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<title>Direct coupling</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Direct coupling</span></span>

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<p>In electronics, <b>direct coupling</b> or <b>DC coupling</b> (also called <b>conductive coupling</b><sup id="cite_ref-:0_1-0" class="reference"><a href="#cite_note-:0-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> and <b>galvanic coupling</b>) is the transfer of electrical <a href="Energy" title="Energy">energy</a> by means of physical contact via a conductive medium, in contrast to <a href="Inductive_coupling" title="Inductive coupling">inductive coupling</a> and <a href="Capacitive_coupling" title="Capacitive coupling">capacitive coupling</a>. It is a way of interconnecting two circuits such that, in addition to transferring the AC signal (or information), the first circuit also provides <a href="DC_bias" title="DC bias">DC bias</a> to the second. Thus, DC blocking capacitors are not used or needed to interconnect the circuits. Conductive coupling passes the full spectrum of <a href="Frequencies" class="mw-redirect" title="Frequencies">frequencies</a> including <a href="Direct_current" title="Direct current">direct current</a>.

</p><p>Such <a href="Coupling_(electronics)" title="Coupling (electronics)">coupling</a> may be achieved by a <a href="Wire" title="Wire">wire</a>, <a href="Resistor" title="Resistor">resistor</a>, or common <a href="Terminal_(electronics)" title="Terminal (electronics)">terminal</a>, such as a <a href="Binding_post" title="Binding post">binding post</a> or metallic <a href="Chemical_bond" title="Chemical bond">bonding</a>.

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<p>The provision of DC bias only occurs in a group of circuits that forms a single unit, such as an <a href="Op-amp" class="mw-redirect" title="Op-amp">op-amp</a>. Here the internal units or portions of the op-amp (like the input stage, voltage gain stage, and output stage) will be direct coupled and will also be used to set up the bias conditions inside the op-amp (the input stage will also supply the input bias to the voltage gain stage, for example). However, when two op-amps are directly coupled the first op-amp will supply any bias to the next – any DC at its output will form the input for the next. The resulting output of the second op-amp now represents an offset error if it is not the intended one.

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<p>This technique is used by default in circuits like <a href="Integrated_circuit" title="Integrated circuit">IC</a> op-amps, since large coupling <a href="Capacitor" title="Capacitor">capacitors</a> cannot be fabricated on-chip. That said, some discrete circuits (such as <a href="Power_amplifier" class="mw-redirect" title="Power amplifier">power amplifiers</a>) also employ direct coupling to cut cost and improve low frequency performance.

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<div class="mw-heading mw-heading2"><h2 id="Offset_error">Offset error</h2></div>

<p>One advantage or disadvantage (depending on application) of direct coupling is that any DC at the input appears as a valid <i>signal</i> to the system, and so it will be transferred from the input to the output (or between two directly coupled circuits). If this is not a desired result, then the term used for the output signal is <i>output offset error</i>, and the corresponding input signal is known as <i>input offset error</i>.

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<div class="mw-heading mw-heading3"><h3 id="Error_correction">Error correction</h3></div>

<p>Temperature drift and device mismatches are the major causes of offset errors, and circuits employing direct coupling often integrate offset nulling mechanisms. Some circuits (like power amplifiers) even use coupling capacitors—except that these are present <i>only</i> at the input (and/or output) of the whole system but not between the individual circuit units inside the system.

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<div class="mw-heading mw-heading2"><h2 id="Advantages">Advantages</h2></div>

<p>The advantage of direct coupling is very good low frequency response, often from DC to the highest operating frequency that the system will allow. All applications that require monitoring of slowly changing signals (such as those from <a href="Thermistor" title="Thermistor">thermistors</a>, <a href="Thermocouple" title="Thermocouple">thermocouples</a>, <a href="Strain_gage" class="mw-redirect" title="Strain gage">strain gages</a>, etc.) must have a very good DC amplification with minimum offset errors and hence they must be directly coupled throughout, and have offset correction or trimming incorporated into them.

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<ul><li><a href="Direct-coupled_amplifier" title="Direct-coupled amplifier">Direct-coupled amplifier</a></li>

<li><a href="Electromagnetic_compatibility" title="Electromagnetic compatibility">Electromagnetic compatibility</a></li>

<li><a href="Electromagnetic_interference" title="Electromagnetic interference">Electromagnetic interference</a></li>

<li><a href="Galvanic_isolation" title="Galvanic isolation">Galvanic isolation</a></li>

<li><a href="Ohmic_contact" title="Ohmic contact">Ohmic contact</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFAlexanderO._Sadiku2013" class="citation book cs1">Alexander, Charles K.; O. Sadiku, Matthew N. (2013). <i>Fundamentals of Electric Circuits</i> (5th ed.). McGraw-Hills. p. 556. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-07-338057-5</bdi>. <q>The circuits we have considered so far may be regarded as conductively coupled, because one loop affects the neighboring loop through current conduction. When two loops with or without contacts between them affect each other through the magnetic field generated by one of them, they are said to be magnetically coupled.</q></cite></span>

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</style><span class="citation FS1037C MS188"><span class="noviewer" typeof="mw:File"><span></span></span> This article incorporates <a href="Copyright_status_of_works_by_the_federal_government_of_the_United_States" title="Copyright status of works by the federal government of the United States">public domain material</a> from <cite class="citation cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20220122224547/https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm"><i>Federal Standard 1037C</i></a>. <a href="General_Services_Administration" title="General Services Administration">General Services Administration</a>. Archived from <a rel="nofollow" class="external text" href="https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm">the original</a> on 2022-01-22.</cite> (in support of <a href="MIL-STD-188" title="MIL-STD-188">MIL-STD-188</a>).</span></li></ul>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://learnemc.com/common-impedance-coupling">Common Impedance Coupling</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-05-05" href="https://en.wikipedia.org/wiki/?title=Direct_coupling&oldid=1288834917">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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