We have fabricated a prototype of interface devices between SFQ and CMOS circuits using HTS quasi-particle injection devices. By the injection of quasi-particles, the bridge area becomes resistive and high voltage appears at the drain electrode. As a test of device operation, we applied the signal of a function generator to the gate electrode and observed that the device successfully repeated on/off operation. We also succeeded in explaining the device characteristics by considering the thermal effects.

New bandpass filters (BPFs) with stub resonators are proposed for creating multiple attenuation poles. Firstly, the stub-dependent characteristics of the distributed-element stubs are examined theoretically. Secondly, the new BPFs with resonators of combined stubs are proposed. An advantage of these filters is the possibility of controlling the number of attenuation poles. The design of the proposed filter is carried out based on the general filter design with the narrow-band approximation technique. The transmission and reflection characteristics of the proposed BPFs are also examined theoretically and experimentally. The miniaturization of the filters is also carried out using the resonator with loaded-element stubs. The discussions lead us to the conclusion that the proposed design method of the filters are useful for controlling the number of attenuation poles of the BPF.

We present a design framework of a high-end server based on Single-Flux-Quantum (SFQ) circuit technologies. The server proposed here has multiple microprocessors and memories, which are mounted on a single board or package and are connected each other by SFQ interconnection switches. The extremely large bandwidth up to 100 Gbps/channel in the interconnection will be realized because of high throughput nature of the SFQ circuits. SFQ memories or Josephson-CMOS hybrid memories are employed as the shared memory of the multiprocessor. The SFQ microprocessors are constructed based on the complexity-reduced (CORE) architecture, in which complexity of the system is eased in exchange for using a high clock rate of the SFQ circuits. The processor is so-called Java-processor that directly executes the Java Byte Codes. Assuming a proper advancement of the Nb/AlOx/Nb integrated circuit process technology, we have estimated that the power consumption of the server system including a cryocooler is reduced by a factor of twenty as compared to the future CMOS system with the same processor performance, while the SFQ system has 100 times of magnitude larger memory-processor bandwidth.

High-end telecommunication systems in the larger nationwide networks of the next decade will require routers having a packet switching throughput capacity of over 10 Tbps. In such future high-end routers, the packet switch, which is the biggest bottleneck of the router, will need higher processing speeds than semiconductor devices. We propose a high-end router system architecture using single flux quantum (SFQ) technology. This system consists of semiconductor line card units and an SFQ switch card unit. The features of this switch card architecture are (1) using internal speedup architecture to reduce effective loads in the network, (2) using a packet switch scheduler to attain non-blocking characteristics. This architecture can expand the switching capacity to a level greater than tens of Tbps scale, keeping with non-blocking characteristics.

We have designed the Half Adder (HA) circuit and the Carry Save Serial Adder (CSSA) circuit based on pipeline architecture. Our HA has the structure of a two-stage pipeline and consists of 160 Josephson Junctions (JJs). Our CSSA has the structure of a four-stage pipeline with a feedback loop and consists of 360 JJs. These circuits were fabricated by the NEC standard process. There are two issues which should be considered in the design. One is parameter spreads generated by the fabrication process and the other is leakage currents between the gates. We have introduced a parameter optimization method to deal with the parameter spreads. We have also inserted three stages of JTLs to reduce leakage currents. We have experimentally confirmed the correct operations of these circuits. The obtained bias margins were 33.1% for the HA and 24.6% for the CSSA.

This article describes simulation study on SQUID applications for Single-Flux-Quantum(SFQ) Logic Circuits. Here, a SQUID is compatible to a Quantum Flux Parametorn (QFP). Several new circuits based on a SQUID are investigated. A cascaded SQUID is proposed with the signal amplitude in the same order of an SFQ. An SFQ-pulse driving circuits with the new SQUID are successfully simulated. An SFQ trap which catches SFQs is newly proposed. Focusing on a circulating current of a segment in a Josephson transmission line (JTL), an SFQ-pulse is non-destructively detected by a SQUID. A conventional SQUID inserted in a JTL operates as a gate which controls SFQ-pulse transmission through it. Compatibility of SQUIDs and SFQ circuits is demonstrated.

We have proposed a top-down design methodology for the RSFQ logic circuits based on the Binary Decision Diagram (BDD). In order to show the effectiveness of the methodology, we have designed a small RSFQ microprocessor based on simple architecture. We have compared the performance of the 8-bit RSFQ microprocessor with its CMOS version. It was found that the RSFQ system is superior in terms of the operating speed though it requires extremely large area. We have also implemented and tested a 1-bit ALU that is one of the important components of the microprocessor and confirmed its correct operation.

SQUID (Superconducting QUantum Interference Device) Photoscanning is an analytical technique intended for the noninvasive evaluation of semiconductor wafers and device structures. This method is based on the detection of the magnetic field of photocurrents locally induced in the sample under investigation by a focused laser beam. The magnetic field is monitored by means of a sensitive SQUID magnetometer while scanning the sample surface with the laser beam. Doping inhomogeneities in electronic grade silicon, grain boundaries in solar silicon, and defects in photovoltaic device structures have been analyzed.

We describe here development of a multichannel high-Tc SQUID magnetometer system for measurement of cardiac magnetic fields, aiming at future application of diagnosis of heart diseases. Two types of direct-coupled SQUID magnetometers were fabricated and used: single pickup coil magnetometer having flux dams to suppress the shielding current that would induce flux penetration and the consequent low-frequency noise, and double pickup coil magnetometer having no grain boundary junctions and flux dams on the pickup coil. The superconducting film of both the magnetometers had holes and slots, leaving 5 µm-wide strip lines, to suppress trapping and penetration of magnetic flux vortices in environmental fields. We studied different schemes of active shielding to reinforce the efficiency of field-attenuation of magnetically shielded room (MSR). A feedback-type compensation using a normal detection coil wound around the wall of MSR and a selective cancellation of 50 Hz noise by means of adaptive filter were developed. Such combination of passive and active shielding, based on the use of simple MSR, would be suitable in a practical low-cost magnetometer system for clinical MCG examination. We fabricated a liquid nitrogen cryostat that could contain up to 20 magnetometer-capsules at 4 cm separation in a flat bottom, with a distance of 16 mm between the air and liquid nitrogen. The cryostat was set in a gantry, which had rotational, vertical and horizontal freedoms of movement, in a moderate-shielding MSR that was combined with the developed active shielding. Measurements of MCG were performed for normal subject using eight magnetometers operating simultaneously.

Thermally activated magnetic-flux entry into a pickup coil through a flux dam in high Tc superconducting quantum interference device (SQUID) is studied. The behavior of this thermal activation is analyzed in terms of the circulating current flowing in the pickup coil. It is shown that the thermal activation can be prevented when the circulating current becomes much below a critical current of the flux dam. It is also shown that we need a long waiting time in order to realize this situation since the circulating current logarithmically decays with time in the case of the thermal activation. The relationship between the thermal activation and the circulating current is qualitatively confirmed with the experiment. We also show a method in order to forcibly reduce the circulating current instead of the thermal activation. In this case, we can prevent the thermal activation without the long waiting time.

We have developed and demonstrated a novel technique for electrical inspection and electrical failure analysis, which can detect open, high-resistance, and short circuits without the need for electrical contact with the outside of the LSI chip or the board on which the LSI chip is mounted. The basic idea of the technique is the detection of the magnetic field produced by OBIC (optical beam induced current) or photo current. A DC-SQUID (superconducting quantum interference device) magnetometer is used to detect the magnetic field. This scanning laser-SQUID microscopy ("laser-SQUID" for short) has a spatial resolution of about 1.3 µm. It can be used to distinguish defective chips before bonding pad patterning or after bonding without pin-selection. It can localize any defective site in the chip to within a few square microns.

We have designed a torque magnetometer using a 60-kG split-type superconducting magnet. A balance torque compensates the torque acting on a sample in the magnetic field. The feedback circuit for a sample direction consists of an optical position sensor, a moving coil, and a PID controller. We measured the coil current to know a sample torque. The whole torque machinery is directly rotated by a stepping motor of angular resolution 0.0036. An advantage of the torque apparatus is a wide dynamic range up to 1000 dyncm. The sample temperature can be controlled between 4 K and 300 K.

We have developed a new torque magnetometer on the basis of a 4-K refrigerator. The system temperature can be lowered down to 1.5 K by pumping liquefied helium from a top loading sample space. A piezoresistor bridge on a Si cantilever is used to detect torque acting on a sample. A transverse magnetic field is supplied by a variable-field permanent magnet up to 10 kG. We find that a sensitivity of our torque magnetometer is Δ τ 10-10 Nm.

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.

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.

A new structure of a low-loss high temperature superconducting (HTS) filter is proposed by using quarter-wavelength coplanar waveguide (CPW) resonators. A 4-pole Chebyshev band-pass filter with the center frequency 5.0 GHz and the 0.01 dB-ripple fractional bandwidth 3.2% is designed based on the theory of direct-coupled resonator filters using K- and J-inverters. This filter is fabricated by using a high-Tc superconductive YBCO film deposited on a MgO dielectric substrate. The frequency response of the filter measured at 60 K agrees very well with the theoretical one. The insertion loss is 0.22 dB. The insertion loss of this filter is the lowest in HTS-CPW filters presented so far.

A rapid Pseudo-Noise (PN) acquisition scheme is proposed. The proposed scheme consists of a phase alignment detector and Voltage Controlled Clock (VCC) loop. The VCC loop is used to control the phase update of the local PN signal. It has an auxiliary signal that provides the loop with two stable locking points as well as the direction of each phase update. The performance of the proposed scheme is evaluated by simulation. Results show that the proposed scheme acquires the phase two to three times faster than the conventional coherent serial scheme, and 1.5 times faster than of that in [10], at a small amount of additional hardware.

This paper presents an improved spectral subtraction method for speech enhancement. A new noise estimation method is derived in which the noise is assumed to be white. By using the property that a white noise spectrum is flat, high frequency components of a noisy speech spectrum are averaged and the standard deviation of the noise is estimated. This operation is performed in the analysis segment, thus the spectral subtraction method combined with the new noise estimation method does not need non-speech segments and as a result can adapt to non-stationary noise conditions. The effectiveness of the proposed spectral subtraction method is confirmed by experiments.

We report our studies on the spectral sensitivity of superconducting NbN thin-film single-photon detectors (SPD's) capable of GHz counting rates of visible and near-infrared photons. In particular, it has been shown that a NbN SPD is sensitive to 1.55-µm wavelength radiation and can be used for quantum communication. Our SPD's exhibit experimentally measured intrinsic quantum efficiencies from 20% at 800 nm up to 1% at 1.55-µm wavelength. The devices demonstrate picosecond response time (<100 ps, limited by our readout system) and negligibly low dark counts. Spectral dependencies of photon counting of continuous-wave, 0.4-µm to 3.5-µm radiation, and 0.63-µm, 1.33-µm, and 1.55-µm laser-pulsed radiations are presented for the single-stripe-type and meander-type devices.