An active feedback resonator (AFR) is a kind of circuit which functions as a high unloaded Q resonator. The AFR employs an active feedback loop which compensates for the energy loss of a conventional microwave resonator. Owing to an active element in the AFR, thermal noise should be taken into account when designing the AFR. In order to simplify a circuit design using the AFR we introduced noise temperature (Tn) for the AFR. In addition, we describe the AFR design which gives minimum noise temperature. Finally, the noise temperature, measured in an AFR as a band elimination filter, is compared with the theoretical value to evaluate the AFR.

High-speed learning of neural networks using the multifrequency oscillation method is demonstrated for first time. During the learning of an analog neural network integrated circuit implementing the exclusive-OR' logic, weight and threshold values converge to steady states within 2 ms for a learning speed of 2 mega-patterns per second.

The transient spectral spread of directly modulated DFB LD's, which appears in the time-resolved chirping measurement, is studied experimentally and numerically. Such a phenomenon has been already reported as a side mode oscillation called "subpeak", but there has been little argument as to the physical origin. We make it clear that the subpeak is a spurious mode due to the influence of the photodetector bandwidth. The minimum photodetector bandwidth which is necessary in the time-resolved chirping measurement is examined. Furthermore the distortion of the long-distance transmitted waveform is also explained by one mode oscillation.

This paper briefly considers future broadcasting technologies, including digital television as a system for the near future and three-dimensional television as a part of a system to be developed rather later. However, due to limitations of space, this paper discusses only video technologies in detail. First, the status of bit reduction technologies for digital television is described and then satellite digital broadcasting and terrestrial digital broadcasting are also discussed. The authors stress the necessity of the further development of digital video compression technologies. Later, we discuss three-dimensional television, we describe requirements for the service and the present status of the technologies. And last, the paper considers the future prospects for a three-dimensional television service.

This paper presents a simple numerical method for calculating the stationary transmission and reflection characteristics of a variety of nonlinear Fably-Perot resonators. In nonlinear media, Maxwell's equations are directly solved by using a numerical integration of complex variables. The input-output characteristics of the Kerr-like nonlinear film without reflection mirrors and with multilayer mirrors have been calculated to demonstrate the usefulness and versatility of the proposed method and to find out resonator configurations exhibiting optical bistability at low incident-power levels. The effects of saturation in the nonlinear permittivity on the input-output characteristics have also been investigated. It has been found that a single nonlinear film with oblique incidence exhibits optical bistability without using reflection mirrors even if the refractive index of the film is low. This offers a simple method for measuring third-order nonlinearities of optical materials.

Existing algorithmic debugging methods which can locate faults under the guidance of a system have a number of shortcomings. For example, some cannot be applied to imperative languages with side effects; some can locate a faulty function but cannot locate a faulty statement; and some cannot detect faults related to missing statements. This paper presents an algorithmic critical slice-based fault-locating method for imperative languages. Program faults are first classified into two categories: wrong-value faults and missing-assignment faults. The critical slice with respect to a variable-value error is a set of statements such that (1) a wrong-value fault contained in any instruction in the critical slice may have caused that variable-value error, and (2) a wrong-value fault contained in any instruction outside the critical slice could never have caused that variable-value error. The paper also classifies errors found during program testing into three categories: wrong-output errors, missing-output errors, and infinite-loop errors with no output. It finally shows that it is possible to algorithmically locate any fault, including missing statements, for each type of error.

AlGaAs/GaAs HBT ICs for high bit-rate optical transmission systems, such as preamplifier, D-F/F, differential amplifier, and laser driver, have been newly developed using the hetero guard-ring fully self-aligned HBT (HGFST) fabrication process. In this process, the emitter mesa is ECR-RIBE dry etched using a thick emitter-metal system of WSi and Ti-Pt-Au as etching mask, and a hetero guard-ring composed of a depleted AlGaAs layer is fabricated on p GaAs extrinsic base regions. This process results in highly uniform HBT characteristics. The preamplifier IC exhibits a DC to 18.5-GHz transimpedance bandwidth with a transimpedance gain of 49 dBΩ. The rise time and fall time for the D-F/F IC are 30 and 23 ps, respectively. The laser driver IC has a 40-mAp-p output current swing. The differential amplifier exhibits a DC to 12.1-GHz bandwidth with a 14.2-dB power gain.

It has been reported that generalization performance of multilayer feedformard networks strongly depends on the attainment of saturated hidden outputs in response to the training set. Usually standard Backpropagation (BP) network mostly uses intermediate values of hidden units as the internal representation of the training patterns. In this letter, we propose construction of a 3-layer cascaded network in which two 2-layer networks are first trained independently by delta rule and then cascaded. After cascading, the intermediate layer can be viewed as hidden layer which is trained to attain preassigned saturated outputs in response to the training set. This network is particularly easier to construct for linearly separable training set, and can also be constructed for nonlinearly separable tasks by using higher order inputs at the input layer or by assigning proper codes at the intermediate layer which can be obtained from a trained Fahlman and Lebiere's network. Simulation results show that, at least, when the training set is linearly separable, use of the proposed cascaded network significantly enhances the generalization performance compared to BP network, and also maintains high generalization ability for nonlinearly separable training set. Performance of cascaded network depending on the preassigned codes at the intermediate layer is discussed and a suggestion about the preassigned coding is presented.

We describe an approach for modelling a person's face for model-based coding. The goal is to estimate the 3D shape by combining the contour analysis and shading analysis of the human face image in order to increase the quality of the estimated 3D shape. The motivation for combining contour and shading cues comes from the observation that the shading cue leads to severe errors near the occluding boundary, while the occluding contour cue provides incomplete surface information in regions away from contours. Towards this, we use the deformable model as the common level of integration such that a higher-quality measurement will dominate the depth estimate. The feasibility of our approach is demonstrated using a real facial image.

Recently, studies aiming at the next generation of visual communication services which support better human communication have been carried out intensively in Japan. The principal motive of these studies is to develop new services which are not restricted to a conventional communication framework based on the transmission of waveform signals. This paper focuses on three important key words in these studies; "intelligent," "real," and "distributed and collaborative," and describes recent research activities. The first key word "intelligent" relates to intelligent image coding. As a particular example, model-based coding of moving facial images is discussed in detail. In this method, shape change and motion of the human face is described by a small number of parameters. This feature leads to the development of new applications such as very low bit-rate transmission of moving facial images, analysis and synthesis of facial expression, human interfaces, and so on. The second key word "real" relates to communication with realistic sensations and virtual space teleconferencing. Among various component technologies, real-time reproduction of 3-D human images and a cooperative work environment with virtual space are discussed in detail. The last key word "distributed and collaborative" relates to collaborative work in a distributed work environment. The importance of visual media in collaborative work, a concept of CSCW, and requirements for realizing a distributed collaborative environment are discussed. Then, four examples of CSCW systems are briefly outlined.

A learning procedure of a three layer neural network with limited structure, called a multi-valued neural network, is proposed. The three layer net has a single linear neuron in its output layer. All input weights of a number of hidden neurons are identical. The network takes k+1 distinct stable values, where k is the number of hidden neurons. The proposed learning procedure consists of two parts, Phase and Phase . The former is one for the learning of weights between the hidden and output layers, and the latter is one for those between the input and the hidden layers. The network is applied to classification of numerals, which shows the effectiveness of the proposed learning procedure.

Switched-current (SI) is a current-mode analog sampled-data signal processing technique realizable in standard digital CMOS technologies. In this paper, new switched-current (SI) mirrors using OTAs (operational transconductance amplifiers) are proposed. These circuits are less sensitive to clock-feedthrough noise than conventional SI mirrors by virtue of linear I-V/V-I transformations. In addition, the current gain of the proposed mirror is electronically tunable. Not only inverting mirrors but also noninverting mirrors can be realized by this method.

Novel three-dimensional structures for passive elements--inductors, capacitors, transmission lines, and airbridges--have been developed to reduce the area they consume in GaAs MMICs. These structures can be formed with a simple technology by electroplating along the sidewalls of a photoresist. Adopting the new structures, most passive elements in MMICs have been shrunk to less than 1/4 the size of conventional ones.

This paper presents a hardware architecture design methodology for hidden markov model based recognition systems. With the aim of realizing more advanced and user-friendly systems, an effective architecture has been studied not only for decoding, but also learning to make it possible for the system to adapt itself to the user. Considering real-time decoding and the efficient learning procedures, a bi-directional ring array processor is proposed, that can handle various kinds of data and perform a large number of computations efficiently using parallel processing. With the array architecture, HMM sub-algorithms, the forward-backward and Baum-Welch algorithms for learning and the Viterbi algorithm for decoding, can be performed in a highly parallel manner. The indispensable HMM implementation techniques of scaling, smoothing, and estimation for multiple observations can be also carried out in the array without disturbing the regularity of parallel processing. Based on the array processor, we propose the configuration of a system that can realize all HMM processes including vector quantization. This paper also describes that a high PE utilization efficiency of about 70% to 90% can be achieved for a practical left-to-right type HMMs.

Oversampled analog-to-digital (A/D) converters based on sigma-delta (ΣΔ) modulation are attractive for VLSI implementation because they are especially tolertant of circuit nonidealities and component mismatch. Oversampled ΣΔ modulator has some points which must be improved. Some of these problems are based on the small input signal and the integrator leak. In this paper,ΣΔ A/D converter having a dither circuit to improve the linearity and the compensation technique of the integer leak are presented. By the simulation, the most suitable dither to improve the linearity of the modulator is obtained as follows: the amplitude is 1/150 of input signal maximum amplitude, the frequency is 4-times of the signal-band. Using the compensation circuit of the integrator leak, 72 dB of dynamic range is obtained when op-amp gain is 30 dB.

This paper deals with the uniqueness of a solution of the basic equation obtained from the analysis of resistive circuits including ideal diodes. The equation in consideration is of the type of (A-)X=b, where A is a constant matrix, b a constant vector, X an unknown vector satisfying X 0, and a diagonal matrix whose diagonal elements take the value 0 or 1 arbitrarily. The necessary and sufficient conditions for the equation to have a unique solution X 0 for an arbitrary vector b are shown. Some numerical examples are given for the illustration of the result.

The performance of analog circuits is strongly influenced by their layout. Performance specifications are usually translated into physical constraints such as symmetry, common orientation, and distance constraints among certain components. Automatic digital layout tools can be adopted and modified to deal with the imposed performance constraints on the analog layout. The selection and modifications of algorithms to handle the analog constraints became the area of research in analog layout systems. The existing systems are characterized by the use of stochastic optimization techniques based placement, grid based or channel routers, and lack of compaction. In this paper, algorithms for analog circuit placement, routing, and compaction are presented. The proposed algorithms consider the analog oriented constraints, which are important from an analog layout point of view, and reduce the computation cost. The placement algorithm is based on a force directed method and consists of two main phases, each of which includes a tuning procedure. In the first phase, we solve a set of simultaneous linear equations, based upon the attractive forces. These attractive forces represent the interconnection topology of given blocks and some specified constraints. Symmetry constraint is considered throughout the tuning procedure. In the second phase, block overlap resulting from the first phase is resolved iteratively, where each iteration is followed by the symmetry tuning procedure. Routing is performed using a line expansion based gridless router. Routing constraints are taken into account and several routing priorities are imposed on the nets. The compactor part employs a constraint graph based algorithm while considering the analog symmetry constraints. The algorithms are implemented and integrated within an analog layout design system. An experimental result for an OP AMP provided by MCNC benchmark is shown to demonstrate the performance of the algorithms.

In this paper we present an Overlapped Block Gauss-Seidel (OBGS) algorithm for the solution of large scale LSEs (Linear System of Equations) based on array architecture which we have already proposed. Better partitioning for processor array usually requires (1) balanced block size, and (2) minimum coupling between blocks for better convergence. These conditions can well be satisfied by overlapping some variables in computation algorithm. The mathematical implication of overlapped partitioning is discussed at first, and some examples show the effectiveness of OBGS algorithm. Conclusion points out that the convergence properties can well be improved by proper choice of overlapped variables. An efficient algorithm is given for choosing block and variables in order to realize above conditions.

This paper presents ceramic multi-layer substrates for mobile communication using alumina-glass composite ceramics and co-fired copper conductors. Electrical characteristics in GHz frequencies of the substrate, copper conductor, transmission line, via hole and coupling between the striplines were evaluated. The results showed that the ceramic multi-layer substrate had good electrical characteristics enough for GHz-band applications. Using the ceramic multi-layer substrates, one can drastically reduce the size of RF circuit boards for mobile communication equipment.

The approximation of the gain characteristics of linear phase FIR digital filters is reduced to the approximation by cosine polynomials. Therefore we can easily obtain an optimum solution under the LMS of Chebyshev error criterion. However the optimum solution does not always meet practical specifications, especially in the case where the gain is specified strictly at some angular frequencies. On the other hand in such a case, it is known that interpolation technique can be suitably applied for the approximation mentioned above. However, in this case, we encounter another difficulty in the approximation caused by interpolation. In order to overcome the above difficulty, this paper proposes a new method utilizing both of the interpolation and LMS techniques. Some parameters included in approximating functions are used to satisfy prescribed interpolating conditions and the other parameters are used to minimize the approximation error under the LMS criterion. In addition, interpolation technique is extended to include the case in which also higher derivatives are taken into interpolation conditions to make smooth interpolation. An example is shown to illustrate the effectiveness of the proposed method.