A 0.004-mm2 Portable Multiphase Clock Generator Tile for 1.2-GHz RISC Microprocessor

Portable multiphase clock generators capable of adjusting its clock phase according to input clock frequencies have been developed both in a 0.18-mum and in a 0.13-mum CMOS technologies. They consist of a full-digital CMOS circuit design that leads to a simple, robust, and portable IP. In addition, their open-loop architecture lead to no jitter accumulation and one-cycle lock characteristic that enables clock-on-demand circuit structures. The implemented low power clock generator tile in a 0.13-mum CMOS technology occupies only 0.004 mm ² and operates at variable input frequencies ranging from 625 MHz to 1.2 GHz within a plusmn 2% phase error having one-cycle lock time.     

A Wireless Power Interface for Rechargeable Battery Operated Medical Implants

This brief presents a highly integrated wirelessly powered battery charging circuit for miniature lithium (Li)-ion rechargeable batteries used in medical implant applications. An inductive link and integrated Schottky barrier rectifying diodes are used to extract the DC signal from a power carrier while providing low forward voltage drop for improved efficiency. The battery charger employs a new control loop that relaxes comparator resolution requirements, provides simultaneous operation of constant-current and constant-voltage loops, and eliminates the external current sense resistor from the charging path. The accuracy of the end-of-charge (EOC) detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Experimental results in 0.6-mum 3M-2P CMOS technology indicate that plusmn1.3% (or plusmn20 muA) EOC accuracy can be obtained under worst case conditions for a comparator offset voltage of plusmn5 mV. The circuit measures roughly 1.74 mm² and dissipates 8.4 mW in the charging phase while delivering a load current of 1.5 mA at 4.1 V (or 6.15 mW) for an efficiency of 73%.     

Proposal for Highly Nonlinear Dispersion-Flattened Octagonal Photonic Crystal Fibers

A highly nonlinear photonic crystal fiber (HNL-PCF) based on an octagonal structure with isosceles triangular-latticed cladding is proposed for the telecommunication window. The finite-difference method with anisotropic perfectly matched boundary layer is used to investigate the guiding properties. It is demonstrated that it is possible to design a simple HNL low-loss dispersion-flattened PCF with a nonlinear coefficient of the order 27 W^-1km^-1 at a 1.55-mum wavelength. According to simulation, ultraflattened dispersion of 0 plusmn 0.5 ps/nm/km is obtained in a 1.46- to 1.66-mum wavelength with low confinement losses less than 0.06 dB/km in the entire band of interest.     

Saturation of 1047- and 1064-nm Absorption in Cr4+:YAG Crystals

To investigate the physical mechanism of the saturation process in Cr⁴⁺:YAG crystals we solved the three coupled rate equations which describe the saturable absorber. We experimentally verified this model using two lasers with nanosecond pulses and continuous-wave radiation. We used crystalline and ceramic Cr⁴⁺-doped YAG saturable absorbers with various initial transmissions. The ratio between the ground and the excited-state absorption cross section at 1064 nm was measured to be between 3.8 plusmn 0.2 and 4.7 plusmn 0.2 for crystalline and 3.6 plusmn 0.1 for ceramic Cr⁴⁺:YAG. The ratio between the above named cross sections at 1047 nm was found to be 6.2 plusmn 0.2 for both crystalline and ceramic Cr⁴⁺:YAG. With these results the ground-state and the excited-state absorption cross sections at 1047 nm were calculated to be (9.55plusmn0.01)times10^-19 cm² and (1.54plusmn0.03)times10^-19 cm², respectively     

A 16–46 GHz Mixer Using Broadband Multilayer Balun in 0.18-μm CMOS Technology

A 16-46 GHz mixer using broadband balun fabricated in standard 0.18-mum CMOS process is demonstrated. The broadside-coupled balun with wide bandwidth and low insertion loss utilizes the inherent 3D multilayer structure in CMOS process. The mixer exhibits radio frequency bandwidth from 16 to 46 GHz with a conversion loss ranging from 13 plusmn 1.5 dB, and achieves bandwidth over 103% with a compact chip size of 0.24 mm².     

Spectroscopy and Lasing of Yb-Doped ${hbox {NaY}}{({hbox {WO}}_{4})}_{2}$: Tunable and Femtosecond Mode-Locked Laser Operation

Tetragonal (space group f4 macr) single crystals of NaY(WO₄)₂ doped with Yb to a density of 4.52 times 10²⁰ cm^-3 have been employed as laser active materials for the 1-mum spectral range, operating at room temperature. Using Ti:sapphire laser pumping, slope efficiencies as high as 74.6% were achieved without special cooling for the pi-polarization. The Yb-laser was continuously tunable from 1003.7 to 1073.0 nm with a birefringent filter. Pulses as short as 53 fs were obtained at 1035 nm by SESAM passive mode-locking with intracavity dispersion compensation and additional extracavity pulse compression using analogous prism pairs. Experimental data on the spectroscopic properties of Yb³⁺ in the 5-300 K temperature range and the room temperature optical properties of this novel Yb-host is also presented.     

Measurement of trabecular bone thickness in the limited resolution regime of in vivo MRI by fuzzy distance transform

Trabecular or cancellous bone, the type of bone found in the vertebrae and near the joints of long bones, consists of a network of plates and struts. Accurate measurement of trabecular thickness is of significant interest, for example, to assess the effectiveness of anabolic (bone forming) agents of patients with osteoporosis. Here, we introduce a new fuzzy distance transform (FDT)-based thickness computation method that obviates binary segmentation and that can effectively deal with images acquired at a voxel size comparable to the typical trabecular bone thickness. The method's robustness is shown on the basis of micro-CT images of human trabecular bone, resampled at progressively coarser resolution and after application of rotation and addition of noise as a means to simulate the in vivo situation. Reproducibility of the method is demonstrated with micro-CT images by comparing histograms of thickness within and between data sets and with micro-MRI volume data sets of human volunteers imaged repeatedly. Finally, with in vivo micro-MR images from a prior study in rabbits subjected to corticosteroid exposure, it is demonstrated that short-term treatment resulting in trabecular thinning can be quantified with the new method.     

Inside Vertical-Cavity Surface-Emitting Lasers: Extracting the Refractive Index From Spatial-Spectral Mode Images

We present a method to extract the internal effective refractive index of a vertical-cavity surface-emitting laser (VCSEL) from its transverse mode images. High spatial and spectral resolution mode images of an oxide-guided VCSEL were obtained using an etalon filter and an imaging spectrometer. The refractive index and the oxide radius were extracted from the field intensity distribution and the spectral wavelength of the laser modes. The procedure was repeated at two different currents and both gave a refractive index step of 0.046 plusmn 0.006 with a 14.1-mum oxide diameter. With several degrees of freedom for error available in the refractive index extraction, this method may be extended to ion-implanted, photonic crystal, and noncircular devices     

Experimental Demonstration of Novel High-Voltage Epilayer RESURF GaN MOSFET

We report on the experimental demonstration of a novel n-channel GaN epilayer RESURF GaN MOSFET with good tradeoff between breakdown voltage and specific on-resistance for the first time. Device with 4-mum channel length and 16-mum RESURF length has breakdown voltage up to 730 V with specific on-resistance 34 mOmegamiddotcm² (V_G - V_T = 20 V), best reported to date.     

A theoretical study of the contrast recovery and variance of MAPreconstructions from PET data

We examine the spatial resolution and variance properties of PET images reconstructed using maximum a posteriori (MAP) or penalized-likelihood methods. Resolution is characterized by the contrast recovery coefficient (CRC) of the local impulse response. Simplified approximate expressions are derived for the local impulse response CRC's and variances for each voxel. Using these results we propose a practical scheme for selecting spatially variant smoothing parameters to optimize lesion detectability through maximization of the local CRC-to-noise ratio in the reconstructed image.     

Low-Threshold and High-Efficiency Operation of Distributed Reflector Laser With Wirelike Active Regions

A high differential quantum efficiency of about 50% from the front facet and low threshold current operation have been achieved. By modifying the doping profile in 1.55-mum distributed reflector lasers, waveguide loss was reduced from 6-7 to 4 cm^-1 . Injection currents of 4.2 and 3.6 mA were obtained to achieve a 1-mW output power for lasers with uniform and phase-shifted grating structures, respectively.     

Characterization of refractive index profiles in silver-sodiumion-exchanged glass waveguides for homogeneous refracting waveguidestructures

The refractive index profiles are investigated for Ag⁺-Na⁺ ion-exchanged waveguides in soda-lime glass. The waveguides with the highest index change, used to design homogeneous refracting waveguide lenses and prisms, are fabricated at 350°C using concentrated melt with composition of 10 mol.% AgNO₃ and 90 mol.% NaNO₃. The profiles of two- and three-mode waveguides are reconstructed from the measured mode refractive indexes. The linear correlation between the index change and the silver concentration in glass is experimentally confirmed. The concentration profiles are numerically simulated on the base of diffusion-exchange theory. It is established that the values of the maximum in index profile near the glass surface tend to a saturation value after a long exchange time     

An 8-bit 20-MS/s ZCBC Time-Domain Analog-to-Digital Data Converter

An 8-bit 20-MS/s time-domain analog-to-digital data converter (ADC) using the zero-crossing-based circuit technique is presented. Compared with the conventional ADCs, signal processing is executed in both the voltage and time domains. Since no high-gain operational amplifier is needed, this time-domain ADC works well in a low supply voltage. The proposed ADC has been fabricated in a 0.18-mum CMOS process. Its power dissipation is 4.64 mW from a supply voltage of 1.8 V. This active area occupies 1.2 times 0.7 mm². The measured signal-to-noise-distortion ratio achieves 44.2 dB at an input frequency of 10 MHz. The integral nonlinearity is less than plusmn1.07 LSB, and the differential nonlinearity is less than plusmn0.72 LSB. This time-domain ADC achieves the effective bits of 7.1 for a Nyquist input frequency at 20 MS/s.     

High-Efficiency 808-nm InGaAlAs–AlGaAs Double-Quantum-Well Semiconductor Lasers With Asymmetric Waveguide Structures

The InGaAlAs-AlGaAs double-quantum-well semiconductor lasers grown by molecular beam epitaxy show high quantum efficiency and high power conversion efficiency at continuous-wave power output using asymmetric waveguide structures. The threshold current density and slope efficiency of the device are 180 A/cm² and 1.4 W/A, respectively. The internal loss and the internal quantum efficiency are 1.1 cm^-1 and 97%, respectively. The 75% maximum power conversion efficiency is achieved in 100-mum stripe widths 808-nm-emitting laser diodes with 1000-mum cavity length.     

Effect of a Two-Step Recess Process Using Atomic Layer Etching on the Performance of In0.52Al0.48As/In0.53Ga0.47As p-HEMTs

The characteristics of 0.15- mum InAlAs/InGaAs pseudomorphic high-electron mobility transistors (p-HEMTs) that were fabricated using the Ne-based atomic layer etching (ALET) technology and the Ar-based conventional reactive ion etching (RIE) technology were investigated. As compared with the RIE, the ALET used a much lower plasma energy and thus produced much lower plasma-induced damages to the surface and bulk of the In_0.52AI_0.48As barrier and showed a much higher etch selectivity (~70) of the InP spacer against the In_0.52Al_0.48As barrier. The 0.15-mum InAlAs/InGaAs p-HEMTs that were fabricated using the ALET exhibited improved G_m,max (1.38 S/mm), I_ONn/I_OFF(1.18X10⁴), drain-induced barrier lowering (80 mWV), threshold voltage uniformity (V_th,avg = -190 mV and alpha = 15 mV), and ftau (233 GHz), mainly due to the extremely low plasma-induced damage in the Schottky gate area.     

2.45-GHz CMOS Reflection-Type Phase-Shifter MMICs With Minimal Loss Variation Over Quadrants of Phase-Shift Range

CMOS reflection-type phase shifters with minimal insertion-loss variation over quadrants of phase-shift range are presented. Two performance enhancement techniques are proposed. First, the 3-dB quadrature hybrid is designed with a phase-compensated inductively coupled hybrid. Second, an impedance-transformed pi-resonated varactor network is presented to provide a full 360deg phase range, using a MOSFET varactor with limited reactance variation range. The design considerations and simulation are described. Two experimental 2.45-GHz phase shifters were implemented in 0.18-mum CMOS technology. One has a measured phase-shift range of 120deg with the insertion loss of 5.6 plusmn 1.2 dB in 2.33-2.60 GHz and the other has a phase range larger than 340deg with the insertion loss of 10.6 plusmn 2 dB in 2.44-2.55 GHz. Both chips are extremely compact with sizes of 0.72 and 0.66 mm², respectively, and consume zero dc power.     

Sectioned Images of the Cadaver Head Including the Brain and Correspondences With Ultrahigh Field 7.0 T MRIs

Unlike computed tomographic images and magnetic resonance images (MRIs), sectioned images of the human body with real color and high resolution have certain advantages in learning and teaching anatomy. Comparisons between sectioned images of the brain and MRIs are useful in many ways. Therefore, we prepared 312 MRIs at ultrahigh field 7.0 T (axial direction $0.4 times 0.4 times 0.4 hbox{mm}^{3}$ voxel size) of a cadaver brain, 2343 sectioned images (axial direction, 0.1 mm intervals, $0.1times 0.1 {hbox{mm}}^{2}$ pixel size, and 48 bits color) by serial-sectioning the cadaver head, 234 segmented images in which brain regions were separately delineated (1 mm intervals and $0.1times 0.1 {hbox{mm}}^{2}$ pixel size) by outlining 64 head structures in sectioned images. Three-dimensional images of 64 head structures were made by volume reconstruction from sectioned images. In this research, advanced techniques and equipment enabled us to prepare quality 7.0-T MRIs, sectioned images, and segmented images of the head. These images are expected to contribute to our understanding of the topographic neuroanatomy of the head and to aid interpretations of MRIs and CTs of the human brain.      

Transport of the photoexcited electron-hole plasma in InP

Transport properties of the photoexcited electron-hole plasma in n-type InP have been studied by the spatial-imaged, time-resolved Raman scattering technique with 30μm and 0.1μm spatial resolution for lateral and perpendicular transport, respectively, and on a picosecond time scale. The plasma density ranging from 1 × 10¹⁶ to 2 × 10¹⁷ cm⁻³ was deduced from fitting of the Raman spectra with the plasmon-LO phonon scattering theory which took into account the contributions from free holes. In contrast to the experimental results of Young and Wan who found that ordinary diffusion equation was sufficient to fit their transient plasma density-time profiles in semi-insulating InP, our experimental measurements have shown that perpendicular transport (i.e., expansion into the bulk crystal) of the plasma in n-type InP can be very well described by a modified diffusion equation including the effect of drifting away from the surface based on a hydrodynamic model. The transient plasma density-time profiles were studied at T = 300K and for an initial injected plasma density n 2 × 10¹⁷ cm⁻³. The plasma has been found to expand laterally at a velocity V 5 × 10⁴ cm/sec and perpendicularly into the crystal at a velocity Vp 1.5 × 10⁵ cm/sec.     

Metamorphic AlInAs/GaInAs HEMTs on GaAs Substrates by MOCVD

Metamorphic AlInAs/GaInAs high-electron mobility transistors with very good device performance have been grown by metal-organic chemical vapor deposition (MOCVD), with the introduction of an effective multistage buffering scheme. Measured room-temperature Hall mobilities of the 2-DEG were over 8000 cm²/V ldr s with sheet carrier densities larger than 4 times 10¹² cm^-2. Transistors with 1-mum gate length exhibited transconductance up to 626 mS/mm. The unity current gain cutoff frequency f_T and the maximum oscillation frequency f_max were 39.1 and 71 GHz, respectively. These results are very encouraging toward the manufacturing of metamorphic devices on GaAs substrates by MOCVD.     

An Ultra-Wideband Distributed Active Mixer MMIC in 0.18-μm CMOS Technology

In this paper, a distributed circuit topology for active mixers suitable for ultra-wideband operations is presented. By employing nonuniform artificial transmission lines with the complementary transconductance stages in the Gilbert-cell multiplier, the proposed mixer demonstrates broadband characteristics at microwave frequencies while maintaining a high conversion gain (CG) with improved gain flatness. Using a 0.18-mum CMOS process, the proposed circuit is implemented, exhibiting a -3-dB bandwidth of 28 GHz. With a local-oscillator power of 3 dBm and an IF frequency of 10 MHz, the fabricated circuit has a CG of 12.5plusmn1 dB and an average input third-order intercept point (IIP₃) of 0 dBm within the entire frequency range. The fully integrated wideband mixer occupies a chip area of 0.87times0.82 mm² and consumes a dc power of 20 mW from a 2-V supply voltage