Motor connector What is a DVI connector? Connectors for connecting output devices

If your monitor connects to your computer via DisplayPort or DVI, it still meets modern standards. But what is the difference between DisplayPort and DVI, we will now explain.

Signal type

Both technologies allow digital signals to be transmitted from the computer to the screen. This results in a significant improvement in image quality compared to the old VGA technology.

DVI comes in several flavors that are labeled differently. DVI-I can transmit both analog and digital signals, DVI-D only works with digital signals. But with the help of DisplayPort, only digital information is exchanged.

Screen resolution

A significant difference between DVI and DisplayPort is screen resolution, which is critical to image quality.

DVI provides two options here. With the so-called mono-channel signal transmission method, a maximum resolution of 1600x1200 pixels is achieved. Dual-channel transmission is possible - then the resolution reaches 2560x1600 pixels. This requires a special connecting cable with an increased number of contacts.

With DisplayPort technology you can achieve much higher resolution. The DP 1.3 standard, available since 2014, provides a resolution of 5120x2880 pixels.

Connectors: external difference

The systems use different connectors, which differ even purely visually. DVI connectors are significantly larger than DisplayPort connectors. For mono-channel transmission they have 18+5 contacts, and for dual-channel transmission they have 24+5 contacts, with the last five serving as analog extension. The DVI plug is tightly connected to the monitor (screwed in) to ensure uninterrupted signal transmission.

DisplayPort connectors are much smaller and similar to USB connectors. They require much less space than DVI plugs. They connect to devices in a standard way, without additional screws. Most systems have a mechanical cable retention device to prevent the cable from falling out of the slot.

Playing video and audio

With DVI you can only transmit images. For transfer sound signals separate cables must be used. But DisplayPort transmits both image and sound.

Another way to connect a computer to an output device is the HDMI standard. In fact, this is an add-on over DVI that expands the capabilities of the technology: the HDMI channel can transmit high-definition audio and digital video.

Compatibility

DisplayPort is electrically compatible with DVI. If, for example, you have a DisplayPort connection on your PC and a DVI connection on your monitor, you can connect both devices to each other using an adapter. The video card in the computer detects this and adjusts the signals accordingly.

Connecting cable length

Among other things, the length of the connecting cable varies. For DVI it can be a maximum of five meters. But for DisplayPort, the cable length can range from 7 to 10 meters.

Using Multiple Monitors

The advantage of DisplayPort is the ability to connect multiple devices. If you want to connect more than one monitor to your computer, you only need one DisplayPort slot on the computer for the first monitor. With DVI this is not possible: it requires appropriate distributors.

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 resolution of 1600x1200 (UXGA) with 1.92 million pixels and a vertical refresh rate of 60 Hz, the monitor requires high throughput. 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(Dual Link DVI), then 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. Yes, and reducing the horizontal refresh rate may not give much good result in some applications.

To solve this problem, the DVI specification stipulates additional mode work, called Dual Link. IN 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 30" display with 2560x1600 resolution from Dual interface Link already there's no escape.

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.

On at the moment you can find six different DVI connectors. Among them: DVI-D for completely digital connection in single-channel and dual-channel 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 manufacturers graphic cards equip their products with a dual-link DVI-I connector, even if the card has one port. Using an adapter DVI-I port Can be converted to VGA analog 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 the output of two DVI 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. For comparison, many graphics cards nVidia processors 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 based on the map.

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). For evaluation DVI compatibility so-called eye diagrams are created representing 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 most big problems with sequential high speed transmission associated with signal phase jitter. If there is no such effect, then you can always clearly highlight the signal on the chart. Most signal jitter is generated by the graphics chip's clock signal, resulting in low-frequency jitter in the 100 kHz to 10 MHz range. 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 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). This is why the clock signal is also transmitted over the 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 error. 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 may introduce delay into the clock signal (remember that data signals and clock signals have different frequency ranges), additional delay may affect the quality of signal reception.

Among the most common interfaces for connecting monitors to a PC are DVI-I and DVI-D. What are the features of each of them?

Facts about DVI-I

DVI-I interface involves the use of two types of signal transmission channels - analog and digital. Moreover, the structure of their location in the cable may differ depending on one of the two modifications of the interface in question - DVI-I Single Link and DVI-I Dual Link.

DVI-I Single Link devices support 1 digital and 1 analog channels. Moreover, both of them function independently. Activation of any of them is related to which specific device is connected to the PC’s video card and how the connection between devices is made. Devices of the DVI-I Dual Link type, in turn, implement 3 data transmission channels - 2 digital and 1 analog.

Facts about DVI-D

DVI-D interface involves the use of only digital data transmission technologies. Depending on the cable modification, 1 or 2 channels can be used.

Using a single-channel DVI-D interface, you can transmit data at a resolution of about 1920 by 1200 pixels and a frequency of 60 Hz. However, these resources will not be enough to reproduce 3D images created using technologies like nVidia 3D on a PC monitor.

The presence of dual-channel DVI-D interfaces in the cable structure allows you to transfer video data to high resolution- 2560 by 1600 pixels. In addition, the presence of two digital channels makes it possible, when using such a cable, to broadcast 3D images on monitors in a resolution of 1920 by 1080 pixels and a frequency of 120 Hz.

Comparison

The main difference between DVI-I and DVI-D is that the first standard supports both digital and analog data transmission technologies, while the second supports only digital ones. Accordingly, when connecting a monitor to a PC via DVI-D, you should check whether it is analog.

Visually DVI-D interface- in all modifications - differs from DVI-I in the absence of four holes in the side of the connector.

In fact, both standards under consideration are combined into a DVI-I Dual Link connector. There is also, by the way, the DVI-A interface, which supports only analog data transmission technology.

Having determined what the difference is between DVI-I and DVI-D, we will record the main conclusions in the table.

Often the choice of a video card is made according to the criteria of an already purchased monitor or its desired type and image quality. For example, a digital LCD monitor requires DVI connectors. Although modern developments often offer absolutely universal solutions, it’s still worth double-checking. Because for resolutions higher than 1920 by 1200 with digital image transmission, you only need DVI connector Dual Link.

What are DVI connectors used for?

DVI connectors perform important functions transferring images to various types monitors, they are divided into several types, advanced digital and analog signals. Most modern video cards are equipped with a DVI interface, which is presented mainly in two different types DVI-I and DVI-D.

What is DVI-I?

This type is considered the most common in video cards due to its versatility. "I" stands for "integrated". This interface uses two types of transmission channel, namely analog and digital. They function separately from each other, and have different modifications:

This device has 1 digital channel and 1 analogue. They absolutely do not depend on each other. Which of them will function depends on the type of connection to the video card and on the mechanism directly to which the connection is made. This type is not used in professional equipment, because eliminates the possibility of transmission to thirty-inch and LCD monitors, namely the use of wider screen resolutions (more than 1920 by 1080).

What is DVI-D?

This interface provides exclusively digital technologies for data transmission, and can also have several channels. This type, namely DVI-D Single Link, allows feeding at a frequency 60 Hz, in resolution 1920 by 1200 dots, but this is not enough to connect to 3D monitors. In turn, there is a second type for this. Let's take a closer look at it!

D - this is “digital”, translated as “digital”, as mentioned above, it does not have an analog channel, but at the same time allows greater possibilities for transmitting digital data. Dual – means “2” channels. This advantage makes it possible to operate NVidia 3D, feeding images to a 3D monitor, because two channels allow for 120 Hz and wide resolution capabilities.

Key differences between DVI-I and DVI-D

“I” supports both digital and analogue transmission forms; in “D” only digital is possible, so if connected to an analog monitor, DVI-D will not be able to transmit the right signal. Externally, they also differ; unlike dvi-i, dvi-d does not have four holes. The “D” connector is much less common on video cards, but it guarantees the most best quality digital image. Often used for professional CRT monitors. Mostly this type found in integrated video cards. When, in turn, it is dvi-i that is most common on popular consumer video cards, due to its two functionality. Considering the connection data, there is also exclusively analog form transmission is DVI-A, used very rarely.

What do they have in common?

Of course, this is the versatility of DVI-I and the possibility of transmission, both digital and analog signal . With the help of additional adapters and combinations, “I” efficiently carries out any form of transmission, and the use of this type for an analog screen is almost no different from “D”. In modern products, the first option is used much more often than the second and, moreover, almost always!

If you have any doubts about the alignment of the video card and screen connectors, it is recommended to immediately contact a specialist, because Most often, in case of an error, you will have to either replace one of the devices or use possible alternatives and additional cables, which may distort the image. The best option It is considered to be purchasing DVI-D for a digital monitor, or a universal dvi-i that can function even when replacing an analog monitor with a digital one. For more information about which of the above connectors will provide the best quality, it is best to consult when purchasing.

To transmit video signal to digital form A DVI (digital visual interface) connector is used. It was created when video media appeared in digital format – DVDs, and when it was necessary to transfer video from a computer to a monitor. The then existing methods of transmitting an analog signal did not allow achieving high quality pictures, because physically transmit an analog signal high resolution at a distance is impossible.

Video distortion can always occur in the communication channel, this is especially noticeable on high frequencies oh, and HD quality just implies the presence of high frequencies in the signal spectrum. To avoid these distortions, we tried to switch to a digital signal and abandon analog when processing and transmitting video from the media to the display device. Then, in the late 90s, several companies joined forces to create a digital interface for transmitting video data, eliminating DAC (digital-to-analog) and ADC (analog-to-digital) converters from the path. The result of their work was the creation of the video signal transmission format - DVI.

External dvi view connector:

View of the dvi connector inside:

Basic parameters of the dvi interface

This type of connection transmits information about the main components of the RGB signal (red, green, blue). Each component uses a separate twisted pair in the DVI cable, and there is a separate twisted pair cable for transmitting synchronization signals. It turns out that the DVI cable consists of four twisted pairs. A twisted pair connection allows you to use the principle of differential data transmission, when the interference has a different phase in each conductor and is subtracted at the receiver, but this technical features and it is not necessary to know them. Each color component is allocated 8 bits, and, in general, 24 bits of information are transmitted to each pixel. Maximum speed data transfer reaches 4.95 Gbit/s, at this speed it is possible to transmit a signal with a resolution of 2.6 megapixels at a frame rate of 60 Hz. An HDTV signal, whose resolution is 1980x1080, has a resolution of slightly more than 2 megapixels, so it turns out that a high-resolution signal of 1980x1080 at 60 Hz can be transmitted through the DVI connector. There is only a limit on the cable length. It is believed that a high-resolution signal can be transmitted with a cable up to 5 meters long, otherwise distortion may occur in the image. When transmitting a signal with a lower resolution, increasing the length of the DVI cable is allowed. It is also possible to use intermediate amplifiers if a larger length is still needed to transmit the video signal.

For greater compatibility, the DVI connector was made to support an analog signal. This is how three types of DVI connectors appeared:

1. 1) DVI-D transmits only digital signal;
2. 2) DVI-A transmits only analog signal;
3. 3) DVI-I is used for transmission and digital signals and analog.

The connector itself for all three types is used the same, so they are completely compatible, only they have a difference in the connected contacts in the connector.

There are also two data transfer modes: single link (single mode), dual link (double mode). Their main difference is in the supported frequencies. If in single mode the maximum signal can be 165 MHz, then in dual mode the limitation is imposed by the physical characteristics of the cable. This suggests that DVI Dual Link cables can transmit signals with higher resolution and over longer distances. That is, if, when using a single link cable, there is interference in the image of the LCD TV in the form of colored dots, then you can try replacing it with a dual link. Structurally, a dual mode DVI cable is distinguished by the use of double twisted pairs to transmit color components.

Features of the dvi connector

To implement such speeds, a special TMDS coding method. And in any DVI connection, a TMDS transmitter is used on the transmitting side for encoding, and the RGB signal is restored on the receiving side.

Additionally can be used in DVI interface DDC channel (Display Data Channel), which provides the source processor with EDID display information. This information provides details about the display device and includes information about the brand, model number, serial number, release date, screen resolution, screen size. Depending on this information, the source will produce a signal with the required resolution and screen proportions. If the source refuses to provide such information, it may block the TMDS channel.

Same as HDMI interface DVI supports HDCP content protection system. Such a protection system is called intelligent protection and it is called so because of its implementation and the ability to set different levels of protection depending on the different cases, so this protection does not block normal data exchange (for example, when copying). It is implemented on the principle of exchanging passwords with all devices connected via DVI.

Only the image is transmitted through the DVI connector, and the sound will have to be transmitted through additional channels. Some video cards have the ability to transmit audio via a DVI cable, but special adapters are used for this and this feature is additionally implemented in the video card itself. And then it is no longer a pure DVI interface. With a normal connection, audio needs to be transmitted additionally.