IPC International Community magazine an association member publication
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100 I-CONNECT007 MAGAZINE I MAY 2026 In high-speed designs, the distinction between common-mode and differential-mode is becoming increasingly critical in PCB routing. While most designers are familiar with differential routing as a technique for certain signals on the PCB, many may not realize its underlying purpose. Differential routing is used to mitigate differential mode noise in the system. To understand this, we need a bit of electrical engineering background on signal and current flow in a system. The current that flows from the source (driver) down the positive trace to the load (receiver) flows in a loop, and within that loop, the current is con- stant. This current must return (RTN) from the load (receiver) back to the source (driver). Because the current flows in one direction from the driver to the receiver and then in the opposite direction from the receiver back to the driver, these two currents are thought to be equal in magnitude and opposite in polarity. This means any noise from the sources is moving in different directions, creating differen- tial noise. Common-mode noise, on the other hand, occurs when noise (current) from an external source, such as EMI, appears on both the signal line and the re- turn line traveling in the same (common) direction. 100 I-CONNECT007 MAGAZINE I MAY 2026 BY K R I ST I N M OY E R , G LO BA L E L ECT RO N I C S AS S O C I AT I O N Common vs. Differential Mode in Routing and Signal Integrity F E AT U R E A RT I C L E