Impact of Serpentine Routing on Multi-gigabit Signal Transmission


Reading time ( words)

Abstract

This article discusses the impact of PCB serpentine routing on high-speed signal integrity in terms of impedance discontinuity, insertion loss and eye diagram opening and differential to common mode conversion for signal transmission at 1Gbps (i.e., lower-speed grade) and 10Gbps (i.e., higher speed grade). This investigation is performed using Keysight ADS.

Introduction

Serpentine is a technique to minimize skew or misalignment of differential pairs (Figure 1). The number of segments and intra-pair spacing of serpentining impacts the high-speed signal transmission. As the intra-pair gap is enlarged for serpentining, the characteristic impedance of the PCB trace in differential mode will rise, as governed by Equations 1 and 2. This leads to impedance discontinuity, signal reflection, and ultimately, attenuation. The signal attenuation is heavily dependent on the number of segments and intra-pair spacing of the serpentine. Besides impedance discontinuity, increasing the intra-pair spacing at serpentine segments also loosens the electromagnetic coupling within the differential signal pair, and eventually worsens the differential to common-mode conversion that weakens the immunity of the channel against common-mode noise or crosstalk.

To read this entire article, which appeared in the October 2018 issue of Design007 Magazine, click here.

Share

Print


Suggested Items

Martyn Gaudion on Signal Integrity Modelling and Stackup Tools

12/11/2018 | Pete Starkey, I-Connect007
The accuracy of signal integrity modelling continues to improve, and stackup tools are becoming widely used, which now include material suppliers' datasheet information. During the recent electronica show in Munich, Germany, Martyn Gaudion, managing director at Polar Instruments, explained how Polar often serves as a bridge between PCB design and fabrication, and why educating his customers is so critical.

Max Seeley’s PCB Design Career is No Fish Story

11/14/2018 | Andy Shaughnessy, Design007 Magazine
Max Seeley, senior electrical, PCB, and manufacturing engineer with 3M, was an instructor at the first AltiumLive event in 2017, and he made a return visit to this year’s event in San Diego. I asked Max why he decided to come back to AltiumLive this year and to share the story of his rather circuitous journey into PCB design, which included a turn as a custom aquarium builder. Everyone in PCB design has a different backstory.

Altium Designer Increasingly Used for High-Speed Design

11/05/2018 | Andy Shaughnessy, Design007 Magazine
I recently met with Mark Forbes, the director of technical marketing at Altium, during the AltiumLive event in San Diego. We discussed Mark’s class on MCAD/ECAD collaboration and the success of AltiumLive, as well as the growth of Altium users who design high-speed PCBs with Altium Designer.



Copyright © 2018 I-Connect007. All rights reserved.