DVI

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DVI是一种视频信号传输的标准，专为提高液晶显示器、等离子显示器、投影仪等平板显示设备的图像质量而设计，由Digital Display Working Group(DDWG)提出。

[编辑] 概述

The DVI interface uses a digital protocol in which the desired brightness of pixels is transmitted as binary data. When the display is driven at its native resolution, all it has to do is read each number and apply that brightness to the appropriate pixel. In this way, each pixel in the output buffer of the source device corresponds directly to one pixel in the display device, whereas with an analog signal the appearance of each pixel may be affected by its adjacent pixels as well as by electrical noise and other forms of analog distortion.

Previous standards such as the analog VGA were designed for CRT-based devices and thus did not use discrete time. As the analog source transmits each horizontal line of the image, it varies its output voltage to represent the desired brightness. In a CRT device, this is used to vary the intensity of the scanning beam as it moves across the screen.

However, when using digital displays (such as LCD) with analog signals (such as VGA), there is an array of discrete pixels and a single brightness value must be chosen for each. The decoder does this by sampling the voltage of the input signal at regular intervals. When the source is also a digital device (such as a computer), this can lead to distortion if the samples are not taken at the center of each pixel, and there are also problems with crosstalk.

[编辑] 信号编码原理

DVI信号是将显卡中经过处理的待显示R.G.B数字信号与H.V信号进行组合，按最小非归零编码，将每个像素点按10hit的数字信号进行并→串转换，把编码后的R.G..B数字流与像素时钟等4组信号按照T.M.D.S.方式进行传输，其每路码流速率为原像素点时钟的10倍，以1024×768×70的分辨率为例，像素时钟为75MHz，码流时钟为75MHz×10,为0.75GHz。一般DVI的码流在0.24GHz到1.65GHz之间。

[编辑] 接口定义

Image:DVI interface.jpg

[编辑] Technical discussion

The data format used by DVI is based on the PanelLink serial format devised by the semiconductor manufacturer Silicon Image Inc. This uses Transition Minimized Differential Signaling (TMDS). A single DVI link consists of four twisted pairs of wire (red, green, blue, and clock) to transmit 24 bits per pixel. The timing of the signal almost exactly matches that of an analog video signal. The picture is transmitted line by line with blanking intervals between each line and each frame, and without packetization. No compression is used and DVI has no provision for only transmitting changed parts of the image. This means the whole frame is constantly re-transmitted.

With a single DVI link, the largest resolution possible at 60Hz is 2.6 megapixels. The DVI connector therefore has provision for a second link, containing another set of red, green, and blue twisted pairs. When more bandwidth is required than is possible with a single link, the second link is enabled, and alternate pixels may be transmitted on each. The DVI specification mandates a fixed single link cutoff point of 165 MHz, where all display modes that require less than this must use single link mode, and all those that require more must switch to dual link mode. When both links are in use, the pixel rate on each may exceed 165 MHz. The second link can also be used when more than 24 bits per pixel is required, in which case it carries the least significant bits.

Like modern analog VGA connectors, the DVI connector includes pins for the display data channel, version 2 (DDC 2) that allows the graphics adapter to read the monitor's extended display identification data (EDID).

[编辑] 接口分类

DVI有DVI1.0和DVI2.0两种标准，其中DVI1.0仅用了其中的一组信号传输信道(data0-data2)，传输图像的最高像素时钟为165M，信道中的最高信号传输码流为1.65GHz，最高分辨率可达1600×1200×60。而DVI2.0则用了全部的两组信号传输信道(data0-data5)，传输图像的最高像素时钟为330M，可支持1920×1280分辨率，支持HDMI格式，每组信道中的最高信号传输码流也为1.65GHz。目前还没有DVI2.0的应用，因此目前所说的DVI都是指DVI1.0标准。

DVI定义了DVI-I(Integrated)和DVI-D(Digital)两种接口，从接口定义上可以看出，DVI-I实际上是在DVI-D的基础上增加了模拟接口。

A Male DVI-I Plug

[编辑] Connector

DVI connector pins (view of plug)

The DVI connector usually contains pins to pass the DVI-native digital video signals. In the case of dual-link systems, additional pins are provided for the second set of data signals.

The DVI connector may also incorporate pins to pass through the legacy analog signals using the VGA standard. This feature was included in order to make DVI universal, as it allows either type of monitor (analog or digital) to be operated from the same connector.

The DVI connector on a device is therefore given one of three names, depending on which signals it implements:

• DVI-D (digital only)
• DVI-A (analog only)
• DVI-I (digital & analog)

The connector also includes provision for a second data link for high resolution displays, though many devices do not implement this. In those that do, the connector is sometimes referred to as DVI-DL (dual link).

DVI is the only widespread standard that includes analog and digital transmission options in the same connector. Competing standards are exclusively digital: these include a system using low-voltage differential signalling (LVDS), known by its proprietary names FPD (for Flat-Panel Display) Link and FLATLINK; and its successors, the LVDS Display Interface (LDI) and OpenLDI.

USB signals are not incorporated into the connector, as they were into the VESA M1-DA connector used by InFocus on their projector systems, and in the Apple Display Connector, which was used by Apple Computer until 2005. The VESA M1 connector is essentially the VESA Plug & Display (P&D) connector, which was itself originally named the Enhanced Video Connector (EVC). The pinout of the Apple Display Connector is electrically compatible with the VESA P&D/M1, but physically the shell of the connector is a different shape.

Some new DVD players, TV sets (including HDTV sets) and video projectors have DVI/HDCP connectors; these are physically the same as DVI connectors but transmit an encrypted signal using the HDCP protocol for copyright protection. Computers with DVI video connectors can use many DVI-equipped HDTV sets as a display.

[编辑] 技术指标

[编辑] 数字指标

• Minimum clock frequency: 21.76 MHz
• Maximum clock frequency in single link mode: Capped at 165 MHz (3.7 Gbit/s)
• Maximum clock frequency in dual link mode: Limited only by cable quality (more than 7.4 Gbit/s)
• Pixels per clock cycle: 1 (single link) or 2 (dual link)
• Bits per pixel: 24

• Example display modes (single link):
  • HDTV (1920 × 1080) @ 60 Hz with 5% LCD blanking (131 MHz)
  • UXGA (1600 × 1200) @ 60 Hz with GTF blanking (161 MHz)
  • WUXGA (1920 × 1200) @ 60 Hz (154 MHz)
  • SXGA (1280 × 1024) @ 85 Hz with GTF blanking (159 MHz)
• Example display modes (dual link):
  • QXGA (2048 × 1536) @ 75 Hz with GTF blanking (2×170 MHz)
  • HDTV (1920 × 1080) @ 85 Hz with GTF blanking (2×126 MHz)
  • WQXGA (2560 × 1600) pixels (30" LCD)
  • WQUXGA (3840 × 2400) @ 41 Hz

GTF (Generalized Timing Formula) is a VESA standard.

[编辑] 模拟指标

• RGB bandwidth: 400 MHz at −3 dB

[编辑] 参见

• ADC - Apple Display Connector, a similar, now-obsolete connector that can still be found on some older Macs.
• VGA connector analog video (an older standard, though very common on current computer hardware)
• High-Definition Multimedia Interface (HDMI), a forward-compatible standard, that also includes digital audio transmission
• Unified Display Interface (UDI), a proposed future standard to replace both DVI and HDMI
• DisplayPort, another proposed standard, incompatible with DVI and HDMI
• LCD TV
• DMS-59, a way to combine 2 analog and 2 digital signals in one connector
• DFP an older type of digital video link

[编辑] 外部连接

• The DVI specification at the Digital Display Working Group
• DVI video pinout
• DVI Basics Guide