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The current state of CAD - a users' perspectiveIn our previous CAD Benchmark in the May issue, a panel of CAD vendors gave their views on the state-of-the-art in design tools and the challenges that lie ahead. In this month's Benchmark Helen Duncan turns the tables and lets some of the CAD users air their opinions. Send us your comments on this article Download the article in Adobe PDF format [approx 93 kB]
In our last CAD Benchmark in the May issue of Microwave Engineering Europe, a panel of CAD vendors gave their views on the state-of-the-art in design tools and the challenges that lie ahead. In this month's Benchmark Helen Duncan turns the tables and lets some of the CAD users air their opinions on how the software meets their needs, and what they believe the vendors' future priorities should be. These opinions, voiced during personal interviews, have been combined with some of the results of the interactive research survey that was carried out at European Microwave Week (EuMW) in Munich last month, to produce an overall picture of how users rate the performance of their CAD tools in comparison with their expectations. Because of the complexity of this topic, the paper is being printed in two parts: Part Two will appear in the February issue. As a follow-up to this, we would like invite readers to place their own comments here on our Web site, and hope to print a selection of these comments either alongside Part Two or in a future issue of the journal, early next year. Packages The distribution of users between premium CAD suites such as Agilent (HP) EEsof ADS and Ansoft, and the budget packages is more complex than might be expected. Although the CAD vendors might prefer to believe otherwise, the majority of RF and microwave designers use a variety of software packages for different applications, exploiting the particular strengths of each where they are considered most applicable. Among those I spoke to personally, the average number of CAD packages used regularly by any one user was around four. This flexibility means that ease of import and export is a concern that many users have highlighted as being of major importance to the way they carry out their designs. In the EuMW survey 51% out of a total of 325 CAD users said that compatibility between competing software packages was in need of improvement, while 47% highlighted integration of different types of simulator as an area they would particularly like to see improved. Figure 1 gives a summary the responses for all the possible improvements that users were asked about.
Figure 1: Responses to question "In what area(s) do you feel that microwave and RF CAD could be improved?" from the interactive survey at EuMW (Sample base: 325 replies)
Another area of particular concern, expressed by 55% of the sample, is the effectiveness of nonlinear active device models and libraries. In the opinion of Steve Cripps of Hywave Associates, "Too many CAD vendors, in their haste to compile an attractive product, assemble model libraries using data that has been obtained from unverified sources. Even if a reliable, verified model is available, too often the difficulties associated with implanting it into a given CAD program can be formidable". Agilent EEsof was singled out by Kevin Jarman of ComDev as having good set of FET models, although the fact that these are only available in ADS-compatible format is a disadvantage. Dr. Jonathan Leckey of Celeritek's European design centre in Belfast, Northern Ireland, also praised Agilent's wide library of parts and the support it gives them. On the whole MESFETs and PHEMTs for low-noise amplification seem to be well catered for, while good models for power devices and bipolar transistors are more difficult to obtain. Simulation results Accuracy of simulation results does not appear to be an issue now that the microwave CAD industry has reached a stage of relative maturity. All the users agreed that both linear and nonlinear simulation results from all the packages they used were both competent and trustworthy. They do all have particular strengths and weaknesses, however: Ansoft Serenade was singled out as having paid particular attention to millimetric frequencies, while Agilent EEsof was considered to have the edge for cellular applications. Ease of use Speed and ease of use are features that cannot be overstated in importance. Several users have commented that the larger commercial packages appear to be hampered by legacy code that makes them slower at performing some functions than their newer, leaner counterparts. We hope to explore the reality behind this in future issues. In some ways this reflects the essential nature of software: each time a new version is introduced, the program size and processing requirements increase by an order of magnitude - a criticism commonly directed at Microsoft. This was an area where a relative newcomer, Microwave Office from Applied Wave Research (AWR) came in for particular praise. According to Ralph Green of Roke Manor Research in the UK, "As we move towards a more complete system-on-a-chip approach, we need to use both time domain and frequency domain capability, and no one package solves all these issues." Architecture "The one that is most encouraging is Microwave Office - it has been written more recently so has a different basic architecture - although other packages individually do give equally valid results." Kevin Jarman of ComDev agrees: "The ease of use (of Microwave Office) is excellent. The fact that it is entirely object-oriented and can keep files and layout together is particularly useful." One of Microwave Office's most popular features is its ability to reduce simulation and circuit layout times by allowing adjustment of layout or circuit parameters, by means of slider controls, and simultaneous display of simulated performance. In a straight comparison of small signal (linear) simulation speed between Microwave Office and ADS, Jonathan Leckey reported that a frequency sweep and graphic display that took 30s on ADS was accomplished in around 1s on Microwave Office, with both packages running on an identical 300MHz PC with 128Mb RAM. He also particularly liked the fact that AWR includes a 2.5D simulator as part of its basic package, whereas Momentum is an optional extra for ADS.
Figure 2: Screen shot from AWR Microwave Office showing use of slider control for varying parameters during simulation
Even for large organizations the cost of software is a major issue. Both Ansoft and Agilent EEsof seek to promote a "corporate solution" approach: although this can impress the purchasing decision makers, it is not popular with the grass-roots designers who on the whole prefer to work with a range of tools. Although cost of entry is an important issue, the users' financial concerns also extend to support and maintenance costs, which can often dwarf the initial outlay. This is a problem that is not confined to the traditional RF and microwave packages, but one that also hinders the acceptance of RF software from mainstream CAD vendors such as Cadence and Mentor Graphics. Budget For these reasons, budget packages such as Genesys from Eagleware are obviously popular, although many users will run this package alongside a heavier weight suite to provide alternative solutions for critical parts, or to carry out rapid changes to the design of certain components without running a full-scale simulation. Genesys attracted favourable comments for its accessibility and ease of use, and is considered relatively sophisticated despite its modest price tag. Some users commented on the fact that its look and feel of the version they are using betrays its DOS roots, although this is becoming less noticeable with progressive new versions. Upgrades One area that has worried several users is the impression that sometimes software upgrades are released without all the bugs having been fully ironed out. To quote one disgruntled user: "It seems that software is the only industry where the manufacturer can sell you an unfinished product!" This particular comment was not levelled at any one supplier, but another user felt that early versions of ADS, the product that pulls together the interfaces and capabilities of the original EEsof Series IV and HP MDS, did not adequately support all the functions of its predecessors and also showed a marked degradation in speed, problems that were rapidly addressed by a further upgrade. Future priorities In terms of priorities for future developments, there was a feeling that the software should make better use of the availability of cheap processing power. Packages that utilise multi-threading, spreading tasks across multiple processors, will make life a lot easier for the user, especially when considering power-hungry electromagnetic simulations. A larger selection of linear models, particularly in microstrip and coplanar waveguide, are also an item high on users' wish lists. In Part Two we will explore some of the above issues further, and also focus on the particular problems and concerns of the users of 3D electromagnetic simulators.
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