Digital Visual Interface (DVI) and other digital display interfaces

The push is on to make displays digital, whether they’re legacy CRTs (Cathode Ray Tubes) or newer LCDs (Liquid Crystal Displays)—because a digital monitor provides both excellent picture quality and higher transfer bandwidths.

There are three main types of digital video interfaces: P&D, DFP, and DVI. P&D (Plug & Display, also known as EVC), the earliest of these technologies, supports both digital and analogue RGB connections and is now used primarily on projectors. DFP ( Digital Flat-Panel Port) was the first digital-only connector on displays and graphics cards; it’s being phased out.

There are two types of DVI connectors in use: DVI-D and DVI-I. DVI-D is a digital-only connector like DFP, but it offers much faster data transfer and higher resolution along with power-saving modes. DVI-I handles both digital and analogue connections like P&D does, but it’s somewhat smaller. Manufacturers such as Intel®, IBM, Compaq®, HP®, Fujitsu®, and NEC® are backing DVI technology, particularly the DVI-I connector type because it can do what previously required separate analogue and digital connectors.

All these standards are based on transition-minimised differential signalling (TMDS). In a typical single-line digital signal, voltage is raised to a high level and decreased to a low level to create transitions that convey data. TMDS uses a pair of signal wires to minimise the number of transitions needed to transfer data. When one wire goes to a high-voltage state, the other goes to a low-voltage state. This balance increases the data-transfer rate and improves accuracy.