Items Tagged with 'transmission line'

Reduction of microstrip FEXT plays an important role in microwave engineering, as microstrip coupled line backward couplers suffer from poor directivity when not compensated. In this article, Henning Mextorf presents a general approach to improve directivity which does not require a modification of the dimensions of the coupled line structure and provides closed form solutions for optimum capacitor values.

Successfully designing a PCB with more than one impedance while maintaining a manufacturable and economical product can be a difficult challenge. By examining the histories and uses of various impedances, Lee Ritchey simplifies the process and discusses the ideal impedance for PCB stackup design.

“Over the years I’ve come to realize that, particularly in signal integrity, half-wave resonances are often the cause of ugly S-parameters. You can argue that any type of resonance would cause problems, and you would be right. However, half-wave resonances are easily formed in topologies.” This article summarizes observations from Gustavo Blando on the formation and mitigation of half-wave resonances, and includes an in-depth study on the topic in PDF format from the author.

Designing the right PCB stackup can make or break product performance. If the product has circuitry that is impedance and transmission loss sensitive, then paying attention to conductor surface roughness is paramount. Sometimes, however, the roughness of adjacent reference plane(s) is overlooked. If the adjacent high-speed signal layer uses smoother copper than one or both reference planes, a higher insertion loss than expected for that layer will occur and possibly cause a product to fail compliance. So, how is this determined before finalizing the stackup? Read on to find out.

Signal integrity engineers almost always have to work with S-parameters. If you have not had to work with them yet, then chances are you will sometime in your career. As speed moves up in the double-digit GB/s regime, many industry standards are moving to serial link-based architectures and are using frequency domain compliance limits based on S-parameter measurements.

The attenuation in a uniform differential pair has two root causes: conductor loss and dielectric loss. By understanding how design decisions affect these two fundamental root causes, we can develop a few simple guiding principles which point us in the right directions to reduce the attenuation of a channel. These are the directions to follow when loss is important. In some cases, increasing the differential impedance will decrease loss, and in some cases it will increase the loss. Read on to see why.

The dielectric constant, Dk, of a laminate will affect the characteristic impedance of a transmission line and its time delay. If you hope to achieve a specific target characteristic impedance on the first pass, it is essential to know the Dk of each laminate layer.  Here is a quick, simple way of measuring it.

Do students really understand transmission lines? Do YOU really understand transmission lines? Here is a problem I may give my students, if I am feeling particularly cruel

What happens when you apply current to a trace? How long until disaster ensues? Douglas Brooks and Johannes Adam melted some boards, turned traces into flames, and applied some equations to shed some light on these questions.

We care about maintaining the same differential impedance for the same reason we care about maintaining the same instantaneous impedance of a single-ended (SE) transmission line: to avoid reflections. SIJ’s EAB member Bert Simonovich explains the fundamentals and why it matters.