Known Limitations

Genesys leverages the Volterra theory to simulate multitone behavior when using single-tone X-parameter models giving us the ability to see Inter-Modulation Products (IMD) when more than one tone is present in the simulation. The Volterra approximation is impressively accurate as long as no more than one of the tones are at a power level high enough to cause compression. As a rule of thumb, keep secondary tones 20 dB or more below the desired carrier to avoid this condition.

Extracting non-linear X-parameter models of mixers is challenging—especially when they must be highly optimized for online use. We almost have it worked out, but out of an abundance of caution we have decided not to publish our mixer models in the simulator just yet. In the meantime, please select from one of the four behavioral mixers. Feel free to contact sales@xmicrowave.com if you want help choosing the best X-MWblock mixer to purchase for your design.

Accurate RF simulation requires that the underlying algorithms account for both forward and reverse signal propagation throughout the circuit. Circuits comprised of purely passive components do not pose much of a challenge to this requirement, but the same cannot be said for active/non-linear components. Due to the added complexity of signal convolution with interdependencies, some circuits may take much longer (if ever) to converge. A “big hammer” approach to eliminating this problem is to prevent any and all reverse flow. We believe that a better compromise is to add just a little reverse isolation in the form of embedded theoretical isolators at the ports of non-linear X-parameter models allowing the simulation to converge much quicker while still yielding reasonable results. Therefore, expect all non-linear models to convey 5-10 dB more reverse isolation than their real world counterparts.

This is a limitation we imposed on Genesys for the purpose of making simulations take less time. We think it is a reasonable compromise and has little impact on the intended applicability of the online simulator. Owners of Keysight’s Genesys software do not experience this limitation.

Simulations normally take 10-20 seconds to complete**. Despite our continuing effort to optimize the models and simulation parameters for speed and accuracy there are situations where a simulation may take much longer. For this reason the shared nature of the online simulator resources necessitates that we impose a simulation time limit of 2 minutes. Most circuits will complete within this time window. If your design keeps hitting the time limit then please review the Simulator Survival Guide for tips on how to avoid the 2 minute limit.

** The total wait time a user will experience is the sum of the time it takes to perform the simulation plus the time waiting in the simulation queue.