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In this article, the proposed monolithic gallium nitride (GaN)-based driver uses the diode-emulated technique to reduce reverse conduction through a meta-stable fast (MSF) comparator with sub-0.2-ns deadtime. In addition, an active bootstrap controller with a fast discharge loop is used to reduce parasitic effects to improve the driving capability, thereby increasing the switching frequency. Furthermore, the proposed gate driver with dual $dv/dt$ control can reduce the gate-ringing during turn-on/turn-off. Experimental results show that the GaN-based monolithic driver can achieve an operating frequency of 50 MHz and a slew rate of 120 V/ns. At 50 MHz, the conversion of 48-to-5 V can achieve a peak efficiency of 95.4% at the load current of 3.5 A. [ABSTRACT FROM AUTHOR]

We investigated the imaging performance of a fast convergent ordered-subsets algorithm with subiteration-dependent preconditioners (SDPs) for positron emission tomography (PET) image reconstruction. In particular, we considered the use of SDP with the block sequential regularized expectation maximization (BSREM) approach with the relative difference prior (RDP) regularizer due to its prior clinical adaptation by vendors. Because the RDP regularization promotes smoothness in the reconstructed image, the directions of the gradients in smooth areas more accurately point toward the objective function’s minimizer than those in variable areas. Motivated by this observation, two SDPs have been designed to increase iteration step-sizes in the smooth areas and reduce iteration step-sizes in the variable areas relative to a conventional expectation maximization preconditioner. The momentum technique used for convergence acceleration can be viewed as a special case of SDP. We have proved the global convergence of SDP-BSREM algorithms by assuming certain characteristics of the preconditioner. By means of numerical experiments using both simulated and clinical PET data, we have shown that the SDP-BSREM algorithms substantially improve the convergence rate, as compared to conventional BSREM and a vendor’s implementation as Q.Clear. Specifically, SDP-BSREM algorithms converge 35%-50% faster in reaching the same objective function value than conventional BSREM and commercial Q.Clear algorithms. Moreover, we showed in phantoms with hot, cold and background regions that the SDP-BSREM algorithms approached the values of a highly converged reference image faster than conventional BSREM and commercial Q.Clear algorithms. [ABSTRACT FROM AUTHOR]

This article presents a one-stage buck converter with an accurate nanosecond ON-time ($T_{\mathrm{\scriptscriptstyle ON}}$) control for 48–1-V direct conversion for automotive applications. In order to overcome the low duty cycle from 48 to 1 V, the proposed high-voltage storage and low-voltage boost (HSLB) bootstrap circuit can reduce the level shifter delay to close to zero and the bootstrap delay to less than 2 ns. In addition, the early comparison $T_{\mathrm{\scriptscriptstyle ON}}$ generator can reduce the comparator delay ($T_{d\_{}{\mathrm{ comp}}}$) to close to zero at steady state to achieve precise nanosecond pulse $T_{\mathrm{\scriptscriptstyle ON}}$. On the other hand, $T_{d\_{}{\mathrm{ comp}}}$ can be quickly extended to increase $T_{\mathrm{\scriptscriptstyle ON}}$ by 540% to achieve fast transient with the recovery time of 3 $\mu \text{s}$ , in case load changes from 200 mA to 1 A. Based on the precise nanosecond $T_{\mathrm{\scriptscriptstyle ON}}$ , the OFF-time is extended by the load-dependent current limiting OFF-time modulation for improving light-load efficiency. Experimental results show that the peak efficiency reaches 96.5%, 95.1%, and 92.8% when $V_{\mathrm {IN}}$ is 12, 24, and 48 V, respectively, for $V_{\mathrm {OUT}} = 1$ V. [ABSTRACT FROM AUTHOR]

We propose HyFRIS-Net to jointly estimate the hybrid reflectance and illumination models, as well as the refined face shape from a single unconstrained face image in a pre-defined texture space. The proposed hybrid reflectance and illumination representation ensure photometric face appearance modeling in both parametric and non-parametric spaces for efficient learning. While forcing the reflectance consistency constraint for the same person and face identity constraint for different persons, our approach recovers an occlusion-free face albedo with disambiguated color from the illumination color. Our network is trained in a self-evolving manner to achieve general applicability on real-world data. We conduct comprehensive qualitative and quantitative evaluations with state-of-the-art methods to demonstrate the advantages of HyFRIS-Net in modeling photo-realistic face albedo, illumination, and shape. [ABSTRACT FROM AUTHOR]

To overcome the challenges of large reactive energy transmission loss and high current stress, which ocurr during the operation of auxiliary commutated circuit (ACC) of novel parallel resonant dc-link inverter (PRDCLI), an improved modulation strategy for reactive energy transmission loss is herein proposed based on the discontinuous pulsewidth modulation (DPWM), which adopts sawtooth carrier wave with alternating positive and negative slopes and shunt dead zone. Compared with the original modulation strategy, based on minimizing the ACC operation frequency, the proposed modulation strategy is able to realize all switches soft-switching, and avoid the superposition of resonant current and load current during the operation of ACC, thus, effectively reducing the reactive energy transmission loss and the current stress of auxiliary switches of the ACC. Under the proposed modulation strategy, the equivalent circuits in different operation modes are divided, and the operation principle, voltage/current stress, loss distribution, and optimal parameter design method of novel PRDCLI are researched. Eventually, the proposed modulation strategy is verified by experiments on a 5-kW/40-kHz prototype made by SiC mosfet. [ABSTRACT FROM AUTHOR]

In this article, the design of a fourth-harmonic gyrotron with 1-kW-level output power at 1 terahertz (THz) is presented. A unique advantage of this design is that, with a well-optimized magnetic-cusp large-orbit electron gun, the designed gyrotron can operate from first-harmonic to fourth-harmonic in multiple discrete bands by varying the confining magnetic field strength. By carefully balancing the competing modes, the gyrotron can be tuned to operate at six candidate modes, including TE1,2 for fundamental harmonic, TE2,3 and TE2,4 for second-harmonic, TE3,5 and TE3,6 for third-harmonic, and TE4,8 for fourth-harmonic interactions. As the main operating mode, the TE4,8 can generate a peak output power of 1.68 kW, with an output efficiency of about 2.1%, and a magnetically controlled frequency tuning range of about 1.5 GHz around 1 THz. The impact of the longitudinal nonuniformity of the cavity at high-harmonic interaction was also studied. It shows that a radial tolerance of several micrometers will significantly elevate the start-oscillation current and deteriorate output performance. This design is to produce a THz source with ultra-wideband tuning capability ranging from the submillimeter-wave to 1-THz bands. [ABSTRACT FROM AUTHOR]

A three dimensional (3-D) geometry-based channel model is proposed for intelligent reflecting surface (IRS)-assisted unmanned aerial vehicle (UAV) multiple-input multiple-output (MIMO) communication scenarios where the users are located on the edge of IRS service area. In order to reduce the interference between different IRS reflection units, we first construct an optimization problem about the statistical propagation phases of different IRS reflection units, and then derive the optimal statistical propagation phase by solving the designed optimization problem. Finally, we align the proposed statistical propagation phases of IRS with the stronger components to derive suboptimal IRS reflection phases. Using derived IRS reflection phases, the statistical properties are investigated. The numerical results show that the proposed IRS reflection phases can enhance the received signal strength and reduce the multipath fading effect. Also, it can be observed that when the number of IRS reflection units increases, the spatial correlation significantly decreases. [ABSTRACT FROM AUTHOR]

This article presents a three-switch (3S) boost converter with hysteresis current control applied in MiniLED panels. It uses only three power switches to achieve high conversion ratio (=7.5) and low inductor current (20% lower than conventional boost converters). Meanwhile, the charging time of the flying capacitor will increase as the duty cycle increases. It enables the proposed 3S boost converter to have a high drive current (=1.2 A). In addition, the right half-plane (RHP) zero of the proposed topology is related to the switching frequency. By dynamically adjusting the position of RHP zero during transients, the recovery time and output voltage drop can be reduced at the same time. When the load increases from 120 mA to 1.2 A, the recovery time can be accelerated to 42 $\mu \text{s}$ , and the maximum efficiency can reach 97.4%. [ABSTRACT FROM AUTHOR]