In the five short years that I have been in the RF and Microwave design industry, I have seen the demand (and need) for quick and accurate electronic design simulations escalate rapidly. I have also had the opportunity to interact with many design engineers during this time who have come to the same conclusion – they need more accuracy. Whereas ideal component simulation models or s-parameter files were once acceptable, this is much less often the case now. Parasitics have a considerable effect on component response, and even more so as design frequency increases. Labor and material costs multiply with each design iteration, so it is very important to limit these cycles and achieve a successful design early on.
Ideal models are good for low frequency design. Above 1GHz, the parasitic effects are significant and usually increase with frequency. To get a good high frequency simulation, there are several important factors to incorporate, each adding to the level of overall accuracy. One factor is the accurate representation of circuit layout in the simulation schematic. It is very important that the microstrip features are carefully defined. Another critical element is the use of accurate component models. S-parameter models are effective when the component S2P measurements are taken under the same conditions as those being used in the design: substrate, pad dimensions, part value, etc. If the conditions do not match, the simulation will not be as accurate as possible. S-parameter models are also limited when it comes to troubleshooting complete designs. If designs need to be modified, the s-parameter component models need to be removed/replaced in the schematic to test different values and/or different substrates.
For nearly 15 years, Modelithics has been developing unique advanced simulation models that represent commercially-available passive components and active devices. The models offer scalable design parameters, such as substrate properties and pad dimensions. In addition, Modelithics Microwave Global Models™ represent an entire part series, so part values can be changed, tuned, and optimized without switching the model in the schematic. The highlight of Modelithics models is that they simulate the parasitic “real-world” response of passive components and active devices over scalable substrate properties. This provides much higher accuracy over ideal component models and increased convenience and efficiency over s-parameter measurement models, making advanced equivalent circuit models one of the important factors in good high frequency design.
One of the most noticeable trends in RF and microwave electronic design is the integration of electromagnetic (EM) simulation. Beyond the effects of substrate, layout, pad size, and design components, there are environmental and 3D field interactions between all of those elements. The ANSYS HFSS 3-D EM simulator accurately captures these complex field interactions, and adds yet another noticeable level of improvement to the precision of electronic design.
Modelithics models are compatible with ANSYS HFSS, installing seamlessly into the Electronics Desktop under the Component Libraries. The simulations with these combined tools have shown to give excellent simulation-to-measurement agreement. A high-pass filter design was carefully set up in the ANSYS Schematic Editor, including microstrip interconnects, surface mount components and pads, and detailed substrate layer properties. The surface mount components were represented by Modelithics Microwave Global Models™ for specific commercially available RCL components (Figure [1]). The layout, including board effects, was analyzed in the ANSYS HFSS electromagnetic simulation tool. The models allowed for quick design optimization after accounting for parasitics and electromagnetic effects. This process resulted in excellent simulation-to-measurement agreement as shown in Figure [2].
The integration of ANSYS HFSS EM co-simulation with Modelithics models for high frequency design and simulation is a powerful combination, and is effective in generating a very accurate first-pass design to reduce iteration time and cost. To learn more, visit the ANSYS MVP (Modelithics Vendor Partner) website.
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