June, 2005 Microwave Review

Software Architecture for Circuit Simulation

Stephen Maas

Abstract— Engineering design and analysis (EDA) software circuit simulators has traditionally focussed virtually exclusively on the scientific calculations performed by the software. Software technology, however, has matured to the point where it can provide significant improvements in the ability of EDA software to address the full requirement of the engineering design flow. In this paper we describe some of those technologies.

Keywords — Circuit Simulation, EDA, Software.

I. INTRODUCTION

Engineering design and analysis (EDA) software has traditionally addressed only the matter of “crunching numbers,” the technical calculations that the software performs. The needs of the RF and microwave industries go far beyond this, however; they have evolved to the point where technical capability, by itself, no longer meets the complex needs of circuit and system designers. In order to achieve a high level of design productivity, the architecture of the software system—not just the analytical capabilities—must be addressed. At the same time, software technology can enhance the analytical capabilities of a circuit simulator. In this paper, we show ways in which that can be accomplished.

Our long-term goal has been to make use of modern software technology to enhance the ability of RF and microwave engineers to design circuits and systems. We have implemented many of the ideas expressed in this paper, in a commercial software product [1]. It differs from other tools in that it is designed to address design- flow issues as well as technical capabilities. We believe that the use of modern software technology, which has largely been ignored by both the research and commercial communities, can do much to provide great efficiencies in the design process.

II. D ESIGN F LOW

By the term design flow, we mean the overall process of designing a circuit, from conception through electrical design and layout, to tape-out (in the case of monolithic circuits) or fabrication (of hybrids). Design flows that exist commonly throughout industry have significant, well-known, and commonly-encountered bottlenecks.

For example, consider a simple function: electromagnetic (EM) analysis of a part of a microstrip circuit. In traditional simulators, the structure to be analyzed must be drawn in the EM simulator’s drawing tool, analyzed, and the results, in the form of scattering (S) parameters, returned to the circuit simulator. If the circuit does not work, the process must be repeated, and at each iteration, there is a genuine chance that errors will occur. Throughout the process, there is no way to view the results and ascertain that they are indeed valid. In effect, the designer depends on human infallibility to guarantee that the results are correct, and that the circuit simulated in the EM simulator is precisely the one that finally is laid out. This is a dangerous thing to do, especially when a large number of circuit components must be simulated. The same problem occurs in layout. Layout is frequently performed by a technician, based on a sketch provided by the design engineer. The circuit is copied at least twice, once by the engineer and once by the technician, and ample opportunities exist for errors to occur and for changes to be made that are not reflected in the circuit description in the simulator. Usually, considerable modification of the layout takes place, much of which may be outside the control of the design engineer.

Design-flow issues such as these can be addressed though software technology, as opposed to simulation technology. There are two aspects to this. The first is to basic architecture of the EDA software itself, designed as a complete system. The second is the use of modern software technologies that are available to the software designer. Many technologies that have been developed in the past decade can ease the task of designing high-frequency circuits and systems, and smooth the design flow. The results are improved designs, reduced error, and decreased cost.

III. S OFTWARE I NTEGRATION

Initially, a circuit simulator consisted of an analytical “engine,” plus modules to provide and process data (Fig. 1).

Stephen Maas is Chief Scientist of Applied Wave Research, Inc.,

1960 E. Grand Ave., Suite 430, El Segundo, California, USA 90245

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between simulators can do much to smooth design flow and to eliminate sources of human error. Attempts at such integration began around 1990, and involved the use of supervisory software to control the flow of data between dissimilar tools, such as simulators, layout tools, and display modules (Fig. 2). Such software had mixed success. It happens that the supervisory function is surprisingly complex, often requiring millions of lines of code, an, as a result, d software configured in this manner often has been unreliable. However successful or unsuccessful in terms of functionality, such software introduces a layer of complexity that is not fundamentally necessary. It is necessitated only by the need to interconnect existing,

is component architecture, which we describe shortly. Of course, the basic design of the software system, in the absence of such special technologies, can also do much to provide seamless integration between functions.

IV. A RCHITECTURAL C HARACTERISTICS

A. Object Oriented Design

Object-oriented design (OOD) involves the use of software objects, sometimes called classes, which contain data and the functions to manipulate those data. Those objects initialize themselves on coming into scope and release allocated memory when no longer needed. Objects can inherit other objects, allowing for substantial code reuse. Object-oriented design allows functions within the software system to be self contained, so modifying one part has minimal effect on other parts of the system.

OOD exists for dealing with the complexity of large software systems, which otherwise might become unmanageable. Without the use of such techniques, large software systems become so complex, with so many interactions between parts, that it is virtually impossible to modify one part and make certain that the modifications have no unforeseen effect on other parts.

It is important to emphasize that OOD is an architectural method, not a programming language. Programming in C++ or some other “object-oriented” language does not automatically achieve these benefits; the underlying architecture, which is an engineering design, must be successful. Conversely, it is possible to create object-oriented architectures in programming languages that are not designed to be object oriented; for example, the original version of APLAC, an object-oriented circuit simulator developed at Helsinki University of Technology, was written in C.

B. Single-Database Architecture

In our architecture, all data are contained in a single database. Circuit elements in different simulation functions are simply different views of the same data. For example, a microstrip line is a symbol in a schematic window, with a certain length and width, but in the layout it is a GDSII cell showing the line. If the length, for example, is changed in the schematic, the length changes instantaneously in the layout, since both views access the same data item. It is literally impossible for the layout to become inconsistent with the circuit description. In this way, human errors in the layout process are substantially reduced. C. Component Architecture

Component architecture allows the integration of dissimilar software at the object-code level. In Microsoft Windows, the implementation is called COM, for Component Object Model. COM works by defining interfaces and statistically unique identifiers that allow one software object to access the functionality of another. COM objects need not know anything about their clients beyond the interfaces. Much of the MS Windows operating system, and many Windows programs, are implemented in COM. For example, the various parts of Microsoft Office are COM clients.

COM is a binary standard, so COM objects can be written in any programming. language. They are implemented in dynamic link libraries (DLLs). COM objects need not even be located on the host computer; they can be relocated on a network.

COM allows great versatility in linking third-party simulators to a common application program interface (API). It is also valuable in allowing users to write programs that operate the API and its clients directly.

D. Component-Based Simulation Systems

Extensive use of COM interfaces allows a simulation systems to be created from a user-selected mix of simulators and model sets. We foresee the time, in the near future, when a user will be able to create a custom simulation system, addressing his particular needs, from a broad range of third-party simulators and models. Already, users of our design environment can employ various third-party electromagnetic simulators, which integrate seamlessly with the rest of the system. This capability is currently being extended to include circuit simulator interfaces.

26

27

In the past, circuit simulators used netlists to enter data. A netlist is simply a list of components, excitations, and their nodal connections. Later, schematic-capture modules were included. Those modules allowed users to enter the circuit

graphically, then created a netlist, which was delivered to the

simulator. The use of schematic capture modules decreased the

probability of error in the design of large circuits, but also

created a data-flow bottleneck between the circuit description and the simulator, because the simulator could not send data directly to the schematic.

To avoid this problem we eliminate the netlist. Circuit equations are formulated directly from the component database, and the database is maintained in memory during this process. This makes the formulation process very fast, and allows for bidirectional data transfer between the simulator and the database.

C. Dependency Hierarchy

All objects maintain a dependency hierarchy. When an object (e.g., an EM structure) is modified, the information about the modification ripples through the hierarchy and all objects (specifically, subcircuits) are marked for reanalysis. Objects that do not depend on that structure are not reanalyzed. This prevents unnecessary computation, eliminating unnecessary computational effort. This is especially important for structures that require long analyses, such as electromagnetic simulations. Figure 3 illustrates the dependency hierarchy for a circuit. suppose, for example, that we want the S parameters of object A, which might be a part of a larger circuit. Object B, another subcircuit, has been modified. Because of the dependency pointers, the system knows that object A, object B, and the two objects between B and A, which depend on B, must be reanalyzed. However, the objects to the left of A are unaffected by the changes to B, and thus need not be recalculated.

to which the measurement applies are marked for analysis, and

finally their dependencies are similarly marked. The analysis then proceeds in the logical manner, computing only the elements that have been marked and ignoring the rest. D. Caching and the Speed-Memory Trade-Off We cache all data, and delete it only when it has become invalid. This minimizes reanalysis, and is essential for such functions as real-time tuning, described below.

There is a fundamental trade-off between speed and memory use in any simulator. To minimize the use of memory, it is essential to delete data as soon as it is not immediately needed, and to reuse the memory space. Unfortunately, the recreation of these data, which is frequently necessary, requires extra computation time. If the data are saved, however, computation

time is reduced, but more memory space is used. Because of the high cost of memory, simulators developed before the mid 1990s invariably minimized memory use at the expense of speed. Today, memory is cheap, so it makes much

more sense to use memory and minimize computation time. Unfortunately, the decision to minimize memory of computation is a fundamental one, and it is difficult to convert a simulator designed to minimize memory into one that minimizes computation. E. Real-Time Tuning

It is possible to tune any linear circuit in our simulators in real time, and many nonlinear circuits as well. This is accomplished by reducing the untuned part of a circuit to a single admittance matrix, at each analysis frequency. The untuned part is then reduced and the results cached. This reduced admittance matrix is then connected to the tuned elements and analyzed. The dimension of the reduced Y matrix is simply the number nodes of the tuned elements plus the number of ports and

28

measurement points. The speed of tuning then depends on the number of circuit elements in the optimization, not on the size of the original circuit. Thus, arbitrarily large circuits can be

as objects, like other objects, not as the “focal point” of the system. Simulator objects can be used in a variety of ways throughout the system. For example, suppose a nonlinear device model requires S parameter data as part of its set-up

process. The model can invoke the linear simulator, have it read

a file of data, convert it to Y parameters, and store it. As another

example, suppose that a user wants to use an EM model that

does not have data for the desired dimensions in its database. The model invokes the EM simulator, creates the necessary data, and stores it in the database.

This creates an interesting and apparently backward situation in which the model uses the simulator; normally, we expect the opposite. The advantages of this arrangement, however, are increased versatility and code reuse. G. Use of Frequency-Domain Data in Time-Domain Simu-lators

A perennial problem has been the need to use fre-quency-domain data in time-domain simulation. A practical approach is to create a LaPlace representation of an impedance

or admittance function. A number of technologies have been

developed to include LaPlace data in time- domain simulation, including asymptotic waveform expansion [2] and numerical LaPlace inversion [3]. Given the network function, it is also possible to realize it as an RLC network. Whatever method is used, it is necessary somehow to create a pole-zero representation of the required data (e.g., a set of measured S parameters or the results of and EM simulation).

We use a practical method in which we create a network (1)

used with S parameter blocks, transmission lines, EM simulations, and similar frequency-domain data. The terms c n and p n are residues and poles, respectively, and d and h are real. This is easily converted to a time-domain response. Iterative and recursive numerical techniques are used for finding c n , p n , d, h.

V. C ONCLUSIONS

We have shown that attention to software architecture, in

contrast to analytical capability, can do much to enhance the

design flow of an engineering organization. This is

accomplished by tight integration of simulator functions, through the use of modern software design techniques. The result is improvements in engineering productivity, cost, and time to market of engineered products. A CKNOWLEDGEMENT The author would like to thank his colleagues at Applied Wave Research and other institutions, too many to list individually, whose work and insights contributed to the

information in this paper. R EFERENCES [1] Microwave Office , Applied Wave Research, Inc. 1960 E.

Grand Ave., El Segundo, CA 90245, USA. [2] V. Raghavan, J. E. Bracken, and R. A. Rohrer, “AWESpice: A General Tool for the Accurate and Efficient Simulation of Interconnect Problems,” Proc. 29th ACM/IEEE Design Automation Conf., 1992, p. 87. [3] J. Vlach and K. Singhal, Computer Methods for Circuit Analysis and Design , 2nd. ed., Chapman & Hall, New York, 1994.

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2002年6月大学英语六级(CET-6)真题试卷及答案 试卷一 Part I Listening Comprehension (20 minutes) Section A Directions: In this section, you will hear 10 short conversations. At the end of each conversation, a question will be asked about what was said. Both the conversation and the question will be spoken only once. After each question there will be a pause. During the pause, you must read the four choices marked A), B), C) and D), and decide which is the best answer. Then mark the corresponding letter on the Answer Sheet with a single line through the centre. Example: You will hear: You will read: A) 2 hours. B) 3 hours. C) 4 hours. D) 5 hours. From the conversation we know that the two are talking about some work they will start at 9 o’clock in the morning and have to finish at 2 in the afternoon. Therefore, D)“5 hours”is the correct answer. Y ou should choose [D] on the Answer Sheet and mark it with a single line through the centre. Sample Answer [A] [B] [C] [D] 1. A) Registering for courses. B) Getting directions. C) Buying a new computer. D) Studying sociology. 2. A) The man will probably have to find a roommate. B) The man is unlikely to live in the suburbs. C) The man will probably have to buy a car. D) The man is unlikely to find exactly what he desires. 3. A) Painting a picture. B) Hosting a program.

2014年6月大学英语六级真题及答案最全.doc

Part I Writing ( 30minutes) 1、Directions: For this part, you are allowed 30 minutes to write an essay explaining why it is unwise to put all your eggs in one basket. You can give examples to illustrate your point .You should write at least 150 words but no more than 200 words. 2、Directions: For this part, you are allowed 30 minutes to write an essay explaining why it is unwise a person by their appearance. You can give examples to illustrate your point .You should write at least 150 words but no more than 200 words.（小编写的就是这篇，还行~~） 3、Directions: For this part, you are allowed 30 minutes to write an essay explaining why it is unwise to jump to conclusions upon seeing or hearing something. You can give examples to illustrate your point .You should write at least 150 words but no more than 200words. Part Ⅲ Reading Comprehension (40 minutes) For investors who desire low risk and guaranteed income, US government bonds are a secure investment because these bonds have the financial backing and full faith and credit of the federal government. Municipal bonds, also secure, are offered by local governments and often have___ 36___such as tax-free interest. Some may even be___37___. Corporate bonds are a bit more risky. Two questions often___38___first-time corporate bond investors. The first is “If I purchase a corporate bond, do I have to hold it until the maturity date?” The answer is no. Bonds are bought and sold daily on___39___securities exchanges. However, if you decide to sell your bond before its maturity date, you’re not guaranteed to get the face value of the bond. For example, if your bond does not have___40___ that make it attractive to other investors, you may be forced to sell your bond at a___ 41___, i.e., a price less than the bond's face value. But if your bond is highly valued by other investors, you may be able to sell it at a premium, i. e ., a price above its face value. Bond prices generally___42___inversely (相反地) with current market interest rates. As interest rates go up, bond prices fall, and vice versa (反之亦然）. Thus, like all investments, bonds have a degree of risk. The second question is “ How can I___43___the investment risk of a particular bond issue?” Standard & Poor's and Moody’s Investors Service rate the level of risk of many corporate and government bonds. And___44___, the higher the market risk of a bond, the higher the interest rate. Investors will invest in a bond considered risky only if the 45 return is high enough. 注意：此部分试题请在答题卡2作答。

6月大学英语六级真题答案完整版卷一【VIP专享】

听力试题 长对话一 9. C) Export bikes to foreign markets. 10. B) The government has control over bicycle imports. 11. A) Extra costs might eat up their profits abroad. 12. C) Conduct a feasibility study. 长对话二 文都网校 13. B) Anything that can be used to produce power. 14. D) Oil production will begin to decline worldwide by 2025. 15. B) Start developing alternative fuels. 短文1 答案 16. A) The ability to predict fashion trend. 17. D) Purchasing handicrafts from all over the world. 18. B) She is doing what she enjoys doing. 短文2 答案 文都网校 19. B) Get involved in his community. 20. A) Deterioration in the quality of life. 21. D) They are too big for individual efforts. 22. C) He had done a small deed of kindness. 23. B) Pressure and disease. 24. A) It experienced a series of misfortunes. 25. C) They could do nothing to help him. 26. are supposed to 27. inserting 28. drawing-out 29. distinguished 、管路敷设技术通过管线不仅可以解决吊顶层配置不规范高中资料试卷问题，而且可保障各类管路习题到位。在管路敷设过程中，要加强看护关于管路高中资料试卷连接管口处理高中资料试卷弯扁度固定盒位置保护层防腐跨接地线弯曲半径标等，要求技术交底。管线敷设技术中包含线槽、管架等多项方式，为解决高中语文电气课件中管壁薄、接口不严等问题，合理利用管线敷设技术。线缆敷设原则：在分线盒处，当不同电压回路交叉时，应采用金属隔板进行隔开处理；同一线槽内强电回路须同时切断习题电源，线缆敷设完毕，要进行检查和检测处理。、电气课件中调试对全部高中资料试卷电气设备，在安装过程中以及安装结束后进行 高中资料试卷调整试验；通电检查所有设备高中资料试卷相互作用与相互关系，根据生产工艺高中资料试卷要求，对电气设备进行空载与带负荷下高中资料试卷调控试验；对设备进行调整使其在正常工况下与过度工作下都可以正常工作；对于继电保护进行整核对定值，审核与校对图纸，编写复杂设备与装置高中资料试卷调试方案，编写重要设备高中资料试卷试验方案以及系统启动方案；对整套启动过程中高中资料试卷电气设备进行调试工作并且进行过关运行高中资料试卷技术指导。对于调试过程中高中资料试卷技术问题，作为调试人员，需要在事前掌握图纸资料、设备制造厂家出具高中资料试卷试验报告与相关技术资料，并且了解现场设备高中资料试卷布置情况与有关高中资料试卷电气系统接线等情况 ，然后根据规范与规程规定，制定设备调试高中资料试卷方案。 、电气设备调试高中资料试卷技术电力保护装置调试技术，电力保护高中资料试卷配置技术是指机组在进行继电保护高中资料试卷总体配置时，需要在最大限度内来确保机组高中资料试卷安全，并且尽可能地缩小故障高中资料试卷破坏范围，或者对某些异常高中资料试卷工况进行自动处理，尤其要避免错误高中资料试卷保护装置动作，并且拒绝动作，来避免不必要高中资料试卷突然停机。因此，电力高中资料试卷保护装置调试技术，要求电力保护装置做到准确灵活。对于差动保护装置高中资料试卷调试技术是指发电机一变压器组在发生内部故障时，需要进行外部电源高中资料试卷切除从而采用高中资料试卷主要保护装置。

2015年6月英语六级(卷一)

2015年6月大学英语六级考试真题（第一套） Part I Writing Directions: For this part, you are allowed 30 minutes to write an essay commenting on the saying “Knowledge is a treasure, but practice is the key to it.” You can cite one example or two to illustrate your point of view. You should write at least 150 but no more than 200 words. Part II Listening Comprehension (30 minutes) Section A 1. A) Prepare for his exams. B) Catch up on his work. C) Attend the concert. D) Go on a vacation. 2. A) Three crew members were involved in the incident. B) None of the hijackers carried any deadly weapons. C) The plane had been scheduled to fly to Japan. D) None of the passengers were injured or killed. 3. A) An article about the election. B) A tedious job to be done. C) An election campaign. D) A fascinating topic. 4. A) The restaurant was not up to the speakers' expectations. B) The restaurant places many ads in popular magazines. C) The critic thought highly of the Chinese restaurant. D) Chinatown has got the best restaurant in the city. 5. A) He is going to visit his mother in the hospital. B) He is going to take on a new job next week. C) He has many things to deal with right now. D) He behaves in a way nobody understands. 6. A) A large number of students refused to vote last night. B) At least twenty students are needed to vote on an issue. C) Major campus issues had to be discussed at the meeting. D) More students have to appear to make their voice heard. 7. A) The woman can hardly tell what she likes. B) The speakers like watching TV very much. C) The speakers have nothing to do but watch TV. D) The man seldom watched TV before retirement. 8. A) The woman should have retired earlier. 4 B) He will help the woman solve the problem. C) He finds it hard to agree with what the woman says. D) The woman will be able to attend the classes she wants.