{"id":1831,"date":"2017-10-27T08:00:31","date_gmt":"2017-10-27T15:00:31","guid":{"rendered":"http:\/\/www.autodesk.com\/products\/eagle\/blog\/?p=1831"},"modified":"2023-07-18T15:23:58","modified_gmt":"2023-07-18T22:23:58","slug":"spice-simulation-part-2-operating-point-analysis","status":"publish","type":"post","link":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/spice-simulation-part-2-operating-point-analysis\/","title":{"rendered":"SPICE Simulation Part 2: Running Your First Simulation – DC Operating Point Analysis"},"content":{"rendered":"\n

Welcome back to our SPICE Simulation Series, Part 2! In this blog, we\u2019ll be running one of the most fundamental simulations in <\/span>Autodesk EAGLE 8.4<\/span><\/a>, DC operating point analysis. This method will allow you to analyze the behavior of a circuit when a DC voltage or current is applied. In our example project, we’ll be verifying the expected current from a voltage source to ground. This simulation might sound simple on the outside, but it\u2019s a great way to learn the basics of how SPICE simulation works in EAGLE. Let\u2019s try it out!<\/span><\/p>\n\n\n

Our Example Project<\/h2>\n\n\n

The SPICE simulator in <\/span>Autodesk EAGLE 8.4<\/span><\/a> comes with a ton of pre-configured designs. Each design is set up for a specific simulation type. For our operating point analysis, we\u2019ll be working with a primary circuit taken from a popular undergraduate textbook as shown below:<\/span><\/p>\n\n\n\n

\"eagle<\/figure>\n\n\n\n

This circuit is typically used in basic circuit design<\/a> classes to teach students how to calculate currents and voltages. It features two voltage sources and three resistors. We want to confirm that our current is 0.1 mA as it travels through node A to ground.<\/span><\/p>\n\n\n\n

To open this example project, look for the <\/span>KVL project folder<\/b> within the <\/span>Project \u00bb ngspice<\/b> directory in your <\/span>Autodesk EAGLE control panel<\/b>. <\/span><\/p>\n\n\n\n

\"kvl<\/figure>\n\n\n\n

As we mentioned, this project is already set up for SPICE simulation, but what does that mean? It means that all of the schematic symbols are already SPICE enabled or have SPICE models attached to them. Without these models, the circuit would not be simulatable. There\u2019s no visual difference between a part that is SPICE simulation ready and one that isn\u2019t on your schematic. To determine if your symbol is SPICE compatible, you can do the following:<\/span><\/p>\n\n\n\n

    \n
  1. Right-click the schematic symbol and select <\/span>Properties<\/b>.<\/span><\/li>\n\n\n\n
  2. In the <\/span>Properties dialog<\/b> look at the value in the <\/span>Library field<\/b>.<\/span><\/li>\n\n\n\n
  3. Select OK<\/b> to close the dialog.<\/li>\n<\/ol>\n\n\n\n
    \"part<\/figure>\n\n\n\n

    Here we can see that this part is from the <\/span>ngspice simulation<\/span><\/em> library. This is a managed online library that ships with Autodesk EAGLE 8.4 which contains other pre-configured SPICE parts.<\/span><\/p>\n\n\n\n

    One thing to keep in mind is that if you make your own SPICE compatible parts, this library value will be different when viewing a symbol\u2019s properties. However, when working with preconfigured parts, the ngspice-simulation library is an indicator that your symbol is simulation ready.<\/span><\/p>\n\n\n

    The Simulation Dialog<\/h2>\n\n\n

    Every SPICE simulation is run from the <\/span>Simulation dialog<\/b> in Autodesk EAGLE 8.4. You can open this in one of two ways. Either select the <\/span>Simulation<\/b> at the top of your interface or enter \u201csim\u201d in the <\/span>command line<\/b> and press <\/span>Enter<\/b>. You\u2019ll notice four tabs when you open the simulation dialog, let\u2019s walk through each before running our operating point analysis.<\/span><\/p>\n\n\n

    Configuration Tab<\/h3>\n\n\n
    \"configuration<\/figure>\n\n\n\n

    The first tab is where you\u2019ll set the simulation type. The left-hand side contains all of the available simulation options. <\/span>Operating Point<\/b> is selected by default since that\u2019s what our design is configured for. However, if you open another ngspice example project, another simulation type will be the selected default.<\/span><\/p>\n\n\n\n

    On the right, you have your <\/span>DC Sim<\/b> and <\/span>Transient Sim<\/b> options. You likely won\u2019t ever need to change these values unless your simulation runs into converging or timestamp issues. These and other common SPICE related issues can be resolved by tweaking the DC sim and Transient Sim options. For example, turning on RSHUNT is a conventional method to help a troublesome circuit converge.<\/span><\/p>\n\n\n\n

    \"dc<\/figure>\n\n\n\n

    For this walkthrough we\u2019ll leave all these values at default. If you change one by mistake just press <\/span>reset <\/b>to start fresh.<\/span><\/p>\n\n\n\n

    \"reset<\/figure>\n\n\n\n

    An essential button on this tab is the <\/span>Save Netlist button<\/b>. Whenever you make a change to a symbol value or name on your schematic, pressing this button will update your SPICE netlist configuration. There\u2019s also the <\/span>Simulate button<\/b>, which we\u2019ll be working with later. <\/span><\/p>\n\n\n

    Netlist Tab<\/h3>\n\n\n
    \"netlist<\/figure>\n\n\n\n

    The Netlist tab displays a raw text format of your netlist configuration, which includes your simulation settings, devices, models, and more. The netlist is a text-based representation of your visual schematic. If you change values here, it won\u2019t change anything on your schematic.<\/span><\/p>\n\n\n\n

    Under the <\/span>Options heading<\/b> are all of the values that you set in the Configuration tab. You can also change these values directly here if you\u2019d prefer. <\/span><\/p>\n\n\n\n

    \"netlist<\/figure>\n\n\n\n

    Look under the <\/span>Devices heading<\/b>, and you\u2019ll see all of the parts connected in your schematic. <\/span><\/p>\n\n\n\n

    \"netlist<\/figure>\n\n\n\n

    The format goes like this:<\/span><\/p>\n\n\n\n

    Component Type, Reference Designator, Net\/Pin Connections, Symbol Value <\/span><\/pre>\n\n\n\n
    For example, <\/span><\/p>\n\n\n\n
    R_R1 A B 10k<\/span><\/pre>\n\n\n\n
    This device is a resistor, <\/span>R<\/b>, with reference designator <\/span>R1<\/b>, pins connected to nets <\/span>A <\/b>and <\/span>B<\/b>, with a resistance value of <\/span>10k<\/b>. <\/span><\/p>\n\n\n\n
    You can quickly copy and paste information to\/from your netlist and also make quick changes to parameters. For example, we could change our R1 resistor to 12k, or our V1 voltage source to 3.5V, and then immediately run our simulation based on this edited netlist. This is a great option if you want to quickly test values and compare results without having to change your schematic. <\/span><\/p>\n\n\n\n
    One important note, when you select the <\/span>Save Netlist button<\/b> on your <\/span>Configuration tab<\/b> this will recreate the netlist with parameters from your schematic. Use this button if you ever tweak values and want to revert to your default netlist values.<\/span><\/p>\n\n\n
    Simulator Output & Plot Tabs<\/h3>\n\n\n
    \"op<\/figure>\n\n\n\n
    These last two tabs are where all of your simulation outputs will display. Raw text results will display in the <\/span>Simulator Output tab<\/b>, and the <\/span>Plot tab<\/b> will provide a visual graph for transient analysis methods.<\/span><\/p>\n\n\n\n
    Since our operating point analysis is only measuring values at a single point in time results will only be displayed in the Simulator Output tab.<\/span><\/p>\n\n\n\n
    The Simulator Output tab is also where you can see any errors with your simulation. This tab is important to review for simulation specific errors. For example, changing the value on a symbol might work for EAGLE, but not the SPICE simulator. When a simulation is run, EAGLE will check all of your component values and alert you about any simulation errors. Here\u2019s an example below:<\/span><\/p>\n\n\n\n
    \"simulation<\/figure>\n\n\n
    Running an Operating Point Analysis<\/h2>\n\n\n
    Let\u2019s now run your first operating point analysis simulation with the following steps:<\/span><\/p>\n\n\n\n
      \n
    1. Open the <\/span>KVL.sch<\/span> example from the <\/span>Project \u00bb ngspice<\/b> folder in the <\/span>Autodesk EAGLE Control Panel<\/b>. <\/span><\/li>\n\n\n\n
    2. Select the <\/span>Simulation\u00a0icon<\/b> to open the <\/span>Simulation dialog<\/b>. <\/span><\/li>\n\n\n\n
    3. Operating Point<\/b> should be selected as the default <\/span>Simulation Type<\/b>, with <\/span># of points<\/b> set to 500, and <\/span>temperature<\/b> set to 25. <\/span><\/li>\n\n\n\n
    4. Select the <\/span>Simulate button<\/b> to run your operating point analysis.<\/span><\/li>\n<\/ol>\n\n\n\n
      When the simulation completes, you\u2019ll be taken to the <\/span>Simulator Output tab<\/b>. Here you can see a breakdown of the voltage and current as it travels through each node in the circuit.<\/span><\/p>\n\n\n\n
      \"simulator<\/figure>\n\n\n\n
      If you close the Simulation dialog, you\u2019ll also see simulation results displayed on your schematic in blue. Here you can see that we\u2019re getting 0.1 mA of current through node A to ground. You can toggle the display of simulation results on your schematic by selecting the <\/span>OP Results Toggle<\/b> at the top of your interface.<\/p>\n\n\n\n
      \"op<\/figure>\n\n\n\n
      What if your circuit wasn\u2019t performing as expected? Instead of changing symbol values and going through the whole process again, you can quickly run a simulation by changing values in your netlist. Here\u2019s how:<\/span><\/p>\n\n\n\n
        \n
      1. In the <\/span>Simulation dialog<\/b>, select the <\/span>Netlist tab<\/b>.<\/span><\/li>\n\n\n\n
      2. Under the Devices heading<\/b>, change the value of one of the components.<\/li>\n\n\n\n
      3. Select the <\/span>Simulate button<\/b> to run your operating point analysis. <\/span><\/li>\n<\/ol>\n\n\n\n
        Again you\u2019ll be taken to the Simulator Output Tab to analyze your simulation results. Tweaking values in the netlist tab make easy work of finding the right fit for parameter values. <\/span><\/p>\n\n\n\n
        \"op<\/figure>\n\n\n
        SPICE Made Simple<\/h2>\n\n\n
        Operating point analysis is one of many SPICE simulation methods available in Autodesk EAGLE 8.4. If you ever need to analyze the voltage and current of a circuit at a specific point in time, then this is your simulation of choice.  Or if you need to inquire about the values of components like MOSFETs, you should run an Operating Point analysis.  In future blogs, we\u2019ll be looking at more advanced simulation methods including DC Sweep, AC Sweep, and Transient Analysis. Be on the lookout for more installments in our SPICE Simulation Series soon!<\/span><\/p>\n\n\n\n
        Have you been following along? Try the new SPICE simulation for free! <\/span>Download Autodesk EAGLE 8.4 now<\/span><\/a>.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"
        We\u2019re turning up the heat! Learn how to run your first operating point analysis in the Autodesk EAGLE 8.4 integrated SPICE simulator.<\/p>\n","protected":false},"author":2425,"featured_media":1808,"menu_order":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[434],"tags":[],"coauthors":[],"class_list":["post-1831","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-eagle","dhig-theme--light"],"acf":[],"yoast_head":"\nHow-To SPICE Simulation Operating Point | EAGLE | Blog<\/title>\n<meta name=\"description\" content=\"Learn how to run a DC operating point analysis simulation to analyze current and voltage for electronic circuits. 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