Procedure for direct calculation of characteristic admittancematrix of coupled transmission lines

Physical design of contemporary electronic circuits and systems involves their analysis with interconnections modeled as transmission lines. Algorithms proposed in the literature for calculation of characteristic admittance matrix are based on eigenanalysis and have inherent ambiguities associated with this method when multiple eigenvalues occur. In this paper, the underlying theory and details of a new algorithm developed for unconditionally unique results are given     

Experimental evaluation of electrical conductivity of microtubules

Microtubules (MTs) are self-assembled proteinaceous filaments with nanometer scale diameters and micrometer scale lengths. Through conductivity measurements in microchannels we shed some light on electrical properties of microtubules. Measuring electrical resistance we were able to detect the dynamic disassembly of MTs and determine an upper limit for the electrical conductivity of MT. The measurements yielded the value of 90 Ω⁻¹ m⁻¹ as the upper limit for the conductivity of MTs, which is in the order of conductivity observed in inorganic intrinsic semiconductors.     

Effect of randomness of Cu-Sn intermetallic compound layerthickness on reliability of surface mount solder joints

A statistical reliability analysis on thermal fatigue lifetime of surface mount solder joints, considering randomness of Cu-Sn intermetallic compound (IMC) layer thickness, is presented. Based on published thermal fatigue life test data, the two-parameter Weibull distribution of the thermal fatigue lifetime for a fixed IMC layer thickness is found, and a K-S goodness-of-fit test is conducted to examine the goodness of fit of the assumed Weibull distribution. Then, the Weibull parameters as functions of IMC layer thickness are obtained. Considering the randomness of IMC layer thickness, the MTTF and reliability of surface mount solder joints on thermal cycles are analyzed. For surface mount solder joints formed under the same conditions and loaded during the same thermal cycling as stated in the publication, numerical results of the MTTF and reliability are presented. The results show that when the mean value of MC layer thickness is low (e.g., smaller than 1.5 μm), the effect of randomness of IMC layer thickness is significant; i.e., the MTTF has strong dependence on IMC layer thickness distribution; and the reliability is significantly different at high thermal cycles. When the mean value of IMC layer thickness is high (e.g., greater than 2.0 μm), the effect of randomness of IMC layer thickness is negligible. Therefore, the presented results are important to the reliability study of surface mount solder joints. Even though the validity of the presented results based on the test data remains to be verified from other sources of data, the proposed statistical method is generally applicable for thermal fatigue reliability analysis of surface mount solder joints. By combining the proposed method with the forming mechanism of IMC layer under varying manufacturing and loading conditions, a comprehensive reliability analysis on thermal fatigue lifetime of surface mount solder joints can be expected     

Programmable Analog/Digital Arrays in Control and Simulation

This paper presents an investigation of dynamically reconfigurable mixed-signal circuits implementing adaptive controllers and plant simulators. Motorola Field Programmable Analog Array described in this paper are used to build adaptive controllers and plant simulators for predictive control. The reported experimental studies describe performance and programmability of the Field Programmable Analog Array necessary for application in adaptive control and simulation. The experimental structure is based on 2 parallel Field Programmable Analog Array chips, analog multiplexer and multiplexer's control logic, which is steered by a digital system such as a desktop computer or a Field Programmable Gate Array. Dynamic reconfiguration is used in this system for adaptive control or adaptive processing in general. Modeling and measurements of the transitions in the internal blocks of the two Field Programmable Analog Array chips working in parallel, and analysis of limitations resulting from hardware imperfections are presented.     

Application of multiobjective optimization in selection of printed wiring boards

This paper presents an application of multiobjective optimization in optimal selection of number of signal layers in printed wiring board (PWB). The criteria considered in optimization are: cost, electrical performance, and reliability. The reliability of system is influenced by the operating temperature, which is determined by the power dissipated in parts placed on the board, ambient temperature, and cooling technology. In evaluating cooling and calculation of junction temperature both heat conduction through the board and forced air cooling are considered. Designers have to deal with multiple, conflicting criteria because of variety of requirements that packaging should meet. However, sophisticated methods developed for multiobjective optimization are not yet used in packaging design. This paper describes some of the methods used in solving multicriteria optimization and gives an example of application to design of PWB. The weighting method is applied to find the optimal solution first. The graphical form of optimality of different weights for different criteria is presented. The distance based methods, which include l/sub 1/-distance, l/sub 2/-distance, l/sub /spl infin//-distance, and the geometric distance method, are also applied to determine the optimal number of signal layers. The results from different methods are compared and discussed.     

Clarification of a decoupling method for multiconductortransmission lines

The authors provide a clarification of a decoupling method employed in the analysis of multiconductor transmission lines. They show that the use of a similarity transformation yields more efficient and stable numerical algorithms for computation of eigenvalues and characteristic impedance/admittance matrices of the telegrapher's equations than those based on a congruence transformation. The algorithms are easy to implement in existing software and, thus, their utilization is recommended     

Ultra-fast hybrid analog-digital computation with convenient simulation-language software

The succession of digital program steps in typical hybrid analog digital computer simulations is so similar to the stepwise solution of differential-equation systems that well-established continuoussystem-simulation languages, and especially interactive digital simulation systems, can serve as excellent hybridcomputer software with little modification. In particular, the block-diagram-oriented DARE II simulation language can control the ultra-fast LOCUST analog computer to produce unprecendented hybrid execution speed while still permitting quite simple programming. Examples include iterative optimization, computation of hybrid-computer Monte Carlo statistics, and digital two-variable function generation in a hybrid-computer loop.     

Analysis of transients in nonuniform and uniform multiconductortransmission lines

The author presents an effective method for computation of the transient response of multiple nonuniform transmission lines. This time-domain analysis technique can predict reflections and crosstalk. The proposed spectral technique is used to transform partial differential equations describing a system of transmission lines into a set of linear ordinary differential equations, which can be solved with one of the many well-developed integration techniques. Numerical experiments performed with the prototype program showed that the method can solve specific problems (lossless, uniform lines) just as fast as less general methods based on modal analysis exploiting the particular properties of lines