How to Terminate LVDS Connections
Yaser Ibrahim, High-Speed Data and Clocks Group
Connecting an LVDS driver, such as DS90LV011A,
DS90LV027A, or DS90LV047A, to an LVDS receiver,
such as DS90LV012A, DS90LV028A, or
DS90LV048A, is fairly simple and only requires a 100-
Ω
differential termination resistor across the input
terminal pair of the receiver as shown in
Figure 1.
This
termination resistor, which should be placed as close
to the receiver as possible, is needed to generate the
differential voltage across the receiver inputs, and to
match the transmission line impedance to reduce
reflections. Some LVDS receivers have integrated
100-Ω termination resistors, such as DS90LT012A,
SN65LVDT34, or SN65LVDT32B. An external
termination should not be used when using such a
receiver.
Zo = 50
Ÿ
100
LVDS Driver
Zo = 50
Ÿ
LVDS Receiver
Figure 2. Alternative LVDS Connection with DC
Coupling
AC Coupling Configuration
Figure 3
shows the termination in the case of AC-
coupled configuration. Note that for AC coupling the
data transmitted needs to be DC-balanced (for
example, using 8b/10b encoding). In
Figure 3,
the
resistor network at the input of the receiver restores
the DC common mode to 1.2 V (assuming Vcc= 3.3 V)
which is in the middle of the input common mode
range for a standard LVDS receiver. Additionally, the
resistor network provides the 100-Ω termination at the
input of the receiver. If a termination resistor is
integrated into the LVDS receiver, then larger resistor
values should be selected in order not to alter the
effective termination resistance at the input of the
receiver. Suggested values are 10 kΩ for the pull up
and 5.7 kΩ for the pull down. The value of AC coupling
capacitors depends on the operating frequency, as it
needs to block the DC component, but look like a short
circuit for the AC component. A capacitor value of 0.1
µF should be adequate for high data rates (1 Mbps
and above).
V
CC
V
CC
Figure 1. LVDS Connection with DC Coupling
An alternative termination scheme is shown in
Figure 2,
which has a split termination and a capacitor
from the center tap to ground. The capacitor filters
common-mode noise and helps with transmission line
skew (which could be due to differential lines
mismatch or driver output skew). The value of the
capacitors depends on the operating frequency, as it
needs to look like a short circuit for the AC component
of the signal. A capacitor value of 0.1 µF should be
adequate for most high data rates (1 Mbps and
above).
130
0.1
…F
Zo = 50
Ÿ
LVDS Driver
Zo = 50
Ÿ
0.1
…F
130
50
DC Coupling Configuration
Zo = 50
Ÿ
0.1 µF
This document discusses termination and biasing
schemes for LVDS drivers and receivers with DC and
AC coupling configurations. It also shows termination
schemes for multidrop and multipoint (M-LVDS)
connections.
Zo = 50
Ÿ
LVDS Driver
50
LVDS Receiver
LVDS Receiver
82
Figure 3. LVDS Connection with AC Coupling
82
SLAA840 – May 2018
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How to Terminate LVDS Connections
Yaser Ibrahim, High-Speed Data and Clocks Group
Copyright © 2018, Texas Instruments Incorporated
1
www.ti.com
An alternative circuit is shown in
Figure 4
which uses a
split termination and a capacitor, in addition to a
biasing resistor network. The capacitor filters common-
mode noise and helps with transmission line skew.
Another advantage of this circuit is lower power
consumption when compared to the circuit in
Figure 3.
V
CC
10 k
Zo = 50
Ÿ
LVDS Driver
Zo = 50
Ÿ
0.1
…F
50
Multidrop LVDS Termination
When using LVDS transceivers in a multidrop
configuration, only one termination is needed which is
placed at the input terminals of the farthest receiver as
shown in
Figure 7.
Zo = 50 Ÿ
100
0.1
…F
LVDS Driver
Zo = 50 Ÿ
LVDS Receiver
0.1
…F
LVDS Receiver
5.7 k
LVDS
Receiver
LVDS
Receiver
50
...
Figure 4. Alternative LVDS Connection with AC
Coupling
Another variation on the circuit in
Figure 3
is shown in
Figure 5.
It uses only one pair of resistors to provide
the biasing on the negative input terminal. The positive
input terminal will also get the common mode voltage
through the 100-Ω termination. The advantage of this
method is reduced component count. The
disadvantage is that there is some differential skew
between the positive and negative input terminals.
V
CC
Figure 7. Multidrop LVDS Termination
M-LVDS Termination
When using M-LVDS transceivers, such as
SN65MLVD206B, SN65MLVD204B, or
SN65MLVD040, in a half duplex multipoint
configuration, termination is needed on both ends of
the bus as shown in
Figure 8.
It is not necessary to
place the termination close the receivers, rather at the
farthest points of both ends of the bus.
Zo = 50
Ÿ
100
100
Zo = 50
Ÿ
MLVDS
Xceiver
MLVDS
Xceiver
0.1
…F
Zo = 50
Ÿ
10 k
Zo = 50
Ÿ
0.1
…F
5.7k
100
LVDS Driver
LVDS Receiver
...
Figure 8. Half Duplex M-LVDS Termination
If using full duplex M-LVDS transceivers, such as
SN65MLVD205A or SN65MLVD207, then two
differential pairs are utilized, and each of them needs
two terminations on both ends of the connection as
shown in
Figure 9.
Zo = 50
Ÿ
100
100
Zo = 50
Ÿ
Zo = 50
Ÿ
100
100
Zo = 50
Ÿ
RX
TX
Figure 5. AC-Coupled LVDS Connection with
Reduced Component Count
When using an LVDS receiver with a wide common
mode range, such as SN65LVDS33, SN65LVDS34,
SN65LVDS348, and SN65LVDS352, which have an
input common mode range from –4V to 5V, a common
mode biasing resistor network is not needed. Only the
100-Ω termination is needed, as shown in
Figure 6.
0.1
…F
Zo = 50
Ÿ
100
LVDS Driver
Zo = 50
Ÿ
0.1
…F
LVDS Receiver
...
RX
TX
Figure 6. AC-Coupled LVDS Connection When
Using Wide Common Mode LVDS Receiver
2
How to Terminate LVDS Connections
Yaser Ibrahim, High-Speed Data and Clocks Group
Figure 9. Full Duplex M-LVDS Termination
SLAA840 – May 2018
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Copyright © 2018, Texas Instruments Incorporated
MLVDS
Xceiver
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