Exactly How Electromagnetic Should Be Part Of A Design Flow

By Cadence Design Systems, Inc.

INTRODUCTION

Modern RF/microwave design flows make extensive use of electromagnetic (EM) analysis in many ways, and its co-existence and concurrency with circuit design and analysis can not be underestimated. Prior to the circuit design and especially in larger designs, EM tools are used to create "library" parts such as inductors, transitions, and antennas. While these parts are fairly self-contained, they must ultimately be integrated into the overall design where at the very least they must be connected to the rest of the circuit or in a more complex case be coupled to it. During both early and later stages of design, designers will switch from circuit-based models to EM analysis of critical interconnects to better understand couplings and achieve greater accuracy. EM analysis is used again before the design goes to manufacturing, so that the metal in the design can be analyzed one more time to verify circuit performance alongside design rule check (DRC), layout versus schematic (LVS), and even design for manufacturability.

An overriding issue common to all these applications is that at some level the EM solver must interact with other tools. The raw materials that the solver takes as input are geometries or structures, but are no more than a layout with electrical material properties for all the layers. At the other end of the process, the EM solver produces S-parameters or some other linear model representation. Some solvers can output SPICE netlists directly, which must be integrated with the rest of the design in a circuit simulator. Achieving all this successfully has historically been a less-than-seamless chore of duplicating geometries or exporting and importing structures from the design or layout tool to the solver. The results must then be imported into the circuit simulator. While much effort has gone into automation of moving GDSII or DXF from layout tools to the solver, most of these tools lack real-time integration and have a "batch mode" feel, as though things were "auto-magically" going on behind the scenes.