AN-5017 Datasheet, PDF (1/5 Pages) Fairchild Semiconductor – LVDS Fundamentals

AN-5017
LVDS Fundamentals
Fairchild Semiconductor
Application Note
December 2000
Revised June 2005
Introduction
With the recent developments in the communications mar-
ket, the demand for throughput is becoming increasingly
more crucial. Although older differential technologies pro-
vide significant signal integrity benefits compared to single-
ended technologies, many of them consume much more
power at lower throughput than LVDS.
The LVDS standard was created to address applications in
the data communications, telecommunications, server,
peripheral, and computer markets where high-speed data
transfer is necessary. LVDS offers a low cost, high speed,
low power solution when compared to the standards of the
past.
What is LVDS?
LVDS is defined in the TIA/EIA-644 standard. It is a low
voltage, low power, differential technology used primarily
for point-to-point and multi-drop cable driving applications.
The standard was developed under the Data Transmission
Interface committee TR30.2. It specifies a maximum data
rate of 655 Mbps although some of today’s applications are
pushing well above this specification for a serial data
stream.
Compared to other differential cable driving standards like
RS422 and RS485, LVDS has the lowest differential swing
with a typical voltage swing of 350 mV with a typical offset
voltage of 1.25V above ground. See Figure 1.
FIGURE 1. Signal Level Comparison
LVDS features a low swing differential constant current
source configuration which supports fast switching speeds
and low power consumption. Figure 2 shows this configu-
ration. This allows for other features not found in single
ended technologies such as Common Mode Rejection and
Failsafe, which will be discussed later in this application
note.
FIGURE 2. Driver/Receiver Schematic
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