AN-1177
APPLICATION NOTE
One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
LVDS and M-LVDS Circuit Implementation Guide
by Dr. Conal Watterson
INTRODUCTION
LVDS/M-LVDS APPLICATION CONSIDERATIONS
Low voltage differential signaling (LVDS) is a standard for
communicating at high speed in point-to-point applications.
Multipoint LVDS (M-LVDS) is a similar standard for multi-
point applications. Both LVDS and M-LVDS use differential
signaling, a two-wire communication method where receivers
detect data based on the voltage difference between two
complementary electrical signals. This greatly improves noise
immunity and minimizes emissions.
This application note considers the following aspects
concerning LVDS/M-LVDS circuit implementation:
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Bus types and topologies
Clock distribution applications
Characteristics of LVDS/M-LVDS signaling
Termination and PCB layout
Jitter and skew
Data encoding and synchronization
Isolation
LVDS
LVDS is a lower power alternative to emitter-coupled logic
(ECL) or positive emitter-coupled logic (PECL).The primary
standard for LVDS is TIA/EIA-644. An alternative standard
sometimes used for LVDS is IEEE 1596.3—SCI, scalable
coherent interface. LVDS has been widely adopted for high-
speed backplane, cabled, and board-to-board data transmission
and clock distribution, as well as communication links within a
single PCB.
WHY USE LVDS OR M-LVDS?
LVDS and M-LVDS are compared to other multipoint and point-
to-point protocols in Figure 1. Both standards have low power
requirements. LVDS and M-LVDS are characterized by differential
signaling with a low differential voltage swing. M-LVDS specifies
an increased differential output voltage compared to LVDS in order
to allow for the increased load from a multipoint bus.
Both protocols are designed for high-speed communication.
Typical applications utilize PCB traces or short wired/backplane
links. The common mode range of LVDS is designed for these
applications. M-LVDS has an extended common mode range
compared to LVDS to allow for the additional noise in a multipoint
topology.
Advantages of LVDS include
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Communication at speeds of up to 1 Gbps or more
Reduced electromagnetic emissions
Increased immunity to noise
Low power operation
Common-mode range allowing differences of up to 1 V
in ground offset
MULTIPOINT
LOW POWER, HIGH SPEED
MEDIUM DISTANCES (MAX. 20m TO 40m)
TYP. DATA RATE: 100Mbps, 200Mbps
M-LVDS
M-LVDS
The standard TIA/EIA-899 for multipoint low voltage differ-
ential signaling (M-LVDS) extends LVDS to address multipoint
applications. M-LVDS allows higher speed communication
links than TIA/EIA-485 (RS-485) or controller area network
(CAN) with lower power. See the References section for a list of
the standards referred to in this application note.
LONG DISTANCES (>1km)
TYP. MAX. DATA RATE: 16Mbps
RS-485
ROBUST PROTOCOL
MEDIUM DISTANCES (MAX. 40m)
MAX. DATA RATE: 1Mbps
CAN
POINT-TO-POINT
Additional features of M-LVDS over LVDS include
LOW POWER, HIGH SPEED
SHORT DISTANCES (MAX. 5m TO 10m)
MAX. DATA RATE: >1Gbps
LVDS
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Increased driver output strength
Controlled transition times
Extended common-mode range
HIGH SPEED
SHORT DISTANCES
MAX. DATA RATE: ~3Gbps
PECL
Option of failsafe receivers for bus idle condition
Figure 1. Comparison of Communication Standards
Rev. 0 | Page 1 of 12
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