{"id":64543,"date":"2025-05-12T10:12:39","date_gmt":"2025-05-12T07:12:39","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=64543"},"modified":"2026-09-30T18:37:28","modified_gmt":"2026-09-30T15:37:28","slug":"stripline-pcb-differential-impedance","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/stripline-pcb-differential-impedance\/","title":{"rendered":"Stripline PCB Differential Impedance Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Differential Pair Impedance in Stripline Geometry<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"64543\" data-favorite-title=\"Stripline PCB Differential Impedance\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/stripline-pcb-differential-impedance\/\" data-favorite-excerpt=\"Estimate the differential impedance of a stripline pair on a multilayer PCB. Enter the single-ended impedance, trace spacing, and height to the reference plane to get Z_diff in ohms.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-engineering\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/engineering\/stripline-pcb-differential-impedance\/\" method=\"POST\" class=\"calculator\" id=\"calculator-64543\" data-post=\"64543\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Single-Ended Impedance<\/label><div class=\"term\">Z\u2080<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"singleended_impedance\" id=\"field-1\" aria-describedby=\"calc-unit-1 calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"1\" value=\"50\"\/><div class=\"unit\" id=\"calc-unit-1\">\u03a9<\/div><small id=\"calc-info-1\">Single-ended characteristic impedance of one stripline<\/small><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Spacing Between Lines<\/label><div class=\"term\">s<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"spacing_between_lines\" id=\"field-2\" aria-describedby=\"calc-unit-2 calc-info-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.001\" value=\"0.2\"\/><div class=\"unit\" id=\"calc-unit-2\">mm<\/div><small id=\"calc-info-2\">Distance between the centers of the differential pair traces<\/small><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-3\">Substrate Height<\/label><div class=\"term\">h<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"substrate_height\" id=\"field-3\" aria-describedby=\"calc-unit-3 calc-info-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.001\" value=\"0.2\"\/><div class=\"unit\" id=\"calc-unit-3\">mm<\/div><small id=\"calc-info-3\">Distance from the trace to the reference plane<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"64543\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Differential Impedance<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"\u03a9\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"64543\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" 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aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Stripline Differential Impedance Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ Z_{\\text{diff}} = 2Z_0 \\left( 1 - 0.347 \\, e^{-2.9 \\left( \\frac{s}{h} \\right)} \\right) \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\( Z_{\\text{diff}} \\) \u2014 differential impedance of the pair (\u03a9)<\/li>\n<li>\\( Z_0 \\) \u2014 single-ended characteristic impedance of one stripline trace (\u03a9)<\/li>\n<li>\\( s \\) \u2014 spacing between the centers of the two traces of the pair<\/li>\n<li>\\( h \\) \u2014 distance from the trace to the reference plane (same units as \\( s \\))<\/li>\n<\/ul>\n<p>Only the ratio \\( s\/h \\) matters, so spacing and height can be entered in any consistent unit (mm, mil, \u00b5m). This empirical model applies to symmetric stripline: two identical traces embedded between two reference planes, with equal dielectric above and below the trace. The coupling term \\( 1 - 0.347 e^{-2.9s\/h} \\) shows that tighter coupling (smaller spacing relative to height) lowers the differential impedance below the uncoupled value of \\( 2Z_0 \\).<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Stripline Differential Impedance \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a 50 \u03a9 stripline pair is routed on an inner layer of a multilayer board. The traces are 0.2 mm apart, and each trace sits 0.2 mm from the nearest reference plane.<\/p>\n<p>\\[ \\frac{s}{h} = \\frac{0.2}{0.2} = 1 \\]<\/p>\n<p>\\[ e^{-2.9 \\cdot 1} \\approx 0.0550 \\]<\/p>\n<p>\\[ Z_{\\text{diff}} = 2 \\cdot 50 \\cdot \\left( 1 - 0.347 \\cdot 0.0550 \\right) = 100 \\cdot 0.9809 \\approx 98.09~\\Omega \\]<\/p>\n<p><strong>Result:<\/strong> the differential impedance is approximately 98.09 \u03a9 \u2014 close to, but slightly below, the 100 \u03a9 you would get from two completely uncoupled 50 \u03a9 traces.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the Calculator<\/h2>\n<ol>\n<li>Enter the <strong>Single-Ended Impedance<\/strong> of one trace of the pair in ohms. If you do not know it yet, compute it first with the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/stripline-impedance\/\">Stripline Impedance Calculator<\/a>.<\/li>\n<li>Enter the <strong>Spacing Between Lines<\/strong> \u2014 the center-to-center distance between the two traces of the differential pair.<\/li>\n<li>Enter the <strong>Substrate Height<\/strong> \u2014 the distance from the trace to the adjacent reference plane (half the dielectric thickness between the two planes of a symmetric stripline).<\/li>\n<li>Read the <strong>Differential Impedance<\/strong> in ohms. Make sure spacing and height use the same unit; only their ratio enters the formula.<\/li>\n<\/ol>\n<h2>What Is Stripline Differential Impedance?<\/h2>\n<p>A stripline is a copper trace routed on an internal layer of a multilayer PCB, fully embedded in dielectric material and sandwiched between two reference (ground or power) planes. This construction gives stripline traces a homogeneous environment, predictable characteristic impedance, and better immunity to electromagnetic interference than surface traces \u2014 at the cost of harder routing and debugging.<\/p>\n<p>A differential pair is two matched traces that carry one signal as the voltage difference between them. Interfaces such as USB, HDMI, PCIe, LVDS, and gigabit Ethernet rely on differential signaling because it rejects common-mode noise and reduces electromagnetic emissions. Each of these standards specifies a target differential impedance \u2014 commonly 90 \u03a9 (USB), 100 \u03a9 (Ethernet, PCIe, LVDS), or 85 \u03a9 for some high-speed variants \u2014 and both the driver and receiver are designed to match it.<\/p>\n<p>The differential impedance of a pair is not simply twice the single-ended impedance. Because the two traces are physically close, they are capacitively and inductively coupled. This coupling makes the differential impedance lower than \\( 2Z_0 \\), and the effect strengthens as the spacing \\( s \\) shrinks relative to the height \\( h \\). When the traces are far apart (\\( s\/h \\gg 1 \\)), the coupling term vanishes and \\( Z_{\\text{diff}} \\to 2Z_0 \\). When they are tightly coupled, the pair can drop several ohms below \\( 2Z_0 \\) \u2014 the example above shows a 50 \u03a9 pair settling near 98 \u03a9 instead of 100 \u03a9.<\/p>\n<p>Matching the differential impedance to the target matters because any discontinuity \u2014 a wrong impedance segment, a via, a break in the reference plane \u2014 reflects part of the signal energy. Reflections cause overshoot, ringing, jitter, and eye-diagram closure, which at multi-gigabit data rates translate directly into bit errors. Designers typically aim to hit the target impedance within about \u00b110% along the entire route.<\/p>\n<h2>Assumptions, Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>Symmetric stripline only.<\/strong> The formula assumes identical traces placed symmetrically between two reference planes with uniform dielectric. It does not apply to <a href=\"https:\/\/wpcalc.com\/en\/engineering\/microstrip-pcb-impedance\/\">microstrip<\/a> (outer-layer) traces or asymmetric (dual-stripline) stackups.<\/li>\n<li><strong>Empirical accuracy.<\/strong> The expression is a closed-form approximation. Expect results within roughly \u00b15% of full 2D field-solver values for typical geometries. For production designs, always verify with a field solver or controlled-impedance stackup tool from your PCB fabricator.<\/li>\n<li><strong>Wide spacing decouples the pair.<\/strong> With \\( s\/h \\) above about 3, the coupling term is negligible and the answer is essentially \\( 2Z_0 \\). In that regime, focus your tuning effort on the single-ended impedance.<\/li>\n<li><strong>Tight coupling lowers impedance.<\/strong> If the calculated value is too high, reduce the spacing between the traces; if it is too low, increase the spacing or adjust the trace geometry so \\( Z_0 \\) rises.<\/li>\n<li><strong>Keep the pair symmetric along the route.<\/strong> Maintain equal trace lengths, identical layer usage, and a continuous reference plane under the entire pair. Avoid routing other signals between the two traces of the pair, and keep unrelated aggressor traces away to limit crosstalk \u2014 see the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pcb-microstrip-crosstalk\/\">PCB Microstrip Crosstalk Calculator<\/a> for evaluating that coupling.<\/li>\n<li><strong>Units must be consistent.<\/strong> The calculator only uses the ratio \\( s\/h \\), so mixing mm and mil between the two fields is a common source of large errors.<\/li>\n<li><strong>Connector and termination matching.<\/strong> When the source or load needs a matching network to bridge impedance levels, the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/pi-network-impedance-matching\/\">PI Network Impedance Matching Calculator<\/a> can help design it.<\/li>\n<\/ul>\n<h2>Quick Reference: Coupling vs. Differential Impedance<\/h2>\n<table>\n<thead>\n<tr>\n<th>Spacing-to-height ratio \\( s\/h \\)<\/th>\n<th>Coupling factor \\( 0.347e^{-2.9s\/h} \\)<\/th>\n<th>\\( Z_{\\text{diff}} \\) for \\( Z_0 = 50\\ \\Omega \\)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0.5<\/td>\n<td>0.0829<\/td>\n<td>91.71 \u03a9<\/td>\n<\/tr>\n<tr>\n<td>1.0<\/td>\n<td>0.0191<\/td>\n<td>98.09 \u03a9<\/td>\n<\/tr>\n<tr>\n<td>2.0<\/td>\n<td>0.0010<\/td>\n<td>99.90 \u03a9<\/td>\n<\/tr>\n<tr>\n<td>3.0<\/td>\n<td>\u2248 0.00005<\/td>\n<td>\u2248 100 \u03a9<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The table shows how quickly the pair decouples: beyond \\( s\/h = 2 \\), the differential impedance is within 0.1% of \\( 2Z_0 \\), and further spacing changes provide no measurable benefit.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Estimate the differential impedance of a stripline pair on a multilayer PCB. Enter the single-ended impedance, trace spacing, and height to the reference plane to get Z_diff in ohms.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[4],"tags":[92],"class_list":["post-64543","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-rf-microwave"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64543","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=64543"}],"version-history":[{"count":3,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64543\/revisions"}],"predecessor-version":[{"id":66021,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64543\/revisions\/66021"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=64543"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=64543"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=64543"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}