Computers have become almost like partners to many RF/microwave design engineers. Nowadays, circuit theory is stored into a computer-aided-engineering (CAE) software program, available with a keystroke. But as with any computer program, a skilled operator is needed and in the case of RF/microwave circuit design, the circuit or electromagnetic (EM) simulator can only take a design so far. An effective computer-aided-design (CAD) and computer-aided-manufacturing (CAM) software layout program is needed to translate a design from theory into a practical printed-circuit board (PCB).
CAD layout tools assume that an engineer has an understanding of the differences in PCB materials. Each PCB laminate material is characterized by a set of parameters that determine the ultimate performance of the transmission lines and circuits fabricated on that material. Better CAD layout tools are often programmed with a set of critical parameters for commercially available PCB material suppliers, or otherwise allow users to enter these parameters for a desired PCB material.
Engineers on a budget may have learned some of the basics of using a CAE software tool from a "freeware" software program or free trial version of a full-fledged CAE software product. The same often holds true for CAD and CAM software. and many of these tools can be found on the website EverythingPCB, which lists not only PCB layout software, but schematic capture programs, design tools, and autorouting software. Express PCB and Advanced Circuits also offer free layout software.
AutoCAD from Autodesk is one popular software tool available in a free trial version. Available free of charge for 30 days, AutoCAD 2012 is the latest version of the two-dimensional (2D) and three-dimensional (3D) PCB layout software. Available in versions for personal computers (PCs) and Macintosh computers, the firm also offers the layout and solid-object modeling software as part of various design suites .
EAGLE software from Cadsoft is another popular PCB layout tool available in both PC and Macintosh versions. The software includes schematic editor, layout editor, and a library of editable circuit modules with an easy-to-learn graphical user interface (GUI). It also features flexible user language programs (ULPs) for creation of custom features.
EAGLE's layout editor supports PCBs with as many as 16 signal layers with 0.1-m circuit feature resolution on a maximum circuit drawing area of 64 x 64 in. (1.6 x 1.6 m). It allows operators to perform manual signal-trace routing or autorouting, and performs a design rule check (DRC) on a layout to ensure that all connections, including plated through holes (PTHs) in multilayer circuit boards, have been properly made and all requirements for properly manufacturing the PCB at a commercial board house have been met. The EAGLE layout editor is supplied with a full set of circuit-element libraries, including conventional and surface-mount-technology (SMT) components like resistors, capacitors, and inductors. EAGLE's schematic editor automatically generates a PCB layout and transfers a netlist for that design to the layout editor.
The PADS series of software tools from Mentor Graphics consist of three sets of software products: the DS, LS, and ES suites of software. The PADS DS collection was created for users trying to develop quick circuits, with interactive tools, such as advanced component search functions, integrated within the software to help speed a layout. the PADS LS software includes tools for PCB layout, 3D signal routing, and 3D viewing and analysis to speed and simplify checking of interconnections in single-layer and multilayer circuits. The PADS ES package provides everything in the LS collection, with the addition of high-speed routing code, analog and signal-integrity (SI) simulation, and thermal-analysis tools.
OrCAD PCB Designer from Cadence Design Systems is a suite of software tools that supports PCB layout creation, including a constraint manager, a design capture tool, a PCB editor, an auto/interactive router, and interfaces for driving routers, CAD machines, and prototype machines. The OrCAD PCB Editor is the heart of this suite of tools, providing interactive environments for creating and editing a wide range of single-layer to multi-layer PCBs. In addition the OrCAD Capture tools allow fast simulation cycles, allowing users to experiment with different design configurations.
Pantheon software from Intercept Technology supports PCB artwork creation and verification with automatic component placement and routing for RF, digital, and combination high-speed circuits. The software is fortified by full DRC capabilities as well as with interactive routing, advanced area-fill capabilities, complete circuit-element database, and advanced viahole options.
When layouts reach the density of a monolithic microwave integrated circuit (MMIC), accurate layout tools are essential to achieving success in terms of a repeatable and manufacturable circuit. Layout software such WaveMaker LAYOUT software from Barnard Microsystems supports the layout of single-layer and multilayer PCBs, integrated optical devices, gallium arsenide (GaAs) and silicon MMICs, and even test fixtures. The layout software, which runs on standard Windows-based PCs, can import and export layout data in a variety of formats.
Agilent Genesys from Agilent Technologies has been developed to simplify microwave circuit-board as well as system design and layout. Available in six different languages, the software combines the use of X-parameters (nonlinear S-parameters) with powerful EM simulation and circuit layout tools. Layouts can be created from a schematic diagram, from imported artwork, or from a direct drawing for an EM simulation. A 3D viewer allows an operator to perform interactive rotation, zooming, and vertical stretching to verify correct circuit geometries before fabricating a PCB. In addition, Genesys can work with Agilent's versatile Momentum EM simulation software, and can link to the powerful Sonnet Suites of EM simulation software tools from Sonnet Software.
Genesys employs the same nonlinear models as the company's popular Advanced Design System (ADS) design software. Agilent also equips Genesys with its Testlink capability to capture measured data from vector network analyzers, spectrum analyzer, oscilloscopes, and other test instruments directly into Genesys for simulation and display. It supports over 140 different instruments from more than 14 manufacturers. This level of integration greatly simplifies the task of designing and fabricating complex RF/microwave circuits and even MMIC devices.