SN65LVDS1, SN65LVDS2, SN65LVDT2

SLLS373L – JULY 1999 – REVISED DECEMBER 2014

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Layout Guidelines (continued)

In the case of two adjacent single-ended traces, one should use the 3-W rule, which stipulates that the distance

between two traces must be greater than two times the width of a single trace, or three times its width measured

from trace center to trace center. This increased separation effectively reduces the potential for crosstalk. The

same rule should be applied to the separation between adjacent LVDS differential pairs, whether the traces are

edge-coupled or broad-side-coupled.

Figure 28. 3-W Rule for Single-Ended and Differential Traces (Top View)

You should exercise caution when using autorouters, because they do not always account for all factors affecting

crosstalk and signal reflection. For instance, it is best to avoid sharp 90° turns to prevent discontinuities in the

signal path. Using successive 45° turns tends to minimize reflections.

12.1.5 Crosstalk and Ground Bounce Minimization

To reduce crosstalk, it is important to provide a return path to high-frequency currents that is as close as possible

to its originating trace. A ground plane usually achieves this. Because the returning currents always choose the

path of lowest inductance, they are most likely to return directly under the original trace, thus minimizing

crosstalk. Lowering the area of the current loop lowers the potential for crosstalk. Traces kept as short as

possible with an uninterrupted ground plane running beneath them emit the minimum amount of electromagnetic

field strength. Discontinuities in the ground plane increase the return path inductance and should be avoided.

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