Design & SimulationFebruary 16, 2022

# Between Circuit and 3D Simulation: Broadband Macromodeling

This blog post covers the role of circuit and 3D field simulation…
Michelangelo Bandinu

This blog post covers the role of circuit and 3D field simulation for designing electronics, with a white paper on how to generate a SPICE circuit simulation model from S-parameters using broadband macromodeling and netlist/subcircuit extraction.

Circuit simulation versus 3D field simulation

There are two broad types of simulation that have long been used in electronic and electrical engineering. On the one hand, you have circuit simulation: this type of simulation models currents and voltages across circuit components, and is fast and powerful with the capability to model complex nonlinear components such as semiconductors. On the other hand, there is also 3D electromagnetic field simulation: this calculates the propagation of electromagnetic fields through space, and accurately captures the interaction between components that are coupled over a distance.

Traditionally, circuit simulation has been used to design printed circuit boards (PCBs), chip packages and integrated circuits, while 3D field simulation was used for radio and microwave components such as antennas. But as data rates increase, the frequencies of electronic signals are increasing too, to the point that they are now effectively microwaves. This means that they do not remain isolated within the signal lines but instead can propagate across the PCB and potentially cause interference issues and other signal integrity (SI), power integrity (PI) and electromagnetic compatibility (EMC) concerns.

Simulation can analyze these issues at the layout stage, modeling the transmission of data through the channels to identify issues. Figures such as eye diagrams and bathtub plots can be calculated, and potential mitigation approaches can be tested. However as mentioned, the full analysis of high-speed PCBs requires aspects of both circuit and 3D field simulation.

What is a macromodel?

This is where broadband macromodeling comes in. A macromodel of a component describes its electromagnetic behavior in a way that is compatible with circuit simulation, drawing on scattering parameter data calculated with 3D field simulation. Macromodeling enables SI/PI and EMC simulations of complex high-speed electronics to be carried out efficiently in order to identify and mitigate potential issues.

In order to be accurate, a macromodel needs to obey two rules:

• First, it must be passive. The law of conservation of energy means that a component can never output more power than is input. A component that violates this is both unrealistic and can cause simulation problems (since the power will increase and system will not converge).
• Secondly, it must be causal. The cause must always precede the effect in time, and the response from an interconnect should never anticipate the excitation.

Dassault Systèmes SIMULIA has a solution for broadband macromodeling, which generates high-fidelity, causal, passive macromodels, using the 3D electromagnetic simulation tool CST Studio Suite with the macromodeling module IdEM. IdEM produces SPICE (Simulation Program with Integrated Circuit Emphasis) models which can be used with any circuit simulation tool.