Software Simulators Speed Design Cycle

Nov. 12, 2008
Simulation and validation capabilities continue to push software toward eventually guaranteeing first-pass success.

Time-to-market pressures force designers to search for an edge. For many, that edge comes in the form of computer-aidedengineering (CAE) simulation tools. Such software is available to simulate devices as well as system components. It can perform both linear and nonlinear circuit and system simulations. In addition, a host of software companies offer platforms for time-domain and electromagnetic (EM) simulation. To keep up with design advances and ever-changing standards, these software platforms are in a constantly evolving state.

For example, Sonnet Software's Sonnet planar EM simulator is up to Version 12. Current design methodologies can create "tunable" EM analyses by including dozens if not hundredsof Sonnet-exclusive calibrated internal ports. With these internal ports, the designer can access nearly any point within a high-frequency circuit. This version's solver engine can automatically split an analysis into multiple threads for faster computation. In doing so, it places a solver process thread on each processor core within a multiple-processor personal computer (PC). It can therefore speed an analysis by means of parallel processing.

Sonnet's computing process is to fill and then solve a matrix. To speed up a matrix solution, Sonnet Suites Version 12 uses proprietary algorithms. Processing speed can be further increased by applying a cluster-computing approach. Among other new features, this version's solver recognizes large areas in a design that do not need fine meshing. It automatically invokes large subsections where there is minimal impact on modeling accuracy. In addition, nearly all analysis and geometrical parameters can be written as equations.

Version 14.1 of Zeland Software's IE3D EM Design System also promises speed improvements via full implementation of OpenMP multiprocessor support. Version 14.1 offers an improved graphical user interface (GUI) to simplify layout editing and visualization. It also implements non-isotropic metallic types for more accurate and efficient modeling of pin via arrays in modeling RF IC structures. An advanced simulation algorithm is implemented for accurate modeling of thick metal with multi-fold simulationspeed improvement.

By specifically targeting metamaterials, another design tool strives to enable cost and size reductions in wireless products like antennas, filters, and phase shifters. This EM design tool, which is known as Concerto, hails from Vector Fields, a part of Cobham plc. Vector Fields is involved in the threeyear, $6-million Advanced Materials for Ubiquitous Leading-edge Electromagnetic Technologies (AMULET) research and development project. Vector Fields' role in AMULET, which is aimed at developing next-generation conformal antennas and arrays for aerospace systems, is to provide antenna developers with enhanced design tools to simulate metamaterial structures. The most recent version of Concerto shows some benefits of faster simulation by exploiting the periodic nature of metamaterial structures (see Figure).

Antennas also are one of the target applications for Remcom's XFdtd full-wave, 3D EM solver based on the finite-difference-timedomain (FDTD) method. XFdtd Release 7.0, which is slated to be available early next year, is designed to increase user productivity by increasing both speed and flexibility. For example, user-interface refinements should simplify the learning curve for new users. In addition, experienced users will be able to undertake more challenging problems with the program's advanced meshing, parameterization, and scripting functions.

To simplify filter design, Applied Wave Research or AWR enabled the integration of Nuhertz Technologies' filter synthesis and analysis software, Nuhertz Filter, within its own Microwave Office software. Nuhertz Technologies has developed a direct-synthesis strategy for determining the element values that control lowpass or high-pass quadruplet zeros controlled group delay. This approach reduces computation time while eliminating unnecessary circuit components that result from traditional equalization techniques.

Time-domain simulation has been a strength of Computer Simulation Technology's CST MICROWAVE STUDIO, which is part of the CST STUDIO SUITE. Version 2009 of the CST STUDIO SUITE EM-simulation software boasts the following: new and enhanced solver technology; true transient 3D EM/circuit co-simulation using LINMIC technology with CST MICROWAVE STUDIO; a transient thermal solver to simulate the heating process; bio-heat equation for realistic modeling of physiological cooling; a significant performance increase in Integral Equation solverparticularly for structures smaller than 20 wavelengths; and true geometry adaptation. Aside from redefining the mesh, the tetrahedral frequency-domain solver's mesh adaptation function snaps to a modeled geometry. In addition, the user interface has been ported to 64-b processing to handle the increasing complexity of imported models.

Meshing enhancements also can be seen in the latest version of the HFSS software for 3D full-wave EM simulation. This widely used product hails from Ansoft, which became part of Ansys this past summer. With Version 11.1, new higher-order hierarchical-basis functions combine with an iterative solver to provide fast, accurate solutions to large structures. This version also includes an enhanced port solver, lower-frequency coverage, and lower noise floor. In addition, Floquet Ports enable designers of phased-array antennas and frequencyselective surfaces to obtain separate fields into modes.

According to How-Siang Yap, Agilent's Advanced Design System (ADS) Product Marketing Manager, today's customers want the ability to co-design the chip, package, and board in one simulation platform without the need to redefine the problem multiple times to disjointed standalone circuit, system, and EM simulation tools. This past August, the company debuted an integrated 3D EM simulation solution for RF-module design that vows to eliminate the need for standalone EM tools. Dubbed EMDS-for-ADS, the simulator promises to help designers accurately predict the 3D EM interactions of embedded passive components in RF modules. At the same time, it co-simulates with active circuits to maximize wireless subsystem performance. EMDS-for-ADS accounts for the finite dielectric boundaries of RF modules. Thanks to its new finite-element mesher and high-capacity iterative solver, it vows to deliver better accuracy, speed, and capacity for RF system-in-package (SIP) and RF-module designs. EMDS-for- ADS is part of the new Agilent Advanced Design System 2008 Update 2.

An expanded nonlinear transistor library is now available for Agilent's ADS as well. The Modelithics NLT Library consists of high-accuracy, nonlinear, and noise models from leading semiconductor manufacturers. Among the stringent design requirements that it addresses are noise, substrate-scalability, temperature dependence, broad bandwidth, and high power. The Version 3.0 upgrade adds several new models including chip and wire models for several popular gallium-arsenide (GaAs) MESFET transistors. Also included are two new high-power gallium-nitride (GaN) HEMT models.

According to Dr. Larry Dunleavy, Modelithics' President and CEO, "Simulation model libraries are a different kind of acquisition for most companies. People are not used to paying for models outright, but the status quo in terms of poor models leading to multiple design iterations is actually more costly. We see a growing appreciation especially among younger engineersin the value of simulation-based design and the importance of high-quality, consistent device models as an enabling component of this trend."

Although these software offerings specifically target this industry, many microwave and RF designers also leverage the more general-purpose digital, analog, and math environments. Take Maplesoft's Maple, for example. This tool gives both engineers and scientists an interface for solving complex mathematical problems and creating technical documents. In addition, COMSOL Multiphysics 3.5 offers Parasolid file format support and a bidirectional Autodesk Inventor interface. It achieves raised efficiency, increased performance, and reduced memory requirements through the implementation of new solvers and the revised implementation of existing ones. In addition, the RF Module 3.5 introduces new circuit ports for simulating the connection of a transmission line or an antenna and an external circuit.

RF and microwave designs are growing increasingly complexespecially as they are squeezed in alongside high-speed digital and analog functions. As a result, the role of software will only become more critical. Eventually, software may even be able to ensure first-pass success.

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