Beyond Design: Faster than a Speeding Bullet


Reading time ( words)

In a previous Beyond Design column, Transmission Lines, I mentioned that a transmission line does not carry the signal itself, but rather guides electromagnetic energy from one point to another. The speed of a computer does not depend intrinsically on the speed of electrons, but rather on the speed of energy transfer between electronic components. Electron flow in a multilayer PCB is extremely slow—about 10 mm per second—so, how does the signal travel so fast, how fast does it actually transfer information and what are the limitations?  

In optical communications, electrons don’t carry the signal—photons do. And we all know that photons travel at the speed of light. So surely, optical fibers must transmit information much faster than copper wires or traces on a multilayer PCB? Actually, photons and electrons transmit data at the same speed. The limiting factor is the relative permittivity (dielectric constant) of the medium in which the signal propagates. 

An optical fiber is a cylindrical dielectric waveguide made of low-loss materials such as fused silica glass. It has a central core in which light is guided, and embedded in an outer cladding of slightly lower refractive index. The silica glass used has a dielectric constant (Er or Dk) = 3.78 @25GHz. Whereas, for instance, Panasonic’s new Megtron 7, low Dk, glass PCB laminate has an Er = 3.3 at the same frequency. 

To read this entire article, which appeared in the February 2016 issue of The PCB Design Magazine, click here.

Share




Suggested Items

Pulsonix Collision Avoidance to Bring Mechanical Capabilities Into ECAD

05/19/2022 | I-Connect007 Editorial Team
The I-Connect Editorial Team recently spoke with Bob Williams, managing director of Pulsonix. He discussed some of the new features in the upcoming version of the Pulsonix PCB design tool, Version 12, including collision avoidance and other 3D options that allow certain MCAD functions within the ECAD environment.

A Textbook Look: Signal Integrity and Impedance

05/18/2022 | Pete Starkey, I-Connect007
Believing that I knew a bit about signal integrity and controlled impedance, I was pleased to take the opportunity to connect with an educational webinar that I hoped would extend my knowledge. In the event I was surprised at how little I actually knew, and the webinar was an excellent learning opportunity. The webinar was introduced and expertly moderated by Anna Brockman of Phoenix Contact in Germany.

Designing in a Vacuum Q&A: Carl Schattke

05/11/2022 | Andy Shaughnessy, Design007 Magazine
Not long ago, I caught up with Carl Schattke, CEO of PCB Product Development LLC and a longtime PCB designer, for his thoughts on “designing in a vacuum.” As Carl points out, if you follow PCB design best practices, knowing the identity of your fabricator is not a “must-have.” He also offers some communication tips for discovering the information you do need, including one old-fashioned technique—just asking for it.



Copyright © 2022 I-Connect007. All rights reserved.