SN65MLVD203B datasheet(23/40 Pages) TI

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10 Layout

10.1 Layout Guidelines

10.1.1 Microstrip vs. Stripline Topologies

As per SLLD009, printed-circuit boards usually offer designers two transmission line options: Microstrip and

stripline. Microstrips are traces on the outer layer of a PCB, as shown in Figure 10-1.

Figure 10-1. Microstrip Topology

On the other hand, striplines are traces between two ground planes. Striplines are less prone to emissions and

susceptibility problems because the reference planes effectively shield the embedded traces. However, from the

standpoint of high-speed transmission, juxtaposing two planes creates additional capacitance. TI recommends

routing M-LVDS signals on microstrip transmission lines if possible. The PCB traces allow designers to specify

the necessary tolerances for ZO based on the overall noise budget and reflection allowances. Footnotes 12, 23,

and 34 provide formulas for ZO and tPD for differential and single-ended traces. 2 3 4

Figure 10-2. Stripline Topology

10.1.2 Dielectric Type and Board Construction

The speeds at which signals travel across the board dictates the choice of dielectric. FR-4, or equivalent, usually

provides adequate performance for use with M-LVDS signals. If rise or fall times of TTL/CMOS signals are less

than 500 ps, empirical results indicate that a material with a dielectric constant near 3.4, such as Rogers™ 4350

or Nelco N4000-13 is better suited. Once the designer chooses the dielectric, there are several parameters

2 Howard Johnson & Martin Graham.1993. High Speed Digital Design – A Handbook of Black Magic.

Prentice Hall PRT. ISBN number 013395724.

3 Mark I. Montrose. 1996. Printed Circuit Board Design Techniques for EMC Compliance. IEEE Press. ISBN

number 0780311310.

4 Clyde F. Coombs, Jr. Ed, Printed Circuits Handbook, McGraw Hill, ISBN number 0070127549.

www.ti.com

SN65MLVD203B

SLLSFG7 – AUGUST 2020

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