DVI digital display interface standard

Digital Visual Interface (DVI) is a display interface developed to adapt to the rapid development of digital flat panel displays. At present, most computers and external display devices are connected through an analog VGA interface. The display image information generated digitally inside the computer is converted into R, G, and B by the D/A (digital/analog) converter in the graphics card. The three primary color signals and horizontal and field synchronization signals are transmitted to the display device through cables. For analog display devices, such as analog CRT monitors, the signal is directly sent to the corresponding processing circuit to drive and control the picture tube to generate images. For digital display devices such as LCD and DLP, the display device needs to be equipped with a corresponding A/D (analog/digital) converter to convert analog signals into digital signals. After two conversions of D/A and A/D, some image details are inevitably lost.

There were also some digital interface standards before DVI, but they failed to become industrial standards. Currently, low voltage differential signaling (LVDS) digital interface is used in portable systems to connect to LCD displays, but this technology is not suitable for desktop displays. Other digital interfaces, such as the Digital Flat Panel (DFP) standard, the Video Electronics Standards Association's Plug and Display standard (VESA(r) Plug and Display), and the OpenLDI standard have also not been generally accepted by the industry. On the contrary, the DVI standard is expected to become the standard digital interface for flat panel displays. This was established in 1999 by the Digital Display Working Group (DDWG) composed of Silicon Image, Interl, Compaq, IBM, HP, NEC, Fujitsu and other companies. Digital display interface standard launched in April.

TMDS

The basis of the DVI standard is Silicon Image's PanelLink interface technology, which is a high-speed serial interface that uses Transition Minimized Differential Signaling (TMDS) to transmit data to the monitor.

TMDO transmits data through transitions between "on" and "off" states, using an advanced encoding algorithm such as Boolean exclusive OR (XOR) or exclusive non-OR (XNOR) operations to minimize transitions to avoid additional electromagnetic waves. Interference (EMI) effects on cables, with the addition of balanced direct current (DC) signal operation. Figure 1 shows the display data (pixel) flow of the TMDS mechanism, in which the input eight-bit data is encoded into ten-bit transition-minimized, DC-balanced characters. (The first eight bits are encoded data, the ninth bit is used to identify whether the data uses XOR or XNOR logic encoding, and the tenth bit is used for DC balance.)

As shown in Figure 1, DVI allows two TMDS chains, each chain consists of three data channels, used to transmit RGB information, with a maximum bandwidth of 165MHz, equivalent to 165M pixels per second.

Note: The bandwidth required for a given resolution is determined by the monitor's refresh frequency and blanking interval (including the sum of the line and field blanking intervals), and can be calculated by the following formula:

Resolution × refresh rate × (1 + blanking interval) = pixels/second

For example, to display SXGA resolution, 60Hz refresh rate, and 5% blanking interval, then:

1280×1024×60×1.05=82,565,360

In this case, it is shown that the required bandwidth of SXGA is 83MHz, and a single-chain TMDS utilizing 165MHz bandwidth is sufficient.

Table 1 reviews the resolutions of standard PC monitors. Table 2 summarizes the bandwidth allowed by the DVI1.0 specification. The bandwidth of a single chain supports flat panel display resolutions exceeding 1920×1080 (60Hz), and the bandwidth of a double chain is sufficient to support resolutions up to 2048×1536. Both chains share the same clock and therefore have the same bandwidth. The system allows both single- and dual-link connections, depending on monitor capabilities.

plug and play

The DVI specification supports hot plugging of DVI display devices (DVI monitors and display adapters). Although Microsoft's Windows operating system currently does not support hot plugging of DVI devices, future Windows operating systems will include this feature.

Table 1 Display resolution

Table 2 Resolutions supported by DVI1.0

DVI also supports VESA's Display Data Channel (DDC) and Extended Display Identification Data (EDID) specifications. DDC is a standard communication channel between display adapters and monitors; EDID is a standard data format that contains monitor information, such as manufacturer information, monitor timing, maximum image size and color performance. EDID information is stored in the display and communicated via DDC. EDID and DDC allow communication between the system, monitor, and graphics adapter so that the system can be configured based on the monitor's characteristics.

DVI connector

The DVI connector has 24 pins and can accommodate two TMDS chains and VESA DDC and EDID. The DVI specification defines two types of connectors:

*DVI-Digital (DVI-D), only supports digital displays

*DVI-Integrated (DVI-I), supports digital displays and is compatible with analog displays.

Shown in Figure 2 are the DVI-D and DVI-I sockets located on the back of the PC. The DVI-D connector from a digital flat panel display has a 12-pin or 24-pin socket (a single-chain DVI-I plug uses only 12 or 24 pins). The DVI-I connector accepts a 12-pin or 24-pin DVI plug, or A new type of analog plug with 4 additional pins and a ground plane to maintain constant impedance for analog RGB signals.

Chipset supporting DVI standard

There are currently several manufacturers that provide DVI chipsets that support personal computers and digital displays, with leading ones including Silicon and TI. Among them, TI has launched five new transmitters and seven receiver chips, all of which use TMDS core technology and are compatible with DVI1.0. The new components offer a wide frequency range (25 to 165MHz) and support a variety of display resolutions, from VGA to UXGA. DVI transmitters can be used in notebook computers, desktop computers, and full-featured personal computers; DVI receivers can be used in LCD monitors, digital monitors, and digital projectors.

Application of DVI interface standard in LCD flat panel displays

At present, some companies have successfully applied the DVI standard to digital flat-panel displays. For example, Shanghai Contech Electronic Technology Co., Ltd. has applied it to 17-inch LCD displays. This solution uses Silicon Image's chip SiI151 as the DVI receiver, which converts the TMDS signal into a dual-pixel RGB digital signal, sends it to the image scaling chip for processing, and then outputs it to the LCD screen. The system block diagram is shown in Figure 3. This product also has a DDC channel and can be plug-and-play. After testing, when the DVI interface cable length is 15 meters, the image is clear without interference or distortion.