Learning Forum

[ansysqueries]

Hi folks,

I was trying to simulate a device on HFSS which involves some lumped components. I drew rectangles where the lumped component is supposed to connect one metal to another. I assigned the rectangles with the lumped RLC boundary condition. I got the resonant frequency of my device with lumped components. I wanted to export the whole setup to ADS. So, I replaced the lumped RLC boundary condition with lumped ports excitation. I simulated the same structure simply by replacing the lumped RLCs with lumped ports. The snp file of the device was exported to ADS. I replaced the lumped ports with actual lumped components on ADS. I used the same values for the lumped components as in the lumped RLCs. However, I see a significant variation in the resonant frequency of the device when simulated on ADS. It shifts from 2 GHz to 2.5 GHz. 

 

Has anyone experienced similar problems? Any tips will be appreciated. Thanks in advance. 

[Sorceress Gia]

There could be a few issues going on depending on how you setup the ports / lumpedRLC boundaries... However, ANSYS Electronics Desktop has it's own built-in circuit simulator and I would recommend using it instead of ADS as it offers many more features as well as a dynamic link to HFSS.

Insert a new 'circuit' design into your AEDT project - then you can drag and drop your HFSS model with lumped port into the circuit schematic to create a dynamically linked HFSS-Circuit model. Terminate the ports in the schematic with your lumped elements and define the system ports, then assign a sinusoidal power excitation to the system ports, then setup & solve a 'linear network analysis'. After it's solved you can right click on the HFSS block in your circuit model and select 'push excitations' which will allow you to visualize any field quantity in HFSS under the conditions defined in the circuit model.

After importing the HFSS model into Circuit - you may also find it useful to enable differential ports to help visualize and ensure the connections are correct. To do this, right click on the HFSS block in the circuit schematic, and select 'Edit Symbol... Pin Locations'. Then in the drop down menu, select 'Add individual reference pin per port'.

 

Best,

[ansysqueries]

Hi Peter,

Thank you so much for the reply. I will try the HFSS circuit model you mentioned. 

I am still curious to know why there is a difference in the results between the case with lumped RLCs and lumped ports. I set up the lumped ports by using rectangular sheets. I used Assign Excitation > Lumped port and then drew the integration line along the path of current. I did a similar procedure for lumped RLCs by using Assign Boundary > Lumped RLC and then provided a value to the resistor/capacitor. The figure below shows the rectangular sheets (green) used for the boundary conditions/excitation. The long one is a resistor and the short one is a capacitor. I am curious about this because I do not think it is the problem with ADS. I suspect that this difference in the results come from the HFSS simulations itself. The main problem is that lumped ports simulation on HFSS will not generate any meaningful results that we can analyse. The results can only be verified after importing the snp files to a circuit simulator. 

Is there something wrong with my setup? Anything to be modified and tried?

[Sorceress Gia]

How are the ports contacting the structure? They appear to be overlapping? The edge of the port should be only touching the edge of the connecting conductors on each side...

[ansysqueries]

Yes. They are touching the surface of the adjacent metal. The metal (orange) is actually curved. That is the reason why I placed it on top of the surface. Is that not correct?

[Sorceress Gia]

yes, it needs to be in contact only along the edges... you can create an arbitrarily shaped sheet by drawing a poly-line where the last segment ends at the point where the first segment begins...  in this case, start by drawing a poly-line on the upper top-left corner of the rectangular conductor... then draw the next segment by clicking on the lower-left side of the rectangular conductor. Then connect the next point to one of the faceted vertices of the curved surface... continue along the curved edge with points wherever there are vertices... finally, click on the point where the poly-line started, then move away from the point and right-click anywhere and select 'done'... You should now have an arbitrarily shaped 2D sheet that is in contact with both edges where you can define your port...

Also keep in mind these are differential ports - if they are represented as single ended ports, whether in ADS or AEDT Circuit, you will be shorting one side of the port to your system ground in the circuit model...

[ansysqueries]

Thanks for the reply. I will re-run the simulations with that change. Any idea how that would affect the simulations? Would it add more parasitic resistance/inductance?

Also keep in mind these are differential ports - if they are represented as single ended ports, whether in ADS or AEDT Circuit, you will be shorting one side of the port to your system ground in the circuit model...

Yes. I set it up as differential ports using the differential snp box on ADS. But, thanks for confirming that point. 

[Swadesh]

Can you please describe a little bit about differential port. I am doing similar type of simulation currently.