New charge pump power-factor-correction electronic ballast with awide range of line input voltage

A new charge pump power-factor-correction (CPPFC) electronic ballast with a wide range of line input voltage is proposed in this paper. Circuit derivation and DC-bus voltage stress at start-up mode are discussed. The average lamp current control with switching frequency modulation is developed to achieve constant lamp power operation and low-crest factor. The proposed CPPFC electronic ballast is analyzed, implemented, and evaluated. It features continuous line input current, low total harmonic distortion (THD), constant lamp power operation, low-crest factor, and less switching current stress with low-DC-bus voltage stress for the line voltages from 180 to 265 V     

Analysis and measurements of magnetic field exposures for healthcare workers in selected MR environments.

There are concerns about workers repeatedly exposed to magnetic fields exceeding regulatory limits with respect to modern magnetic resonance imaging (MRI). As a result, there is need for an ambulatory magnetic field dosimeter capable of measuring these fields in and around an MRI scanner in order to evaluate the regulatory guidelines and determine any underlying exposure risks. This study presents results of tri-axial measurements using an ambulatory magnetic field dosimeter worn by workers during normal working shifts. We recorded and analyzed magnetic field exposures in and around 1.5 T, 2 T, and 4 T magnets during routine patient procedures. The data was integrated and averaged over time and evaluated against the latest exposure standards. Time-varying magnetic fields occur when individuals move through spatially non-uniform static magnetic fields or during gradient-pulsed magnetic fields or a combination of both. Our previous numerical analysis shows that at certain positions surrounding the MRI scanner ends, such fields may induce current densities and electric fields that may exceed the relevant EU, ICNIRP, and IEEE standards. A high-speed acquisition version of the dosimeter measured gradient- pulsed fields at positions accessible by MRI workers near the scanner ends, and the results were evaluated and compared against the numerical simulations and the standards. Our measurements confirm that workers can be exposed to magnetic fields exceeding the guidelines at positions near the gradient coil ends during clinical imaging and a high degree of correlation exists with the numerical results. While the time-weighted average magnetic field exposures in 1.5 T, 2 T, and 4 T were all within the regulatory limits during static magnetic field measurements, the peak limits for the head can be exceeded in some circumstances. This study presents a small number of routine shifts of data that provide indicative results of magnetic field exposure in real situations.     

Analysis and Measurements of Magnetic Field Exposures for Healthcare Workers in SelectedMR Environments

There are concerns about workers repeatedly exposed to magnetic fields exceeding regulatory limits with respect to modern magnetic resonance imaging (MRI). As a result, there is need for an ambulatory magnetic field dosimeter capable of measuring these fields in and around an MRI scanner in order to evaluate the regulatory guidelines and determine any underlying exposure risks. This study presents results of tri-axial measurements using an ambulatory magnetic field dosimeter worn by workers during normal working shifts. We recorded and analyzed magnetic field exposures in and around 1.5 T, 2 T, and 4 T magnets during routine patient procedures. The data was integrated and averaged over time and evaluated against the latest exposure standards. Time-varying magnetic fields occur when individuals move through spatially non-uniform static magnetic fields or during gradient-pulsed magnetic fields or a combination of both. Our previous numerical analysis shows that at certain positions surrounding the MRI scanner ends, such fields may induce current densities and electric fields that may exceed the relevant EU, ICNIRP, and IEEE standards. A high-speed acquisition version of the dosimeter measured gradient-pulsed fields at positions accessible by MRI workers near the scanner ends, and the results were evaluated and compared against the numerical simulations and the standards. Our measurements confirm that workers can be exposed to magnetic fields exceeding the guidelines at positions near the gradient coil ends during clinical imaging and a high degree of correlation exists with the numerical results. While the time-weighted average magnetic field exposures in 1.5 T, 2 T, and 4 T were all within the regulatory limits during static magnetic field measurements, the peak limits for the head can be exceeded in some circumstances. This study presents a small number of routine shifts of data that provide indicative results of magnetic field exposure in real situations.     

Broad-band reflection traveling-wave LiNbO3 modulator

A velocity matched traveling-wave Mach-Zehnder interferometer (MZI) in LiNbO₃ operating in reflection, is reported and drive voltages are compared to those for single-pass devices of the same length. The device achieves double-pass operation by simultaneously reflecting the optical and RF waves, Broad-band operation to 20 GHz with drive voltages from 0.5 to 1 V (<0.5 GHz) to ~4.5 V (at 20 GHz) is observed with the reflection device. This performance is superior to that of the single-pass device, which has drive voltages of 2.1 V (dc) to ~4.5 V (at 20 GHz)     

Multidisciplinary Placement Optimization of Heat Generating Electronic Components on a Printed Circuit Board in an Enclosure

A multidisciplinary placement optimization methodology for heat generating electronic components on a printed circuit board (PCB) subjected to forced convection in an enclosure is presented. In this methodology, thermal, electrical, and placement criteria involving junction temperature, wiring density, line length for high frequency signals, and critical component location are optimized simultaneously using the genetic algorithm. A board-level thermal performance prediction methodology based on channel flow forced convection boundary conditions is developed. The methodology consists of a combination of artificial neural networks (ANNs) and a superposition method that is able to predict PCB surface and component junction temperatures in a much shorter calculation time than the existing numerical methods. Three ANNs are used for predicting temperature rise at the PCB surface caused by a single heat source at an arbitrary location on the board, while temperature rise due to multiple heat sources is calculated using a superposition method. Compact thermal models are used for the electronic components thermal modeling. Using this optimization methodology, large calculation time reduction is achieved without losing accuracy. To demonstrate its capabilities, the present methodology is applied to a test case involving multiple heat generating component placement optimization on a PCB.     

An effective compensation method for the mutual coupling effect in phased arrays for magnetic resonance imaging

An effective compensation method to compensate for the mutual coupling effect in magnetic resonance imaging (MRI) phased arrays is introduced. This method uses the knowledge of the position of the signal source in MRI, i.e., the active slice, to define a new mutual impedance that accurately quantifies the coupled voltages and enables them to be removed from the terminal voltages almost completely. Numerical results using the method of moments show that the percentage errors in the compensated voltage are at least on the order of 10/sup -5/% and the isolations between two coils are more than 120 dB even at a low-field case of 0.5 T (f/sub 0/=21.3 MHz). This method can be implemented by either software or hardware.     

Static noise margin variation for sub-threshold SRAM in 65-nm CMOS

The increased importance of lowering power in memory design has produced a trend of operating memories at lower supply voltages. Recent explorations into sub-threshold operation for logic show that minimum energy operation is possible in this region. These two trends suggest a meeting point for energy-constrained applications in which SRAM operates at sub-threshold voltages compatible with the logic. Since sub-threshold voltages leave less room for large static noise margin (SNM), a thorough understanding of the impact of various design decisions and other parameters becomes critical. This paper analyzes SNM for sub-threshold bitcells in a 65-nm process for its dependency on sizing, V/sub DD/, temperature, and local and global threshold variation. The V/sub T/ variation has the greatest impact on SNM, so we provide a model that allows estimation of the SNM along the worst-case tail of the distribution.     

An experimental test of a theory of lightning-induced voltages onan overhead wire

Measured and calculated voltages induced on an unenergized overhead power line by lightning return strokes at distances greater than 5 km from the line are presented. The experiment was performed at the NASA Kennedy Space Center during the summer of 1985 and involved the simultaneous measurement of the voltage induced at one end of the top phase of a three-phase power line and the two horizontal components of the return-stroke magnetic field incident on the line. The effective ground conductivity was determined from previous simultaneous measurements of the vertical and horizontal electric fields. Experiments were performed for two cases: (1) all phases of the power line open-circuited, and (2) one end of the top line terminated at 600 Ω with the other end open-circuited and the other two phases open-circuited at both ends. The waveshapes of the measured and calculated voltages are in reasonably good agreement, and the reasons for observed discrepancies are discussed     

A new decoupling method for quadrature coils in magnetic resonance imaging

A powerful decoupling method is introduced to obtain decoupled signal voltages from quadrature coils in magnetic resonance imaging (MRI). The new method uses the knowledge of the position of the signal source in MRI, the active slice, to define a new mutual impedance which accurately quantifies the coupling voltages and enables them to be removed almost completely. Results show that by using the new decoupling method, the percentage errors in the decoupled voltages are of the order of 10(-7) % and isolations between two coils are more than 170 dB.     

High voltage degradation of GaN High Electron Mobility Transistors on silicon substrate

We have electrically stressed GaN High Electron Mobility Transistors on Si substrate at high voltages. We observe a pattern of device degradation that differs markedly from previous reports in GaN-on-SiC HEMTs. Similarly to these devices, the gate leakage current of GaN-on-Si HEMTs increases by several orders of magnitude at a certain critical voltage and this increase is irreversible. However, in contrast with devices on SiC, the critical voltage varies substantially across the wafer, even over short distances, with values as high as 75 V being observed. In addition, for voltages below the critical voltage, we observe a prominent degradation in the drain current and the source and drain resistances, something not observed in devices on SiC. This degradation is almost completely recoverable under UV illumination. We attribute these results to the high mismatch that exists between GaN and Si that leads to a large concentration of electrically active traps and a lower and non-uniform initial strain in the AlGaN barrier. This is evidenced by observed correlations between threshold voltage and maximum drain current in fresh devices and their corresponding critical voltages.     

An OTA-based CMOS bandpass filter for NMR applications

One of the very popular medical imaging techniques used in present-day radiology is the magnetic resonance imaging (MRI) which is based on the phenomenon of nuclear magnetic resonance (NMR) in the hydrogen atoms present in the body. There is ever-increasing research in electronic circuit design for biomedical applications using NMR. Earlier magnetic resonance imagers operated at a magnetic field strength of 0.3?T. The present imagers operate at a magnetic field of 1.5?T, the resonance frequency of the nuclei being 64?MHz. This article presents a CMOS bandpass filter (BPF) design for NMR applications. The overall BPF design is realised in 180?nm CMOS technology which occupies an active area of 24.23?×?33.125?µm² and consumes 0.165?mW of power from a 1.5?V supply.     

Drain-bias dependence of threshold voltage stability of amorphous silicon TFTs

Amorphous silicon (a-Si:H) thin-film transistors (TFTs) used in emerging, nonswitch applications such as analog amplifiers or active loads, often have a bias at the drain terminal in addition to the gate that can alter their threshold voltage (V/sub T/) stability performance. At small gate stress voltages (0/spl les/V/sub ST//spl les/15 V) where the defect state creation instability mechanism is dominant, the presence of a bias at the TFT drain decreases the overall shift in V/sub T/(/spl Delta/V/sub T/) compared to the /spl Delta/V/sub T/ in the absence of a drain bias. The measured shift in V/sub T/ appears to agree with the defect pool model that the /spl Delta/V/sub T/ is proportional to the number of induced carriers in the a-Si:H channel.     

High-voltage operation of field-effect transistors in siliconcarbide

Buried-gate field-effect transistors with blocking voltages up to 600-700 V have been fabricated in 6H polytype silicon carbide using a trench technology. The devices achieve drain currents of up to 60 mA for a channel width of 0.72 mm and have a turn off gate voltage of about 40 V. We report on the device characteristics and analyze the performance under high-voltage device operation     

Complementary Logic Gates and Ring Oscillators on Plastic Substrates by Use of Printed Ribbons of Single-Crystalline Silicon

CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by transfer printing of p-type and n-type single crystalline ribbons of silicon. The gain and the sum of high and low noise margins of the inverters were as high as ~150 and 4.5 V at supply voltages of 5 V, respectively. The frequencies of the ring oscillators reached 2.6 MHz at supply voltages of 10 V. These results, as obtained with devices that have relatively large critical dimensions (i.e., channel lengths in the several micrometer range), taken together with good mechanical bendability, suggest promise for the use of this type of technology for flexible electronic systems.     

Integrated circuits for a bidirectional implantable pulsed Doppler ultrasonic blood flowmeter

The application of integrated circuits in medical implants and the complexity of these implants have increased at a rapid pace in the past few years. The need, however, still exists for a highly accurate and stable telemetry system for the measurement of blood flow. Two custom-designed ICs have been realized to resolve this problem. These ICs form the heart of a totally implantable pulsed Doppler ultrasonic bidirectional blood flowmeter; one circuit performs the basic timing functions, and the second implements low-level linear signal processing. For a small implanted package (3.8/spl times/2.8/spl times/0.8 cm/SUP 3/), these ICs must meet the stringent requirements of low-voltage operation (2.2-2.8 V), low power (<40 mW), high stability (short-term timing jitter <50 ppm), and the minimum of external components. Using a quadrature direction detecting technique, the circuits sense both positive and negative flow and produce a multiplexed telemetry signal. The approach used minimizes parts count and power drain and maximizes channel-to-channel matching in the multiplexed signal.     

An Optically Coupled System for Quantitative Monitoring of MRI-Induced RF Currents Into Long Conductors

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions.      

Interaction of spatially modulated pump and FIR waves in Raman laser

The propagation of spatially modulated IR pump and FIR generated waves interacting in the active gas medium of Raman laser is simulated numerically. Stationary nonlinear diffraction of monochromatic beams is studied for the isolated homogeneously broadened three-level system without any limitations on the values of field strength and frequency offset. It is shown that FIR radiation is trapped in the active wave guide induced owing to the nonlinear refractive index mechanism and gain inhomogeneity across the pump wave beam. Nonlinear focus positions and on-axis focal intensities for both fields are calculated.     

A 1.2-V Highly Linear Balanced Noise-Cancelling LNA in 0.13-μm CMOS

In this paper, a current-to-voltage combiner is proposed to realize a highly linear, balanced noise-cancelling low-noise amplifier (LNA) capable of low-voltage operation. The current-to-voltage combiner, implemented in the load of the amplifier, converts the output currents of the parallel common-gate (CG) and common-source (CS) stages of the LNA to voltages, equalizes the amplitudes of the voltages, and combines the voltages to a single output voltage. Since only a CS stage and passive components are employed to cancel the noise and distortion due to the CG input impedance matching circuit, high linearity is achieved in spite of the low supply voltage of 1.2 V. The LNA achieves a noise figure (NF) of 3.0 dB at 2.1 GHz with an input-referred third-order intercept point (IIP3) of +10.5 dBm while consuming 10.5 mA from a 1.2-V supply. The amplifier is fabricated in 0.13-mum CMOS process.     

A time-dependent and two-dimensional numerical model for MOSFET device operation

A time-dependent and multi-dimensional numerical modeling for semiconductor device operation is proposed, in which the quasi-Fermi potentials for electrons and holes rather than the carrier densities are directly analyzed. Fundamental equations for the quasi-Fermi potential are reduced to a diffusion equation that includes a drift term. Boundary conditions are straightforwardly derived from the device physics and are shown in a mathematically simple manner, independent of device structure complexities. From the viewpoint of numerical procedure, a combination of an implicit time integral and upwind difference scheme is adopted. The quasi-Fermi potential is a gradually changing value between the maximum and minimum external applied voltages, and the present method is suitable for numerical modeling.A time dependent and two dimensional analysis program has been developed. The advantages of the present modeling are demonstrated through the carrying out of sample calculations of, for example, MOSFET switching characteristics. Quick and stable convergence in the numerical scheme has been obtained over the range of practically used operation voltages.     

Improving mobility and electrochemical stability of a water-gated polymer field-effect transistor

Water-gated organic transistors have attracted considerable attention in the field of biosensors, thanks to their capability of operating in the aqueous environment typical of biological systems at very low voltages (∼1 V). Some examples have been recently reported in the literature, employing different organic materials as the active semiconducting layer, ranging from small molecules to single crystals. Here we report on water-gated polymer-based organic-field effect devices using poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT) as the active layer. Very promising electronic performances, in terms of mobility and operating voltages are obtained; notably, the charge carrier mobility is in the order of 0.08 cm²/V s, which is of the same order of magnitude of values reported for single-crystal based water-gated devices, and consistent with values reported for solid-state polymer dielectric transistors. Moreover, the pBTTT-based device shows improved electrochemical stability, as compared to previously reported polymer based water-gated devices. Importantly, good functioning of the device is demonstrated also when water is replaced by physiological-like solutions. Critical to the transistors operation, besides the good transport properties of the active material, is the key-role played by alkyl side chains and ordered morphology of the polymer at the interface with the liquid environment, which we highlight here for the first time. Our contribution overall provides a useful step towards the development of bio-organic sensors, with enhanced properties in terms of sensitivity and stability, and for a successful exploitation of organic based field effect transistors in biotic/abiotic interfaces.