{"id":403,"date":"2018-10-02T15:58:48","date_gmt":"2018-10-02T15:58:48","guid":{"rendered":"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/?page_id=403"},"modified":"2018-10-02T15:58:48","modified_gmt":"2018-10-02T15:58:48","slug":"hysteresis-and-the-schmitt-trigger-glossary-entry","status":"publish","type":"page","link":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/glossary-2\/hysteresis-and-the-schmitt-trigger-glossary-entry\/","title":{"rendered":"Hysteresis and the Schmitt Trigger (Glossary Entry)"},"content":{"rendered":"<p>A technique for reducing (and sometimes effectively eliminating) the effects of noise when detecting if a signal crosses a threshold. Consider the figure below. This shows an analogue signal <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/ql-cache\/quicklatex.com-0dc782a6afdc3bd89c6b52fd82f79ba1_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#86;&#95;&#123;&#105;&#110;&#125;&#40;&#116;&#41;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"43\" style=\"vertical-align: -5px;\"\/>\u00a0varying with respect to time <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/ql-cache\/quicklatex.com-6b97bb0f65c75b6cc0fba1868749478d_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#116;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"6\" style=\"vertical-align: 0px;\"\/>.<\/p>\n<p><span class=\"Apple-converted-space\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-404\" src=\"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/uploads\/sites\/94\/2018\/10\/Hysteresis.png\" alt=\"\" width=\"781\" height=\"441\" srcset=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/uploads\/sites\/94\/2018\/10\/Hysteresis.png 781w, https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/uploads\/sites\/94\/2018\/10\/Hysteresis-300x169.png 300w, https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/uploads\/sites\/94\/2018\/10\/Hysteresis-768x434.png 768w\" sizes=\"auto, (max-width: 781px) 100vw, 781px\" \/><\/span><\/p>\n<p>Consider the example of the blue waveform in the figure.<\/p>\n<p>The signal is below the lower threshold at <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/ql-cache\/quicklatex.com-82471c1f597280d17ec570a21a5adb05_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#116;&#61;&#48;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"39\" style=\"vertical-align: 0px;\"\/>, so the output is GREEN.<span class=\"Apple-converted-space\">\u00a0<\/span><\/p>\n<ul>\n<li>In the <b>GREEN<\/b> (lower) state, the system will only switch to the RED state when the signal crosses above the <b>upper<\/b> threshold of 1.98V.<\/li>\n<li>Once in the <b>RED<\/b> (upper) state, the system will now only switch to the GREEN state when the signal crosses below the <b>lower<\/b> threshold of 1.32V.<\/li>\n<\/ul>\n<p>As the signal rises above the upper threshold of 1.98V, the output state changes state to RED. Note that signal noise causes the signal to dip down below 1.98V shortly after, but that is ignored as it is still above the lower threshold.<span class=\"Apple-converted-space\">\u00a0<\/span><\/p>\n<p>Later, the signal drops below the lower threshold causing a state change. Again due to noise, the signal rises above the lower threshold but is once again ignored as it does not exceed the upper threshold.<span class=\"Apple-converted-space\">\u00a0<\/span><\/p>\n<p>For this example, the noise margin is <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-content\/ql-cache\/quicklatex.com-c009614992bce29f10278d931c3ed8f3_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#40;&#49;&#46;&#57;&#56;&#86;&#32;&#45;&#32;&#49;&#46;&#51;&#50;&#86;&#41;&#61;&#48;&#46;&#54;&#54;&#86;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"196\" style=\"vertical-align: -5px;\"\/>.<\/p>\n<p>A device that employs this technique in this way is known as a Schmitt Trigger <a href=\"https:\/\/en.wikipedia.org\/wiki\/Schmitt_trigger\">https:\/\/en.wikipedia.org\/wiki\/Schmitt_trigger<\/a><\/p>\n<p><span class=\"Apple-converted-space\">\u00a0<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A technique for reducing (and sometimes effectively eliminating) the effects of noise when detecting if a signal crosses a threshold. Consider the figure below. This shows an analogue signal \u00a0varying with respect to time . Consider the example of the blue waveform in the figure. The signal is below the lower threshold at , so&hellip; <a class=\"more-link\" href=\"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/glossary-2\/hysteresis-and-the-schmitt-trigger-glossary-entry\/\">Continue reading <span class=\"screen-reader-text\">Hysteresis and the Schmitt Trigger (Glossary Entry)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":153,"menu_order":55,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-403","page","type-page","status-publish","hentry","entry"],"_links":{"self":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/403","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/comments?post=403"}],"version-history":[{"count":1,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/403\/revisions"}],"predecessor-version":[{"id":405,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/403\/revisions\/405"}],"up":[{"embeddable":true,"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/pages\/153"}],"wp:attachment":[{"href":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/wp-json\/wp\/v2\/media?parent=403"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}