{"id":4896,"date":"2025-09-26T11:12:00","date_gmt":"2025-09-26T11:12:00","guid":{"rendered":"https:\/\/lp.szlogic.cn\/uncategorized\/common-mode-noise-in-ethernet-systems\/"},"modified":"2026-06-22T09:04:14","modified_gmt":"2026-06-22T09:04:14","slug":"common-mode-noise-in-ethernet-systems","status":"publish","type":"post","link":"https:\/\/resourceslp.szlogic.cn\/it\/products\/common-mode-noise-in-ethernet-systems","title":{"rendered":"Rumore in modo comune: definizione, cause e mitigazione nei sistemi Ethernet"},"content":{"rendered":"<figure class=\"wp-block-image aligncenter size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1200\" height=\"712\" src=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af.jpg\" alt=\"Common-Mode Noise\" class=\"wp-image-4891\" srcset=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af.jpg 1200w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af-300x178.jpg 300w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af-1024x608.jpg 1024w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af-768x456.jpg 768w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/4f1f31dcf42b4eb48924d81973b5c7af-18x12.jpg 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" ><strong>\ud83d\udd04 <\/strong>Introduzione<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Rumore in modo comune<\/strong> is a common challenge in Ethernet and other high-speed digital systems. It occurs when identical noise voltages or currents appear on both conductors of a pair relative to ground. Left unmitigated, it can lead to <a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/glossary\/what-is-electromagnetic-interference\/\"><strong>interferenza elettromagnetica (EMI)<\/strong><\/a>, compliance failures, and degraded signal integrity. This article explains the concept, causes, measurement methods, and suppression techniques of common-mode noise \u2014 with a focus on Ethernet design and <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/store-17548-lan-transformer.htm\">LINK-PP LAN transformers<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; What Is Common-Mode Noise?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Common-mode noise refers to unwanted signals that appear <strong>in the same phase<\/strong> on two conductors relative to ground.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Formula:<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" width=\"1200\" height=\"404\" src=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2.webp\" alt=\"Common-Mode Noise\" class=\"wp-image-4892\" srcset=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2.webp 1200w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2-300x101.webp 300w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2-1024x345.webp 1024w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2-768x259.webp 768w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/38069609f4834aabaa23e45eed593ba2-18x6.webp 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">In contrast, the useful <strong>che quelle in modo differenziale.<\/strong> signal is:<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" width=\"1200\" height=\"270\" src=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0.webp\" alt=\"differential-mode Noise\" class=\"wp-image-4893\" srcset=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0.webp 1200w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0-300x68.webp 300w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0-1024x230.webp 1024w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0-768x173.webp 768w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/2307f84b96d14325b7b70a2cb8d821e0-18x4.webp 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">While differential-mode signals carry data, common-mode noise represents interference that may radiate as EMI or couple into sensitive circuitry.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Differential Mode vs Common Mode<\/h2>\n\n\n\n<figure class=\"wp-block-table\">\n<table class=\"has-fixed-layout\">\n<colgroup><col style=\"min-width: 25px;\"\/><col style=\"min-width: 25px;\"\/><col style=\"min-width: 25px;\"\/><\/colgroup><tbody><tr><th colspan=\"1\" rowspan=\"1\"><p>Aspetto<\/p><\/th><th colspan=\"1\" rowspan=\"1\"><p>Differential Mode<\/p><\/th><th colspan=\"1\" rowspan=\"1\"><p>Common Mode<\/p><\/th><\/tr><tr><td colspan=\"1\" rowspan=\"1\"><p>Signal<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Opposite polarity on conductors<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Same polarity on both conductors<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\"><p>Scopo<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Carries data<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Unwanted interference<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\"><p>Radiation<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Relatively low<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>High, cables act as antennas<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\"><p>Reference<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Between lines<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Relative to ground<\/p><\/td><\/tr><tr><td colspan=\"1\" rowspan=\"1\"><p>Mitigazione<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p>Pair symmetry, impedance control<\/p><\/td><td colspan=\"1\" rowspan=\"1\"><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/glossary\/ethernet-common-mode-choke-cmc-guide\/\">Induttori per modo comune<\/a>, isolation<\/p><\/td><\/tr><\/tbody>\n<\/table>\n<\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Causes of Common-Mode Noise<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><strong>External coupling<\/strong>: Switching circuits or nearby cables can induce equal disturbances on both lines.<\/p><\/li><li><p><strong>Ground potential differences<\/strong>: Mismatched system grounds create common-mode offsets.<\/p><\/li><li><p><strong>Mode conversion<\/strong>: Layout or driver imbalance converts differential signals into common mode.<\/p><\/li><li><p><strong>Parasitic capacitance<\/strong>: Line-to-chassis coupling at high frequencies promotes current leakage.<\/p><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Why Common-Mode Noise Matters in Ethernet<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><strong>Compatibilit\u00e0<\/strong>: Excessive common-mode emissions can cause systems to fail EMI\/EMC tests.<\/p><\/li><li><p><strong>per interfacce ottiche ed elettriche ad alta velocit\u00e0<\/strong>: High common-mode levels reduce differential receiver rejection.<\/p><\/li><li><p><strong>Interference risk<\/strong>: Noise can couple into nearby analog or control circuits.<\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/knowledge-center\/lan-transformer-isolation-voltage-explained\/\"><strong>Isolation stress<\/strong><\/a>: Particularly in PoE systems, common-mode current may strain isolation boundaries.<\/p><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Measuring Common-Mode Noise<\/h2>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1200\" height=\"457\" src=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c.jpg\" alt=\"Measuring Common-Mode Noise\" class=\"wp-image-4894\" srcset=\"https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c.jpg 1200w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c-300x114.jpg 300w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c-1024x390.jpg 1024w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c-768x292.jpg 768w, https:\/\/resourceslp.szlogic.cn\/wp-content\/uploads\/2026\/05\/056227254efc485ca072aa71a7ae704c-18x7.jpg 18w\" sizes=\"(max-width: 1200px) 100vw, 1200px\" \/><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><strong>Clamp-on current probes + spectrum analyzers<\/strong>: Detect total common-mode current on cables.<\/p><\/li><li><p><strong>LISN (Line Impedance Stabilization Network)<\/strong>: Separates and measures conducted emissions.<\/p><\/li><li><p><strong>Transfer impedance method<\/strong>: Converts probe readings into accurate current values.<\/p><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Mitigation Strategies<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" >Common-Mode Chokes<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/glossary\/ethernet-common-mode-choke-cmc-guide\/\">Common-Mode Chokes (CMCs)<\/a> present high impedance to common-mode currents while allowing differential Ethernet signals to pass, making them the most effective filter.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >Balanced PCB Design<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Matched trace lengths, controlled impedance, and minimizing skew reduce mode conversion.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >Schermatura<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Utilizzando <strong>STP (shielded twisted pairs)<\/strong> with proper chassis grounding lowers capacitive coupling.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" >Isolamento<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\"><a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/store-17548-lan-transformer.htm\">Trasformatori LAN<\/a> provide galvanic separation and reduce common-mode transfer, though inter-winding capacitance must be considered in EMI budgets.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >\ud83d\udd04 Conclusione<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Rumore in modo comune<\/strong> is a major source of EMI in Ethernet and PoE designs. Effective suppression requires a combination of <strong>common-mode chokes, balanced PCB layouts, shielding, and isolation<\/strong>. By leveraging LINK-PP <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/products\/443538.htm\">Trasformatori LAN<\/a> and <a target=\"_blank\" rel=\"\" href=\"https:\/\/www.l-p.com\/products\/488807.htm\">RJ45 magjacks<\/a> with optimized EMI performance, engineers can achieve both regulatory compliance and robust Ethernet operation. Clear documentation of compatibility parameters \u2014 such as data rate, PoE current rating, insertion loss, and isolation \u2014 further simplifies design choices for customers.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" >&#x1f504; Further Reading<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Explore more technical resources from LINK-PP:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/glossary\/insertion-loss-impact-on-rj45-magjack\/\">Insertion Loss Impact on RJ45 Magjack<\/a><\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/knowledge-center\/emc-ems-emi-electromagnetic-compatibility-susceptibility-interference\/\">Electromagnetic Compatibility \u2014 EMC, EMS, EMI<\/a><\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/knowledge-center\/ieee-802-3-ethernet-standard-explained\/\">Standard IEEE 802.3 Ethernet spiegato<\/a><\/p><\/li><li><p><a target=\"_blank\" rel=\"\" href=\"https:\/\/resourceslp.szlogic.cn\/it\/glossary\/what-is-a-capacitor\/\">What Is a Capacitor<\/a><\/p><\/li>\n<\/ul>","protected":false},"excerpt":{"rendered":"<p>Comprendi il rumore in modo comune: cos\u2019\u00e8, come influisce sull\u2019Ethernet\/EMI e come sopprimerlo mediante componenti magnetici e filtri. Una guida pratica per ingegneri.<\/p>","protected":false},"author":1,"featured_media":4895,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[28],"tags":[23],"class_list":["post-4896","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-products","tag-link-pp-lan-transformers"],"blocksy_meta":[],"acf":[],"_links":{"self":[{"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/posts\/4896","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/comments?post=4896"}],"version-history":[{"count":4,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/posts\/4896\/revisions"}],"predecessor-version":[{"id":11365,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/posts\/4896\/revisions\/11365"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/media\/4895"}],"wp:attachment":[{"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/media?parent=4896"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/categories?post=4896"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/resourceslp.szlogic.cn\/it\/wp-json\/wp\/v2\/tags?post=4896"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}