Digital Video Interface (DVI)

All connection types we’ve seen so far use analog signals. HDMI connection, which we will see on next page, uses digital signals. DVI, on the other hand, can carry both analog and digital signals. Here are the types of DVI connectors available:

• DVI-A: Analog connection.
• DVI-D: Digital connection. Usually when we say “DVI” we are referring to DVI-D.
• DVI-I: Cable or connector that can carry both DVI-A and DVI-D signals. DVI-A cables can carry only DVI-A signals and DVI-D cables can carry only DVI-D signals.
• Single Link: Allows screen resolutions up to 1920 x 1080 pixels at 60 frames per second.
• Dual Link: Allows screen resolutions up to 2048 x 1536 pixels at 60 frames per second.

On Figure 26 you can see the differences between these connectors.

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Figure 26: DVI connector types.

So, what is that all about? If you have a device that produces analog signal, it will have a DVI-A connector and you can only connect it to a display that has a DVI-A connector. You can use a DVI-A cable or a DVI-I cable to make this connection. The same idea goes for digital devices: if your device has a DVI-D connector you can only connect it to a display that has also a DVI-D connector. You will have to use a DVI-D or DVI-I cable to do such connection. You cannot connect a DVI-A device to a DVI-D display and vice-versa.

If your device has a DVI-I connector – which is the case of video cards – this means that it produces both analog and digital signals. You should use a cable (DVI-A or DVI-D) according to the kind of connection your display supports, analog or digital.

Of course using digital connection is the best, but you are limited to what kind of connection your product offers. But you should not worry so much about these several different kinds of connections available. Today almost all consumer electronics products feature digital connection, so you will find either a DVI-D or a DVI-I connector and you will probably be using a DVI-D or DVI-I cable, which fit both connectors, so you have nothing to worry about  – just see the examples below.

Since computers, digital cable/satellite converters and DVD, Blu-Ray and HD-DVD players are digital equipments, when transmitting video signals using an analog media like the VGA or component video outputs they must first convert the signals from digital to analog. On the other end of the cable, the LCD monitor, HDTV set or videoprojector must convert the analog signal back to digital, since these devices are also digital. There is image quality drop in this process of converting the signal from digital to analog and then back to digital.

So the  advantage of using DVI-D or HDMI connection is that you skip these digital/analog/digital conversions, thus improving image quality.

All PC video cards nowadays offer at least one DVI output (usually a dual-link DVI-I connector, allowing you to connect displays with analog or digital connection),  as you can see on Figure 27. You can also find DVI connectors (usually a DVI-D connector) on LCD monitors, digital cable/satellite converters, HDTV sets, videoprojectors and some DVD players. If they don’t have a DVI connector they will have a HDMI connector, which is even better.

DVI-D and DVI-I connectors can be easily converted into HDMI, as HDMI is fully compatible with DVI-D, and that’s why you probably won’t find products with these two connections available at the same time. We will talk more about this on next page.

So to connect your PC to your video monitor, videoprojector or HDTV you should use DVI connection instead of the traditional VGA connector, as it will provide the best image quality possible. If your HDTV has a HDMI connector you can connect your PC to it using a DVI-to-HDMI converter or cable, as we will show on next page. The same idea is valid to consumer electronics products: to connect your digital cable/satellite converter to your HDTV set use this connection (as mentioned, if your HDTV set has a HDMI connector instead of a DVI one you can use an adapter or cable to convert the DVI connector into HDMI).

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Figure 27: DVI output (DVI-I dual link connector) on a video card.

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 Figure 28: DVI output (DVI-D dual link connector) on a digital cable TV converter.

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Figure 29: DVI input (DVI-D single link connector) on a HDTV set.

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Figure 30: DVI-D single link cable.

We posted a tutorial on how to connect your PC to your HDTV panel. On this tutorial you will find a lot of useful information on how to use this connection. Please read it if you want to connect your PC to a HDTV panel or any other device with DVI input.

It is very interesting to note that DVI-I outputs can be transformed into VGA outputs by the use of an adaptor that usually comes with the video card (see Figure 28), if the DVI-I connector has analog signals (DVI-A) present – which is the case with all video cards. Thus you can transform the DVI-I connector of your video card on a second VGA output, allowing you to connect two video monitors to your computer. This connection, however, will be analog, not digital, since the VGA connection uses analog signals and you are using the DVI-A signals from the connector to generate this output.

Connecting two DVI devices to your PC, however, is only possible if you have a video card with dual DVI outputs, since converting a VGA output to DVI is not possible as VGA output uses analog signals and video monitors featuring a DVI input usually require digital signals (i.e. a DVI-D connector).

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Figure 31: Two DVI to VGA adaptors.

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