Link Between Signal Integrity and Impedance Matching

Impedance matching is needed to prevent reflections when a signal propagates along an interconnect. When the interconnect and the load’s input impedance are unequal, there will be a reflection at the interface between them. But, what does a reflection mean in an interconnect? And, more specifically, what signal-integrity problems can be attributed to impedance mismatches?

When reflections occur at an impedance mismatch, the resulting reflection can create multiple signal-integrity problems like standing waves and resonance, intersymbol interference (ISI), and low power transfer to the load: When power is reflected from an impedance mismatch, the load will not receive the power to run properly. For digital signals, strong reflections can prevent a logic circuit from switching.

An impedance mismatch can be evaluated and its effects on signal integrity can be determined. When you extract an impedance mismatch from a finished layout, you can determine how interconnects and circuits might need to change to ensure signal integrity. Some possible changes include the addition of termination components, careful design of impedance-matching networks, and redesigning traces to adjust their impedance.

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Team SimTech

Cadence Design Systems