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ADN4697E_

LVDS and M-LVDS Circuit Implementation Guide

Analog Devices 

AN-1177

Application Note

For Type 1 M-LVDS receivers, a positive VOD ≥ +50 mV

corresponds to a Logic 1 and a negative VOD ≤ −50 mV

corresponds to a Logic 0.

In between these voltage thresholds is the transition region.

If an input signal remains at a voltage level between the

thresholds, the receiver output is undefined under LVDS; it

can be high or low. This can occur if no active LVDS driver is

connected to the receiver, or if there is a short circuit. Analog

Devices LVDS receivers incorporate a failsafe feature, so that in

these cases, the receiver output is high.

LVDS

RECEIVER

OUTPUT

M-LVDS TYPE 1

RECEIVER

OUTPUT

M-LVDS TYPE 2

RECEIVER

OUTPUT

(depending on the cable type). M-LVDS can generally be

transmitted across longer cables due to the increased driver

strength, but data rates of hundreds of Mbps require shorter

cables than data rates of only tens of Mbps. Figure 12 provides

a general indication of the combinations of LVDS and M-LVDS

data rates and cable lengths typical for some applications.

1200

1000

800

LVDS

600

0.15

0.10

0.05

0

–0.05

–0.10

–0.15

LOGIC 1

UNDEFINED*

LOGIC 0

LOGIC 1

UNDEFINED

LOGIC 0

LOGIC 1

UNDEFINED

LOGIC 0

0.15

0.10

0.05

0

–0.05

–0.10

–0.15

*LOGIC 1 FOR LVDS RECEIVERS WITH FAILSAFE

Figure 11. Receiver Thresholds for LVDS and M-LVDS

With M-LVDS, any node on the bus can transmit, but when

no node is active, all driver outputs are disabled. As with LVDS,

this results in a differential output voltage in the undefined

region for Type 1 receivers. In order to provide a failsafe

condition, M-LVDS defines Type 2 receivers that have an

offset receiver threshold of >= +150 mV for a logic high and

<= +50 mV for a logic low. This means that the failsafe output

from Type 2 M-LVDS receivers is a logic low. Receiver

thresholds are shown in Figure 11 for LVDS receivers, M-LVDS

Type 1 receivers and M-LVDS Type 2 receivers.

TRANSMISSION DISTANCE

Both LVDS and M-LVDS transmission distances are affected by

two main factors: the transmission medium and the data rate.

The standard deciding factor of whether a given transmission

distance is practical, is how much jitter is observed by receiving

nodes. This is application dependent; some applications require

5% or less jitter, whereas others tolerate up to 20%.

PCB traces typically allow transmission distances on the order

of tens of centimeters, whereas twisted pair cable allows

transmission on the order of meters for LVDS or tens of meters

for M-LVDS. Different specifications of PCB construction or

cable types affect the signal differently and thus have an impact

on the maximum transmission distance.

Higher data rates greatly constrain the transmission distance;

LVDS at 1 Gbps might only be transmitted across high-quality

cables of 1 meter (possibly with additional signal conditioning),

but at 100 Mbps may be transmitted across 10 meters

400

M-LVDS

200

0

0

5

10

15

20

25

CABLE LENGTH (m)

Figure 12. Cable Length (Twisted-Pair) vs. Data Rate for Some Typical LVDS

and M-LVDS Applications

Other factors influencing the maximum distance include:

• The transmitter specifications.

• Other transmission medium components, such as vias (on

PCB traces) or connectors for cables.

• For M-LVDS or multi-drop LVDS, the number of nodes on

the bus and the stub lengths.

TIA/EIA-644 (LVDS) and TIA/EIA-899 (M-LVDS) recommend

testing intended cable lengths in the application if possible, due

to the multiple factors involved that affect the possible cable

length. This allows the jitter on the received signal to be

measured, providing a guide as to how practical a given cable

type and length is. Measurements can be taken using an eye

diagram; the ADN4696E driver output is shown in Figure 13.

1ns/DIV

Figure 13. ADN4696E Driver Output Eye Diagram

Rev. 0 | Page 6 of 12

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