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A design may be 50 ohm nominal impedance, and the PCB is tested to show that it has the correct impedance within some tolerance. The tolerance is sometimes ± 10%, other times ± 5% or less. In the past, one of OEM customers’ main concerns when dealing with their PCB fabricators was characteristic impedance. Many times, a PCB design is considered controlled impedance and the PCB fabricator is held to a specification for impedance control.
As digital rates continue to increase, there are more requests for fabricators to perform insertion loss and other types of electrical testing. Understanding the basics of digital signaling can help explain why these new electrical tests are desired for ensuring a quality PCB for high-speed digital applications.
Digital pulses are made up of analog sine waves. In order to make a digital pulse, sine waves of different frequencies are added together to form the digital pulse. Each of these sine waves is a high-frequency RF wave at a specific frequency. As an example, when a 10 Gbps pulse is generated from a combination of the RF waves, the frequencies used will be approximately 5 GHz, 15 GHz, 25 GHz and 35 GHz added together. Actually there can be more, but this is a simple example of showing the adding of sine waves using the fundamental harmonic (5 GHz), 3rd harmonic (15 GHz), 5th harmonic (25 GHz) and the 7th harmonic frequency at 35 GHz.
Figure 1 shows how the digital pulse can be formed from adding these sine waves.
Nolan Johnson, I-Connect007
Nolan Johnson checks in with Polar’s Martyn Gaudion on the evolving needs of global PCB manufacturing markets in a post-pandemic world, where generating accurate PCB specification documentation is essential to successfully navigating today's rampant supply chain constraints. Polar has positioned itself to meet these needs through agile software product developments that allow OEMs and fabricators to simulate material interactions and end-product specifications, including in-demand features like a comprehensive "structure view" that allows users to visualize all the transmission lines on a given a PCB. Though keeping pace with the demands of a rapidly growing industry has been challenging, Polar's commitment to innovation has kept its software suite ahead of the curve.
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.
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.