We are developing a superconducting analog-to-digital converter (ADC) as a readout for high-resolution X-ray detectors based on a superconducting tunnel junction (STJ). The ADC has a sensitive front end which consists of a DC superconducting quantum interference device (SQUID). A signal current is digitized by this front end without using any preamplifiers. A single-flux-quantum (SFQ) pulse train whose frequency is proportional to the input current is launched by the front end, and integrated by a digital counter. The counter has a 10-bit resolution, and the integrated value is scanned and transferred to room-temperature processing modules with a frequency of 40 MHz. In this paper, the design of the ADC is described, and the preliminary results of the ADC performance test are shown. The performance of the STJ accompanied by the ADC is discussed in terms of the X-ray energy resolution.

In this paper, we propose a turbo equalization scheme for GMSK signals with frequency detection. Although the channel is AWGN, there exists severe ISI (Inter-Symbol Interference) in the received signal due to the premodulation Gaussian baseband filter in the transmitter as well as the narrowband IF filter in the receiver. We regard these two filters as a real number inner convolutional encoder. The ISI equalizer for this inner encoder and the outer decoder for a RSC (Recursive Systematic Convolutional) code, are connected through a random (de-)interleaver. These inner and outer decoders generate the reliability values in terms of LLR (Log Likelihood Ratio), using MAP or SOVA algorithm with SISO (soft input and soft output). Moreover iterative decoding with the limitation of LLR values are employed between two decoders to achieve a turbo equalization for GMSK frequency detection. Through computer simulations, the proposed system shows the BER=10-5 at Eb/N0=8.8 dB, when we take BT=0.6 (IF filter bandwidth multiplied by symbol duration) with the iteration number of 3. This means 3.1 dB improvement compared with the conventional scheme where the inner ISI equalizer is concatenated with the outer hard decision Viterbi decoder.

The FDTD method needs Fourier analysis to obtain the fields of a single frequency. Furthermore, the frequency spectra of the fields used in the FDTD method ordinarily have wide bands, and all the fields in FDTD are treated as real numbers. Therefore, if the permittivity ε and the permeability µ of the medium depend on frequency, or if the surface impedance used for the surface impedance boundary condition (SIBC) depends on the frequency, the FDTD method becomes very complicated because of convolution integral. In the electromagnetic theory, we usually assume that the fields oscillate sinusoidally, and that the fields and ε and µ are complex numbers. The benefit of introduction of the complex numbers is very extensive. As we do in the usual electromagnetic theory, the authors assume that the fields in FDTD oscillate sinusoidally. In the proposed FDTD, the fields, ε, µ and the surface impedances for SIBC are all treated as the complex numbers. The proposed FDTD method can remove the above-mentioned weak points of the conventional FDTD method.

With the emerging technology of photonic networks, careful design becomes necessary to make most of the already installed fibre capacity. Appropriate numerical tools are readily available. Usually, these are based on the split-step Fourier method (SSFM), employing the fast Fourier transform (FFT). With N discretization points, the complexity of the SSFM is O(N log2N). For real-world wavelength division multiplexing (WDM) systems, the simulation time can be of the order of days, so any speed improvement would be most welcome. We show that the SSFM is a special case of the so-called collocation method with harmonic basis functions. However, for modelling nonlinear optical waveguides, various other basis function systems offer significant advantages. For calculating the propagation of single soliton-like impulses, a problem-adapted Gauss-Hermite basis leads to a strongly reduced computation time compared to the SSFM . Further, using a basis function system constructed from a scaling function, which generates a compactly supported wavelet, we developed a new and flexible split-step wavelet collocation method (SSWCM). This technique is independent of the propagating impulse shapes, and provides a complexity of the order O(N) for a fixed accuracy. For a typical modelling situation with up to 64 WDM channels, the SSWCM leads to significantly shorter computation times than the standard SSFM.

A new low-voltage, all-in-one ESD (electrostatic discharging) protection circuit was designed. One such ESD protection unit is enough to protect each I/O pad against ESD stresses of all modes, i.e., from I/O to power supply and ground positively and negatively. This novel ESD circuit features adjustable trigger-voltage, i.e., 5 V to 60 V, with low turn-on threshold down to 5 V, symmetric active discharging channels in all directions, fast response time of 0.1 to 0.3 ns, and high ESD performance/area ratio of greater than 80 V per micrometer width. It was implemented in commercial BiCMOS technologies and achieved 14 kV human body model (HBM) and 15 kV air-gap IEC ESD protection levels. This compact ESD structure can not only provide adequate ESD protection, but also minimize the ESD-induced parasitic effects, which makes it a suitable ESD protection solution for mixed-signal and RF ICs in very deep sub-micron regime.

In this article we present the subject of wideband channel modeling and simulation, stressing the method of orthogonalization. We compare the performance of this simulation method using Karhunen-Loeve, Wavelets and other basis over radio channels represented via the Input-Delay Spread Bello Function.

A fuzzy-like phenomenon is observed in a chaotic neural network operating as dynamic autoassociative memory. When an external stimulation with properties shared by two stored patterns is applied to the chaotic neural network, the output of the network transits between the two patterns. The ratio of the network visiting two stored patterns is dependent on the ratio of the Hamming distances between the external stimulation and the two stored patterns. This phenomenon is similar to the human decision-making process, which can be described by fuzzy set theory. Here, we analyze the fuzzy-like phenomenon from the viewpoint of the fuzzy set theory.

To the aim of developing industrializable low-cost electronic techniques for the compensation of non-linearities in Radio-over-Fibre networks, a semiconductor laser circuit model and a predistortion circuit configuration have been implemented and simulated. The CAD procedure illustrated indicates the steps to obtain a broadband compensation (0.4-2 GHz) of both second- and third-order distortions.

We have designed a demultiplexer (DMUX) with a simple structure, high-speed operation circuits and large bias margins. By using a binary-tree architecture and clock-driven circuits, multi-channel DMUXs can be constructed easily from the same elemental circuits, i.e., 1-to-2 DMUX, consisting of a T-FF and a 1-to-2 switch. By applying cell-level optimization and Monte Carlo simulation, bias margins and operation frequency of the circuits were enlarged. Logical operations of the 1-to-2 DMUX and a multi-channel DMUX, e.g., a 1-to-4 DMUX were experimentally confirmed. It was also confirmed that the large margins, 33% of the DMUX (1-to-2 switch) was kept up regardless the degree of integration, and that the 1-to-2 DMUX can operate up to 46 GHz by using measure of average voltages across Josephson junctions.

In this paper, characteristics of a digital system dedicated to the fast execution of the FDTD algorithm, widely used for electromagnetic simulation, are presented. Such system is conceived as a module communicating with a host personal computer via a PCI bus, and is based on a VLSI ASIC, which implements the "field-update" engine. The system structure is defined by means of a hardware description language, allowing to keep high-level system specification independent of the actual fabrication technology. A virtual implementation of the system has been carried out, by mapping such description in a standard-cell style on a commercial 0.35 µm technology. Simulations show that significant speed-up can be achieved, with respect to state-of-the-art software implementations of the same algorithm.

It is of considerable interest to study the vortex behavior of a multiply connected superconductor for potential applications of vortex devices. Our sample is made of a type-I superconductor Pb and a capillary plate. The nominal sizes are 1-µm in hole diameter and 1.8-µm in lattice pitch. The microholes form triangular lattice while a superconducting network consists of a honeycomb lattice. When each hole accommodates a single vortex 0, an applied magnetic field becomes a nominal matching field (7.83 G). We measure the magnetization curve of sample by means of a SQUID (superconducting quantum interference device) magnetometer in the accurate small fields on the order of Gauss. We find a sharp magnetization peak at 8.2 G at temperatures near the critical temperature Tc.

We propose a new decidable subclass of term rewriting systems (TRSs) for which strongly normalizing (SN) property is decidable. The new class is called almost orthogonal inverse finite path overlapping TRSs (AO-FPO-1-TRSs) and the class properly includes AO growing TRSs for which SN is decidable. Tree automata technique is used to show that SN is decidable for AO-FPO-1-TRSs.

The size dependent properties of the intrinsic Josephson junctions in Bi2Sr2CaCu2Oy single crystal mesas in the external magnetic field are studied. The mesas of (1-140) µm long with 7-29 junctions were fabricated and their current-voltage characteristics were measured in external magnetic field applied parallel to the CuO2 layers up to 0.16 T. In zero magnetic field, multiple resistive branches with large hysteresis were observed in the current-voltage characteristics for the fabricated mesas. Almost identical critical currents were also observed for all the junctions in each mesa. With applied magnetic field, Ic of the longer mesas showed a complex magnetic field dependence as compared to that of the short mesas (of about 1 µm in length). It was observed that the lower critical magnetic field of the junctions decreased and approached a constant value with increasing number of junctions and also with increasing length of the junctions. Similar magnetic behavior was obtained by numerical simulations based on coupled sine-Gordon equations for such stacked junctions.

We report the measurements on the ramp-edge type Josephson and quasiparticle tunnel junctions with the different interface angle geometry using high-Tc YBa2Cu3O7-y (YBCO) electrodes. The YBCO/I/Ag tunnel junctions with different crystal-interface boundary angles are fabricated for the investigation of zero bias conductance peak. The angle dependent zero bias conductance peak typical to a dx2-y2-wave superconductor is observable. For Josephson junctions, YBCO ramp-edge junctions with different ab-plane electrodes relatively rotated by 45are fabricated using a CeO2 seed-layer technique. The temperature dependence of the maximum Josephson current for YBCO/PBCO/YBCO junctions (PBCO: PrBa2Cu3O7-y) exhibits angle-dependent behavior, qualitatively different from the Ambegaokar-Baratoff prediction. Under microwave irradiation of 9 GHz, the Shapiro steps appear at integer and/or half integer multiples of the voltage satisfying Josephson voltage-frequency relation, whose behavior depends on the sample angle geometry. The results are reasonably interpreted by the dx2-y2-wave theory by taking the zero energy state into account.

Lymph-node detection system using a high Tc SQUID and ultra-small particles was proposed. Pseudo lymph nodes containing small iron particles were made and the magnetic signal was measured. The SQUID signal was proportional to the weight of the iron in the fluid. At the distance of 20 mm, the detectable minimum weight of the iron was 40 µg. We demonstrated that the possibility of the application of the system to the human body.

Scaled models for an anatomical head model and a simple head model are used to investigate the effects of head size on SAR characteristics for a cellular phone exposure at 835 MHz. From the results, we can see that a larger head produces a higher localized SAR and a lower whole-head averaged SAR.

Iterative schemes for demodulating M-ary orthogonal signaling formats in direct-sequence code-division multiple access (DS-CDMA) systems are proposed and compared with the standard noncoherent matched filter receiver. Interference cancellation, i.e., (approximative) removal of the multiple access interference (MAI) by means of subtraction is studied. The considered system is similar to the uplink (reverse link) of an IS-95 system. Hence, the received signals from the concurrent users are asynchronous, and no pilot signals are available for channel estimation. A decision-directed algorithm is proposed for estimating the time-varying complex channel gains of a multipath channel. The receivers are evaluated on Rayleigh-fading channels and are shown to provide large capacity gains compared with the conventional receiver.

Recent DSP applications have many significant issues such as higher system performance, lower power consumption, higher design flexibility, faster time-to-market, and so on. Neither a conventional ASIC nor a conventional DSP can necessarily satisfy all the requirements at once nowadays. Therefore, an alternate for DSP applications will be needed to complement the drawbacks of ASICs and DSPs. This paper introduces a new computing paradigm called configurable computing or reconfigurable computing, which has more potential in terms of performance and flexibility. Conventional silicon platforms will not satisfy the conflicting demands of standard products and customization. However, silicon platforms such as FPGAs for configurable or reconfigurable computing are standardized in manufacturing but customized in application. This paper also presents a brief survey of the existing silicon platforms that support configuration or reconfiguration in the application domain of digital signal processing such as image processing, communication processing, audio and speech processing. Finally, we show some promising reconfigurable architectures for the digital signal processing and discuss the future of reconfigurable computing.

We fabricated ramp-edge junctions with barriers by modifying surface and integrating ground-planes. The fabricated junctions had current-voltage characteristics consistent with the resistive shunted-junction model. We also obtained a 1-sigma spread in the critical current of 7.9% for 100 junctions at 4.2 K. The ground-plane reduced the sheet inductance of a stripline by a factor of 3. The quality of the ground-plane was improved by using an anneal in oxygen atmosphere after fabrication. The sheet inductance of a counter-electrode with a ground-plane was 1.0 pH per square at 4.2 K.

This paper introduces a probabilistic modeling of alarm observation delay, and shows a novel method of model-based diagnosis for time series observation. First, a fault model is defined by associating an event tree rooted by each fault hypothesis with probabilistic variables representing temporal delay. The most probable hypothesis is obtained by selecting one whose Akaike information criterion (AIC) is minimal. It is proved by simulation that the AIC-based hypothesis selection achieves a high precision in diagnosis.