Principle of VGA interface
Speaking of the VGA interface, many friends will not be unfamiliar with it, because this interface is the most important interface on the computer display. From the era of huge CRT display, the VGA interface has been used, and it has been used until now, and the VGA interface is still used. Known as the D-Sub interface.
Many people think that only the HDMI interface can transmit HD signals, but it is wrong, because the VGA connection can also display 1080P images, and even the resolution can be higher, so use it to connect display devices. There is no problem in watching HD video, and although it is an analog interface, since the VGA decomposes the video signal into R, G, B primary colors and HV line signals for transmission, the loss in transmission is still relatively small.
Reasons for the VGA interface: The information processed by the graphics card is ultimately output to the display. The output interface of the graphics card is the bridge between the computer and the display. It is responsible for outputting corresponding image signals to the display. CRT monitors can only accept analog signal input for design and manufacturing reasons, which requires the graphics card to output analog signals. The VGA interface is the interface for outputting analog signals on the graphics card, and the VGA (Video Graphics Array) interface, also called the D-Sub interface. Although the LCD monitor can directly receive digital signals, many low-end products use a VGA interface in order to match the VGA interface card.
Function of VGA Interface
The role of the display is to ultimately carry the information processed by the graphics card, and the link between them requires a bridge. The output interface of the graphics card plays this role, and it is responsible for outputting the corresponding signal. Because of the design and manufacturing reasons, the CRT display can only accept analog signal input, and the VGA interface is the interface for outputting analog signals on the graphics card. Many low-end products also use a VGA interface in order to match the graphics card.
At present, most computers and external display devices are connected through an analog VGA interface, and digitally generated display image information is converted into digital signals of R, G, and B by the digital/analog converter in the video card. The field sync signal is transmitted to the display device via a cable. However, when used for connecting a display device such as a liquid crystal, the image loss during the conversion process causes the display effect to slightly decrease.
For analog display devices, such as analog CRT displays, the signal is sent directly to the corresponding processing circuit, which drives the control tube to generate an image. For digital display devices such as LCD and DLP, a corresponding A/D (analog/digital) converter is required in the display device to convert the analog signal into a digital signal. After the D/A and A/D2 conversions, some image details are inevitably lost. The VGA interface is useless for CRT displays.
Advantages of the DVI interface
Considering the compatibility issue, the current graphics card generally uses the DVI-I interface, which can be connected to the ordinary VGA interface through the conversion connector. Display with DVI interface generally uses DVI-D interface, because such display also generally has VGA interface, so there is no need for DVI-I interface with analog signal. Some monitors only have a DVI-I interface and no VGA interface. The DVI interface of the display device has the following major advantages:
1. Fast
DVI transmits digital signals, digital image information is directly transmitted to the display device without any conversion, thus reducing the digital → analog → digital cumbersome conversion process, greatly saving time, so it is faster It effectively eliminates the smear phenomenon, and uses DVI for data transmission, the signal is not attenuated, the color is purer and more realistic.
2 Picture is clear
The internal transmission of the computer is a binary digital signal. If the VGA interface is used to connect the LCD display, the signal needs to be converted into the R, G, B primary color signals and the line and field synchronization through the D/A (digital/analog) converter in the graphics card. Signals, which are transmitted to the LCD through analog signal lines, also require a corresponding A/D (analog/digital) converter to convert the analog signal into a digital signal again to display the image on the LCD. In the above D/A, A/D conversion and signal transmission process, signal loss and interference are inevitable, resulting in image distortion or even display error, and the DVI interface does not need to perform these conversions, thereby avoiding signal loss, so that The sharpness and detail of the image have been greatly improved.
3. Support HDCP protocol
The DVI interface can support the HDCP protocol, laying the foundation for viewing high-definition video with copyright. However, if you want the graphics card to support HDCP, it is not possible to have a DVI interface. You need to install a dedicated chip, and you must pay the unrecognized HDCP authentication fee. Therefore, there are not many video cards that actually support the HDCP protocol.
The HDCP signal is the same as the DVI from the interface form, pin definition, and data format. It is only for the sake of confidentiality. The data is encrypted and conforms to the HDCP protocol requirements. Considering that this is only a different level of agreement, we can consider the two equally.
DVI interface standard
DVI interface and VGA interface are different, DVI interface has many standards, you must understand when using the display. DVI is divided into five standards. Among them, DVI-D and DVI-I are divided into two types: “dual channel” and “single channel”. We usually see single channel version. The cost of dual channel version is very high, so only some professional equipments have It is difficult for ordinary consumers to see.
DVI-A is an analog transmission standard that can be seen in late-stage large-screen professional CRTs. However, because there is no essential difference between VGA and VGA, the performance is not high, so DVI-A has actually been abandoned. As for the DFP interface, this is an early digital specification that has been deprecated. About the various characteristics of the DVI signal.
