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Low Voltage Differential Signaling (LVDS) technology is redefining data transmission at the physical layer interface. It is bringing high speeds and low power to this critical interface -- an essential step in meeting the high bandwidth requirements of tomorrow's networking, telecommunications and multimedia applications. This backgrounder answers the basic questions regarding LVDS technology: what is it, where is it used, why is it important and how does it work.

What is LVDS?

LVDS is a new data interface standard that is defined in the TIA/EIA-644 and the IEEE 1596.3 standards. It is essentially a signaling method used for high-speed transmission of binary data over copper. It uses a lower voltage swing than other transmission standards. This low voltage differential is what delivers higher data transmission speeds and inherently greater bandwidth at lower power consumption.

LVDS can achieve signaling rates as high as 655 megabits per second (Mbps). It consumes as little as one-eighth the power of RS-422 drivers. Since the receivers respond only to differential voltages, they are relatively immune to noise such as common-mode signal reflections. In addition, LVDS emits less electromagnetic interference (EMI) than other data transmission standards.

Where is LVDS used?

General purpose LVDS technology addresses point-to-point physical layer interfaces. These include intra-system connections via printed circuit board traces or cables. The ultimate rate and distance of LVDS data transfer is dependent on the attenuation characteristics of the media and the noise coupling to the environment.

Applications for general purpose LVDS include central office, PBXs, switches, repeaters and basestations -- all in the telecommunications field. In addition, it is used in hubs and routers in data communications, and other applications such as digital cameras, printers and copiers.

Outside the TIA/EIA 644 standard lies multipoint LVDS. Multipoint LVDS supports backplane applications such as proprietary buses and small computer system interface or SCSI. SCSI is a high-performance peripheral interface that distributes data independently of the host computer. It's used with devices such as hard disk drives, tape drives, CD-ROMs and scanners.

In addition to general purpose point-to-point applications and multipoint applications, LVDS has been used for several years as an interface to flat panel displays. As a result, it is used extensively in notebook computers.

Why is LVDS important?

Physical layer interfaces are often a critical bottleneck in any application that requires high bandwidths, such as telecommunications and high-speed networking. For example, achieving higher data transmission on the backplane in a wireless basestation is critical to increasing the variety of services offered over wireless phones -- services such as full Internet capability, sending and receiving email and someday, even high-quality video.

With its high speeds, low power and low cost profile, LVDS is today the most promising technology to address the physical layer interface. A direct comparison of LVDS to other data interface standards can be found in the accompanying fact sheet: "Profiles of Today's Data Transmission Standards."

How does LVDS work?

An LVDS driver converts a TTL/CMOS signal into a low-voltage differential signal. This differential signal can travel at rates up to 655 Mbps over media such as copper cables or printed circuit board traces to the LVDS receiver. The receiver then translates the differential signal back into a TTL/CMOS signal.

Using a differential signal reduces the system's susceptibility to noise and reduces EMI emissions -- in addition, to delivering high speeds. This results in a very cost-effective solution to some of the greatest bandwidth bottlenecks in many transmission applications.

LVDS offers designers flexibility around their power supply solution, working equally well at 5V, 3.3V and lower. As a result, designers can reuse their LVDS solution even as systems move to lower voltages.

Finally, LVDS has simple termination requirements -- usually one resistor at the inputs of the receiver compared to multiple resistor solutions for other standards.

Texas Instruments and LVDS

Texas Instruments (TI) introduced its first LVDS devices in 1996. Since then, the TI LVDS portfolio has grown to 17 devices -- making it one of the broadest in the industry. TI offers designers a variety of footprints, allowing them to choose the configuration that best fits their design application.

In addition, TI's LVDS product line is fully supported with documentation and evaluation tools. TI offers a Data Transmission data book to help designers select the appropriate LVDS device. The LVDS Designers Guide offers advice for effectively implementing an LVDS solution. Application notes offer designers solutions to their design challenges. In addition, evaluation modules (EVMs) are available to help designers evaluate TI's LVDS products.

TI is committed to LVDS technology and brings 30 years of leadership experience in data transmission to the LVDS market.