Fast Slew Rate Research Articles

FPGA Implementation of Sliding Mode Control and Proportional-Integral-Derivative Controllers for a DC–DC Buck Converter

DC–DC buck converters have been designed by incorporating different control stages to drive the switches. Among the most commonly used controllers, the sliding mode control (SMC) and proportional-integral-derivative (PID) controller have shown advantages in accomplishing fast slew rate, reducing settling time and mitigating overshoot. The proposed work introduces the implementation of both SMC and PID controllers by using the field-programmable gate array (FPGA) device. The FPGA is chosen to exploit its main advantage for fast verification and prototyping of the controllers. In this manner, a DC–DC buck converter is emulated on an FPGA by applying an explicit multi-step numerical method. The SMC controller is synthesized into the FPGA by using a signum function, and the PID is synthesized by applying the difference quotient method to approximate the derivative action, and the second-order Adams–Bashforth method to approximate the integral action. The FPGA synthesis of the converter and controllers is performed by designing digital blocks using computer arithmetic of 32 and 64 bits, in fixed-point format. The experimental results are shown on an oscilloscope by using a digital-to-analog converter to observe the voltage regulation generated by the SMC and PID controllers on the DC–DC buck converter.

Evaluation and Suppression Method of Turn-Off Current Spike for SiC/Si Hybrid Switch

SiC MOSFET/Si IGBT (SiC/Si) hybrid switch usually selects the gate control pattern that SiC MOSFET turns on earlier and turns off later than Si IGBT, with the aim of making the hybrid switch show excellent switching characteristics of SiC MOSFET and reduce switching loss. However, when SiC MOSFET turns off, the fast slew rate of drain source voltage causes the current spike in Si IGBT due to the effects of parasitic capacitance charging and carrier recombination, which will produce additional turn-off loss, thus affecting the overall efficiency and temperature rise of the converter. Based on the double pulse test circuit of SiC/Si hybrid switch, the mathematical model of the turn-off transient process is established. The effects of the remnant carrier recombination degree of Si IGBT, the turn-off speed of SiC MOSFET and the working conditions on the turn-off current spike of hybrid switch are evaluated. Although adjusting these parameters can reduce the turn-off current spike somewhat, additional losses will be introduced. Therefore, a new method to suppress the turn-off current spike is proposed to balance the power loss and current stress.

Development of Compton-PET hybrid imaging system with CeBr3-SiPM arrays

Positron emission tomography (PET) and single photon emission computed tomography (SPECT) are both established imaging technologies in nuclear medicine that are clinically available. However, simultaneous PET and SPECT nuclide imaging is difficult to accomplish with current equipment because of their distinct principles. In light of this, we have developed and demonstrated a GAGG scintillator based Compton-PET hybrid imaging system capable of performing PET and Compton imaging simultaneously. Alternatively, the CeBr3 scintillator possesses more desirable properties, including a high light yield (>60000 photons/MeV), a fast decay time (∼19 ns), and an excellent energy resolution (<4%@662 keV). Herein, we developed an 8 × 8 array of CeBr3 detector based instrumentation by using 64 channel fast signal processing slew rate limited Time over Threshold (ToT) based application-specific integrated circuits and a field programmable gate array ToT data acquisition system with a 62.5 ps accuracy. Furthermore, we evaluated the system’s basic performances. The mean and greatest energy resolutions were 10.1% and 6.0% (FWHM) for 662 keV. The time resolution was 239 ps (FWHM) after offset calibration. We also achieved a proof-of-concept based on single source.

Inaccurate Switching Loss Measurement of SiC MOSFET Caused by Probes: Modelization, Characterization, and Validation

SiC metal-oxide-semiconductor field-effect transistor (MOSFET) has a fast switching speed and high slew rate. However, its ultrashort switching time approximates the rise time and propagation delay of the measurement instruments, which results in an inaccurate assessment of the switching loss and challenges the thermal design of the power converter. In this article, aiming to reveal the principles of accurate measurement for the switching behavior of SiC MOSFET, insightful models are proposed for baseline probes and transient trajectories to characterize the measurement error of the switching losses. By using the Gaussian function, the mathematical models for the rise time, bandwidth, and propagation delay of the measurement instruments are achieved, which is also confirmed by the surveyed specifications of commercial probes. Concerning the accurate measurement, the turn-on and turn-off losses of the SiC MOSFET influenced by the rise time and propagation delay of probes are comprehensively modeled and characterized. With respect to different current probes, voltage probes, and gate driver resistances, extensive experiments are demonstrated to confirm the validity of the proposed models. The experimental findings are in line with the conducted predictions of the proposed models. It is found that, due to the very fast switching transients of the SiC MOSFET, the limited bandwidth and inevitable propagation delay of measurement instrument may result in a prominent error of the switching loss and impede the widespread implementation of the SiC MOSFET.

An enhanced fast slew rate recycling folded cascode Op-Amp with general improvement in 180 nm CMOS process

This paper presents a new technique to improve CMOS recycling folded cascode (RFC) operational amplifier (Op-Amp). Our modification is based on shorting two nodes in the conventional RFC circuit. It causes that the seen resistance from the created new node be half of the conventional RFC counterpart and makes it to double the slew rate. Compared to it, our circuit is also capable to enhance DC gain and unity gain bandwidth (UGBW) with increasing output resistance of differential pair. Moreover, our proposed improvements are in better fast-settling time, input referred noise, input offset voltage, total harmonic distortion (THD), common mode rejection ratio (CMRR) and power supply rejection ratio (PSRR) in the same power consumption. Simulation results in 180 nm CMOS process indicates that the proposed amplifier has 1.5 times the unity gain bandwidth (185 MHz versus 125 MHz) and also has 7 times gain boosting (75 dB versus 58 dB) with better figure of merit (FOM) in the same power consumption, driving capacitor load of 10 pF @1.2 V power supply. The results also demonstrate that the temperature sensitivity, power supply variations and process corners have a negligible effect on the proposed amplifier stability.

Superconducting nanowire single-photon detector with integrated impedance-matching taper

Conventional readout of a superconducting nanowire single-photon detector (SNSPD) sets an upper bound on the output voltage to be the product of the bias current and the load impedance, IB × Zload, where Zload is limited to 50 Ω in standard r.f. electronics. Here, we break this limit by interfacing the 50 Ω load and the SNSPD using an integrated superconducting transmission line taper. The taper is a transformer that effectively loads the SNSPD with high impedance without latching. At the expense of reduced maximum counting rate, it increases the amplitude of the detector output while preserving the fast rising edge. Using a taper with a starting width of 500 nm, we experimentally observed a 3.6× higher pulse amplitude, 3.7× faster slew rate, and 25.1 ps smaller timing jitter. The results match our numerical simulation, which incorporates both the hotspot dynamics in the SNSPD and the distributed nature in the transmission line taper. The taper studied here may become a useful tool to interface high-impedance superconducting nanowire devices to conventional low-impedance circuits.

Single-Inductor Multioutput-Level Buck Converter for Reducing Voltage-Transition Time and Energy Overheads in Low Power DVS-Enabled Systems

Dynamic voltage scaling (DVS) is a useful technique to optimize performance and efficiency of CMOS digital processors using dc–dc converters that require to meet extremely fast slew rate demand. However, there exist conflicting design criteria in existing DVS power supply architectures. This paper proposes a single-inductor multioutput-level buck converter for low power DVS-enabled systems. Under the time optimal voltage transition recovery, the proposed architecture: first, achieves the performance much beyond system's physical limits compared to conventional synchronous and multiphase buck converter based architectures; and second, can overcome conflicting power circuit design criteria in existing architectures. Also, a high-resolution quantized voltage can be realized by using a voltage-dithering technique. An analytical framework is considered to formulate various processor and converter-induced energy overheads. A comparative study is shown to evaluate the usefulness of the proposed architecture over the existing approaches under frequent voltage transitions. A prototype single-inductor four-output-level buck converter is tested and the performance improvements are demonstrated using test results.

Magnetic Resonance Imaging Power: High-Performance MVA Gradient Drivers

In high-performance magnetic resonance imaging systems, the gradient driver is required to supply the gradient coil with a large current (>600 A) and a high voltage (>2000 V) to achieve a strong gradient field and a fast slew rate. In addition, extremely high fidelity for reproducing the current command from the central system is very critical to imaging quality. This paper presents the solutions for the different elements of the driver: 1) high-bandwidth (BW) power inverter; 2) ripple cancelation filter; 3) multioutput power supply (PS); and 4) digital control. A high-BW power inverter requires a stacked-bridges structure to achieve a high output ripple frequency with the existing commercial power semiconductor modules. The high voltage and the high frequency for large power modules can be obtained easier and with lower loss using the new silicon carbide devices. The control needs a digital implementation and a very fast processor. Digital control provides compensation and feedforward to improve the response. A capability improvement is obtained by reducing the switching frequency when large currents with a very low-frequency variation are needed. The control can handle it very well, but the filter has to be designed to eliminate more than one ripple frequency. Finally, many PS solutions have been used for multiple isolated outputs, but digital control compensation permits the use of much simpler unregulated PS and keeps the performance. A 2 MVA, 900 A/1200 V, platform has been built and fully tested. The experimental results proved the validity of the proposed structure and the modulation technique.

Merged Flyback–SC-Based Output Stage for Versatile Portable Transcutaneous Electrical Stimulators

This paper introduces a highly flexible multichannel output stage for battery-powered portable electric stimulators (ESs), based on novel power converter architecture. Compared with other solutions, the presented output stage for transcutaneous (surface) stimulations increases the number of applicable therapies, improves the battery operating time through reduced power consumption, and potentially results in more comfortable and shorter healing therapies. The new hybrid switch-mode power converter is a combination of flyback and switched-capacitor (SC) topologies. The flyback steps up the battery voltage and provides galvanic isolation. The following power-efficient SC stage replaces lossy linear current sources (CSs) of conventional solutions and produces pulses with a much higher slew rate, reducing the pulse energy needed to cause the stimulus. The SC also inherently produces pulses with zero-net charge, eliminating bulky blocking capacitors and/or dedicated discharging circuits. The regulation of the amplitudes of the pulses is performed with a new digital voltage-programmed current mode controller, forcing the output of the SC stage to behave as a CS. The flexible digital controller allows for creation of various types of pulses and also features several levels of patient protection. An experimental prototype of the output stage has undergone proof of principle tests with able-bodied individuals. The results show that the new output stage produces pulses with a 1-mA/ns slew rate, about two orders of magnitude higher than the other known solutions. The trials show that the faster slew rate pulses generate the same muscle contraction with 34% lower amplitudes, reducing energy consumption by 55%, allowing longer battery life of portable ES applications.

A Compact Coupled Inductor for Interleaved Multiphase DC-DC Converters

A compact coupled inductor structure is proposed for interleaved multiphase synchronous buck converters used to power computer processors and memories that require high current and fast current slew rate. The new coupled-inductor structure reduces the winding resistor power loss and makes it possible to utilize ferrite magnetic material with low core loss. In this letter, several proposed converter implementations to achieve inverse inductor coupling are illustrated, and inductance and coupling coefficient variations are studied through a simplified reluctance model and Maxwell magnetic simulation. The inductor structure not only can be extended to multiple phases but also can be simplified to a single phase. The operation of the inductor is experimentally verified in a two-phase synchronous buck converter at switching frequency of 1 MHz.

Analysis and Verification of Inductor Coupling Effect in Interleaved Multiphase DC-DC Converters

Interleaved multiphase synchronous buck converters are often used to power computer CPU, GPU, and memory to meet the demands for increasing load current and fast current slew rate of the processors. This paper reports and explains undesired coupling between discrete inductors in typical commercial multiphase applications where space is limited. In this paper, equations of coupling coefficient are derived for single-turn and multiturn Ferrite core inductors commonly used in multiphase converters and are verified by Maxwell static simulation. The influence of the coupling effect on inductor current waveforms is demonstrated by Maxwell transient simulation and confirmed by experiments. The analysis provides a useful tool for mitigating the coupling effect in multiphase converters to avoid early inductor saturation and interference between phases. Design guidelines and recommendations are provided to minimize the unwanted coupling effect in multiphase converters.

Analysis of an Open-Loop Time Amplifier With a Time Gain Determined by the Ratio of Bias Current

Analysis of an open-loop time amplifier shows good agreement between measurements and calculations on the time gain, distortion of time gain, and rms noise and offset of output time difference. The time amplifier is based on the slew rate control method. It achieves a large time gain up to 120 and a wide range of input time difference up to 2 ns. The circuit consists of two precharged capacitors and current sources, where one capacitor is discharged at a fast slew rate during the time interval of the input time difference and then both capacitors are discharged at the same slow slew rate. The time gain is simply determined by the ratio of two bias current values. The proposed time amplifier is followed by an 8-bit TDC to obtain the digital output code. The time gain distortion caused by channel length modulation is less than 1.6% for the input time difference larger than 100 ps. The time offset and the rms noise of output time difference are inversely proportional to the smaller bias current. The rms noise is dominated by the noise of the comparator reference voltage. The time amplifier and TDC consume 0.36 mW and 1 mW, respectively, at 1.2 V supply in a 0.13 μm CMOS process.

A fast slewing cryostat for small sample in vacuo electrical/optical testing in the range 30 K–500 K

A cold finger vacuum cryostat is described in which a sapphire heat conducting element is used to achieve very fast slew rates for a small sample stage over a wide temperature range with optimal matching to a closed cycle helium refrigerator head. When the set temperature is reached it is maintained with very high stability (±5 mK). The target applications are associated with semiconductor electrical material characterisation measurements which require temperature scanning, e.g., thermally stimulated current, deep level transient spectroscopy, and applications which require annealing followed by rapid transition to lower temperature for measurement.

First astrometric observations of space debris with the MéO telescope

The MéO (for Métrologie Optique) telescope is the Satellite and Lunar Laser Ranging (SLR) dedicated telescope of Observatoire de la Côte d’Azur (France) located at plateau de Calern. The telescope uses an altazimuth mount. The motorization of the mount has a capability of 6 deg/s allowing the follow up of Low Earth Orbits (LEO) satellites, as well as Medium Earth Orbits (MEO) and geostationary (GEO) satellites, and the Moon. The telescope has a primary mirror of 1.54 m. It uses a Nasmyth focus equipped with an EMCCD camera. The telescope field of view, defined by the equivalent focal length and the size of the camera, is currently 3.4 arcmin × 3.4 arcmin. Space debris observation with an optical telescope ideally requires a large field of view, accurate pointing, a fast slew rate, a high sensitivity, accurate astrometric positions, and a precise method for orbit propagation. The challenge is to obtain accurate orbits for all debris without compromising the field of view. The MéO telescope has a larger diameter than the ones habitually used for space debris tracking. It should improve the current accuracy of observations in the GEO region. For LEO, such sensitivity should allow observations of small pieces of debris at low altitudes. This paper presents the preliminary experiments carried out to benefit from the high astrometric quality of the instrument, namely the method developed to extract and to compute the astrometric positions of LEO and MEO satellites, as a test of the capabilities of such an instrument (very small field of view, but large aperture) for space debris tracking. Furthermore, we analyse the ability of MéO to keep track of an object for which only a preliminary orbit (computed by the Laplace method from previous observations) is known, so that high precision measurements can be obtained and the object can be catalogued with an updated orbit. The feasibility of our astrometric methods was tested throughout 2010. This paper presents the methods used and the difficulties encountered. The originality of our paper does not strictly reside in the methods used but in their adaptation to a telescope presenting such a small field of view. We discuss our first results obtained for LEO and MEO satellites. In particular, we give an estimate of the astrometric errors for the geodetic satellite Lageos-1 by comparing its positions deduced from our reduction strategy with those obtained from a reference orbit. We also present research to use the Laplace method to produce preliminary orbital elements. In this context, we discuss a novel improvement to the Laplace method. To put it in a nutshell, this article provides original results covering all fields of orbit estimation, from satellites tracking to preliminary orbit determination.

New Technologies for Submillimeter Laser Ranging

We are presenting the work progress and recent results in a development and construction of new technologies for submillimeter laser ranging and picosecond accuracy laser time transfer. The key hardware components: the Start detector and discriminator, the echo signal detector, the timing device and signal cablings were studied in detail. The new devices have been designed, built and tested in our lab. To minimize the systematic errors the photon counting approach has been selected. The ranging chain has been designed and optimized with a goal of single shot resolution of several millimeters and sub-millimeter normal points and overall system stability. The Start detector and discriminator are constructed as a single device to optimize their matching and maintain stability. The NPET timing system based on surface acoustic wave interpolator has a resolution of 800 fs and 4 fs long term stability. The echo detector is based on innovated SPAD detector optimized for high repetition Gate rate and minimal dark count rate. Both the detectors output signals have ultrafast slew rates &lt; 200 ps / 1 V. In connection to the 6 GHz bandwidth of the timing system inputs these fast slew rates improves the timing and temperature stability along with the RF interference immunity. The new low temperature drift signal cables have been selected, tested and used. The new hardware was tested in indoor calibration experiments. We have achieved the single shot resolution of 3 mm rms. The temperature and temporal stability of the individual components is excellent. The drift is typically below 200 fs/K for each contributor. The overall temperature drift of the entire laser ranging chain is below 500 fs/ K. The long term stability of the ground target calibration is better than ± 800 fs within 3 days. During this period the environment temperature changed by more than 4°C. In the sense of time deviation Tdev the stability of 300 fs was achieved. The presented components will enable to carry out laser ranging with submillimeter normal points stability and reproducibility. The accuracy of the “ranging machine” based on these devices will reach sub-mm values, as well. The concept and construction will be presented along with the achieved devices parameters.

Direct measurement of magnetic field gradient waveforms

As eddy currents increase with gradient amplitude and faster slew rate, they have become a greater problem with the advent of higher-performance gradients in modern MRI scanners. Success in eddy current reduction techniques such as active gradient shielding and waveform pre-emphasis, however, require that the residual eddy currents must be measured with high accuracy for image improvement. Traditional MR based gradient calibration techniques, whether based on an entire FID or a gradient echo, measure the integral of gradient waveforms. We have however previously proposed a different category of methods, which employ pure phase encode FIDs and have proven advantageous in directly measuring the gradient waveforms. In this article, we review the basis of these pure phase encode methods. In keeping with the instructional nature of CMRA, we undertake this review by describing specific experiments and the line of the thought behind the experiments. The pure phase encode approach is sensitive to low amplitude gradients (0.001–1 G/cm), and also permits measurement of high amplitude gradients (10–300 G/cm). The inverse Fourier transform permits ready understanding of these pure phase encode methods. The accuracy of pure phase encode gradient measurement is significantly improved by a multiple FID point acquisition, which permits high temporal resolution of the gradient waveform. The accuracy of gradient measurements is also analyzed and improved through elimination of potential artifacts. As one example of the capability of these methods, waveform measurements were undertaken to reduce the repetition time TR for centric scan SPRITE experiments. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 349–360, 2010.

An embedded reset driver for digital micromirror devices (DMDs)

Abstract— A digital micromirror device (DMD) is a micromachined high‐density light‐modulating system widely used in front projectors, high‐definition TVs, and digital cinemas. Although the high‐speed memory and digital control electronics have long been integrated underneath the micromirror array, high‐voltage reset waveforms have to be provided separately and synchronized with the DMD chip to actuate the micromirrors. Using drain‐extended transistors, the high‐voltage driver electronics are successfully integrated on DMDs to generate local reset waveforms having voltage variations up to 30 V at a fast slew rate. At fast‐charging/discharging rates, the transistor reliability requirements are still satisfied and the driver electronics maintain low average current consumption.

위성영상정보를 이용한 강우유출 해석에 관한 연구

Urban watershed can be found in the visible changes in technology, the most realistic satellite images is to use the data. Satellite image data on the indicators for progress on the nature of the change of land use is consistent and repetitive information, regular observation makes possible the detailed analysis of space-time. These remote sensing techniques and the type of course and, by using the time series history, the past, the dynamic model and the randomized prediction methodology for the conversion process if the city and river basin cooperation of the space changes effectively will be able to extrapolate. For each of the main changes in river flow, depending on the area of urbanization as determined according to reproduce the duration of the relationship between the urbanization of the area and runoff can be represented as a linear polynomial expression was, if a linear expression in the two fast slew rate of 0.858 to 0.861 showed up, and fast slew rate of 0.934 to 0.974 for the polynomial are reported. Change of land use changes in the watershed of the flow is one of the most affecting elements. Therefore, changes in land use of the correct classification of rivers is a more accurate calculation of the amount of the floodgate. In particular, using the Landsat images through the image of the land use category, land use past data and calculated using the Markov Chain model and predict the future land use plan in the water control project will be used for large likely.

Fast Load Transient Regulation of Low-Voltage Converters with the Low-Voltage Transient Processor

The transient response of DC-DC converters with large conversion ratios is limited by the asymmetry of the current slew rate through the magnetic elements; under appropriate control, such a converter may respond much faster to an increase in load current than a decrease, or vice versa. In this paper, a low-voltage, unloaded, bidirectional DC-DC converter with a very fast current slew rate, called the low-voltage transient processor (LVTP), is placed in shunt across the output of a conventional DC-DC converter (the ldquoprimary regulatorrdquo) to equalize the effective current slew rate (the combination of the LVTP and primary regulator) seen at the load, so that the transient response to a load increase is the same as the response to a load decrease. The LVTP operates at very low voltages, enabling the use of small magnetic components with low losses even at high-frequency operation, allowing the overall efficiency of the system to be high. To demonstrate the concept, a 3 MHz bidirectional buck LVTP prototype was implemented and placed at the output of a 12-1.2 V microprocessor voltage regulator (VR). The VR with LVTP matched the performance of VRD10.1 VR reference design with half (4.10 mF) of the output capacitance of the original design.

Fast Load Transient Regulation of Low Voltage Converters With the Low Voltage Transient Processor (LVTP)

The transient response of DC-DC converters with large conversion ratios is limited by the asymmetry of the current slew rate through the magnetic elements; under appropriate control, such a converter may respond much faster to an increase in load current than a decrease, or vice versa. In this paper, a low-voltage, unloaded, bidirectional DC-DC converter with a very fast current slew rate, called the low-voltage transient processor (LVTP), is placed in shunt across the output of a conventional DC-DC converter (the ldquoprimary regulatorrdquo) to equalize the effective current slew rate (the combination of the LVTP and primary regulator) seen at the load, so that the transient response to a load increase is the same as the response to a load decrease. The LVTP operates at very low voltages, enabling the use of small magnetic components with low losses even at high-frequency operation, allowing the overall efficiency of the system to be high. To demonstrate the concept, a 3 MHz bidirectional buck LVTP prototype was implemented and placed at the output of a 12-1.2 V microprocessor voltage regulator (VR). The VR with LVTP matched the performance of VRD10.1 VR reference design with half (4.10 mF) of the output capacitance of the original design.