PCB Transmission Lines and Controlled Impedance
In high-speed PCB designs, controlling impedance is crucial for signal integrity. Transmission lines—specific trace structures
on the PCB—help maintain consistent impedance, minimizing signal reflections and preserving signal quality. Here's an
overview of common transmission line types and essential factors to consider for impedance control.
Types of Transmission Lines
1. Microstrip: A single trace routed on an outer layer above a reference ground plane.
Microstrip view on a PCB
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●Application: Suitable for high-speed signals, often used for signals where surface routing is needed.
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●Impedance Control: Depends on trace width, height above the ground plane, and PCB material.
2. Stripline: A trace sandwiched between two ground planes within inner layers of the PCB.
Stripline view in a PCB
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Application: Provides better isolation from external interference, making it ideal for noise-sensitive signals.
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Impedance Control: Controlled by trace width, spacing from ground planes, and dielectric constant of surrounding
materials.
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OrCAD X High-Speed Digital Design Guide
