{"id":1575,"date":"2018-04-23T11:24:28","date_gmt":"2018-04-23T11:24:28","guid":{"rendered":"https:\/\/www.tina.com\/resources\/?page_id=1575"},"modified":"2018-06-21T10:29:08","modified_gmt":"2018-06-21T10:29:08","slug":"11-coupling-between-multiple-inputs","status":"publish","type":"page","link":"https:\/\/www.tina.com\/resources\/home\/practical-operational-amplifiers\/11-coupling-between-multiple-inputs\/","title":{"rendered":"11. Coupling between Multiple Inputs"},"content":{"rendered":"<div class=\"top-navigation\">\n<div class=\"current-page\"><img decoding=\"async\" src=\"https:\/\/www.tina.com\/images\/resource\/people-location-30.png\" \/>CURRENT &#8211; 11. Coupling between Multiple Inputs<\/div>\n<div class=\"previous-page\"><a href=\"https:\/\/www.tina.com\/resources\/home\/10-amplifiers-with-balanced-inputs-or-outputs\/\"><img decoding=\"async\" src=\"https:\/\/www.tina.com\/images\/resource\/leftarrow5.png\" \/>PREVIOUS- 10. Amplifiers with balanced Inputs or Outputs<\/a><\/div>\n<div class=\"next-page\"><a href=\"https:\/\/www.tina.com\/resources\/practical-operational-amplifiers\/12-power-audio-op-amps\/\">NEXT-12. Power Audio Op-amps<img decoding=\"async\" src=\"https:\/\/www.tina.com\/images\/resource\/rightarrow5.png\" \/><\/a><\/div>\n<\/div>\n<p><script>\nfunction setStyle(){ \nheight = document.getElementsByClassName('entry-header')[0].clientHeight;\ndocument.getElementsByClassName('entry-header')[0].style.marginTop = height +\"px\";\ndocument.getElementsByClassName('top-navigation')[0].style.top = Math.round(-(height-20)*2) +\"px\";\n}\nsetStyle();\nwindow.onresize = function(event) {\nsetStyle();\n};\n<\/script><\/p>\n<h6><em>Coupling between Multiple Inputs<\/em><\/h6>\n<div>When more than one input signal is connected to either the inverting or the non-inverting input to the op-amp, coupling between the inputs can result. This is frequently a disturbing problem, since a variation in one channel can produce an unwanted input into an adjoining channel. Consider the dual-input, non-inverting op-amp of Figure 9.47(a), where each channel is\u00a0driven with a voltage source in series with a source resistance (the internal resistance of the voltage source).<\/div>\n<div>\n<div id=\"attachment_1584\" style=\"width: 559px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1584\" class=\"wp-image-1584 size-full\" src=\"https:\/\/www.tina.com\/resources\/wp-content\/uploads\/2018\/04\/Practical-op-ampFigure9-45ABC.png\" alt=\"Coupling between Multiple Inputs, op-amps, operational amplifiers, circuit simulation\" width=\"549\" height=\"325\" srcset=\"https:\/\/www.tina.com\/resources\/wp-content\/uploads\/2018\/04\/Practical-op-ampFigure9-45ABC.png 549w, https:\/\/www.tina.com\/resources\/wp-content\/uploads\/2018\/04\/Practical-op-ampFigure9-45ABC-300x178.png 300w\" sizes=\"auto, (max-width: 549px) 100vw, 549px\" \/><p id=\"caption-attachment-1584\" class=\"wp-caption-text\">Figure 47 &#8211; Coupling between multiple inputs<\/p><\/div>\n<\/div>\n<div>\n<p>The ideal source voltages, <em>v<sub>1<\/sub><\/em> and <em>v<sub>2<\/sub><\/em>, have series resistances, <em>r<sub>1<\/sub><\/em> and <em>r<sub>2<\/sub><\/em> respectively. We begin by writing the equations for the effective voltages, <em>v&#8217;<sub>1<\/sub><\/em> and <em>v&#8217;<sub>2<\/sub><\/em>, into the summing amplifier. We assume that zero current enters the op-amp. With <em>v<sub>2<\/sub><\/em> set equal to zero, as shown in Figure 47(b), the voltage into the op-amp, <em>v&#8217;<sub>2<\/sub><\/em>, is<\/p>\n<div id=\"attachment_1586\" style=\"width: 169px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1586\" class=\"wp-image-1586 size-full\" src=\"https:\/\/www.tina.com\/resources\/wp-content\/uploads\/2018\/04\/Practical-op-amp9-98.png\" alt=\"\" width=\"159\" height=\"51\" \/><p id=\"caption-attachment-1586\" class=\"wp-caption-text\">(98)<\/p><\/div>\n<p>When <em>v<sub>1 <\/sub><\/em>= 0, the <em>v&#8217;<sub>1<\/sub><\/em> voltage is [see Figure 47(c)],<\/p>\n<div id=\"attachment_1588\" style=\"width: 169px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1588\" class=\"wp-image-1588 size-full\" src=\"https:\/\/www.tina.com\/resources\/wp-content\/uploads\/2018\/04\/Practical-op-amp9-99.png\" alt=\"\" width=\"159\" height=\"51\" \/><p id=\"caption-attachment-1588\" class=\"wp-caption-text\">(99)<\/p><\/div>\n<p>Notice that the <em>v&#8217;<sub>2<\/sub><\/em> voltage comes from <em>v<sub>1<\/sub><\/em> and the <em>v&#8217;<sub>1<\/sub><\/em> voltage comes from <em>v<sub>2<\/sub><\/em>. This coupling effect produces undesirable <em>cross-talk <\/em>between the two inputs. The effect can be eliminated by designing a system with <em>r<sub>1<\/sub><\/em> and <em>r<sub>2<\/sub><\/em> approaching zero. Hence, to eliminate coupling, each non-inverting multiple input should be driven with an op-amp that has zero (or very low) output impedance.<\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<div class=\"previous-page\"><a href=\"https:\/\/www.tina.com\/resources\/home\/10-amplifiers-with-balanced-inputs-or-outputs\/\"><img decoding=\"async\" src=\"https:\/\/www.tina.com\/images\/resource\/leftarrow5.png\" \/>PREVIOUS- 10. Amplifiers with balanced Inputs or Outputs<\/a><\/div>\n<div class=\"next-page\"><a href=\"https:\/\/www.tina.com\/resources\/practical-operational-amplifiers\/12-power-audio-op-amps\/\">NEXT- 12. Power Audio Op-amps<img decoding=\"async\" src=\"https:\/\/www.tina.com\/images\/resource\/rightarrow5.png\" \/><\/a><\/div>\n<div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>CURRENT &#8211; 11. Coupling between Multiple Inputs PREVIOUS- 10. Amplifiers with balanced Inputs or Outputs NEXT-12. Power Audio Op-amps Coupling between Multiple Inputs When more than one input signal is connected to either the inverting or the non-inverting input to the op-amp, coupling between the inputs can result. This is frequently a disturbing problem, since [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":917,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"yst_prominent_words":[374,370,375,340,355,351,350,352,354,372,369,367,376,368,339,336,373,343,371,345],"class_list":["post-1575","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/pages\/1575","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/comments?post=1575"}],"version-history":[{"count":30,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/pages\/1575\/revisions"}],"predecessor-version":[{"id":3401,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/pages\/1575\/revisions\/3401"}],"up":[{"embeddable":true,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/pages\/917"}],"wp:attachment":[{"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/media?parent=1575"}],"wp:term":[{"taxonomy":"yst_prominent_words","embeddable":true,"href":"https:\/\/www.tina.com\/resources\/wp-json\/wp\/v2\/yst_prominent_words?post=1575"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}