# Book Excerpt: Signal Integrity by Example, Chapter 3

The following is an excerpt from The Printed Circuit Designer's Guide to... Signal Integrity by Example, written by Fadi Deek of Mentor, a Siemens Business. Deek explores how to reach effective design solutions and make strong engineering tradeoffs through analysis techniques, best design principles, and software tools to achieve accurate simulations and measurements.

Chapter 3: Crosstalk

Root Cause
Crosstalk is another major issue to investigate during signal integrity analysis of a design. Typically, a third of the design’s noise budget is allocated to noise coming from crosstalk. In order to solve crosstalk issues, it is very important to understand the root cause. Coupling between two transmission lines occurs due to fringe electric fields and magnetic fields. When a signal propagates on a transmission line, it will generate fields as shown in Figure 3-1.

The E-fields, in blue, are lines emanating from the signal and return paths on which the signal is propagating and couples to all surrounding metal. That E-field will induce a voltage on any conductors lying inside the field. Similarly, the signal will also generate H-fields that will induce currents on the surrounding metal.

The coupling mechanism can also be described using mutual inductances and capacitances. A signal return path loop has a loop inductance. Any two loops in close proximity will have a loop mutual inductance between them. A signal carrying a time-varying current, di/dt, will couple from one loop to the other through this mutual inductance. Also, the same signal will have a time-varying voltage, dV/dt, and that will capacitively couple to neighboring traces.

Based on this, it is important to keep in mind that as a signal propagates down a trace, the coupling takes place at the location of the transitioning edge, where the dV/dt and the dI/dt are. As a signal propagates, the edge will have a spatial extent along the interconnect. Whether it is a falling or a rising edge, the time varying fields exist where that edge is. The steady state part of the signal does not contribute to coupling since it contains no time varying voltages or currents.

It is very important to mention that once a signal couples onto a trace as noise, the noise will split and propagate in both directions as shown in Figure 3-2.

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## HyperLynx: There’s an App for That

08/05/2022 | I-Connect007 Editorial Team
I recently spoke with Todd Westerhoff, product marketing manager for signal integrity software tools at Siemens. We discussed a new capability called HyperLynx Apps that offers a new take on traditional signal and power integrity analysis, and how that fits in with the Siemens plan to put SI and PI tools into the hands of more designers early in the design cycle.

## Webinar Review: Thermal Integrity of High-Performance PCB Design

08/01/2022 | Andy Shaughnessy, Design007 Magazine
Electrical and mechanical engineers may be working on the same product development teams, but they speak different languages, and they have completely different objectives. As a result, these folks almost never use the same software tools. But Cadence’s new Celsius Thermal Solver is an exception to the rule. In a new CadenceTECHTALK webinar, “How Static and Dynamic IR Drop Analysis Can Help PCB Designs and Challenges,” product manager Melika Roshandell and SerDes SI/PI engineer Karthik Mahesh Rao explain how the EE and ME can both use the Celsius Thermal Solver to achieve their disparate objectives.

## The Great Divide in PCB Simulation Software

07/26/2022 | Zachariah Peterson, NWES
Today’s PCB design engineers have more layout and analysis tools at their disposal than ever before. Over the years we’ve seen layout tools become more automated, rules-driven, and more integrated. Now we even have integration between design tools from different vendors and ranging across domains, starting with basic circuit design, and spanning up to PLM and ERP integration. It really is a great time to be a designer.