Coil Co-Simulation Using HFSS and Circuit

Hello everyone, this is Adel from Ozen Engineering. In this video, I'll show you how to run a coil co-simulation using HFSS and Circuit. I'll start with this coil layout imported into HFSS 3D layout, where the PCB has a circular outline with a rectangular extension.

By default, when exporting the layout to HFSS, the dielectric stackup becomes rectangular. Here, I'll show you how to preserve the circular outline of the stackup during export.

Note that what gets exported from HFSS 3D layout is not the actual geometry, but what HFSS sees as the mesh, based on the solution setup settings. So let's start by adding a solution setup. Right-click on Analysis, Add HFSS solution setup, Advanced. Now let's click on the Advanced Meshing tab.

I'll reduce the arc step size to 1 degree and increase the maximum number of arc points to 32. Let's keep the frequency sweep as is for now; I'll configure it later in HFSS 3D.

Now let's go to HFSS Xtends and click Edit and change the dielectric type from bounding box to conformal to preserve the stackup shape. I'll also increase the size of the radiation box, click Apply, and OK. To view the Xtends, click HFSS Xtends, Show.

Now to export, right-click on Setup1, Export, HFSS Model. Here, select the directory and the file name, then click Save. Now to open the model, go to File, Open, select the model, and click Open. This is our HFSS 3D model.

Here, the solution type is terminal, so I go to HFSS solution type and I change it to model and click OK. The radiation boundary condition is already assigned. Now we need to add an excitation. So I'll assign a circuit port.

I'll start by selecting the edges, right-click, assign excitation, port, circuit port, click next, and finish.

Now let's configure the solution setup, so expand Analysis, and I'll click on Setup 1. Here, I'll change the solution frequency to 10 MHz and I'll reduce the maximum delta S to 0. 01. For the frequency sweep, I'll set it to linear count.

I'll set the start frequency to 1 MHz, the end frequency to 200 MHz, and I set the number of points to 451. We can now run a validation check and run the simulation by clicking Analyze All. Once the simulation is complete, we can view the results of the coil without the tuning capacitors.

I'll start by adding an output variable for the coil inductance. So right-click on Results, go to Output Variables, here I'll name it LCoil, and I'll enter the expression for the inductance in microhenries. Now let's plot the inductance.

So I create a rectangular plot, go to Output Variables, and click New Report. Let's add an X-marker at 10 MHz. So right-click, go to Marker, X-marker. So we have an inductance of 0.57 microhenries, which theoretically requires a capacitance of approximately 444 pF to achieve resonance at 10 MHz.

Now let's make a second plot for the coil's self-resonance. So here I plot the imaginary and real parts of Z 11. Let's place an X-marker. As you can see, the coil's self-resonance is around 76 MHz. Now let's add some tuning capacitors in the circuit.

So I'll go to Desktop, Circuit, here I'll drag and drop the HFSS design into Circuit. Let's add a port, and I'll add two capacitors placed and piloted. I'll create a variable for the first capacitor, let's call it tuningC0, and I'll give it a value.

Now let's expand Circuit and add a linear network analysis. Here, I already have my frequency sweep up to 20 MHz, so I just click OK. Now let's try to click on Circuit and click Analyze. Let's plot the S11, and here I'll place an X-marker at 10 MHz.

As you can see, we have a return loss of minus 10.71 dB at 10 MHz. Now let's tune the capacitors for better return loss. Let's go to Circuit, Design Properties, Local Variables, Tuning, and here I'll include both capacitors.

I'll change the minimum for tuning C1 to 350 pF and the maximum to 450 pF with a step of 1 pF. I'll change the minimum for tuning C0 to 40 pF and the maximum to 60 pF with a step of 1 pF.

Now if I right-click on optiSLang, click Tuning, and check Browse available variations, and here we can tune the capacitors to achieve better return loss. The return loss is now better than minus 21 dB. We can now apply the updated capacitor values.

In the studio, we saw the process of exploring coil layout from HFSS 3D layout to HFSS 3D while preserving the correct stackup shape, setting up the coil simulation in HFSS, and linking the model to Circuit to add tuning capacitors. Thanks for watching, and see you in the next video.

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