Large-signal Analysis Research Articles

Backward wave oscillation suppression study of the helix travelling wave tube

ABSTRACTIn this paper, the effect of backward wave oscillation (BWO) on helix slow wave structure performance for TWT has been described. In this paper both the cases tapered and untapered helix slow wave structure (SWS) have been analyzed, caused by BWO for high gain helix TWT. In house developed the one-dimensional (SUNRAY-1D) large signal analysis model has been used for stability analysis of the helix SWS. The analysis on backward wave amplifier gain has been carried out as a function of the taper parameter and frequency parameter. The position and nature of tapering also affect the electronic efficiency as well as the start oscillation current. Hence, position and nature of tapering have been optimized.

Analysis of nonlinear large signal intrinsic elements for InGaP/GaAs HBT based on Gummel‐Poon model

AbstractA large signal analysis method based on Gummel‐Poon model is proposed to predict nonlinear behavior of InGaP/GaAs HBT. A 2 × 20 μm2 transistor is fabricated with InGaP/GaAs HBT technology. The large signal transconductance Gm, conductance Gbe, and capacitance CBE, CBC are calculated based on the proposed method and measured using a RF testing probe. The calculated and measured results show good consistency up to nonlinear power level. The proposed method is applied to analyze variations of nonlinear large signal intrinsic elements of this transistor with increasing power under different bias conditions, in order to raise benefit of nonlinear consideration for power amplifiers.

Low‐power non‐ideal pulse‐width modulated DC–DC buck–boost converter: design, analysis and experimentation

In this study, parasitic elements (non-idealities) effect on a low-power DC-DC buck-boost converter design is analysed and investigation is carried out by both large (i.e. steady-state) and small signal analysis. The large signal analysis of non-ideal buck-boost converter explored the significant information such as nearly accurate duty cycle, maximum allowable duty cycle and maximum possible output voltage. Further, accurate mathematical design formulae are derived of inductor and capacitor for specified inductor current ripple and output voltage ripple (OVR), respectively. Moreover, consequences of different equivalent series resistance of capacitor on OVR is examined. Subsequently, the exact model of buck-boost converter is procured from the small signal analysis, which is almost analogous to practical system. In order to show the impact of non-idealities on controller design, an internal model control PID controller is designed for ideal, semi-non-ideal and complete non-ideal systems based on their respective models, which shows the controller based on non-ideal model provides very close results to practical system. Conclusively, the complete theoretical explorations are justified by simulations and substantiated by experimental results.

Small and Large Signal Analysis of Photonic Crystal Fano Laser

We analyze the small- and large-signal response of a photonic crystal Fano laser. Conventional current modulation, as well as modulation of the laser via the mirror, is investigated using a numerical approach as well as linear small-signal analysis. The results show that the amplitude modulation bandwidth of one of the laser ports (the through-port) and the frequency modulation bandwidth of another port (the cross-port) extend to the THz region. Large-signal simulations of the laser response to a 500 Gb/s pseudo-random bit sequence modulation of the nanocavity are in good agreement with the predictions of the small-signal analysis. Finally, it is investigated how the design of the Fano mirror, in particular, the quality-factor ( Q ) of the nanocavity, affects the modulation properties.

Adaptive Stabilization of Uncontrolled Rectifier Based AC–DC Power Systems Feeding Constant Power Loads

It is known that, when tightly regulated, actively controlled power converters behave as constant power loads (CPLs). These loads can significantly degrade the stability of their feeder system. The loop-cancelation technique has been established as an appropriate methodology to mitigate this issue within dc–dc converters that feed CPLs. However, this has not yet been applied to uncontrolled rectifier based ac–dc converters. This paper therefore details a new methodology that allows the loop-cancelation technique to be applied to uncontrolled rectifier based ac–dc converters in order to mitigate instability when supplying CPLs. This technique could be used in both new applications and easily retrofitted into existing applications. Furthermore, the key contribution of this paper is a novel adaptive stabilization technique, which eliminates the destabilizing effect of CPLs for the studied ac–dc power system. An equation, derived from the average system model, is introduced and utilized to calculate the adaptable gain required by the loop-cancelation technique. As a result, the uncontrolled rectifier based ac–dc feeder system is always stable for any level of CPL. The effectiveness of the proposed adaptive mitigation has been verified by small-signal and large-signal stability analysis, simulation, and experimental results.

Design of a Microfabricated Planar Slow Wave Structure for a 0.22-THz TWT for Communication, Imaging and Remote Sensing

ABSTRACTA microfabricated planar 0.22 THz TWT is being investigated as a high power, broadband amplifier for ultra-broadband wireless communication, imaging and remote sensing. Planar staggered double-vane-loaded rectangular waveguide slow wave structure (SDV-SWS) is selected for the 0.22 THz TWT because of its wide bandwidth, high impedance and low loss, easy fabrication using MEMS technologies with high precision and surface finish, and inherent compatibility for operation with sheet electron beam. A simplified approach is presented for determining initial design parameters of the SDV-SWS of wide bandwidth and high impedance. The initial design parameters of the SDV-SWS are used for analytically determining the dispersion and the impedance characteristics of the structure which are found comparable with the simulated characteristics by the 3D e.m. field simulator CST code. The SDV-SWS is designed for a planar 0.22 THz TWT with a sheet beam of beam voltage 20 kV and beam current 100 mA. In-house developed large signal analysis code (SUNRAY-p) is used to analyse RF performance of the planar TWT over the band. The RF performance of the 0.22 THz TWT as determined using SUNRAY-p code is found comparable with the simulated results by the CST code over the frequency band.

Enhanced Gain Low-Power CMOS Amplifiers: A Novel Design Approach Using Bulk-Driven Load and Introduction to GACOBA Technique

A new design technique is proposed and discussed for the design of active load using the bulk-driven method. The proposed method uses gate-driven input drivers with bulk-driven MOS load. Further, it is used to design single stage amplifiers, such as common source (CS) and common gate (CG). In addition to the proposed technique, a very efficient method is implemented to improve and control the gain of the amplifiers, which is named as Gain Control by Bulk Amplification (GACOBA) Technique. The large signal, small signal and frequency domain analysis of proposed designs are done and to verify the outcomes it is simulated in SPECTER at 0.7[Formula: see text]V supply with 45[Formula: see text]nm CMOS technology. The result shows that the transconductance and gain of proposed single stage CS amplifier are increased without affecting impedance seen by output node. On the other hand, GACOBA technique is useful for gain enhancement in CS and CG amplifier.

Design of a 0.22THz, 100W Planar TWT for Ultra Wide Band Wireless Communication

Development activities addressed to 0.22THz centre frequency is of significant importance for ultra wideband communication and remote sensing because of the available atmospheric spectral window over a band from 0.20THz to 0.30THz. 0.22THz planar TWT of output power more than 100W, gain more than 30dB, and bandwidth more than 30GHz is designed for high data rate wireless communication, imaging and remote sensing. Planar TWT is designed using a rectangular sheet electron beam of beam voltage 20kV and beam current 100mA, and of beam size 100m (thickness) x 600m (width). A planar staggered double vane loaded rectangular waveguide slow-wave structure (SDV-SWS) of broad bandwidth, high impedance and low circuit loss is designed for the 0.22THz TWT. Planar structure is used because it is compatible for sheet beam operation and it is also easy to fabricate using MEMS technologies. Large signal analysis code SUNRAY-P, developed to determine RF performance of a planar TWT with sheet beam, is used to design the 0.22THz 100W TWT with sever, couplers and phase velocity taper. WR-3 rectangular waveguide of size 864m x 432m is used for the input and the output couplers.

Particle-In-Cell Simulation of a Tapered Cavity for a Millimeter Wave Gyrotron

A waveguide structure, which includes a downtaper, a straight-midsection, and an uptaper waveguide sections with two parabolic-corrections at transitions of waveguide sections along with a raised cosine nonlinear taper, was considered as an interaction structure for the gyrotron. The particle-in-cell (PIC) simulation and large-signal analysis were performed using CST Studio Suite and GYRO-K, respectively, with the proposed structure in nine combinations involving three radius and three magnetic field profiles. The time signal and electric field growth were monitored and the output powers were estimated for the TE6,2 and other competing modes. One of the radius and magnetic field profile combinations leads to 135-kW power in the PIC simulation at ~95 GHz with 49.1% beam-to-wave conversion efficiency. For the same profile combination, GYRO-K estimates ~7.9% power degradation with a 45-MHz lower side frequency shift than that of the PIC simulation.

An Improved Generalized Average Model of DC–DC Dual Active Bridge Converters

Improvements are proposed for generalized average models of dual active bridge (DAB) converters. Generalized average modeling involves a tradeoff between accuracy and tractability. To maintain an acceptable level of complexity, existing DAB models are derived using a first harmonic approximation. These models provide accurate small-signal representations, but are limited as large-signal analysis tools due to persistent steady-state error. This study proposes a modeling framework that provides accurate large and small-signal models without significant increases in the overall complexity. The framework describes DAB operation with a triple phase shift modulation, and is easily simplified for single, dual, or extended phase shift modulation schemes. The special case of a single phase shift modulation, which experiences the most significant large-signal error, is given additional consideration. The framework is applied to open and closed-loop operation, and both large- and small-signal models are discussed. Models are validated in simulation and hardware experiments using a small scale DAB prototype.

Small- and Large-Signal Analyses of Different Low-Pressure-Chemical-Vapor-Deposition SiN x Passivations for Microwave GaN HEMTs

Three types of SiN x passivation for microwave AlGaN/GaN HEMTs were deposited with low-pressure chemical vapor deposition under different deposition conditions, resulting in different silicon contents. The performance of the HEMTs is comprehensively investigated and compared. Both small- and large-signal analyses, such as generation–recombination (G–R) trap analysis, low-frequency noise characterization, and load–pull measurement, are indispensable to evaluate the effectiveness of a surface passivation. A Si-rich SiN x passivation shows excess G–R centers, whereas a Si-poor SiN x passivation exhibits significant current slump (30%). A bilayer SiN x passivation successfully shows not only a small current slump (~9.7%) but also a suppressed G–R trapping/detrapping process. Moreover, the bilayer passivation demonstrates almost 2 orders of magnitude lower gate current noise spectra compared with the single-layer Si-rich SiN x passivation. The capacitance-voltage measurements reveal that the Si-rich SiN x layer removes the deep-level traps at the AlGaN/SiN x interface. Considering both small- and large-signal operations, it is concluded that the bilayer SiN x passivation is a suitable and versatile candidate for microwave GaN devices.

Bregman Storage Functions for Microgrid Control

In this paper, we contribute a theoretical framework that sheds a new light on the problem of microgrid analysis and control. The starting point is an energy function comprising the “kinetic” energy associated with the elements that emulate the rotating machinery and terms taking into account the reactive power stored in the lines and dissipated on shunt elements. We then shape this energy function with the addition of an adjustable voltage-dependent term, and construct so-called Bregman storage functions satisfying suitable dissipation inequalities. Our choice of the voltage-dependent term depends on the voltage dynamics under investigation. Several microgrid controllers that have similarities or coincide with dynamics already considered in the literature are captured in our incremental energy analysis framework. The twist with respect to existing results is that our incremental storage functions allow for a large signal analysis of the coupled microgrid. This obviates the need for simplifying linearization techniques, and for the restrictive decoupling assumption in which the frequency dynamics is fully separated from the voltage one. A complete Lyapunov stability analysis of the various systems is carried out along with a discussion on their active and reactive power sharing properties.

Bifurcation and Large-Signal Stability Analysis of Three-Phase Voltage Source Converter Under Grid Voltage Dips

Three-phase voltage source converters (VSCs) are commonly used as power flow interface in ac/dc hybrid power systems. The ac power grid suffers from unpredictable short-circuit faults and power flow fluctuations, causing undesirable grid voltage dips. The voltage dips may last for a short time or a long duration, and vary the working conditions of VSCs. Due to their nonlinear characteristics, VSCs may enter abnormal operating mode in response to voltage dips. In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. The converter will exhibit an irreversible instability after the dips. The expanded magnitude of ac reactive current may cause catastrophic consequence for the system. A full-order eigenvalue analysis and a reduced-order mixed-potential-theory-based analysis are adopted to reveal the physical origin of the large-signal instability phenomenon. The key parameters of the system are identified and the boundaries of instability are located. The bifurcation phenomenon and a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-by-cycle simulations and experimental measurement on a practical grid-connected VSC prototype.

Large-signal field analysis of a linear beam travelling wave tube amplifier for the anisotropically conducting tape helix slow-wave structure supported by dielectric rods

The large-signal behavior of traveling wave tube amplifier for a linear beam dielectric loaded anisotropically conducting tape helix slow wave structure (SWS) is realized through a swift and reliable field analysis. Using Green’s function sequence, the field components in the SWS are designated as nonlinear functionals of electron arrival time. The electron arrival time in the beam region is formulated into a nonlinear operator in the Banach space mapping form by substituting the axial electric field component into the electron ballistic equation. The nonlinear beam–wave interaction is then obtained by determining the electron arrival time through extensive successive approximations, and thus exact electric and magnetic field components in the tape helix SWS are attained. The numerical computation of the proposed model yields definitive analytical results for the electron exit velocity, induced surface current density, power gain, conversion efficiency, and optimum interaction length.

Small and large signal analysis using circuit model of InGaAs/InP based uni-travel carrier photodiode

An equivalent circuit model of uni-traveling carrier photodiode (UTC-PD) is developed from integral carrier density rate equation and few important properties of the device such as the electrical and optical characteristics are evaluated by employing advanced device physics. Circuit model incorporates chip and package parasitic of the device quite simply to provide practical behaviour of UTC-PD. We have developed small signal ac circuit model which is useful for the analysis of low power modulation characteristics of the device and dc circuit model which is advantageous to find wavelength dependent responsivity fairly accurately. At high optical input power the device bandwidth is found to be increased through enhancement of self-induced field in the absorption region and high output power can be derived from the device when absorption width is large. Such condition calls for large signal analysis. We have developed large signal circuit model by combining few mathematical transformations with small signal circuit model with different circuit element values. Our large signal model is unique that the same circuit can be used for both small and large signal analysis. With large signal model the optical power induced bandwidth improvement and output photocurrent saturation are explained. Large signal model is validated through linearity and IP3 analysis which found close agreement with the measured results.

Nonlinear analysis of beam-wave interaction in a planar THz travelling-wave tube amplifier

Large-signal analysis is presented for analysing non-linear beam-wave interaction in a planar THz TWT with a sheet electron beam. The sheet beam within one RF beam wavelength is represented by uniform rectangular charged discs for confined flow of the beam, and the discs are tracked in small distance steps of forward integration. For a planar THz TWT, a staggered double-vane loaded rectangular waveguide slow-wave structure (SDVSWS) is used. Frequency-domain analysis is used to define the RF circuit field in the SDVSWS and the interaction of the RF circuit field with the electron beam is carried out for steady-state TWT operation. The RF circuit field is considered to be continuous as in a helix SWS and it is represented by transmission line theory at each integration plane. A large-signal analysis code of a helix TWT with pencil beam (SUNRAY-1D) was modified for a planar TWT with a sheet beam. The accuracy of the modified SUNRAY code was checked against the 3D e.m. field simulator (CST-PS) by comparing the output performance for a 0.22-THz planar TWT. The results for the gain and the output power over the operating band given by the two codes were found to be comparable. A significant advantage of the SUNRAY code is that it is very fast compared to the CST code. It takes less than a minute to simulate the RF performance of a typical THz TWT at a single frequency and drive power on a standard PC. The SUNRAY code can therefore, be used interactively for design a complete SWS with input/output couplers, sever, loss profiles and phase velocity taper for a high efficiency high gain THz TWT.

Large Signal Lyapunov-Based Stability Studies in Microgrids: A Review

Microgrid stability studies have been largely based on small-signal linearization techniques. However, the validity and magnitude of the linearization domain are limited to small perturbations. Thus, there is a need to examine microgrids with large-signal nonlinear techniques to fully understand and examine their stability. Large-signal stability analysis can be accomplished by Lyapunov-based mathematical methods. These Lyapunov methods estimate the domain of asymptotic stability of the studied system. In this paper, a survey of Lyapunov-based large-signal stability studies of microgrids is given. Moreover, this paper covers large-signal studies of individual generator and load types in microgrid settings. Stability studies of dc/ac droop controlled inverters, ac/dc and dc/dc converters, and motor drives are explored. The survey shows that few large-signal Lyapunov-based studies have been completed on either individual systems or microgrid systems. This paper highlights the aspects that make Lyapunov-based microgrid stability studies interesting and valuable. This paper also recommends areas that future research could address to improve large-signal stability studies of microgrids.

Large-Signal Analysis and Characterization of a RF SOI-based Tunable Notch Antenna for LTE in TV White Space Frequency Spectrum

Large-Signal Analysis and Characterization of a RF SOI-based Tunable Notch Antenna for LTE in TV White Space Frequency Spectrum

RF Power Analysis on 5.8 GHz Low-Power Amplifier Using Resonant Tunneling Diodes

This letter reports the analysis of RF power characteristics in a microwave amplifier using resonant tunneling diodes (RTDs). The implemented IC shows a return loss of more than 11 dB with a low dc-power consumption of 0.42 mW and a power gain of 8.6 dB at 5.8 GHz. The maximum linear RF output power with a uniform gain of 8.6 dB is measured to be −25.4 dBm at the same frequency. The gain hump phenomenon is observed in an input power range from −32 dBm to −16 dBm, and is shown to arise from a sudden movement of the operating point from the negative differential resistance (NDR) region to the positive differential resistance (PDR) region, based on a large-signal load-line analysis together with a harmonic balance simulation.

Comparison of Full 3D and Unit Cell Models for Waveguide-Embedded Frequency Multiplier Arrays

We present a full wave, large-signal analysis of a waveguide-embedded frequency multiplier array, solving the entire geometry using FEM EM modeling and including every nonlinear element in a Harmonic Balance simulation. The full 3D model employed provides the exact field distribution across the array, thus enabling us to account for substrate resonances, higher order mode excitation, instabilities, and diode yield. The model is compared with measurements on a 247 GHz fixed tuned 72-diode HBV tripler. In this example, higher order mode excitation was found due to the interaction between the filter and the diode array. This can only be observed using a full 3D model, which more accurately predicts the output power versus input power and frequency. Finally, the pros and cons of a full 3D model and a unit cell model for waveguide embedded multiplier arrays are discussed.