System integration and trade-offs of SQUID system for biomagnetic applications

We have been developing SQUID systems for various applications, with special emphasis on systems for biomagnetic applications. In 1987, Koyanagi and Kado fabricated and integrated a SQUID system made entirely of thin-film integrated SQUID. Research and development activities on multichannel SQUID system integration has been undertaken by various groups. The Superconducting Sensor Laboratory (SSL) project was one of the most significant of these activities. Such activities in North America and Europe have mostly been pursued by commercial groups, who have been fabricating commercial systems for end users. However, large-scale system distribution to end users is still impractical because of high costs and the lack of user-friendliness. As former members of the SSL project, some of us at the Kanazawa Institute of Technology began the development of SQUID systems aimed at overcoming previous problems such as high cost and the low level of user-friendliness. In this paper, we describe our concept of system integration and the level of the system’s sophistication.     

Design of a fast digital double relaxation oscillation SQUID

A fast digital Double Relaxation Oscillation SQUID (DROS) with a relaxation oscillation frequency of 100 MHz has been developed. The digital DROS incorporates a DROS and a superconducting up-down counter that supplies the feedback flux. The major advantage of a DROS is that the relaxation oscillations generate an on-chip clock signal and therefore, no external clock is required. In order to maximize the slew rate without compromising the sensitivity, the quantization unit of the feedback flux was adapted to the flux noise of the DROS. This resulted in a designed flux slew rate of 5·10⁶ Φ₀/s. We will discuss the design optimization, numerical simulations, the layout and some experimental results of the digital DROS     

Design criteria for active shielding of inhomogeneous magneticfields for biomagnetic applications

General analytical expressions for the field attenuation and the reaction factor for a spherical active compensated cabin are theoretically derived. The shielding effect of various materials and their thickness on external magnetic disturbances as well as the retroactive effect on the locally generated compensating fields of the compensating coils are then analyzed. A numerical evaluation of the analytical expressions developed is made and directives for practical measures are derived. Comparison with the experimental results obtained from the measurement of shielding properties of an equivalent cubic cabin is made. The so-determined design criteria are then discussed in detail     

Integrated YBa2Cu3O7 magnetometers for biomagnetic applications

Three concepts of integrated magnetometers intended for biomagnetic multichannel systems are investigated: The Ketchen-type magnetometer, the multiloop magnetometer and the magnetometer with integrated multiloop pickup coil (IMPUC). The devices are fabricated from YBa₂Cu₃O₇-SrTiO₃-YBa₂Cu₃O₇ thin-film multilayers, and step-edge grain-boundary Josephson junctions as well as ramp-edge junctions with PrBa₂Cu₃O₇ barriers are employed. The magnetometers are compared regarding their effective flux collecting area, inductance and noise performance. With an optimized layout for the multiloop device, we achieve an effective flux collecting area of 2.3 mm² at an inductance of 145 pH. At 77 K we measure a magnetic flux density noise down to √S_B=60 fT/√Hz at 1 Hz and of 17 fT/√Hz in the white noise regime. Due to the low noise levels of the magnetometers high quality magnetocardiograms were recorded inside a magnetically shielded room without signal averaging. The noise performance of the magnetometers is also analyzed in unshielded environment and in static magnetic fields.     

泵浦带有弛豫振荡的固体激光器的弛豫振荡特性理论研究

对泵浦带有弛豫振荡的固体激光器的弛豫振荡特性进行了系统的理论研究，发现实际光子数的起伏同时具有自身固有的弛豫振荡频率和泵浦光的弛豫振荡频率两种分量．当两者的频率相近时，会呈现出共振加强现象．特别是当两个弛豫振荡的衰减率也相等的时候，共振现象极为强烈．PD反馈能够有效地抑制弛豫振荡．     

A frequency-controlled beam-steering array with mixing frequency compensation for multichannel applications

A frequency-controlled beam-steering planar array with mixing frequency compensation is presented for cost-effective multichannel phased array applications. The new feed networks for frequency compensation not only operate in wide band but also ensure radio-frequency (RF) amplitude imbalance cancellation and progressive phase distribution. The parallel equal power dividers installed in both LO and intermediate-frequency (IF) feed networks provide uniform amplitude and phase distribution, while the fixed delay lines installed in the LO feed network exhibit precise phase progression, compared to a series feed structure. The LO power imbalance caused by the unequal delay line loss between elements is corrected by pumping each mixer into the LO saturation region, leading to linear IF-RF response. Thus, sidelobe degradation and pattern distortion caused by the RF amplitude imbalance, as well as the beam-steering error and beam squint caused by the phase errors of the delay lines, are removed. The proposed feed networks combined with quasi-Yagi antenna arrays and microwave monolithic integrated circuit mixers realize a broad bandwidth of more than 3 GHz in K band for multichannel wireless applications. The K band transmitter/receiver pair proposed in this paper successfully demonstrates two-channel simultaneous RF transmission and single channel 50-Mb/s data communication with 40/spl deg/ scanning. This simple, compact, yet cost-effective planar array ensures multichannel broadband wireless communications with beam-steering capability.     

A multichannel grating cavity laser for wavelength divisionmultiplexing applications

A novel form of wavelength selectable diode laser source is proposed for wavelength division multiplexing (WDM) applications. The source may be used to operate at specific wavelengths across the complete gain spectrum of the laser diode material, but does not require any moving parts. Theoretical simulations indicate that the device can be expected to operate in a single longitudinal mode for channel separations on the order of 1 nm. The potential of using the device to generate parallel streams of WDM data is considered     

Double junction photodiode for X-ray CMOS sensor IC

A CMOS compatible P＋/Nwell/Psub double junction photodiode pixel was proposed, which can effi- ciently detect fluorescence from CsI（T1） scintillation in an X-ray sensor. Photoelectric and spectral responses of P＋/Nwell, NweE1/Psub and P＋/Nwell/Psub photodiodes were analyzed and modeled. Simulation results show P＋/Nweu/Psub photodiode has larger photocurrent than P＋/Nwetl photodiode and Nweu/Psub photodiode, and its spectral response is more in accordance with CsI（T1） fluorescence spectrum. Improved P＋/Nweu/Psub photodiode detecting CsI（T1） fluorescence was designed in CSMC 0.5 #m CMOS process, CTIA （capacitive transimpedance amplifier） architecture was used to readout photocurrent signal. CMOS X-ray sensor IC prototype contains 8 × 8 pixel array and pixel pitch is 100 × 100 μm2. Testing results show the dark current of the improved P＋/Nwell/Psub photodiode （6.5 pA） is less than that of P＋/Nwell and P＋/Nwell/Psub photodiodes （13 pA and 11 pA respectively）. The sen- sitivity of P＋/Nwell/Psub photodiode is about 20 pA/lux under white LED. The spectrum response of P＋/Nwell/Psub photodiode ranges from 400 nm to 800 nm with a peak at 532 nm, which is in accordance with the fluorescence spectrum of Csl（T1） in an indirect X-ray sensor. Preliminary testing results show the sensitivity of X-ray sensor IC under Cu target X-ray is about 0.21 V.m^2/W or 5097e-/pixel @ 8.05 keV considering the pixel size, integration time and average energy of X-ray photons.     

Voltage reference architectures for low-supply-voltage low-power applications

This paper presents a voltage reference generator architecture and two different realizations of it that have been fabricated within a standard 0.18 μm CMOS technology. The architecture takes the advantage of utilizing a sampled-data amplifier (SDA) to optimize the power consumption. The circuits achieve output voltages on the order of 190 mV with temperature coefficients of 43 ppm/°C and 52.5 ppm/°C over the temperature range of 0 to 120°C without any trimming with a 0.8 V single supply. The power consumptions of the circuits are less then 500 nW while occupying an area of 0.2 mm² and 0.08 mm², respectively.     

Vertically self-aligned buried junction formation for ultrahigh-density DRAM applications

In this letter, we present a novel junction integration scheme that enables vertical transistors to have high performance, low leakage, and easy scalability. Controlled solid-phase diffusion is used to form the vertically self-aligned buried strap junction of the vertical transistor. The electric field at the capacitor node junction is carefully optimized by creating a graded junction profile, resulted from a combination of out-diffusion from Arsenic-doped poly-silicon and Phosphorus-doped oxide. The Phosphorus-doped oxide serves as the dopant source for the vertical lightly doped drain, as well as the spacer for the high dose junctions. Integration of the self-aligned junctions into a vertical transistor dynamic random access memory (DRAM) process flow is presented. Significant improvement in the retention characteristics of a 256-Mb DRAM product confirms the applicability of this newly developed junction integration scheme for future DRAM generations.     

Development of MMIC-based modules for multichannel RF/opticalsubcarrier multiplexed communications applications

We present a C-band monolithic microwave integrated circuit (MMIC) transmitter module development for multichannel RF/optical subcarrier multiplexed (OSCM) communication applications. The C-band MMIC transmitter module consists of one fully monolithic four-channel OSCM transmitter IC and four coupled-line filters. This MMIC is designed and implemented in a commercial GaAs MESFET process and coupled line bandpass filters are fabricated on the module board. We present the design and performance of the first fully monolithic IC transmitter module for OSCM packet switched applications     

Optoelectronic feedback loop for relaxation oscillation intensitynoise suppression in Tm-Ho:YAG laser

An optoelectronic feedback loop that can be used to effectively reduce the intensity noise of a 2.1 μm Tm-Ho:YAG laser has been designed. The feedback circuit is based on a variable-gain biquadratic bandpass filter with adjustable central frequency and quality factor, providing a high loop gain around the relaxation oscillation frequency of the laser and a closed-loop phase margin larger than 50°. The relaxation oscillation peak in the intensity noise spectrum was completely suppressed in closed-loop operation, and a noise reduction of up to 24 dB was obtained     

Double ridged waveguide phase shifters for broadband applications

The author presents an electromagnetic mode matching analysis of dual ridged waveguide phase shifters. The waveguide is loaded with a high dielectric material between the ridges, and the troughs are filled with ferrite toroids. The present structure offers nearly twice the bandwidth and less variation in nonreciprocity versus frequency as compared to the conventional dual toroidal phase shifter. An optimum design that maximizes nonreciprocity has been found. Effects of the dielectric constant and the trough dimensions are also presented. A differential phase shift of more than 100°/cm has been predicted for the new phase shifter     

Double gate-MOSFET subthreshold circuit for ultralow power applications

In this paper, we propose MOSFETs that are suitable for subthreshold digital circuit operations. The MOSFET subthreshold circuit would use subthreshold leakage current as the operating current to achieve ultralow power consumption when speed is not of utmost importance. We derive the theoretical limit of delay and energy consumption in MOSFET subthreshold circuit, and show that devices that have an ideal subthreshold slope are optimal for subthreshold operations due to the smaller gate capacitance, as well as the higher current. The analysis suggests that a double gate (DG)-MOSFET is promising for subthreshold operations due to its near-ideal subthreshold slope. The results of our investigation into the optimal device characteristics for DG-MOSFET subthreshold operation show that devices with longer channel length (compared to minimum gate length) can be used for robust subthreshold operation without any loss of performance. In addition, it is shown that the source and drain structure of DG-MOSFET can be simplified for subthreshold operations since source and drain need not be raised to reduce the parasitic resistance.     

Double crucible optical fibre for data link applications

A short distance, data link fibre has been made by the double crucible method. The fibre has a large core (175 ?m), high NA (0.4) and a minimum loss of 7.5 dB/km. By lowering the water content of the fibre the usable wavelength range has been extended to 1.3 ?m     

A transimpedance CMOS multichannel amplifier with a 50 Ω-wideoutput range buffer for high counting rate applications

A fast transimpedance multichannel amplifier has been designed, fabricated in CMOS 1.2-μm technology and tested. Each channel consists of a current sensitive preamplifier followed by a voltage amplification stage and an on-chip buffer able to drive 50 Ω loads with an output range of ±800 mV. Measured peaking time at the output is 40 ns and the circuit recovers to baseline in 90 ns. This results in a counting capability of more than 10⁷ hits/s, Signals of both polarities can be handled. The first two stages consume a total of 2 mW per channel and the 50 Ω buffer consumes another 17 mW. The equivalent noise charge (ENC) is 1100 e^- rms with a slope of 40e^-/pF. The IC is intended for use in gas and solid-state detectors with high particle rate and extensive charge release as in high energy calorimetry     

局部参考光束全息图的形成及应用

在记录全息图时，如果用连续输出的激光器作为照明光源，就必须使用防振性能很好的防振台。在一般情况下，激光器和全部的光学装置都安放在防振台上，被摄物体也必须置于台上。然而，由于防振台不便移动，而有些被摄物体又无法进入实验室和置于防振台上，因此就不能     

Algorithmic ADC operating with a single reference voltage for PLL-based chemical sensing applications

This paper deals with the design of an algorithmic switched-capacitor analog-to-digital converter (ADC), operating with a single reference voltage, a single-ended amplifier, a single-ended comparator, and presenting a small input capacitance. The ADC requires two clock phases per conversion bit and N clock cycles to resolve the N-bits. The ADC achieves a measured peak signal-to-noise-ratio (SNR) of 49.9 dB and a peak signal-to-noise-and-distortion-ratio (SNDR) of 46.7 dB at P_in = ?6dBFS with a sampling rate of 0.25 MS/s. The measured differential-non-linearity and integral-non-linearity are within +0.6/?0.5 and +0.2/?0.5 LSB, respectively. The ADC power consumption is 300 μW and it is implemented in 90 nm CMOS technology with a single power supply of 1.2 V. The ADC saves power at system-level by requiring only a single reference voltage. At system level, this solution is therefore not only robust but competitive as well.