{"id":18014,"date":"2017-11-10T10:04:32","date_gmt":"2017-11-10T18:04:32","guid":{"rendered":"http:\/\/www.autodesk.com\/products\/eagle\/blog\/?p=1896"},"modified":"2023-07-17T23:19:13","modified_gmt":"2023-07-18T06:19:13","slug":"spice-simulation-part-4-transient-analysis-spice-model-mapping","status":"publish","type":"post","link":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/spice-simulation-part-4-transient-analysis-spice-model-mapping\/","title":{"rendered":"SPICE Simulation Part 4: Transient Analysis & SPICE Model Mapping"},"content":{"rendered":"\n

Welcome back to our SPICE Simulation Series, Part 4! <\/span>In Part 3<\/span><\/a> we showed you the ins and outs of DC Sweep and AC Sweep analysis. Now it\u2019s time to dive into the final simulation type in Autodesk EAGLE – Transient analysis. We\u2019ll also be covering a commonly asked question: how do you map SPICE models to existing components?<\/span><\/p>\n\n\n

Transient Analysis Setup<\/h2>\n\n\n

Transient analysis is pretty simple; it simulates the behavior of your circuit\u2019s voltage and current over a defined period of <\/span>time<\/span>. This simulation is perfect for identifying performance issues such as nonlinear distortion, intermodulation, saturation, clipping, and oscillations.<\/span><\/p>\n\n\n\n

A transient analysis in EAGLE takes three variables, Start Time, Stop Time, and TMAX. TMAX defines the maximum allowed step time and can be useful for analyzing oscillators. The other two settings define when the transient analysis starts and stops.<\/span><\/p>\n\n\n

Example Project<\/h3>\n\n\n

The example project we\u2019ll be working with is an opamp circuit that uses subcircuits and models. Let\u2019s open this now. Look for the <\/span>opamp project folder <\/b>within the <\/span>Projects \u00bb ngspice<\/b> directory in your <\/span>Autodesk EAGLE Control Panel<\/b>. Then open <\/span>opamp1.sch<\/b>.<\/span><\/p>\n\n\n\n

\"opamp<\/figure>\n\n\n\n

In this example circuit, we have two<\/span> opamp subcircuits<\/span><\/a>. At the top is our voltage supply with a couple of resistors. This voltage is then fed into the middle circuit where we have a negative feedback amplifier. In the bottom, there\u2019s a filter. What we want to do is look at this circuit in the time domain with transient analysis and see what happens to our voltage and current. <\/span><\/p>\n\n\n

SPICE Models<\/h2>\n\n\n

Let\u2019s talk about SPICE models before running our simulation. When you place a part like an opamp on a schematic, you get a default model called lm741 that\u2019s already mapped to a library. But how do you change this to map to a SPICE model instead?<\/span><\/p>\n\n\n\n

    \n
  1. First, right click on an opamp symbol and select <\/span>Add Model<\/b>.<\/span><\/li>\n\n\n\n
  2. In the Add Model dialog<\/b> select the Map button<\/b> next to the listed part.<\/li>\n\n\n\n
  3. This will open the <\/span>Map to Model dialog<\/b>. Here you can see the loaded model and also the button to load a new model. <\/span><\/li>\n<\/ol>\n\n\n\n
    \"map<\/figure>\n\n\n\n

    Once a new model gets loaded you\u2019ll be taken to the <\/span>Map Pins tab<\/b> to map all of the pins on the symbol to SPICE model inputs. We\u2019re not going to make any changes to our opamp at the moment; we just wanted to show you a quick and easy way to load in a new SPICE model.<\/span><\/p>\n\n\n\n

    \"map<\/figure>\n\n\n

    Netlist Part Models<\/h3>\n\n\n

    When parts get added to SPICE models, this will be shown in your netlist. Let\u2019s see how this looks. Select the <\/span>Simulate button<\/b> at the top of your interface to open the <\/span>Simulation dialog<\/b>, then select the <\/span>Netlist tab<\/b>.<\/span><\/p>\n\n\n\n

    When SPICE models are added to parts, this will be shown in your netlist. To make it clear where models are coming from, the directory for each model is referenced. Here we can see that we have two opamps, one is located in the directory of our opamp project folder, the other is in the global models directory folder.<\/span><\/p>\n\n\n\n

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

    EAGLE will make several attempts to locate models for your parts, looking in this order:<\/span><\/p>\n\n\n\n