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36 I-CONNECT007 MAGAZINE I OCTOBER 2026 (not a signal), which requires the existence of both electric and magnetic fields. When energy is not moving, the magnetic field is zero. Inductance and Signal Integrity: The Geometry of Crosstalk, Noise, and Delay When current flows through a conductor, a magnet- ic field is produced. When a second conductor car- rying current is brought into proximity, a force acts between them. If both currents flow in the same di- rection, then they are additive (think of two parallel trace segments). When the currents flow in oppo- site directions (think of a trace over a return plane), the currents cancel. This implies that two individual traces should be kept well apart to reduce cross- talk, whilst a signal trace should be tightly coupled to its return path (plane) to increase coupling and reduce inductance. Figure 1 illustrates the near-end (NEXT) and far-end (FEXT) crosstalk on victim traces adjacent to a 1.5 V, 1 GHz aggressor. The traces are 4 mils wide, spaced 4 mils apart, and designed for 40 Ω imped- ance. As each victim trace moves farther from the aggressor, the crosstalk naturally diminishes. The self-inductance field loops represent the magnetic field generated by a trace's own current, whereas the mutual-inductance loops are the field lines encircling a trace due to current in a neighboring conductor. These are responsible for crosstalk. The resulting coupling produces ringing, which in turn generates electromagnetic radiation. When current flows in a conductor, a magnetic field forms around it. Bring another conductor close, and the two magnetic fields interact. This is mutual inductance, which is the root cause of crosstalk, switching noise, and timing uncertainty. Figure 1: Near and far end crosstalk for microstrip (simulated in HyperLynx). B E YO N D D ES I G N