A software package has been developed for simulating complex silicon and heterostructure devices in 3D. Device geometries are input with a mouse-driven geometric modeler, thus simplifying the definition of complex 3D shapes. Single components of the device are assembled through boolean operations. Tetrahedra are used for grid generation, since any plane-faced geometry can be tessellated with tetrahedra, and point densities can be adapted locally. The use of a novel octree-like data structure leads to oriented grids where desirable. Bad angles that prevent the convergence of the control volume integration scheme are eliminated mostly through topological transformations, thus avoiding the insertion of many redundant grid points. The discretized drift-diffusion equations are solved with an iterative method, using either a decoupled (or Gummel) scheme, or a fully coupled Newton scheme. Alternatively, generated grids can be submitted to a Laplace solver in order to calculate wire capacitances and resistances. Several examples of results illustrate the flexibility and effectiveness of this approach.

The photonic Space-Division (SD) switching network is attractive for constructing flexible broadband networks. This paper first describes possible applications of the network. A broadband STM switching system, Digital Cross-connect System (DCS) and Video signal distribution switch, especially for HDTV signals, are attractive near term applications. Recent activities on photonic SD switching network developments aiming at these application are also reviewed. A 128 line prototype switching system has been developed. This system utilizes LiNbO3 photonic switch matrices, semiconductor traveling wave amplifiers (TWAs) and three dimensional optical interconnections for multi stage switching networks. It is confirmed that the system has been operating in providing 150Mb/s TV phone services and 600Mb/s HDTV distribution services with high stability. An experimental optical Digital Crossconnect System (optical DCS) has also been demonstrated. Line failure restoration operation at 2.4Gb/s has been successfully demonstrated. These experimental demonstrations prove that practical photonic switching systems are feasible with current technologies.

The power transfer characteristics of a symmetric nonlinear directional coupler (NLDC) are analyzed rigorously using the beam propagation method based on the finite difference scheme. The NLDC consists of two linear waveguides separated by a Kerr-like nonlinear gap layer. The change of nonlinear refractive index along the coupler is precisely evaluated by making use of the second-order iteration procedure with respect to a small propagation length. For the incidence of TE0 mode of the isolated linear waveguide, the highly accurate numerical results are obtained for the behavior of power transfer, and the coupling length and critical power for optical switching. The dependencies of the coupling length and critical power on the width of the gap layer and the input power levels are discussed, compared with those predicted by the coupled-mode approximations.

Naturalness of expressions reflects various pragmatic factors in addition to grammatical factors. In this paper, we discuss relations between expressions and two pragmatic factors: a point fo view of speaker and a hierarchical relation among participants. Degree of empathy" and class" is used to express these pragmatic factors as one-dimensional notion. Then inequalities and equalities of them become conditions for selecting natural expressions. The authors of this paper formulate conditions as principles about lexical and syntactical constraints, and have implemented a sentence generation grammar using the unification grammar formalism.

In this paper, we present a unified model for dialogue understanding involving various sorts of ambiguities, such as lexical, syntactic, semantic, and plan ambiguities. This model is able to estimate and revise the most preferable interpretation of utterances as a dialogue progresses. The model's features successfully capture the dynamic nature of dialogue management. The model consists of two main portions: (1) an extension of first-order logic for maintaining multiple interpretations of ambiguous utterances in a dialogue; (2) a device which estimates and revises the most preferable interpretation from among these multiple interpretations. Since the model is logic-based, it provides a good basis for formulating a rational justification of its current interpretation, which is one of the most desirable aspects in generating helpful responses. These features (contained in our model) are extremely useful for interactive dialogue management.

A unified model for frequency-dependent characteristics of transconductance and output resistance is presented that incorporates the dynamics of quasi-Fermi levels. Using this model, multiple-frequency dispersion and pulse-narrowing phenomena in GaAs MESFETs are demonstrated based on the drift-diffusion transport theory and a Schockley-Read-Hall-type deep trap model, where rate equations for multiple trapping processes are analyzed self-consistently. It is shown that the complex frequency dependence is due to both spatial and temporal effects of multiple traps.

The theoretical modelling bandgap narrowing and percentage of ionized impurity atoms for uncompensated uniformly doped silicon containing conventional impurities (B, P, As, Sb) under thermodynamic-equilibrium conditions is presented. As distinct from existing approaches, this modelling is valid for impurity concentrations up to electrically-active-impurity-concentration limits and for the temperature range from 40 K up to 400 K. A relevant and efficient calculation software is proposed. The results of the calculations are compared with the results extracted by many authors from measurement data. A good agreement between these results is noted and possible reasons of some discrepancies are pointed out. The present modelling and software can be used for investigation of BJT charge-neutral regions as well as diffused or implanted resistors.

It has become more important to shorten development periods of high performance computer systems and their LSIs. During debugging of computer prototypes, logic designers request very frequent LSI refabrication to change logic circuits and to add some functions in spite of their extensive logic simulation by several GFLOPS supercomputers. To meet these demands, an automated on-chip direct wiring modification system has been developed, which enables wire-cut and via-digging by a precise focused ion beam machine, and via-filling and jumper-writing by a laser CVD machine, directly on pre-redesign (original) chips. This modification system was applied to LSI reworks during the development of Hitachi large scale computers M-880 and S-3800, and contributed to shorten system debugging period by four to six months.

Photonic ATM switching systems with Terabit/s throughput are desirable for future broadband ISDN systems. Since electronic LSI-based ATM switching systems are planned to have the throughput of 160Gb/s, a photonic ATM switching system should take the role of the highest layer in a hybrid switching network which includes electronic LSI-based ATM switching systems as its sub-system. This report discusses the state-of-the-art photonic devices needed for a frequency-self-routing ATM photonic switching system with maximum throughput of 5Tb/s. This kind of systems seems to be a moderate system for the first phase photonic switching system with no insuperable obstacle for initiating development, even though none of the devices and technologies required have yet been developed to meet the specifications. On the contrary, for realizing further enlarged throughput as the second-phase photonic switching system, there are huge fundamental research projects still remaining for establishing the technology utilizing the spectrum broadened over 120nm and highly-dense FDM technologies based on homodyne coherent detection, if supposing a simple architecture. "Ultra devices" seem to be the photonic devices based on new tailored materials of which gain and refractive index are designed to realize ultra-wide spectrum utilization.

Novel circuit design techniques for CMOSFET (complementary MOS field-effet transistor)-only bias circuits, which each include a current mirror with a peaking characteristic, a current reference with a positive temperature coefficient, and a voltage reference with an optional temperature dependence, are described. An MOS Nagata current mirror is analyzed, and bias circuits like a CMOS self-biasing Nagata current reference and a CMOS self-biasing Nagata voltage reference, both of which include an MOS Nagata current mirror, are discussed. In addition, a CMOS temperature coefficient shifter, used to add an offset voltage and an optional temperature coefficient to a reference voltage, is also discussed. The CMOS Nagata voltage reference was verified with a breadboard using discrete componente and a 0.15 mV/ temperature dependence.

Numerical simulation of the hydrodynamic semiconductor device equations requires powerful numerical schemes. A Space-time Galerkin/Least-Squares finite element formulation, that has been successfully applied to problems of fluid dynamic, is proposed for the solution of the hydrodynamic device equations. Similarity between the equations of fluid dynamic and semiconductor devices is discussed. The robustness and accuracy of the numerical scheme are demonstrated with the example of a single electron carrier submicron silicon MESFET device.

OTA (Operational Transconductance Amplifier) is a useful circuit in analog signal processing systems, especially in high-frequency applications. Important features of OTA are: infinite input impedance, electrically changeable transconductance (Gm), and much wider operation range without negative feedback such as in OPamp applications. The good linearity of OTA over wide input range is necessary to extend the application fields of OTA. Several techniques are developed to extend the input range with good linearity. In this paper, a highly-linear CMOS-OTA operating under 1 V power supply, is proposed. The concept of the proposed OTA is based on class-AB operation of two n-channel MOSFETs in the saturation region. By improving the input stage circuits, wide input range can be achieved. SPICE simulations are performed to verify the performance of the proposed OTA.

An HDTV still-picture camera that uses four PAL CCD sensors has been developed for use as a high-speed, high-resolution image reader. The CCD sensors are optically coupled to a single lens by a pyramidal mirror. Each CCD sensor reads a quarter of the image and the four quarter-images are combined into one HDTV picture. Discontinuities at the lines where the four images join can be eliminated by white- and dark-level correction and gamma correction. Moreover, smoothing processing using a weighted-mean method is performed to produce a seamless picture. With this processing the camera can consistently produce seamless pictures.

Tunneling generation becomes increasingly important in modern devices both as a source of leakage and for special applications. Mostly, the observed phenomena are attributed to band-to-band tunneling, although from early investigations of Esaki diodes it is well known that at lower field strengths trap-assisted tunneling is responsible for non-ideal IV-characteristics. In this paper we apply microscopic models of trap-assisted and band-to-band tunneling, which were derived from first-principle quantum-mechanical calculations, in a general multi-device simulator. Special simplified versions of the models were developed for the purpose of fast numerical computations. We investigate pn-junctions with different doping profiles to reveal the relative contribution of the two tunneling mechanisms. Simulated currents as function of voltage and temperature are presented for each individual process varying the basic physical parameters. It turns out that the slope of reverse IV-characteristics dominated by trap-assisted tunneling is similar to those which are determined by band-to-band tunneling, if the localized state of the recombination center is only weakly coupled to the lattice. In the model such a slope is produced by field-enhancement factors of the Shockley-Read-Hall lifetimes expressing the probability of tunneling into (or out of) excited states of the electron-phonon system. The temperature dependence of these field-enhancement factors compensates to a certain extent the expected strong temperature effect of the Shockley-Read-Hall process. The latter remains larger than the temperature variation of phonon-assisted band-to-band tunneling, but not as much as often stated. Consequently, the slope of the IV-characteristics and their temperature dependence are not the strong criteria to distinguish between trap-assisted and band-to-band tunneling. The origin of tunnel currents in silicon rather depends on the sum of physical conditions: junction gradient, nature and concentration of defects, temperature and voltage range.

This paper describes an implementation of the finite element method to examine the effects of actual lip shape on the sound radiation. A three-dimensional finite element approach by Galerkin method was used. The accuracy of the calculation of finite element method for the sound radiation was tested by comparing it with the exact solutions for a circular piston radiator on an infinite baffle. Using a set of finite element models of the vocal tract, we calculated the responses to a pure tone input and the sound fields over the frequency range of 100 Hz-7 kHz. The transfer functions are examined in detail for vowels /a/ and /i/ when the shape of the actual lips is simplified as a planeradiation surface. The effects of lip shape on the distribution of sound pressures are also shown in both the vocal tract and the surrounding space of the mouth opening.

This paper describes a segment driver IC for high-quality liquid-crystal-displays (LCDs). Major design issues in the segment driver IC are a wide signal bandwidth and excessive output-offset variation both within a chip and between chips. After clarifying the trade-off relation between the signal bandwidth and the output-offset variation originated from conventional sample-and-hold (S/H) circuits, two wide-band S/H circuits with low output-offset variation have been introduced. The basic ideas for the proposed S/H circuits are to improve timing of the sampling pulses applied to MOS analog switches and to prevent channel charge injection onto a storage capacitor when the switches turn off. The inter-chip offset-cancellation technique has been also introduced by using an additional S/H circuit. Two test chips were implemented using the above S/H circuits for demonstration purposes. The intra-chip output-offset standard deviation of 9.5 mVrms with a 3dB bandwidth of 50 MHz was achieved. The inter-chip output-offset standard deviation was reduced to 5.1 mVrms by using the inter-chip offset-cancellation technique. The evaluation of picture quality of an LCD using the chips shows the applicability of the proposed approaches to displays used for multimedia applications.

Two types of novel nVT level shift circuits based on the square law characteristics of MOSFETs have been proposed. These circuits generate VIN+nVT or VIN-nVT (where VT is a threshold voltage), if the input voltage is applied as the VIN. These circuits can be widely used in MOSFET characterization, compensating VT effect, VT measurement, level shifting, etc. Type 1 is directly derived from the nVT-sift circuit proposed by Wang. Type 2 can reduce a total chip area than type 1 and has a wider input range. SPICE simulations show that the proposed circuits have a very wide input range and a small power consumption.

The aim of this study is to evaluate mental workload (MWL) quantitatively by HRV (Heart Rate Variability) measures. The electrocardiography and the respiration curve were recorded in five different epochs (1) during a rest condition and (2) during mental arithmetic tasks (addition). In the experiment, subjects added two numbers. The work levels (figures of the number in the addition) were set to one figure, two figures, three figures and four figures. The work level had effects on the mean percent correct, the number of answers and the mean processing time. The psychological evaluation on mental workload obtained by the method of paired comparison increased with the work level. Among the statistical HRV measures, the number of peak and trough waves could distinguish between the rest and the mental loading. However, mental workload for each work level was not evaluated quantitatively by the measure. The HRV measures were also calculated from the power spectrum estimated by the autoregressive (AR) model identification. The ratio of the low frequency power to the high frequency power increased linearly with the work level. In conclusion, the HRV measures obtained by the AR power spectrum analysis were found to be sensitive to changes of mental workload.

A new mobility model dependent upon electron concentration is presented for studying the screening effect on ionized impurity scattering. By coupling this model with the drift-diffusion and Hartree models, the effects of self-consistent and quasi-equilibrium screening on carrier transport in heavily doped systems are revealed for first time. The transport mechanism is found to be dominated by the electron-concentration-dependent mobility, and transconductance is shown to be determined by effective mobility and changes from degraded to enhanced characteristics with electron concentration modulation.

A photonic inter-module connector for near-future electronic switching systems is demonstrated through the use of silica-based 88 optical switches. A small-scale switch matrix is sufficient because the near-future systems will consist of a limited number of modules. If an active module is affected by a fatal fault or accident, a stand-by module must quickly take its place. The experimental photonic inter-module connector can switch 156-Mbit/s photonic interconnections between seven subscriber-line-concentrator modules and eight circuit-switching modules.