{"id":2120,"date":"2024-07-19T17:52:52","date_gmt":"2024-07-19T12:22:52","guid":{"rendered":"https:\/\/study.madeeasy.in\/?p=2120"},"modified":"2025-07-16T15:16:43","modified_gmt":"2025-07-16T09:46:43","slug":"what-is-bjt-and-its-configuration","status":"publish","type":"post","link":"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration","title":{"rendered":"What is BJT and its Configuration?"},"content":{"rendered":"<h2 style=\"text-align: justify;\">BJT Configuration<\/h2>\n<ul style=\"text-align: justify;\">\n<li>A configuration refers to the way three terminals of BJT are used in amplifier.<img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2123 size-full\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/bjt-as-a-two-port-divice.jpg\" alt=\"BJI as a Two Port Divice\" width=\"626\" height=\"256\" srcset=\"https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/bjt-as-a-two-port-divice.jpg 626w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/bjt-as-a-two-port-divice-300x123.jpg 300w\" sizes=\"auto, (max-width: 626px) 100vw, 626px\" \/><\/li>\n<li>Based upon the reference or common node a BJT can be used in three configurations as given in Table-3.2.<\/li>\n<\/ul>\n<table class=\"table table-striped table-bordered table-condensed\" style=\"margin: 0 auto; width: 99%;\">\n<tbody>\n<tr>\n<th width=\"61\"><strong>S.No.<\/strong><\/th>\n<th width=\"207\"><strong>Configuration<\/strong><\/th>\n<th width=\"109\"><strong>Input node<\/strong><\/th>\n<th width=\"120\"><strong>Output node<\/strong><\/th>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"61\">1.<\/td>\n<td style=\"text-align: center;\" width=\"207\">Common Base (CB)<\/td>\n<td style=\"text-align: center;\" width=\"109\">E<\/td>\n<td style=\"text-align: center;\" width=\"120\">C<\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"61\">2.<\/td>\n<td style=\"text-align: center;\" width=\"207\">Common Emitter (CE)<\/td>\n<td style=\"text-align: center;\" width=\"109\">B<\/td>\n<td style=\"text-align: center;\" width=\"120\">C<\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: center;\" width=\"61\">3.<\/td>\n<td style=\"text-align: center;\" width=\"207\">Common Collector (CC)<\/td>\n<td style=\"text-align: center;\" width=\"109\">B<\/td>\n<td style=\"text-align: center;\" width=\"120\">E<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>&nbsp;<\/p>\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_79_1 ez-toc-wrap-left counter-hierarchy ez-toc-counter ez-toc-light-blue ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#The-Common-Emitter-Configuration\" >The Common-Emitter Configuration<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#The-Input-Characteristics\" >The Input Characteristics<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#The-Output-Characteristics\" >The Output Characteristics<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#Active-Region\" >Active Region<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#Cut-off-Region\" >Cut-off Region<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#Saturation-Region\" >Saturation Region<\/a><ul class='ez-toc-list-level-4' ><li class='ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#Properties\" >Properties<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-4'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.madeeasy.in\/study\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/#Application\" >Application<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"The-Common-Emitter-Configuration\"><\/span>The Common-Emitter Configuration<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Most transistor circuits have the emitter terminal common to both input and output. Such a <em>Common-Emitter <\/em>(<em>CE<\/em>) or grounded-emitter, configuration is indicated in figure.<\/p>\n<p style=\"text-align: justify;\">In common-emitter configuration, the input current and output voltage are taken as independent variables, whereas the input voltage and output current are the dependent variables.<\/p>\n<p style=\"text-align: justify;\">We may write<\/p>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-2125 size-full aligncenter\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/vbe-f1.jpg\" alt=\"VBE F1\" width=\"205\" height=\"84\" \/><\/p>\n<p style=\"text-align: justify;\">Above equation describes the family of input characteristics and the family of output characteristics respectively.<\/p>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2127 size-full\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/transistor-common-emitter-configuration.jpg\" alt=\"Transistor common-emitter configuration\" width=\"442\" height=\"395\" srcset=\"https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/transistor-common-emitter-configuration.jpg 442w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/transistor-common-emitter-configuration-300x268.jpg 300w\" sizes=\"auto, (max-width: 442px) 100vw, 442px\" \/><\/p>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"The-Input-Characteristics\"><\/span>The Input Characteristics<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Typical input characteristic curves for a p-n-p junction Germanium transistor are given in figure.<\/p>\n<ul style=\"text-align: justify;\">\n<li>With collector shorted to the emitter and forward- biased emitter, the input characteristics are essentially that of a forward biased-diode.<\/li>\n<li>If <em>V<\/em><em><sub>BE<\/sub> <\/em>becomes zero, then <em>I<\/em><em><sub>B<\/sub> <\/em>will be zero, since under these conditions both emitter and collector junctions will be short-circuited.<\/li>\n<li>For any other value of <em>V<\/em><em><sub>CE<\/sub><\/em>, base current for <em>V<\/em><em><sub> BE<\/sub><\/em>= 0 is not actually zero but is too small to be observed in figure.<\/li>\n<li>In general increase in | <em>V<\/em><em><sub>CE<\/sub> | <\/em>with constant <em>V<\/em><em><sub>BE<\/sub> <\/em>causes a decrease in base width W (the Early effect) and results in decreased recombination base current.<\/li>\n<li>These considerations account for the shape of input characteristics shown in figure.<\/li>\n<\/ul>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2130 size-full\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/Typical-common-emitter.jpg\" alt=\"Typical common-emitter\" width=\"417\" height=\"456\" srcset=\"https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter.jpg 417w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-274x300.jpg 274w\" sizes=\"auto, (max-width: 417px) 100vw, 417px\" \/><\/p>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"The-Output-Characteristics\"><\/span>The Output Characteristics<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">Typical output characteristics curves for a p-n-p junction Germanium transistor are given in figure below.<\/p>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2132 size-full\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-output-characteristics.jpg\" alt=\"Typical common-emitter output characteristics \" width=\"807\" height=\"554\" srcset=\"https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-output-characteristics.jpg 807w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-output-characteristics-300x206.jpg 300w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-output-characteristics-768x527.jpg 768w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/Typical-common-emitter-output-characteristics-130x90.jpg 130w\" sizes=\"auto, (max-width: 807px) 100vw, 807px\" \/><\/p>\n<p style=\"text-align: justify;\">The family of curves may be divided into three regions. These are <em><strong>active region<\/strong>, <strong>cut-off region <\/strong><\/em>and <strong><em>saturation region<\/em><\/strong>.<\/p>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"Active-Region\"><\/span>Active Region<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ul style=\"text-align: justify;\">\n<li>In above figure, active region is the area to the right of the ordinate <em>V<\/em><em><sub>CE<\/sub> <\/em>= a few tenths of a volt and above <em>I<\/em><em><sub>B<\/sub> <\/em>= 0.<\/li>\n<li>In this region the transistor output current responds most sensitively to an input signal.<\/li>\n<li>If transistor is to be used as an amplifying device without appreciable distortion, it must be restricted to operate in this region.<\/li>\n<li>It should also be clear that a slight change in a has large effect on the common-emitter curves, and hence that common-emitter characteristics are normally subjected to wide variation even among transistor of a given type. This variability is caused by the fact that <em>I<\/em><em><sub>B<\/sub> <\/em>is the difference between large and nearly equal currents, <em>I<\/em><em><sub>E<\/sub> <\/em>and <em>I<\/em><em><sub>C<\/sub><\/em>.<\/li>\n<\/ul>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"Cut-off-Region\"><\/span>Cut-off Region<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<p style=\"text-align: justify;\">We might be inclined to think that cut-off in figure above occurs at the intersection of the load line with current I<sub>B<\/sub> = 0; however we now find that appreciable collector current may exists under these conditions. We have<\/p>\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-2137 size-full\" src=\"https:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/ifib0.jpg\" alt=\"Cut-off Region\" width=\"581\" height=\"135\" srcset=\"https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/ifib0.jpg 581w, https:\/\/www.madeeasy.in\/study\/wp-content\/uploads\/2024\/07\/ifib0-300x70.jpg 300w\" sizes=\"auto, (max-width: 581px) 100vw, 581px\" \/><\/p>\n<ul style=\"text-align: justify;\">\n<li>The actual collector current with collector junction reverse-biased and base open-circuited is designated by the symbol <em>I<\/em><sub>CEO<\/sub>.<\/li>\n<li>Since, even in the neighbourhood of cut-off, a may be as large as 9 for Germanium, then <em>I<\/em><sub>C\u2243<\/sub>10<em>I<\/em><sub>CO<\/sub> at zero base current.<\/li>\n<li>Accordingly, in order to cut-off the transistor, it is not enough to reduce I<sub>B<\/sub> to zero. Instead, it is necessary to reverse-bias the emitter junction slightly.<\/li>\n<li>In summary, <strong><em>cut-off means that <\/em><em>I<\/em><em><sub>E<\/sub> <\/em><em>= 0, <\/em><em>I<\/em><em><sub>C<\/sub> <\/em><em>= <\/em><em>I<\/em><em><sub> CO<\/sub><\/em><em>, <\/em><em>I<\/em><em><sub>B<\/sub> <\/em><em>= \u2013<\/em><em>I<\/em><em><sub> C<\/sub> <\/em><em>= \u2013<\/em><em>I<\/em><em><sub>CO<\/sub><\/em><em>, and V<\/em><em><sub>BE<\/sub> <\/em><em>is a reverse voltage whose magnitude is of the order of 0.1 V for Germanium and <\/em>0 <em>V for a Silicon transistor<\/em>.<\/strong><\/li>\n<\/ul>\n<h3 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"Saturation-Region\"><\/span>Saturation Region<span class=\"ez-toc-section-end\"><\/span><\/h3>\n<ul style=\"text-align: justify;\">\n<li>The saturation region may be defined as the one where collector junction (as well as the emitter junction) is forward-biased.<\/li>\n<li>In this region bottoming occurs, |V<sub>CE<\/sub>| drops to few tenths of a volt, and the collector current is approximately independent of base current, for given values of V<sub>CC<\/sub> and R<sub>L<\/sub>.<\/li>\n<li>Hence we may consider that onset of saturation takes place at knee of the transistor curves in figure.<\/li>\n<\/ul>\n<h4 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"Properties\"><\/span>Properties<span class=\"ez-toc-section-end\"><\/span><\/h4>\n<ul style=\"text-align: justify;\">\n<li>Moderate input resistance (around 1 k\u2126).<\/li>\n<li>Moderate output resistance (50 k\u2126 to 500 k\u2126).<\/li>\n<li>Moderate current gain (Typical value 49).<\/li>\n<li>Moderate voltage gain.<\/li>\n<li>Highest power gain (Typical value 4226).<\/li>\n<li>Output and input voltages are out of phase i.e. phase shift = 180\u00b0.<\/li>\n<\/ul>\n<h4 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"Application\"><\/span>Application<span class=\"ez-toc-section-end\"><\/span><\/h4>\n<p style=\"text-align: justify;\">It is the most common and frequently used amplifier circuit.<\/p>\n<p style=\"text-align: center;\"><a class=\"btn btn-danger\" role=\"button\" href=\"https:\/\/study.madeeasy.in\/ec\/electronic-devices-circuits\/what-is-the-function-of-a-transistor-in-an-electronic-device\/\" target=\"_blank\" rel=\"noopener\">&lt;&lt; Previous<\/a> | <a class=\"btn btn-success\" role=\"button\" href=\"https:\/\/study.madeeasy.in\/ec\/electronic-devices-circuits\/what-is-bjt-and-its-configuration\/\" target=\"_blank\" rel=\"noopener\"> Next &gt;&gt;<\/a><\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>BJT Configuration A configuration refers to the way three terminals of BJT are used in amplifier. Based upon the reference<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[571,6],"tags":[609,605,606,610,607,608,611],"class_list":["post-2120","post","type-post","status-publish","format-standard","hentry","category-electronic-devices-circuits","category-ec","tag-active-region","tag-bjt-configuration","tag-common-emitter-configuration","tag-cut-off-region","tag-input-characteristics","tag-output-characteristics","tag-saturation-region"],"_links":{"self":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts\/2120","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/comments?post=2120"}],"version-history":[{"count":0,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts\/2120\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/media?parent=2120"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/categories?post=2120"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/tags?post=2120"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}