{"id":46,"date":"2025-05-07T06:23:44","date_gmt":"2025-05-07T06:23:44","guid":{"rendered":"https:\/\/yaveni.com\/blog\/?p=46"},"modified":"2025-05-07T06:23:44","modified_gmt":"2025-05-07T06:23:44","slug":"draw-the-circuit-of-a-mosfet-based-current-mirror-loaded-differential-amplifier","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/draw-the-circuit-of-a-mosfet-based-current-mirror-loaded-differential-amplifier\/","title":{"rendered":"Draw the circuit of a MOSFET-based current-mirror-loaded differential amplifier"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Draw the circuit of a MOSFET-based current-mirror-loaded differential amplifier. Explain the difference(s) between the circuit and a discrete common-source amplifier. Furthermore, explain the current-mirror-loaded spec of the circuit.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-vivid-cyan-blue-color\"><strong>The correct answer and explanation is :<\/strong><\/mark><\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Circuit Diagram:<\/strong><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Here is the basic circuit diagram of a <strong>MOSFET-based current-mirror-loaded differential amplifier<\/strong>:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>           VDD\n            |\n           M3\n           |\n    Drain of M1 -----------+----------- Drain of M2\n         |                |                 |\n         |                |                 |\n        M1               M2                M4\n         |                |                 |\n         +-------|        |        |--------+\n                 |        |        |\n                Source   Source   Drain\n                 of       of      of M4\n                M1       M2\n                 |        |\n                 +--------+\n                      |\n                    Current\n                    Source\n                      I_tail\n                      |\n                     GND<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>M1 &amp; M2<\/strong>: Differential pair transistors<\/li>\n\n\n\n<li><strong>M3 &amp; M4<\/strong>: Current mirror load<\/li>\n\n\n\n<li><strong>I_tail<\/strong>: Bias current source for differential pair<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Explanation (300+ words):<\/strong><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>MOSFET-based current-mirror-loaded differential amplifier<\/strong> is a widely used analog circuit in integrated circuits. It consists of a differential pair of transistors (M1 and M2) with their sources connected together and biased by a tail current source (I_tail). The drains of M1 and M2 are connected to a <strong>current mirror (M3 and M4)<\/strong>, which acts as an active load.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Working Principle:<\/strong><\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The differential input is applied at the gates of M1 and M2.<\/li>\n\n\n\n<li>The tail current I_tail is split between M1 and M2 depending on the input differential voltage.<\/li>\n\n\n\n<li>The current through M1 generates a mirrored current through M4 (assuming M3 and M4 are identical and properly biased).<\/li>\n\n\n\n<li>The voltage at the drain of M2 changes depending on the difference in current between M2 and the mirrored current from M4, producing an amplified differential output.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Comparison to Discrete Common-Source Amplifier:<\/strong><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A <strong>common-source amplifier<\/strong> is a single-transistor amplifier where the input is applied at the gate, and the output is taken from the drain. It uses a passive resistor or active load at the drain. Its gain is limited by the load resistance and has poor common-mode rejection.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Key Differences:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The differential amplifier uses two transistors vs. one in the common-source.<\/li>\n\n\n\n<li>It amplifies the <strong>difference<\/strong> between two inputs, making it suitable for rejecting common-mode signals (e.g., noise).<\/li>\n\n\n\n<li>It employs <strong>active loads (current mirrors)<\/strong> for higher gain and better performance in ICs.<\/li>\n\n\n\n<li>The differential amplifier provides higher <strong>common-mode rejection ratio (CMRR)<\/strong>.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Current-Mirror-Loaded Spec:<\/strong><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The term <strong>&#8220;current-mirror-loaded&#8221;<\/strong> refers to the use of a current mirror (M3 and M4) instead of resistive loads. This provides several advantages:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Higher gain<\/strong>: Because the output resistance of a current mirror is much higher than a resistor.<\/li>\n\n\n\n<li><strong>Better matching<\/strong>: In ICs, MOSFETs can be closely matched.<\/li>\n\n\n\n<li><strong>Improved linearity and performance<\/strong> in analog front-ends.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Draw the circuit of a MOSFET-based current-mirror-loaded differential amplifier. Explain the difference(s) between the circuit and a discrete common-source amplifier. Furthermore, explain the current-mirror-loaded spec of the circuit. The correct answer and explanation is : Circuit Diagram: Here is the basic circuit diagram of a MOSFET-based current-mirror-loaded differential amplifier: Explanation (300+ words): The MOSFET-based current-mirror-loaded [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-46","post","type-post","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/46","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=46"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/46\/revisions"}],"predecessor-version":[{"id":47,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/46\/revisions\/47"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=46"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=46"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=46"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}