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class=md-nav__item> <a href=../../../../user_manual/tutorials/software/snapshot/ class=md-nav__link> <span class=md-ellipsis> Take a Snapshot </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/software/firmware_update/ class=md-nav__link> <span class=md-ellipsis> Firmware Upgrade </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/software/gb_palette/ class=md-nav__link> <span class=md-ellipsis> Change Game Boy Palette </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/software/gmenu2x_wallpaper/ class=md-nav__link> <span class=md-ellipsis> Change GMenu2X Wallpaper </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_1_2> <label class=md-nav__link for=__nav_2_1_2 id=__nav_2_1_2_label tabindex=0> <span class=md-ellipsis> Hardware </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=3 aria-labelledby=__nav_2_1_2_label aria-expanded=false> <label class=md-nav__title for=__nav_2_1_2> <span class="md-nav__icon md-icon"></span> Hardware </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/hardware/teardown/ class=md-nav__link> <span class=md-ellipsis> Teardown </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/hardware/flash_change_sd_card/ class=md-nav__link> <span class=md-ellipsis> Flash & Change micro-SD Card </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/hardware/change_buttons/ class=md-nav__link> <span class=md-ellipsis> Change the Buttons </span> </a> </li> <li class=md-nav__item> <a href=../../../../user_manual/tutorials/hardware/fix_unstuck_screen/ class=md-nav__link> <span class=md-ellipsis> </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3 checked> <label class=md-nav__link for=__nav_3 id=__nav_3_label tabindex=0> <span class=md-ellipsis> Developer's Guide </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_3_label aria-expanded=true> <label class=md-nav__title for=__nav_3> <span class="md-nav__icon md-icon"></span> Developer's Guide </label> <ul class=md-nav__list data-md-scrollfix> <li class="md-nav__item md-nav__item--active md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3_1 checked> <div class="md-nav__link md-nav__container"> <a href=../../ class="md-nav__link "> <span class=md-ellipsis> Hardware Reference </span> </a> <label class="md-nav__link " for=__nav_3_1 id=__nav_3_1_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_3_1_label aria-expanded=true> <label class=md-nav__title for=__nav_3_1> <span class="md-nav__icon md-icon"></span> Hardware Reference </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../architecture/ class=md-nav__link> <span class=md-ellipsis> Architecture </span> </a> </li> <li class=md-nav__item> <a href=https://htmlpreview.github.io/?https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/BOM/ibom.html class=md-nav__link> <span class=md-ellipsis> BOM </span> </a> </li> <li class=md-nav__item> <a href=../../cpu/ class=md-nav__link> <span class=md-ellipsis> CPU </span> </a> </li> <li class="md-nav__item md-nav__item--active md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3_1_4 checked> <label class=md-nav__link for=__nav_3_1_4 id=__nav_3_1_4_label tabindex=0> <span class=md-ellipsis> Power </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=3 aria-labelledby=__nav_3_1_4_label aria-expanded=true> <label class=md-nav__title for=__nav_3_1_4> <span class="md-nav__icon md-icon"></span> Power </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../power_supplies_topologies/ class=md-nav__link> <span class=md-ellipsis> Regulated DC Power Supply Topologies </span> </a> </li> <li class=md-nav__item> <a href=../multiple_voltages/ class=md-nav__link> <span class=md-ellipsis> Multiple Power Supply Voltages </span> </a> </li> <li class=md-nav__item> <a href=../pmic/ class=md-nav__link> <span class=md-ellipsis> PMIC </span> </a> </li> <li class=md-nav__item> <a href=../dram_power/ class=md-nav__link> <span class=md-ellipsis> DRAM Power </span> </a> </li> <li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type=checkbox id=__toc> <label class="md-nav__link md-nav__link--active" for=__toc> <span class=md-ellipsis> Decoupling </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Decoupling </span> </a> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#capacitor-usage class=md-nav__link> <span class=md-ellipsis> Capacitor Usage </span> </a> <nav class=md-nav aria-label="Capacitor Usage"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#load-capacitors class=md-nav__link> <span class=md-ellipsis> Load Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#bulk-capacitors class=md-nav__link> <span class=md-ellipsis> Bulk Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#coupling-capacitors class=md-nav__link> <span class=md-ellipsis> Coupling Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#filter-capacitors class=md-nav__link> <span class=md-ellipsis> Filter Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#decoupling-bypass-capacitors class=md-nav__link> <span class=md-ellipsis> Decoupling (Bypass) Capacitors </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#schematics class=md-nav__link> <span class=md-ellipsis> Schematics </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../screen/ class=md-nav__link> <span class=md-ellipsis> Screen </span> </a> </li> <li class=md-nav__item> <a href=../../audio/ class=md-nav__link> <span class=md-ellipsis> Audio </span> </a> </li> <li class=md-nav__item> <a href=../../buttons/ class=md-nav__link> <span class=md-ellipsis> Buttons </span> </a> </li> <li class=md-nav__item> <a href=../../sd-card/ class=md-nav__link> <span class=md-ellipsis> SD Card </span> </a> </li> <li class=md-nav__item> <a href=../../usb/ class=md-nav__link> <span class=md-ellipsis> USB </span> </a> </li> <li class=md-nav__item> <a href=../../uart/ class=md-nav__link> <span class=md-ellipsis> UART </span> </a> </li> <li class=md-nav__item> <a href=../../magnetic_switch/ class=md-nav__link> <span class=md-ellipsis> Magnetic Switch </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3_2> <div class="md-nav__link md-nav__container"> <a href=../../../software_reference/ class="md-nav__link "> <span class=md-ellipsis> Software Reference </span> </a> <label class="md-nav__link " for=__nav_3_2 id=__nav_3_2_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_3_2_label aria-expanded=false> <label class=md-nav__title for=__nav_3_2> <span class="md-nav__icon md-icon"></span> Software Reference </label> <ul class=md-nav__list data-md-scrollfix> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3_2_1> <div class="md-nav__link md-nav__container"> <a href=../../../software_reference/boot_process/ class="md-nav__link "> <span class=md-ellipsis> Boot Process </span> </a> <label class="md-nav__link " for=__nav_3_2_1 id=__nav_3_2_1_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=3 aria-labelledby=__nav_3_2_1_label aria-expanded=false> <label class=md-nav__title for=__nav_3_2_1> <span class="md-nav__icon md-icon"></span> Boot Process </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../../software_reference/boot_process/boot_rom/ class=md-nav__link> <span class=md-ellipsis> Boot ROM </span> </a> </li> <li class=md-nav__item> <a href=../../../software_reference/boot_process/spl/ class=md-nav__link> <span class=md-ellipsis> SPL </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input 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class=md-nav__link> <span class=md-ellipsis> Glossary </span> </a> </li> </ul> </nav> </li> </ul> </nav> </div> </div> </div> <div class="md-sidebar md-sidebar--secondary" data-md-component=sidebar data-md-type=toc> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#capacitor-usage class=md-nav__link> <span class=md-ellipsis> Capacitor Usage </span> </a> <nav class=md-nav aria-label="Capacitor Usage"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#load-capacitors class=md-nav__link> <span class=md-ellipsis> Load Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#bulk-capacitors class=md-nav__link> <span class=md-ellipsis> Bulk Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#coupling-capacitors class=md-nav__link> <span class=md-ellipsis> Coupling Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#filter-capacitors class=md-nav__link> <span class=md-ellipsis> Filter Capacitors </span> </a> </li> <li class=md-nav__item> <a href=#decoupling-bypass-capacitors class=md-nav__link> <span class=md-ellipsis> Decoupling (Bypass) Capacitors </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#schematics class=md-nav__link> <span class=md-ellipsis> Schematics </span> </a> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <h1>Decoupling</h1> <h2 id=capacitor-usage>Capacitor Usage<a class=headerlink href=#capacitor-usage title="Permanent link">¶</a></h2> <p>So far, we already encountered capacitors for many different usages:</p> <h3 id=load-capacitors>Load Capacitors<a class=headerlink href=#load-capacitors title="Permanent link">¶</a></h3> <p>We have seen load capacitors used with the 2 crystals in the discussion about <a href=/developer_guide/hardware_reference/cpu/#crystals><abbr title="Central Processing Unit">CPU</abbr></a>.</p> <p>A quartz crystal always provides both series and parallel resonance, the series resonance being a few kilohertz lower than the parallel one.</p> <p>Crystals below 30 MHz like ours are generally operated between series and parallel resonance, which means that the crystal appears as an inductive reactance in operation, this inductance forming a <strong>parallel resonant circuit</strong> with externally connected parallel "load" capacitance. Any small additional capacitance added in parallel with the crystal pulls the frequency lower in the range between the series and parallel resonance frequencies, insuring crystal startup and stable operation.</p> <p>For modern circuits, these load capacitors have a typical small value < 20 pF.</p> <h3 id=bulk-capacitors>Bulk Capacitors<a class=headerlink href=#bulk-capacitors title="Permanent link">¶</a></h3> <p>Bulk capacitors are used to prevent a power supply from dropping too far during the periods when current is not available. At the same time, they help to reduce the power supply voltage ripples by smoothing their output voltage.</p> <p>Many such capacitors are used at both the input and output of the numerous linear and switched mode power supplies in the <a href=/developer_guide/hardware_reference/power/pmic><abbr title="Power Management Integrated Circuit">PMIC</abbr> discussion</a>.</p> <p>The main bulk capacitor value is generally high (some µF), but there may be smaller parallel capacitors added for stability.</p> <h3 id=coupling-capacitors>Coupling Capacitors<a class=headerlink href=#coupling-capacitors title="Permanent link">¶</a></h3> <p>As you probably know, capacitors are made of 2 parallel conductive electrodes separated by a (thin) isolating dielectric material (even if these electrodes are rolled or layered to reduce the component size). Thus by construction, no DC (Direct Current) can flow from one electrode to the other, but by influence using the electric field, AC (Alternative Current) still can go through. This is how coupling capacitors are used to link 2 circuits while removing any DC bias voltage on one side or the other of the capacitor.</p> <p>We use such a coupling capacitor in the <a href=/developer_guide/hardware_reference/audio/#schematic>Audio schematic description</a> for feeding the audio power amplifier from the <abbr title="Central Processing Unit">CPU</abbr> audio output.</p> <h3 id=filter-capacitors>Filter Capacitors<a class=headerlink href=#filter-capacitors title="Permanent link">¶</a></h3> <p>We have seen many examples where capacitors are used within passive filter circuits along with resistors or inductors, mainly to remove unwanted frequencies from a power supply or a signal.</p> <h3 id=decoupling-bypass-capacitors>Decoupling (Bypass) Capacitors<a class=headerlink href=#decoupling-bypass-capacitors title="Permanent link">¶</a></h3> <p>We use some decoupling capacitors in the <a href=/developer_guide/hardware_reference/buttons/#schematics>buttons circuit</a>.</p> <p>Active components such as transistors and chips are connected to their power supplies through conductors featuring a (small) common impedance made up of complex (resistive, capacitive and inductive) value. Because of these parasitic components, a device that suddenly draws some current in spikes will generate a drop in its voltage power supply. If many devices are sharing the same power supply and impedance, the state of one device will be coupled to the other ones through the common impedance of the power supply conductors and may affect their operation.</p> <p>In order to decouple the devices, capacitors placed as close as possible to the device power supply input pins are used, which act as local energy storage. These capacitors are also named "bypass capacitors" as they shunt transient energy from the power supplies past the device to be decoupled, right to the GND return path.</p> <p>There may be different capacitors values placed on the same power supply pins in order to filter transients at different frequencies: the bigger the capacitor value, the lower the frequency. A typical value is 100 nF, and values from 1 µF to 10 µF are used for lower frequencies and / or higher current draws, while lower values of a few nF are used for filtering higher frequencies.</p> <p>In essence, decoupling capacitors are not very different in their function from bulk capacitors: the only difference is one of scale, both of current and of transient duration. Bulk capacitors deal with large currents and periods of 10s of ms, whereas decoupling capacitors are used for much lower currents and much briefer periods (typically 10s of ns for TTL or CMOS devices) .</p> <h2 id=schematics>Schematics<a class=headerlink href=#schematics title="Permanent link">¶</a></h2> <p>The last part of the FunKey schematics merely contains only decoupling capacitors:</p> <p><img alt="Decoupling Schematics" class=lightbox src=/assets/images/Decoupling_Schematics.png></p> <p>One exception is the Allwinner V3s <abbr title="Central Processing Unit">CPU</abbr> HPR/HPL circuit which features an RC-to-ground circuit between the amplifier and the preamplifier input with the resistor <strong>R27</strong> and capacitors <strong>C79</strong> and <strong>C81</strong>, as recommended in the <a href=https://github.com/Squonk42/V3s_Documentation/blob/master/V3s%20hardware%20design%20guide%20V1.0_20150519%20EN%20Non%20Official.pdf>V3s hardware design guide</a>.</p> <p>The only other remarkable point left in this schematic is the resistor divider <strong>R25</strong>/<strong>R28</strong> which provides a reference voltage at half the <abbr title="Dynamic Random-Access Memory">DRAM</abbr> power supply voltage level, which is used for the integrated DDR2 <abbr title="Dynamic Random-Access Memory">DRAM</abbr> merged drivers and dynamic on-chip termination already discussed at the end of the previous <a href=/developer_guide/hardware_reference/cpu/#dram><abbr title="Central Processing Unit">CPU</abbr> schematic description</a>.</p> </article> </div> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> © 2020-2024 FunKey Project<br> Last updated on 2024-05-04 by DrUm78<br> <a href=http://creativecommons.org/licenses/by-sa/4.0/ rel=license> <img alt="Creative Commons License" style=border-width:0 src=https://i.creativecommons.org/l/by-sa/4.0/80x15.png> </a><br>This work is licensed under a <a href=http://creativecommons.org/licenses/by-sa/4.0/ rel=license>Creative Commons Attribution-ShareAlike 4.0 International License</a>. </div> Made with <a href=https://squidfunk.github.io/mkdocs-material/ target=_blank rel=noopener> Material for MkDocs </a> </div> <div class=md-social> <a href=https://www.facebook.com/FunKeyProjectOfficial target=_blank rel=noopener title=www.facebook.com class=md-social__link> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 6.5.2 by @fontawesome - 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