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1、20High Frequency Electronics High Frequency Design USING EDA TOOLS How to Get the Most from Todays Advanced EDA Tools By Gary Breed Editorial Director T his article covers two aspects of Electronic Design Automation (EDA) tools and how they are used. First, a number of sug- gestions are offered to h

2、elp you use these tools more efficiently and effec- tively. Then well describe recent efforts by major EDA companies to make their software easier to use for both novice users and advanced designers. EDA tools have become essential in the design of all electronic circuits and systems. It is a useful

3、 reminder to list the major reasons why they are so important: EDA tools use the speed and power of com- putersOf course, this is obvious. But, it is still worth remembering that developing mathematical descriptions of physical phe- nomena is a serious research task, and cap- turing those increasing

4、ly complex mathemat- ics is a challenge for software developers. They use the organizational power of com- putersOnce a project is underway, comput- ers are an ideal way to store, track, analyze, print and share the results. Over the past few years, this part of EDA technology has improved dramatica

5、lly. They capture valuable knowledge of the technologyFirst, the results of research are captured and coded by the EDA development team. Next, the computations are matched to the engineering design process through in- house testing and user feedback. Finally, the successful results of each user beco

6、me a valu- able part of his or her companys Intellectual Property (IP) resources. One rule to remember In my 30+ years of experience, I have heard the following advice many times, given by the best engineers: Computers dont design, engineers do. This statement does not mean that begin- ners should n

7、ot rely on EDA tools to create new designs, or that we shouldnt trust the results. After all, the experience of many bril- liant designers is embedded in these tools! This rule is only meant to remind us of the classic computer problem of “garbage in = garbage out.” Even the best software will somet

8、imes provide unworkable results. The user simply needs to have either the experi- ence or the supervision to confirm that the problems are properly set up and that the results are legitimate. Here are tutorial-level recommendations for users of modern EDA tools, plus a summary of EDA vendors efforts

9、 to help new and experienced users achieve success with their high frequency designs This months cover depicts some of the sim- ulations that an EDA user might perform. From September 2002 High Frequency Electronics Copyright 2002, Summit Technical Media, LLC RadioFans.CN 收音机爱 好者资料库 22High Frequency

10、 Electronics High Frequency Design USING EDA TOOLS EDA usage recommendations The following series of hints, reminders and suggestions has been developed over many years through the authors involvement in the RF and microwave engineering profes- sion. These are not necessarily in a priority order: Fi

11、rst, understand the problem on paperIt is hard to perform any engineering task without an orga- nized approach, and the EDA envi- ronment magnifies errors that arise from a poorly-conceived problem. There is an unconscious tendency to believe what the computer tells you, especially by others in your

12、 design team who may not be aware that your work is less well-defined than it should be. Use your knowledge first, then add the knowledge contained in the soft- wareThis is an extension of the above concept. The standard circuits available in the EDA tools libraries may be perfectly acceptable for p

13、or- tions of many designs, but it is impor- tant to understand when they are not. This requires in-depth knowl- edge of the tool and its capabilities. I have heard too many stories about engineers who simply use whats available from the software because its easy, then let someone else fix it. Keep t

14、he documentation current This needs several exclamation points, according to top engineers. The latest versions of todays EDA tools have better built-in data man- agement than earlier releases. But, it is too easy to discard previous itera- tions after they have been improved. A disk drive “file tra

15、il” is just as important as your engineering note- books “paper trail.” Engineers in small companies should beware; the discipline required to maintain good records is a special challenge, but the development of valuable intellectual property requires it. Use the right tool for the jobThis seems obv

16、ious, but in the heat of the battle to get a project completed, it may seem convenient to “get close enough” with a simulation method that is not up to the task. When EDA vendors emphasize the need to aug- ment linear and non-linear circuit theory simulation with electromag- netic analysis, its not

17、all sales pitch. This years designs are at higher fre- quencies than last years, and EM analysis is more important than ever to assure that the effects of physical size, layout and packaging are taken into account. Tend to the design detailsThis covers a lot of scenarios, from choos- ing right type

18、of segmentation for an EM analysis problem, to using the component model that has the neces- sary accuracy for your application. A current trend is for full-system simu- lation, where the size of the analysis problem is extremely large. It is essential that each part of the system is executed proper

19、ly, since it affects the overall signal chain. Finally, the pet peeve of more than a few engineering managers: Use the optimizer last, not first Yes, there has been much research into optimization algorithms that do not have false convergence at a “local minimum.” But, it is still important for an e

20、ngineer to be close enough to the final answer before optimization to have full confidence that his tools have delivered the right answer. There is an exception to this rule for the exploration of different topolo- gies. For example, an engineer might want to try out several matching net- works. A s

21、mall-size problem can be quickly set up and run through the optimizer. The results can be com- pared to see which topology provides the necessary bandwidth, or if a good match can be obtained using a config- uration with DC continuity for bias- ing. This trial result is then added to the larger circ

22、uit and thoroughly analyzed before a final optimization. These recommendations are fun- damental instructions that we all learned long ago, yet are regularly forgotten or bypassed under the pres- sure to get the current job finished! Taming Complexity, Connecting With Users The headline on this issu

23、es cover refers to the efforts of EDA vendors to make their tools more accessible. The work toward making these increasingly complex tools “easier to use” focuses in these main areas: Helping novice users learn to use the software more quickly; making expe- rienced designers more productive; and hel

24、ping design teams share results and handle large problems. These issues are at opposite ends of the user spectrum, but they repre- sent the reality of engineeringget- ting as much done as possible while remembering to bring the next gener- ation of designers up to speed. The first area to note is th

25、e on- screen user interface. Placing menus, lists, plots, etc. in logical places on the screen is both an engineering and artistic challenge. That challenge continues with organizing the nested commands that are required to access the more detailed functions. All companies are working on this issue,

26、 each with variations in the approach. Users should carefully evaluate how easy it is to navigate around each vendors product. In the area of help for new engi- neers, some EDA companies offer “student version” and “free trial” poli- cies. Ten years ago, this would have been heresy, since many users

27、 would simply rely on the limited-perfor- mance free versions. But those free versions, while useful for pieces of the design puzzle, fall far short of han- dling problems of significant size. However, they give students and .the EDA environment magnifies errors that arise from a poorly- conceived p

28、roblem. RadioFans.CN 收音机爱 好者资料库 24High Frequency Electronics High Frequency Design USING EDA TOOLS beginning engineers an opportunity to apply current technology to small- size problems. An early proponent of this policy was Compact Software (since acquired by Ansoft), which allowed the U.S. amateur

29、 radio organization, the American Radio Relay League, to market ARRL Radio Designer, a $150 limited-feature version of the SuperCompact linear simulator. Radio Designer has now been dis- continued, in part due to the avail- ability of Ansofts free SV (“student version”) editions of Serenade, their l

30、inear and nonlinear simulator, and Ensemble, a planar EM simulator. Sonnet Software was the first com- pany to make planar EM simulation available at no charge. Sonnet Lite is sufficiently powerful to analyze many microstrip and stripline circuits, including coupled lines, filters, inter- connects a

31、nd spiral inductors. Potential customers can gain valuable experience before making the invest- ment in the full-feature version. The company also offers SonnetLitePlus, a budget priced upgrade which handles problems with twice the memory usage, for users with modest analysis requirements. Although

32、not well known in the U.S. until recently, Europeans and the academic community have used the demo version of APLAC for sever- al years. This program gained atten- tion for its non-linear simulation capability, which was not available in other free or demo software. Applied Wave Research (AWR) offer

33、s a 30-day trial version of its software packages, allowing time for learning enough about the product to make a careful evaluation before making a purchase. Other companies have 30-day money back policies that accomplish the same thing, albeit with an initial payment. Another approach to helping no

34、vice users is built-in wizards and standard analysis setups. These can guide a new user through the process of a typical design. As an example, the “DesignGuides”in Agilent Technologies Advanced Design System contain preset setups (such as the load pull setup in the figure below) that can be used as

35、-is or mod- ified to fit a particular need. ADS2001 introduced this and other major enhancements to help make it easier to get up to speed on what is arguably the most thoroughly-config- uredand compli- catedEDA pack- age for high fre- quency design. Most companies system-level simula- tors include

36、stan- dard setups that include parameters for all of the major wireless standards, including 2.5G, 3G, Bluetooth and cur- rent WLAN systems. Making it Easier to Access EDA Computing Power Advanced users of EDA tools can benefit from assistance, too. Some users are true “power users” with a high leve

37、l of competence in a particu- lar toolset.These users want features that make them more productive, especially when using multiple tools, and sharing data with several team members. Compatibility with other tools has been addressed by CST in their Microwave Studio (MWS) and Design Studio. Using an o

38、pen design environ- ment, MWS can be tightly integrated with other compliant software,includ- ing Agilent ADS and Sonnet. CST, along with other 3D electro- magnetic analysis tool vendors such as Zeland, Agilent and Ansoft have devoted significant development resources to the issue of entering the me

39、chanical descriptions of the struc- ture to be analyzed, using standard file formats like DXF or Gerber that are commonly provided by mechani- cal CAD programs. Then, these prod- ucts use carefully-derived and tested algorithms to automatically create the segmentation that will result in an accurate

40、 solution with efficient use of computing resources. Large comprehensive tools like Agilents ADS are loaded with fea- tures that permit the user to use each individual tool, in conjunction with full-system simulation, and even links to and from “real world” test instru- ments that combine simulated

41、and measure results.The recently- announced Ansoft Designer is a major step in this direction for that company. Future Developments There are many more ideas under consideration to help the engineer- EDA tool connection. Online access charged by CPU time, contract EDA services, improved “standard” f

42、ile for- mats and distributed computations are all being developed as options for high frequency designers, with many more ideas yet to be tried. Sonnet Lite has provided a no-cost introduction to EM analysis for many microwave engineers. Agilent ADS includes pre-defined DesignGuides like this load-pull example. RadioFans.CN 收音机爱 好者资料库