8.4 Layout

8.4.1 Layout Guidelines

Reflections and matching are closely related to loop antenna theory, but different enough to warrant their

own discussion. When a PCB trace turns a corner at a 90° angle, a reflection can occur. This reflection is

primarily due to the change of width of the trace. At the apex of the turn, the trace width is increased to 1.414

times its width. This upsets the transmission line characteristics, especially the distributed capacitance and

self–inductance of the trace — resulting in the reflection. It is a given that not all PCB traces can be straight, and

so they will have to turn corners. Figure 8-3 shows progressively better techniques of rounding corners. Only the

last example maintains constant trace width and minimizes reflections.

8.4.2 Layout Example

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Figure 8-3. Trace Example

CD4053B-Q1

SCHS469 – MARCH 2025

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