Sharif Digital Repository

In this paper, a novel method for high-repetition-rate high-power radio frequency (RF) pulse generation, which involves only passive solid-state devices and is capable of being used for generating high power microwaves using a low-to-high power converting scheme based on nonlinear self-compression is proposed. The method is also expected to be of low jitter. In the proposed circuit, two high voltage diodes with proper reverse recovery characteristics are used. The simulation results show that the proposed circuit generates RF pulses, with central frequencies up to gigahertz range. By applying a sub-kilowatt power supply, the maximum output power was well over 10 kW. This power can be... 

A high-power short-pulse generator based on the diode step recovery phenomenon and high repetition rate discharges in a two-electrode gas discharge tube is presented. The proposed circuit is simple and low cost and driven by a low-power source. A full analysis of this generator is presented which, considering the nonlinear behavior of the gas tube, predicts the waveform of the output pulse. The proposed method has been shown to work properly by implementation of a kW-range prototype. Experimental measurements of the output pulse characteristics showed a rise time of 3.5 ns, with pulse repetition rate of 2.3 kHz for a 47-Ω load. The input peak power was 2.4 W, which translated to about... 

Drift step recovery diodes (DSRDs) have a special place in high-power short-pulse generation. In this paper, a cascaded configuration of two DSRD-based high-power short-pulse generators with gas discharge switches was used. The high-power pulses generated in the first stage feed the second stage in order to generate shorter pulses with higher peak powers. A prototype was implemented based on this idea. In the first stage, 1.2-kV pulses were generated from a 50-V power supply. At the output of the second stage, 2.1-kV pulses with a repetition rate of more than 50 Hz were obtained. The output peak voltage was limited by the breakdown voltage of the used DSRD. Repetitive pulses with 4-ns rise... 

A three-phase dual active bridge (DAB) converter is designed and constructed as the DC/DC stage of a 50 kW fast charger station. Recently introduced 300A SiC power modules and drivers are utilized in the converter to obtain a high efficiency. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as over-current, gate under-voltage, or gate overvoltage. In such case the module operates as a leg with two diodes until an external hardware signal resets the driver. The aim of this paper is to provide analysis, simulation and experiments for a three-phase... 

In this paper, a reconfigurable patch antenna with Circular Polarization (CP) diversity with theoretical discussion and verification is proposed for fifth generation (5G) of mobile communication systems. The proposed antenna contains two PIN diodes, which are correctly placed on the ground plane to obtain polarization diversity. By switching between two ON/OFF modes in the PIN diodes, the proposed antenna can support either the RHCP mode or the LHCP mode. An antenna with the well-matched impedance bandwidths (S11 ≤ −10 dB) of 2.5 GHz (27 ∼ 29.5 GHz) and 3 GHz (36 ∼ 39 GHz) and the dual-band 3-dB axial ratios of 6% (27.3–29 GHz) and 8.4% (35–38.2 GHz) operates in both the RHCP and LHCP modes.... 

Small high-quality Au/p-Si Schottky barrier diodes (SBDs) with extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from currentvoltage (IV) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By extrapolating the plots the built-in potential of the Au/p-Si contact was obtained as Vbi=0.5425 V and the barrier height value (ΦB(C-V)) was calculated to be ΦB(C-V)=0.7145 V for Au/p-Si for a typical 100 μm diode diameters. In the present work the... 

Small high-quality Au/P-Si Schottky barrier diodes (SBDs) with an extremely low reverse leakage current using wet lithography were produced. Their effective barrier heights (BHs) and ideality factors from current-voltage (I -V) characteristics were measured by a conducting probe atomic force microscope (C-AFM). In spite of the identical preparation of the diodes there was a diode-to-diode variation in ideality factor and barrier height parameters. By extrapolating the plots the built in potential of the Au /p-Si contact was obtained as Vbi D 0:5425 V and the barrier height value φB(C-V) was calculated to be φB(C-V) D 0:7145 V for Au/p-Si. It is found that for the diodes with diameters... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through (SH) states in a quasi-Z-source inverter (q-ZSI), increase the amplitude of high order harmonics of CMV. In this paper, by using the modulation technique based on odd PWM (OPWM) and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. IEEE  

Nanosecond pulsed-power generators have many applications in industries. As the rise time and fall time of conventional semiconductor switches are usually more than a few nanoseconds, it is necessary to employ special switches or new pulse generating methods to achieve nanosecond pulses. A common method for producing narrow pulse voltage waveforms is using the reverse recovery process of diodes. In this method, a super fast recovery diode is used as an opening switch in an inductor current path. A drift step recovery diode can form a rapid cut-off current front; Hence this method can be an effective solution to generate narrow pulses. This paper describes an investigation about the effect of... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through states in a quasi-Z-source inverter (q-ZSI) increase the amplitude of high-order harmonics of CMV. In this paper, by using the modulation technique based on odd pulse width modulation and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. ©... 

Two-dimensional semiconductor materials can be combined with conventional silicon-based technology and sort out part of the future challenges in semiconductor technologies due to their novel electrical and optical properties. Here, we exploit the optoelectronics property of the silicon/SnS2 heterojunction and present a new class of backward diodes using a straightforward fabrication method. The results indicate an efficient device with fast photoresponse time (5-10 μs), high photoresponsivity (3740 AW-1), and high quantum efficiency (490%). We discuss device behavior by considering the band-to-band tunneling model and band bending characteristics of the heterostructure. This device structure... 

Using a simple nonlinear model based on rate equations, and by employing a harmonic balance method, we develop a theory of optimal mixing in directly modulated semiconductor laser diodes. We perform a consistent numerical solution to the mixing in laser diodes to the arbitrary accuracy and intermodulation index (m, n). Through numerical computations we demonstrate that there is an optimal bias in mixing, corresponding to a relaxation frequency, fr, coinciding with the subcarrier frequency, f1, at which the mixing power is maximized nearly simultaneously for all intermodulation products, fmn. In terms of increasing the signal's current amplitude, it will be shown that it would result in a...