The interface of the display includes VGA, DVI, HDMI, DP, Type-C, Thunderbolt, and there are many versions, how to choose. The characteristics and parameters of each interface are described one by one below.
In addition, how to calculate the data transmission rate requirements for different resolutions, refresh rates, and color depth outputs will be explained later.
VGA
VGA should be the earliest interface for civilian computers. It is a full analog signal, and the highest resolution it can support is 2048K*1536P. Because it cannot reach the 2K resolution we often say, that is, 2560*1440, so we say that the highest resolution of VGA can only reach 1080P. There is nothing wrong with this statement, but the theory is wrong.
DVI
The introduction of DVI is to replace VGA, so some of its technical standards are quite close to VGA. However, it supports both analog and digital signals, so DVI has many interface forms.
First of all, DVI has a variety of interface forms, namely DVI-A (analog signal), DVI-D (digital signal), and DVI-I (analog signal and digital signal). Among them, DVI-D and DVI-I are divided into dual-channel and single-channel. The simplest difference is that the resolution and refresh rate of dual-channel are higher than that of single-channel.
The highest resolution of the DVI interface is 2560*1600 (16:10 ratio), and the highest refresh rate is 120Hz (at 1920*1080P resolution).
HDMI
Usually called an HDMI high-definition line, all of which are digital signals, and HDMI integrates sound transmission into the interface, and one line and one interface can transmit pictures and sounds at the same time.
There are several HDMI interface forms, namely normal size, MiniHDMI, and MicroHDMI. These three interfaces, except for their inconsistent shapes, have the same transmission standards.
In terms of versions, the latest HDMI version is version 2.1, and many display products have already begun to use it. At present, the most mainstream version is 2.0, and the highest resolution it can support (in 16:9 ratio) is 5120*2880. It can reach 244Hz in 1080P, 144Hz in 2K, and 60Hz in 4K.
At the same time, HDMI can only support 21:9 resolution and HDR picture transmission from 2.0.
In addition, there is another disadvantage of using HDMI, that is, HDMI+N card, the grayscale output of the Windows system will change to 16~235 by default, losing 0~15 and 236~255. This is why many people say that the color of the N card is gray, just manually change the output range back.
DP interface
The DP interface is currently the interface with the most advanced performance and the highest degree of standard uniformity among display transmission interfaces. Its full name is Display Prot, and it also supports simultaneous transmission of images and sounds. The DP interface is a standard launched to compete with HDMI. In the same version of the interface, the specification of DP is higher than that of HDMI.
The DP interface has two shapes, one is regular, and the other is MiniDP, which has the same appearance as the first and second generation Thunderbolt interfaces. Apart from the difference in appearance, they are identical in terms of performance and transmission parameters.
The latest version of the DP interface currently released is 2.0, but the products using this interface standard are still rare, and the most mainstream ones on the market are still 1.2 and 1.4.
VESA's official wire requirement for HDR certification is DP1.4a, but there is no difference in the DP signal wire wire, the main difference is in the interface chip. Due to the different standards of cable manufacturers, some DP1.2 cables can also enable HDR, but this does not mean that all DP1.2 can enable HDR.
In addition, the DP interface also has a function, which is the daisy chain. The function of the daisy chain is to output a signal and N monitors to display it synchronously. It only needs the computer to output a signal, and connect all the monitors in series with the DP interface that supports daisy chain, so that the screen of this computer can be displayed synchronously.
Typc-C
In addition to the above four interfaces, there are also Type-C and Thunderbolt interfaces, let's take a look.
Let’s talk about the Type-C interface first. This interface is actually a favorite interface for notebook external connections, because it not only supports simultaneous transmission of screen and sound, but also synchronous charging, and one cable can solve all needs.
In fact, strictly speaking, Type-C cannot be regarded as an interface protocol, because it is only an interface appearance standard. Because of the Type-C interface, it may be a USB transmission interface, a charging port, a signal transmission interface, or a Thunderbolt interface. Have you seen that so many interface protocols adopt the interface appearance of Type-C, and its core appeal is to solve the confusion of the cable interface.
In the field of video transmission, the parameter protocol standard adopted by Type-C is the USB protocol standard. At present, the latest protocol standard of the USB interface is USB4, which integrates the Thunderbolt 3 technical standard from this version (Intel has opened the Thunderbolt protocol to USB), and the transmission rate reaches 40Gbps (HDMI2.1 is 42.6Gbps, DP1. 4 and 2.0 are 25.92Gbps and 77.37Gbps respectively).
Thanks to the technical integration of Thunderbolt 3, the USB4 protocol can also support PD charging.
Therefore, on the Type-C interface of the computer, some only support charging, some only support data transmission, and some support signal transmission. What the Type-C interface can do and how it performs depends on which protocols it supports. Don't blindly see Type-C and think it is very advanced.
As far as image transmission is concerned, the strongest is DP2.0, which can reach 77.37Gbps, but in terms of overall quality, it still uses USB4 protocol Type-C. With a transmission rate of 40Gbps (which can meet 4K/144/10bit), it also supports PD charging up to 100 watts, and it also has USB expansion function, which is the best choice for notebook external monitors.
The so-called USB extensions, such as ultrabooks, only have one Type-C interface, and this interface is connected to an external display. At this time, it is necessary to intervene in devices such as a mouse, keyboard, and mobile hard disk with a USB interface, but the notebook does not provide these interfaces. At this time, these devices can be connected to the USB interface of the monitor.
Connecting these devices to the USB interface of the monitor alone cannot be driven, but through the Type-C interface, these USB devices can be driven through a notebook.
Thunderbolt interface
This interface is the most used by Apple. In the Thunderbolt 1 and Thunderbolt 2 standards, the interface shape adopted is the appearance of MiniDP. Starting from Thunderbolt 3, the interface appearance of Type-C is adopted. So Thunderbolt 3 and Type-C ports have the same shape, how to distinguish them?
There will be a lightning icon next to the Thunderbolt interface.
In fact, whether it is the Thunderbolt 3 interface or the Type-C interface that adopts the USB4 protocol, there is no difference in signal transmission between them. They both have a transmission rate of 40Gbps and a PD charging protocol of up to 100W. The difference is that Type-C supports US extension, while Thunderbolt 3 supports daisy chain.
Now that the interface is finished, what interface should I use?
If it is a notebook external connection and you want to solve all the problems with one cable, then the Type-C interface is undoubtedly the best choice, but you should pay attention to the protocols it supports when choosing.
Secondly, different resolutions, color depth outputs, and refresh rates have different requirements for interfaces. The formula for calculating the screen display bandwidth of the monitor is as follows:
Total pixels * sub-pixels * color depth * refresh rate = total bandwidth
Total pixels = horizontal resolution * vertical resolution
Sub-pixel = RGB pigment number = 3
Suppose you want to output 4K, 10bit, 144Hz picture, the formula is as follows
3840*2160*3*10bit*144 = 35.8Gbps.
In fact, due to differences in signal transmission standards, redundant data is required for signal confirmation during transmission. Typically the transmitted data is about 20% higher than the displayed data. Therefore, the transmission rate requirement for 4K/144/10bit should be 35.8Gbps*1.2=42.9Gbps.
Under the premise of single-line transmission, only DP2.1 can meet this transmission requirement. The transmission rate of Type-C, Thunderbolt 3, and HDMI2.1 of the USB4 protocol is 40Gbps. In this screen transmission, either the color depth output is compressed or the refresh rate is reduced, which cannot meet the original output.
For the output requirements of other resolutions, refresh rates and color depths, you can convert them yourself according to the parameters.
