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Software Eases Design Pain At Various Stages

Although simulation remains essential, many software platforms offer an increasing number of capabilities for specific RF design problems and challenges.

Every spring, people in the US microwave industry eagerly anticipate the major product announcements that will be unveiled at the IEEE Microwave Theory & Techniques Symposium (MTT-S) International Microwave Symposium (IMS). This year's show in Honolulu, Hawaii, did not disappoint them. As always, the exhibition floor teemed with the latest RF components, materials, and product innovations. In addition, test and measurement advances were highly visible. Yet the show floor also reflected a growing trend: the increasing importance of software tools in the microwave industry. It used to be that only the large design houses could afford to use such tools. Over the last decade or so, the increasing affordability of these software tools has combined with their ability to ease bottlenecks at a variety of design stages. As a result, software design tools are now utilized by the majority of RF engineers. The software market has bloomed with this success, offering designers a wide variety of software products and companies from which they can choose.

In the area of three-dimensional (3D) electromagnetic (EM) simulation for high-frequency and high-speed components, for example, Ansoft (Pittsburgh, PA) just debuted HFSS v11 (Fig. 1). This version promises to enable users to perform immense simulations of structures that were previously just too large to solve. Essentially, HFSS v11 combines new higher-order, hierarchical basis functions with an iterative solver. That solver provides accurate fields using smaller meshes, which results in more efficient solutions for large, multi-wavelength structures. In addition, a fault-tolerant, high-quality, finite-element meshing algorithm allows HFSS to simulate very complex models two-to-five-times faster than previous versions while using half of the memory. Among the software's other new features are the following: an enhanced port solver, Floquet ports, a genetic algorithm to expand optimization choices, auto-assign capability for terminals, and Automatic Distributed Solve of discrete and interpolating frequency sweeps. This version also provides Distributed Solve for parametric sweeps, sensitivity, and statistical analysis. For an EM-based design flow, Ansoft dynamically links HFSS to Ansoft's combined frequency- and time-domain circuit simulator, Nexxim, and the company's integrated schematic and design-management front end, Ansoft Designer.

Another popular EM simulator vows to solve the current distribution on 3D and multilayer structures of general shape. Dubbed IE3D, it is a full-wave, method-of-moments (MoM)-based simulator from Zeland Software (Fremont, CA). In mid-March, IE3D 12.12 was released. This version introduced and implemented Conjugate Match Factor (CMF). As long as the chip impedance and basic configuration are provided, CMF allows the designer to judge the quality of an RFID antenna. In addition, the FastEM Design Kit for real-time, full-wave EM design allows engineers to parameterize both planar and 3D structures. They can perform high-accuracy and efficiency IE3D simulations on the structure and extract the FastEM signature from the simulation results. That signature allows the user to perform real-time EM tuning, optimization, and synthesis.

This version of Zeland's IE3D also includes network-distributed EM simulation and optimizations on IE3D, ZDS, and ZDM 12.1. The new implementation of ZDS and ZDM promises to help distributed and multi-license IE3D users to improve simulation efficiency by a factor of 10. In addition, IE3D Version 12.12 significantly improves the speed of the IE3D engine—even without multi-CPU support. An equation-based, schematic-layout editor with Boolean operations permits the engineer to create complicated layouts with parameterized objects in a schematic way. Because all object dimensions are equation-based, users can create structures beyond the coverage of the limited object types available in the library. IE3D 12 simulations automatically yield frequency-dependent, lumped-element, equivalent-circuit models.

Like IE3D, Sonnet Suites from Sonnet Software (Syracuse, NY) can be used in the design of monolithic microwave integrated circuits (MMICs), radio-frequency integrated circuits (RF ICs), planar antennas, and more. Yet the Sonnet Suites develop precise RF models (S-, Y-, Z-parameters or extracted SPICE model) for planar circuits and antennas. The software requires a physical description of a circuit, which comprises the arbitrary layout and material properties for metal and dielectrics. It then employs a method-of-moments (MoM) EM analysis based on Maxwell's equations, which includes all parasitic, cross-coupling, enclosure, and package-resonance effects.

In Sonnet Suites Release 11, which became available in March, co-calibrated internal ports introduce perfectly calibrated connections on the interior of a circuit layout. As a result, models may be connected in the user’s preferred frequency- or time-domain simulator. To remove cross-coupling between ports in the group, the co-calibrated ports are combined in Calibration Groups and simultaneously de-embedded. In addition, Release 11 uses a component to include an electrical- or circuit-theory model into an EM simulation. This component can calibrate the connection with respect to the terminal width of the connecting device. As a result, the discontinuity between a surface-mount pad and the component's terminal width is accurately characterized in Sonnet. It also is included in the EM analysis.

The Sonnet EM Analysis Engine, dubbed em, has now been enhanced for 64-b Windows and Linux platforms. Problem size is therefore limited only by the amount of random-access memory (RAM) on a user's computer. In addition, Release 11 of Sonnet Suites offers a redesigned and re-written Agilent ADS interface, called ebridge. It also simplifies Sonnet's well-known cluster-computing capability, which allows the designer to use many computers to solve large EM analysis. The analysis frequencies are divided between CPUs, which translates into a very sizable time savings. This cluster computing capability can be implemented on an existing computer network without third-party software.

Four separate 3D EM simulation tools comprise the CST Studio Suite from Computer Simulation Technology (CST) GmbH (Darmstadt, Germany): CST Microwave Studio for high-frequency applications, CST EM Studio for low-frequency and statics, CST Particle Studio for charged-particle dynamics, and CST Design Studio for synthesis and circuit simulation. These programs can all be accessed through the CST Design Environment. The latest version, CST Studio Suite 2008, is expected to become available in the fourth quarter of this year. Among this version's enhancements are two new interfaces that streamline the design workflow—especially for engineers involved in signal integrity. The native interface to Mentor Graphics—Expedition uses COM/COM to exchange data of entire layouts, areas, or nets. The second one, which is an ODB++ interface, enables access to layouts from a variety of tools like Mentor Graphics—Board Station and Zuken CR5000. In addition, users of CST Microwave Studio will be able to utilize Sigrity current distributions as field sources and export HSPICE models.

In terms of performance, this new version vows to improve the parallelization of transient and frequency-domain solvers. Plus, ongoing code-optimization projects with Intel guarantee that the latest and upcoming processor generations are fully leveraged. Dedicated hardware-acceleration boards are available for the transient solver. For the direct frequency-domain solver on tetrahedral grids, both memory-usage and speed improvements have been made. CST Design Studio 2008 also allows layouts to be created from schematic blocks for use directly in CWT MWS (Fig. 2). For the benefit of signal-integrity designers, IBIS and Berkeley Spice models can be included in CST DS simulations. Plus, a particle-in-cell (PIC) solver in CST Particle Studio 2008 can deliver the fully consistent simulation of charged particle dynamics in the presence of external and space-charge fields.

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The 2007 versions of Applied Wave Research's (El Segundo, CA) Microwave Office design suite and system simulation software, Visual System Simulator (VSS), were unveiled in late May. Microwave Office now offers a circuit-extraction technology that was developed to increase productivity for designers of next-generation communications products. Because users are able to leverage layout-based models for circuit extraction, ACE automated circuit extraction vows to slash the time required to do the initial modeling of complex interconnects. Plus, designers can accurately perform interconnect modeling at the earliest stages of the design flow.

Additional features in Microwave Office 2007 include enhanced integration with the APLAC harmonic-balance simulation engines, improved EM stackup editor and layout mapping, and new layout features and simulation models. Thanks to integration with the VSS RF Inspector tool, frequency-domain simulation can be performed from within the Microwave Office environment. In addition, expanded Intelligent Net (iNet) technology includes monolithic-microwave-integrated-circuit (MMIC), module, and printed-circuit-board (PCB) design capability. The 2007 version also offers expanded design-rule-checking (DRC) coverage and support and AC and noise analysis with HSPICE.

For its part, the company's VSS 2007 software now includes RFA technology. This system-level, RF architectural-planning and specification tool targets RF communication system engineers who need to quickly create and verify a radio design's initial specifications before committing to hardware and/or a particular circuit design. RFA's new simulation tool, RF Inspector, vows to help designers find potential pitfalls early in the design process at the system-level design phase. Users can therefore identify sources of intermodulation products and undesired spurs of an RF link. VSS 2007 also provides RF-centric measurements, such as integrated phase noise and carrier-to-interference noise ratio (CINR). VSS 2007 comes equipped for WiMAX with a WiMAX mobile library, which is fully compliant with IEEE 802.16e-2005 specifications, a WirelessMAN-OFDMA physical layer, and a WiMAX fixed library (802.16d-2004) receiver.

The Advanced Design System (ADS) RF electronic-design-automation (EDA) software from Agilent EEsof (Santa Rosa, CA) is a mainstay of circuit simulation. The company also offers the RF Design Environment, IC-CAP device modeling software and systems, and GENESYS and SystemVue from Eagleware-Elanix. Thanks to an integrated verification toolkit for signal-integrity design, high-data-rate-interconnect and serial-data-link designers can now find and correct jitter sources while predicting bit-error-ratio (BER) performance. The Agilent Signal Integrity Verification Toolkit is intended for use with the ADS platform. By identifying and analyzing sources of performance-degrading jitter in multi-Gigabit communication link designs, it helps designers find and remove the causes of jitter before hardware prototyping begins.

At the end of May, Agilent also announced the integration of its full-wave, 3D simulator Electromagnetic Design System (EMDS) into the ADS platform. The Agilent EMDS-for-ADS promises to reduce the steps needed for the accurate design of high-frequency RF/microwave modules, RF boards, and planar antennas (Fig. 3). Instead of solely serving as a tool for EM experts, EMDS-for-ADS makes full 3D EM simulation accessible to the entire ADS community of users. The Agilent EMDS-for-ADS allows designers to make informed design decisions and adjustments before physical prototyping begins. It is especially useful when simulating circuits built with non-homogenous planar dielectrics, such as dielectric resonator oscillators (DROs) or the cavities under spiral inductors. It also is useful for verifying the results of planar EM simulations before beginning hardware fabrication.

For the most part, these software platforms target electrical-engineering applications and—even more specifically—issues that arise with RF design. Yet a number of software platforms are able to serve this market while simultaneously satisfying other math and science areas. A couple of prime examples hail from The MathWorks (Natick, MA). The company is probably best known for MATLAB, a high-level language and interactive environment that enables the designer to perform computationally intensive tasks faster than with traditional programming languages like C, C++, and Fortran. The company's Simulink platform provides multidomain simulation and the model-based design of dynamic systems. Because Simulink is integrated with MATLAB, it provides immediate access to an extensive range of tools for algorithm development, data visualization, data analysis and access, and numerical computation.

National Instruments (Austin, TX) has quite a large portfolio of software products to satisfy the needs of a broad range of industries. The company's flagship product, LabVIEW, now allows users to develop extensible code with object-oriented programming. They also can integrate .NET web services with automatic VI interface creation and reuse external code with automatic DLL interface generation. In addition, it is possible to call DLLs dynamically and make use of callbacks.

COMSOL (Stockholm, Sweden) is currently working on bringing its mathematical modeling, simulation, and virtual prototyping to a broader community of engineers. In COMSOL Multiphysics 3.3, the AC/DC Module allows static and quasi-static models to include any coupled physics and nonlinear materials. With the Acoustic Module, the user can model acoustic-wave propagation through solids and fluids. The RF Module permits the designer to specify geometry, physics, and materials without the limitations of RF and microwave simulations. COMSOL Multiphysics 3.3 also flaunts two new labs. The Signals & Systems Lab offers three graphical user interfaces (GUIs) and a large number of functions to support signal processing and analysis, system identification, and statistics. The Optimization Lab contains solvers for the optimization of constrained linear, quadratic, nonlinear objective, and least-squares problems in addition to unconstrained optimization.

Thanks to its ability to compute at up to 500 to 1500 Megacells/second, the EM simulation tool from Schmid & Partner Engineering AG or SPEAG (Zurich, Switzerland) bridges a number of different industries. With Version 12.4 of the SEMCAD X Simulation Platform, the company has introduced new EMC/EMI-related features and methods for material modeling. A significant increase in memory efficiency also was achieved. SEMCAD X V12.4 provides additional optimization goals including OTA parameters, uniformity, and more in GA Optimizer for CAD structures. It also offers metamaterials (double negative), extended dispersive materials, and the modeling of lossy metals and coated sheets. The 3D solid modeling toolbox has been extended as well.

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The industry is witnessing the constant evolution of both circuit and EM simulation. Yet companies are recognizing a need for unique software capabilities as well. Flomerics (Marlborough, MA), for example, does EM while providing software for the analysis of thermal effects. As designers keep working to get more power out of smaller spaces, it will become essential to be able to understand, predict, and analyze thermal aspects of designs. Analog Devices (Norwood, MA) answered a different need with ADIsimPLL, which is a phase-locked-loop (PLL) circuit design and evaluation tool. Version 3.0 improves the range of PLL loop-filter topologies available within the simulator from 9 to 18. Many of the nine new loop-filter topologies include higher-order active filters, which can provide additional spurious rejection. A new dedicated voltage-controlled-oscillator (VCO)/Reference Library File editor allows browsing through a VCO or reference-oscillator library file as well as user entry of VCO tuning and phase-noise data. In addition, the closed-loop gain of the PLL is calculated and displayed on the FreqDomain page. The phase-noise plots have been enhanced to show the contributions from each of the PLL's noise sources.

One of the ways that Modelithics (Tampa, FL) sets itself apart is through its unique libraries. The company's latest CLR Library release is a substrate and part value-scalable, surface-mount, RLC model library. Many of these models now include pad geometry scaling. In addition, some have horizontal/vertical orientation selection. With the Version 4.1 release, all Modelithics Global Models allow pad effects to be de-embedded with a simple simulation mode setting. User-specified pad effects can then be applied. This past March, the company also introduced new class of models to the Modelithics Library of high-accuracy RF and microwave simulation models. The System Component Library (SCL) includes a collection of accurate linear and non-linear models for functional system blocks including filters, switches, attenuators, transformers, amplifiers, and mixers.

Over the past few years, EDA giant Cadence Design Systems (San Jose, CA) has been making steady tracks into the RF arena. For example, the Cadence RF SiP Methodology Kit combines comprehensive links between system design, physical implementation, and manufacturing. As a result, it allows full-system-in-package (full-SiP) electrical analysis and the characterization of critical paths as well as behavioral modeling from overall system-level simulation through bottom-up verification. The company also offers the Cadence RF Design Methodology Kit, which vows to shorten product-development cycle time by increasing silicon predictability and enabling greater RF design productivity. Its capabilities include demonstrating advanced methodologies for intelligently managing RLCK parasitics, inductor synthesis and modeling, full-chip verification through a new—local” envelope technique, and a PLL simulation guide. It also links system-level design with IC design.

These examples offer just a small window into the world of RF software and its seemingly endless capabilities. From performing the narrowest, most challenging task to meeting the EM simulation needs of almost every designer, software is eliminating an increasing amount of design headaches and mistakes. As software development increases, products will emerge to perform new simulations and even execute a large part of the actual design.

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