{"id":3788,"date":"2026-07-08T07:16:37","date_gmt":"2026-07-08T07:16:37","guid":{"rendered":"https:\/\/theemcnews.co.uk\/?page_id=3788"},"modified":"2026-07-08T07:17:41","modified_gmt":"2026-07-08T07:17:41","slug":"implementing-gigabit-power-over-ethernet-to-achieve-emc-compliance-part-1","status":"publish","type":"page","link":"https:\/\/theemcnews.co.uk\/index.php\/implementing-gigabit-power-over-ethernet-to-achieve-emc-compliance-part-1\/","title":{"rendered":"Implementing Gigabit Power over Ethernet to achieve EMC compliance \u2013 Part 1"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-page\" data-elementor-id=\"3788\" class=\"elementor elementor-3788\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f3664dc e-flex e-con-boxed e-con e-parent\" data-id=\"f3664dc\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-9c19a3d elementor-widget elementor-widget-text-editor\" data-id=\"9c19a3d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"wp-block-image\"><figure class=\"aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_poe_lead.jpg?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img fetchpriority=\"high\" decoding=\"async\" class=\"wp-image-1419634\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_poe_lead.jpg?resize=640%2C453&amp;ssl=1\" alt=\"Implementing Gigabit Power over Ethernet to achieve EMC compliance.\" width=\"640\" height=\"453\" data-recalc-dims=\"1\" \/><\/a><\/figure><\/div><p><em>Gigabit Ethernet is a widely used networking standard, normally just for transmitting data signals. An elegant solution is to use the same cable for the power supply, which is the case with \u201cPower over Ethernet\u201d (PoE). EMC aspects must also receive sufficient attention.<\/em><\/p><p>To investigate the EMC properties of the Gigabit Power over Ethernet interface, W\u00fcrth Elektronik started by developing and implementing its own reference design RD022\u00a0<sup>[3]<\/sup>\u00a0(<strong>Figure 1<\/strong>). This \u201cGB PoE+ Ethernet USB adapter\u201d was designed based on reference design RD016 \u201cGB Ethernet USB adapter\u201d\u00a0<sup>[1]<\/sup>.<\/p><figure class=\"wp-block-image aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-1.jpg?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img decoding=\"async\" class=\"wp-image-1419608\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-1.jpg?resize=640%2C512&amp;ssl=1\" alt=\"Reference design RD022.\n\n\" width=\"640\" height=\"512\" data-recalc-dims=\"1\" \/><\/a><figcaption class=\"wp-element-caption\">Figure 1: Reference design RD022 \u201cGB PoE+ Ethernet USB adapter\u201d is a key aspect in EMC considerations<\/figcaption><\/figure><p>The new reference design \u201cGB PoE+ Ethernet USB adapter\u201d has three interfaces:<\/p><ul class=\"wp-block-list\"><li>a USB Type-C\u2122 (USB 3.1)<\/li><li>an RJ45\/Ethernet 1 Gigabit interface with integrated Power over Ethernet supply (PoE+)<\/li><li>a terminal connection to the DC\/DC converter, with an adjustable output voltage of 6\u00a0\u2013\u00a018\u00a0V and a maximum output power of 25\u00a0W<\/li><\/ul><p>The board was developed to familiarize user with PoE technology. As with the design without PoE, the bit error rate and transmission speed can be investigated using a Windows application.<\/p><p>The EMC evaluation of the PoE reference design was performed in two steps: First, the board was tested with the power supply without additional filters. Optimizations were necessary during the tests, which will be explained later. The circuit diagrams are shown in\u00a0<sup>[4]<\/sup>. Reference design RD022 is already based on the optimized design\u00a0<sup>[3]<\/sup>.<\/p><div class=\"code-block code-block-13\"><div class=\"htlad-EET_com_InRead_Video\"><div id=\"htlad-5\" class=\"htl-ad\" data-unit=\"EETimes.\/EET_InRead_Video\" data-lazy-pixels=\"350\" data-sizes=\"0x0:4x4\" data-prebid=\"0x0:\">\u00a0<\/div><\/div><\/div><p>The EMC behavior of the Gigabit Ethernet interface was already discussed in detail based on the RD016 reference design description and Application Note ANP116. The insights gained there regarding shield connection, cable shielding, and the performance of the Ethernet front end also apply to the PoE version. The ideal shield connection determined in ANP116 with two 10 nF capacitors and a parallel SMD varistor is also used here.<\/p><h2 class=\"wp-block-heading\">EMC basics for PoE<\/h2><p>PoE applications are usually compact electronic devices whose power supply is combined with data communication via an Ethernet interface. They are usually multimedia devices, which are covered in EMC standardization CISPR 32 (emission) and CISPR 35 (immunity). The devices tend to be compact and have short lines apart from the Ethernet cable. Typical examples:<\/p><ul class=\"wp-block-list\"><li>WiFi access points<\/li><li>DECT stations (Digital Enhanced Cordless Telecommunications)<\/li><li>IP phones<\/li><li>Surveillance cameras<\/li><li>Monitoring of indoor climate in storage and production facilities<\/li><\/ul><p>The IP phone is an example of a PoE device with comparatively large dimensions, as the phone receiver cable together with the PCB in the phone is a relatively large structure that can act as an antenna. A DECT station is rather compact by comparison. This results in two possible approaches for the reference design during EMC testing:<\/p><ul class=\"wp-block-list\"><li>A short output line or compact load resistor (point of load) \u2013 compact application<\/li><li>Long output lines at the load output \u2013 correspond to a larger PoE application.<\/li><\/ul><p>The advantage of using long cables and a variable resistor during EMC testing is that the load on the switching regulator can be readjusted to always allow maximum power to be achieved. When using a compact TO220 resistor, the load is fixed at 10 \u03a9.<\/p><h2 class=\"wp-block-heading\"><strong>EMC test setup and operating parameters<\/strong><\/h2><p>The schematic test setup shown in\u00a0<strong>Figure 2<\/strong>\u00a0is similar to the test setup used for testing the Gigabit Ethernet interface and was only extended to include the PoE switch and the load. The focus during EMC testing is on the Ethernet interface, the PoE reference design board, and the various load configurations.<\/p><div class=\"wp-block-image\"><figure class=\"aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-2.png?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img decoding=\"async\" class=\"wp-image-1419609\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-2.png?resize=640%2C201&amp;ssl=1\" alt=\"Test setup for the Gigabit PoE board during EMC testing.\" width=\"640\" height=\"201\" data-recalc-dims=\"1\" \/><\/a><figcaption class=\"wp-element-caption\">Figure 2: Test setup for the Gigabit PoE board during EMC testing<\/figcaption><\/figure><\/div><p>The USB interface is considered as a short line; the focus during testing is on the Ethernet front end. As the USB interface is needed to operate the board, it is also evaluated in many tests. During the interference immunity tests, it was found that a direct connection between the USB cable shield and the board GND layer is required for operation at high levels of interference immunity. Only a direct shield connection ensures that the interface remains in a stable operating mode even at high test levels such as 20\u00a0V\/m above 1\u00a0GHz.<\/p><p>The load lines are measured with a 2 to 3\u00a0m cable length for radiated interference emission and interference immunity and should be as short as possible (cable length below 3\u00a0m) with regard to EMC. Burst or conducted RF coupling is not applied to the voltage output of the board.<\/p><p>The notebooks required to operate the board and the PoE switch are operated inside a shielded box in order to eliminate their influence on the results of EMC testing as far as possible.<\/p><h2 class=\"wp-block-heading\"><strong>Influence of the output voltage on emission<\/strong><\/h2><p><strong>Figure 3<\/strong>\u00a0shows that the interference emission of the board is higher at 12\u00a0V and 2\u00a0A output current than at 18\u00a0V and 1.3\u00a0A output current. For this reason, some approaches, such as filter design, are carried out at 12\u00a0V rather than 18\u00a0V.<\/p><div class=\"wp-block-image\"><figure class=\"aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-3.png?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1419610\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/wurth_Figure-3.png?resize=640%2C292&amp;ssl=1\" alt=\"Radiated interference emission from the Gigabit PoE design when operating with long load lines without an external filter and with shielded Ethernet cable (cat5e SF\/UTP).\" width=\"640\" height=\"292\" data-recalc-dims=\"1\" \/><\/a><figcaption class=\"wp-element-caption\">Figure 3: Radiated interference emission from the Gigabit PoE design when operating with long load lines without an external filter and with shielded Ethernet cable (cat5e SF\/UTP)<\/figcaption><\/figure><\/div><h2 class=\"wp-block-heading\"><strong>Output filter for long cables<\/strong><\/h2><p>The isolated switching regulator on the board has no output filter. When connecting long lines and a load resistor, interference may be radiated directly from the switching regulator output, so an output filter may be necessary for large designs or designs with cables.<\/p><p>The filter from\u00a0<strong>Figure 4<\/strong>\u00a0can be used to reduce the radiated interference. This results in an increased margin to the Class B limit of CISPR 32. For larger devices, an output filter with the following components is recommended:<\/p><ul class=\"wp-block-list\"><li>Ferrite Bead (1812 package) with 780 Ohm at 100 MHz (742792515).<\/li><li>MLCC 4.7 \u00b5F X5R 50 V (885012209048)<\/li><li>Common-mode choke for signal lines with 17 \u00b5H (744237152).<\/li><\/ul><div class=\"wp-block-image\"><figure class=\"aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_Figure-4a.png?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1419612\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_Figure-4a.png?resize=640%2C180&amp;ssl=1\" alt=\"Circuit and photo of the output filter for long load lines.\" width=\"640\" height=\"180\" data-recalc-dims=\"1\" \/><\/a><\/figure><\/div><div class=\"wp-block-image\"><figure class=\"aligncenter size-full\"><a href=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_Figure-4b-1.jpg?ssl=1\" target=\"_blank\" rel=\"noreferrer noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-1419617\" src=\"https:\/\/i0.wp.com\/eetimes.com\/wp-content\/uploads\/Wurth_Figure-4b-1.jpg?resize=640%2C427&amp;ssl=1\" alt=\"Figure 4: Circuit and photo of the output filter for long load lines.\" width=\"640\" height=\"427\" data-recalc-dims=\"1\" \/><\/a><figcaption class=\"wp-element-caption\">Figure 4: Circuit and photo of the output filter for long load lines<\/figcaption><\/figure><\/div><p>The capacitors around the common-mode choke form a differential filter with its own leakage inductance. Any coupling caused by stray magnetic fields from the board into the filter, which would result in a differential current, is short-circuited in the process. If a load resistor with short leads or a TO220 resistor is used instead of long lines with a filter, the emission changes.<\/p><p>Reducing the package size of the load resistors does not improve the emission in the absence of an output filter. The emission with filtered long load lines is now partly lower than with compact load resistors.<\/p><p>The\u00a0<a href=\"https:\/\/eetimes.com\/implementing-gigabit-power-over-ethernet-to-achieve-emc-compliance-part-2\" target=\"_blank\" rel=\"noreferrer noopener\">second part of this article<\/a>\u00a0continues with conducted interference emission and immunity testing.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Gigabit Ethernet is a widely used networking standard, normally just for transmitting data signals. An elegant solution is to use the same cable for the power supply, which is the case with \u201cPower over Ethernet\u201d (PoE). EMC aspects must also receive sufficient attention. To investigate the EMC properties of the&hellip; <\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"elementor_header_footer","meta":{"footnotes":""},"class_list":["post-3788","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/3788","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/comments?post=3788"}],"version-history":[{"count":4,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/3788\/revisions"}],"predecessor-version":[{"id":3792,"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/pages\/3788\/revisions\/3792"}],"wp:attachment":[{"href":"https:\/\/theemcnews.co.uk\/index.php\/wp-json\/wp\/v2\/media?parent=3788"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}