Computer-aided design: limitations in automating design anddrafting

The impact of CAD (computer-aided design) on employment and skill is examined. First, the relationship between the adoption of mechanical CAD systems and employment of drafters in the aerospace and automobile industries is assessed. Contrary to many employment projections, drafting employment in these industries increased with increases in the adoption of CAD systems. Second, the effects of design automation and skill transformation capacities of electronic CAD systems on printed circuit board designers are evaluated. Third, the limits to automation of design are explored, suggesting that there are trade-offs between automation of the design process and innovation in product design. The logical limits of software, flaws in programming, and the dynamic nature of product markets are evaluated as factors limiting automation     

Computer-aided design

The November issue of the Proceedings of the IEEE will be a special issue on computer-aided design, consisting of many papers on specialized aspects of this growing field. To put the new development in proper perspective, this article examines just what it is that justifies all the excitement. It discusses the nature of the engineering design process, man-computer systems, both passive and active computer graphics, nongraphic applications, and problems of computer technology, and points out for engineers the importance of computer-aided design for the future.     

Computer-aided design of a tapped microstrip filter

The impedance matrix of a single-section coupled microstrip structure with specific terminations and tapped input/output points has been determined. Design parameters such as the gap spacing, the width of the lines, and the positions of the input and output tap points for a specified filter characteristic, have been optimized with the help of a computer. A tapped line microstrip filter has been fabricated on alumina substrate using a thin-film technique and tested to verify the design procedure.     

Computer-aided photonics design

Photonics-the technology of using particles of light as carriers of information-is catching on because of the advantages of optical fiber over copper cable for data transmission, and the use of optoelectronic techniques for sensing and instrumentation. Here, the author describes how powerful laser models in photonics system simulators are a vital step toward virtual optical benches for optimizing such communication system design     

Computer-aided design of a Si avalanche photodiode

A computer-aided design of a Si avalanche photodiode is presented. As an example, the design of the boron diffused photodiode with a desired time constant is carried out. The choice of an area of an active region is not affected by a diffusion condition but primarily by a substrate impurity concentration. For a very high speed response a moderate substrate impurity concentration must be selected. For a longer time constant than about 0.1 ns an increasing area of an active region is acceptable with a decreasing substrate impurity concentration. In a lightly doped substrate, a uniform multiplication of an active region cannot occur. Using the usual diffusion technique the acceptable highest resistivity of a substrate is about 1-2 Ω.cm. The capacitance of the guard ring occupies a considerable part in a total capacitance. Calculated results are in good agreement with experimental results.     

Computer-aided design in civil engineering

The paper reviews the development and current status of computer-aided design (CAD) in structural-engineering, a branch of civil engineering. The Similarities to and differences from electrical engineering practice are emphasized. The presentation deals first with well-developed CAD application areas, namely those supporting analysis, component selection and the preparation of design documents, Problematic areas, still subject to intense research, in synthesis, optimization, the representation of design specifications, the use of databases and the role of software engineering tools are briefly described.     

Computer-aided design of electronic circuits a user's viewpoint

Computer-aided analysis of electronic circuits is examined from the standpoint of the user. A general discussion of program requirements is presented, and several numerical and practical aspects of computer-aided electronic circuit design are given. The engineer's role is discussed in terms of the information and insight needed by the user, and some of the methods utilized in developing computer analysis capabilities at a particular laboratory are given. On-line design is reviewed, with particular emphasis on graphical input and output systems. A design supervisory program is described that would render on-line circuit design a practical reality. Finally, the impact of on-line systems upon computer-aided analysis is examined with reference to the time-sharing system, OCTOPUS, at Lawrence Radiation Laboratory, Livermore, Calif.     

Computer-aided design of a BPSK spread-spectrum chip set

The design of a binary-phase shift-keyed (BPSK) spread-spectrum chip set with an integrated CAD environment called VANDA is described. VANDA uses the functional compiler concept to integrate system and physical designs, thus allowing complex high-performance integrated circuit chips to be implemented easily. Three functional compilers have been designed and implemented for the design of a spread-spectrum transceiver: a pseudonoise (PN) generator compiler, a direct digital frequency synthesizer (DDFS) compiler, and a Costas loop compiler. Three test chips for a BPSK digital intermediate frequency (IF) spread-spectrum system generated by these compilers have been fabricated and tested. Details of each of the functional compilers and the test chips are described. In addition, the measurement results for digital IF transceiver test boards constructed using these chips are presented     

Computer-aided design tools in chemical engineering process design

This paper reviews the design activity for chemical engineering process design, starting from the earliest step of selecting which products to manufacture and ending with designing the operating procedures for a process plant. At each step we discuss computer-aided design tools which have been or are being developed. Throughout synthesis aids which help make discrete design decisions are contrasted with analysis aids which help to select the proper values for continuous variables. Computer aids are abundant to aid in process design. The future holds promise for an integrated design tool which will aid the engineer from start to finish in his task.     

Computer-aided design of FIR filters

A computer-aided technique for designing FIR digital filters with close to linear phase property is presented. The approach is based on a constrained optimisation problem designed to minimise the mean-square error between a desired response and the filter response over a passband of interest subject to a mean-square stopband constraint. Numerical results are presented to illustrate the performance achievable.<>     

Computer-aided design in VLSI device development

Computer-aided design (CAD) has been used extensively in the development of VLSI MOS technology at Hewlett-Packard Laboratory. The CAD system for MOS device design is described. The development of the p-channel transistor with submicrometer channel length, trench isolation in CMOS, and side-wall-masked isolation (SWAMI) for VLSI technology are then presented, followed by a discussion of the techniques used in the simulation of parasitic capacitances in multilayer interconnects for circuit performance evaluations.     

Computer-aided design of VLSI circuits

With the rapid evolution of integrated circuit (IC) technology to larger and more complex circuits, new approaches are needed for the design and verification of these very-large-scale integrated (VLSI) circuits. A large number of design methods are currently in use. However, the evolution of these computer aids has occurred in an ad hoc manner. In most cases, computer programs have been written to solve specific problems as they have exist and no truly integrated computer-aided desisn (CAD) systems exist for the design of IC's. A structured approach both to circuit desisn and to circuit verification, as well as the development of integrated design systems, is necessary to produce cost-effective error-free VLSI circuits. This paper presents a review of the CAD techniques which have been used in the design of IC's, as well as a number of design methods to which the application of computer aids has proven most successful. The successful application of design-aids to VLSI circuits requites an evolution from these techniques and design methods.     

Computer-aided design of VLSI FIR filters

A CAD tool is presented for producing very high-throughput FIR filters. Because the CAD tool is application-specific, it is a very high-level tool. An engineer only needs to specify 1) the filter order, N; 2) the input word size; and 3) the output word size. Using this information, the CAD tool generates CIF files for a filter system that can process 10N million samples per second. The purpose of the paper is to illustrate the benefits of applying both bit-level systolic array architecture and application-specific CAD to the problem of FIR filtering. The resulting CAD system reduces the costs of very high-throughput FIR filters with respect to design, fabrication, and operation.     

Computer-aided design of the RF-cavity for a high-power S-band klystron

This article describes the computer-aided design of the RF-cavity for a S-band klystron operating at 2856?MHz. State-of-the-art electromagnetic simulation tools SUPERFISH, CST Microwave studio, HFSS and MAGIC have been used for cavity design. After finalising the geometrical details of the cavity through simulation, it has been fabricated and characterised through cold testing. Detailed results of the computer-aided simulation and cold measurements are presented in this article.     

Computer-aided design and optimization of a broad-band high-frequency monolithic amplifier

A monolithic wide-band amplifier for applications in counters from dc to UHF frequencies has been realized. The use of computer-aided design techniques, using a transistor model, and a broad-band feedback configuration has resulted in a monolithic amplifier that previously could only be constructed in hybrid form. This paper describes the development of a new high-frequency transistor model and a dc-coupled monolithic high-frequency amplifier that incorporates a final masking step option to obtain a maximally flat response over a 700-MHz bandwidth.     

Computer-aided design of reflector antennas: the Green Bank RadioTelescope

This paper presents an evaluation of the electrical performance of the Green Bank Telescope (GBT) reflector antenna, operating as single- and dual-offset configurations, as well as a general overview of the GBT system. The GBT dual-offset Gregorian configuration is designed for low cross polarization (XPOL) using the dual-offset reflector antenna (DORA) synthesis package code developed by the authors. The procedure implemented in DORA to upgrade an existing main reflector to a low cross-polarized dual-offset Gregorian reflector antenna is also described in this paper. All computed patterns were obtained with the parabolic reflector analysis code (PRAC) program, also developed by the authors, and with the commercial code GRASP7. The GBT radiation patterns and performance values, which include original data not available anywhere else as far as the authors know, indicate that low XPOL performance can be achieved with a dual-offset configuration, provided that a low XPOL feed is used. The GBT configuration is employed as a case example for the aforementioned procedure. However, an effort is made to present the main conclusions as generically as possible     

Computer-aided design for VLSI circuit manufacturability

It is noted that the nominal design created by CAD tools must often be modified to maximize manufacturing yield. Such maximization must be performed during the design to achieve an acceptable level of initial manufacturing yield and during fabrication to achieve the maximum rate of yield improvement in the entire product development cycle. The manufacturing-oriented component of the CAD of VLSI circuits is discussed. The concept of design for manufacturability is explained, and a number of issues and design problems relevant to achieving a high level of IC manufacturability are examined. An overview of needed and existing CAD tools that can be used to solve previously listed problems is presented     

Computer-aided design of monolithic MESFET distributed amplifiers

A computerized optimization method called simulated annealing is applied to the design of monolithic distributed amplifiers. The element values in the small-signal equivalent circuit model of the MESFETs, the characteristics of the gate and drain transmission lines, and the number of stages are generated to match a specified frequency response by this computer-aided design (CAD) process. The success of this process lies in the fact that it is fully automatic and the only input needed is the desired flat band gain and the 3 dB point. The method itself is sufficiently general that it can be applied to a variety of design problems. Excellent agreement is shown when the distributed amplifier designed is simulated using Touchstone, a popular microwave simulation program     

Computer-aided design of stray-insensitive second-order switched-capacitor filters

A Fortran program for the minimum chip-area design of a Fleischer-Laker stray-insensitive biquad is described.     

Computer-aided design and optimization of NRD-guide modesuppressors

A novel class of optimized nonradiative dielectric waveguide (NRD-guide) mode suppressors are proposed for wideband applications in passive and active NRD integrated circuits. A rigorous field-theoretical analysis is made by using the frequency-domain TLM technique. The optimum design is based on a filter-like scheme with a low-pass filter simulation technique and its performance-prediction algorithm. Compared to the existing choke metallic pattern, the proposed mode suppressor demonstrates excellent capabilities of effectively suppressing unwanted modes while offering a more compact geometry. Using the geometry proposed in this work for a three-section low-pass filter, for example, it is found that the transmission loss of the mode suppressor is better than -30 dB over the frequency band of interest which is well confirmed theoretically and experimentally. In addition, the length of the resulting mode suppressor becomes shorter than its counterpart using the choke metallic pattern by 20%. The theoretical prediction of electrical performance is well confirmed by our measurements