doubling the number of output pixels.

HDMI video output

HDMI interface ( High Definition Multimedia Interface) is intended for connection to DVD players, satellite receivers and video adapters for personal computers modern TVs and home theaters. Today it is the standard for transmission digital audio and video in uncompressed form.

HDMI is completely digital digital format, allowing you to transmit not only high-definition video, but also many digital audio channels using only one cable. An HDMI cable with a signal spectrum width of up to 10 Gbps allows you not only to output high-resolution video, but also simultaneously transmit up to eight channels of high-quality audio.

The HDMI interface is a further development of the DVI-D interface and is fully compatible with it, but has more advanced parameters.

Currently, the following types of HDMI connectors are available:

• Type A, which has 19 contacts and is most widespread.
• Type B, having 29 contacts. It has an extended video channel, which allows you to transmit video information with a resolution higher than 1080p. Currently, this connector is not yet in great demand.
• mini HDMI is designed for use in camcorders and portable devices. It is a variation of the HDMI Type A connector, but has a reduced size.

Please note that the HDMI cable cannot be longer than 15 m.

If we arrange all the video standards described above in increasing order of video signal quality, we get:

• composite video
• S-Video
• component video

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