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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.
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.
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
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Andy Shaughnessy, Design007 Magazine
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