Small-signal Conditions Research Articles

Non-smooth finite-time adaptive stabilisation of cascade switched systems with asymmetric output constraints

In this article, the problem of non-smooth finite-time (FT) adaptive state feedback stabilisation is investigated for asymmetric output-constrained cascade switched nonlinear systems (AOCCSNSs) with mixed powers, parametric uncertainties and zero dynamics. To better address the uncertain parameters and the asymmetric output constraints, a new type of common Lyapunov function (CLF) including a quadratic squared term of the estimated error and a tangent-type barrier Lyapunov function ( T t -BLF) is constructed. Then, with some mild assumptions, such as input-to-state stability (ISS) property of zero dynamics, upper boundedness of subsystems' nonlinear terms and some well-known small signal conditions, state feedback controllers (SFCs) constructed by adding a power integrator (AAPI) technique and the update law to estimate the unknown parameter are proposed to guarantee resultant closed-loop switched systems FT stable. The proposed method for switched systems is presented in a unified manner, capable of addressing FT stabilisation by effectively handling situations with or without output constraints. This is achieved through the construction of T t -BLF, which degenerates into a quadratic form when the output constraint disappears or approaches infinity. At last, the method is verified by a switched RLC circuit system (RLC-CS) and a numerical simulation.

A New Analytical Large-Signal Model for Quasi-Ballistic Transport in InGaAs HEMTs Accommodating Dislocation Scattering

A surface-potential-based analytical large-signal model, which is applicable to both ballistic and quasi-ballistic transport in InGaAs high electron mobility transistors, is developed. Based on the one-flux method and a new transmission coefficient, a new two-dimensional electron gas charge density is derived, while the dislocation scattering is novelly taken into account. Then, a unified expression for Ef valid in all the regions of gate voltages is determined, which is utilized to directly calculate the surface potential. The flux is used to derive the drain current model incorporating important physical effects. Moreover, the gate-source capacitance Cgs and gate-drain capacitance Cgd are obtained analytically. The model is extensively validated with the numerical simulations and measured data of the InGaAs HEMT device with the gate length of 100 nm. The model is in excellent agreement with the measurements under I-V, C-V, small-signal conditions, and large-signal conditions.

Fluctuations in the collected charge in integrating photoconductive detectors under small and large signals: the variance problem

Charge collection efficiency (CE) η 0 under small signal conditions, corresponding to a uniform field in the detector medium, has been widely used in evaluating the performance of photoconductive detectors. The present paper answers the question, ‘What is the variance of the collected charge in an integrating detector as a function of photoinjection level and what are the errors if we continue to use the small signal equations?’ The variance in η 0 under small signals has been theoretically derived in the literature and has been a key factor in the detective quantum efficiency modeling of integrating detectors based on various semiconductors. is a noise source and can degrade the detector performance under incomplete charge collection. The statistical variance in the CE η 0, under small signals and the variance in the CE ηr under an arbitrary injection level r (injected charge divided by charge on the electrodes) have been studied using the Monte Carlo simulation model developed in this work to evaluate the difference between and from small to large signals. Initial injection of electron and hole pairs and their subsequent transport and trapping in the presence of an electric field, which is calculated from the Poisson equation, is used to calculate the photocurrent. Each injected carrier is tracked as it moves in the semiconductor until it is either trapped or reaches the collection electrode. Trapped carriers do not contribute to the photocurrent but continue to contribute to the field through the Poisson equation. The instantaneous photocurrent i ph(t) is calculated from the drift of the free carriers through the Shockley–Ramo theorem. i ph(t) is integrated over the duration of the photocurrent to calculate the total collected charge and hence the CE ηr . The variance in ηr is found from multiple simulations of ηr . The ηr and have been generated over varying charge injection ratios r, the electron and hole ranges μτ, mean photoinjection depths δ and drift mobility ratios b. At full injection, the deviation of the CE variance from the uniform field case ( = may be as much as 40% larger or 20% lower than the small signal model prediction. This study provides the extent of errors involved in the variance of the CE in non-uniform fields and quantifies the increase in errors that can occur in high injection cases. In practice, typical injection ratios are less than 0.2, which means that the magnitude of percentage error is less than 5%.

A low-noise readout circuit design for multi-bit quanta image sensor

This paper presents a novel readout circuit based on low-noise charge transfer amplifier (LCTA) to suppress the readout noise in multi-bit quanta image sensor. A switched capacitor circuit is used in LCTA to reduce the kT/C noise introduced by its load capacitor, and make the noise from ADC further suppressed due to the increase of its output swing. The digital correlated double sampling of single-slope ADC is used to eliminate the fixed noise in LCTA. The low noise readout circuit is implemented by a 110 nm CMOS process. The simulation results show that the random noise of LCTA is reduced by 19% at a gain of 2 V/V compared to the conventional differential charge transfer amplifier. The increased output swing reduces the random noise power of ADC by 61%. In addition, the LCTA equivalent input fixed noise with 29.8 μVrms is eliminated. The proposed low-noise readout circuit improves the signal-to-noise ratio by 4.37 dB at small-signal conditions.

Design of microwave β-(Al x Ga x )2O3/Ga2O3 lateral Schottky barrier diodes

High power microwave Schottky barrier diodes (SBDs) are required to develop detectors and mixers in advance the millimeter-wave (mm-wave) wireless technologies such as fifth generation long-term evolution. To achieve high efficiency and sensitivity in SBDs, materials/structures with high mobility and low series resistance are needed. In this regard, we have proposed the two dimensional electron gas of β-(Al x Ga)2O3/Ga2O3 heterostructure channel lateral SBDs (LSBDs) for the first time. To design high performance LSBDs, detailed physical models of both β-(Al x Ga)2O3 and Ga2O3 were studied and characterized with experimental results. These physical models were used to perform realistic numerical simulations of DC, small signal and large signal conditions. It was observed that the structural and compositional aspects of heterostructure are largely influencing the small signal sensitivity and cut-off frequencies. Also the large signal analysis reveals that the LSBD can operate in linear detection of microwave signals, up to 38 dBm. By scaling down the device to a sub-micron channel length, a cut-off frequency of 1.5 THz was achieved in the proposed LSBD. Comparison with state-of-the-art SBDs, the observations from DC, small signal and large signal analysis recommend the proposed β-(Al x Ga)2O3/Ga2O3 LSBDs for high power and mm-wave/sub-THz detector/mixer application.

Fast Simulation of Analog Circuit Blocks Under Nonstationary Operating Conditions

This article proposes a black-box behavioral modeling framework for analog circuit blocks (CBs) operating under small-signal conditions around nonstationary operating points. Such variations may be induced either by changes in the loading conditions or by event-driven updates of the operating point for system performance optimization, e.g., to reduce power consumption. An extension of existing data-driven parameterized reduced-order modeling techniques is proposed, which considers the time-varying bias components of the port signals as nonstationary parameters. These components are extracted at runtime by a low-pass filter and used to instantaneously update the matrices of the reduced-order state-space model realized as a SPICE netlist. Our main result is a formal proof of quadratic stability of such linear parameter varying (LPV) models, enabled by imposing a specific model structure and representing the transfer function in a basis of positive functions whose elements constitute a partition of unity. The proposed quadratic stability conditions are easily enforced through a finite set of small-size linear matrix inequalities (LMIs), used as constraints during model construction. Numerical results on various CBs, including voltage regulators, confirm that our approach not only ensures the model stability but also provides speedup in runtime up to two orders of magnitude with respect to full transistor-level circuits.

A Digital Correction Method for Increased Dynamic Range in Interferometric Six-Port Radars

In this letter, we demonstrate a digital correction method for extending the dynamic range of a six-port radar system based on detector diodes. An individual diode gain is considered to depend on output voltage, which can be approximated as a linear function in order to extrapolate the diode's square-law response to higher input powers. The individual diode coefficients are extracted during an initial calibration measurement utilizing the interferometric working principle. A six-port junction in combination with power detectors based on Si Schottky diodes operating at 24 GHz has been employed to validate the concept. Reduction of the third- and fifth-order harmonics of up to 35 and 22 dB, respectively, has been achieved at the highest input power of 8 dBm. The correction was applied for a wide range of operating conditions. As a result, the increase in phase error under large-signal and high power operation is effectively compensated and remains low under small-signal conditions. Thus, phase accuracy is maintained beyond the classical dynamic range of detector diodes in six-port applications so far.

Small- and Large-Signal Dynamic Output Capacitance and Energy Loss in GaN-on-Si Power HEMTs

The origin of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</sub> and the energy dissipation due to output capacitance can be roughly separated into two types: resistive loss and capacitive hysteresis loss. The resistive losses are due to the resistance of gallium nitride (GaN) buffer layers and Si-substrate. These loss components can be potentially improved by reengineering the doping concentrations in the buffer stacks and substrate layer. However, the capacitive hysteresis loss that is suspected to be due to trapping dynamics remains largely unexplained. This article presents a physics view of the trapping dynamics related to C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</sub> in the GaN high-electron-mobility transistor (HEMT) under small- and large-signal excitations. It is observed that, under large-signal excitation, traps with shallow energy levels (in the range of 0.5 eV above valence band) are mostly responsible for the charge imbalance and energy dissipation. Under small-signal conditions, deep traps with an energy level of around 0.98 eV from the valence band are the causes for the hysteresis at dc. By identifying dominating types of traps and relevant trap energy levels in GaN HEMT, we can gain important insights on how to optimize the device stack design for high-frequency applications.

There is Plenty of Room for THz Tunneling Electron Devices Beyond the Transit Time Limit

The traditional transmission coefficient present in the original Landauer formulation, which is valid for quasi-static scenarios with working frequencies below the inverse of the electron transit time, is substituted by a novel time-dependent displacement current coefficient valid for frequencies above this limit. Our model captures in a simple way the displacement current component of the total current, which at frequencies larger than the inverse of the electron transit time can be more relevant than the particle component. The proposed model is applied to compute the response of a resonant tunneling diode from 10$\,$GHz up to 5$\,$THz. We show that tunneling electron devices are intrinsically nonlinear at such high frequencies, even under small-signal conditions, due to memory effects related to the displacement current. We show that these intrinsic nonlinearities (anharmonicities) represent an advantage, rather than a drawback, as they open the path for tunneling devices in many THz applications, and avoid further device downscaling.

Nonlinear Stability Analysis of DC-DC Power Electronic Systems by Means of Switching Equivalent Models

The proliferation of renewable energy sources is promoting the use of dc-dc power electronic converters in power distribution systems. It is well-known that the interconnection of power electronic converters can be a source of instabilities. Traditionally, impedance-based stability analyses are performed using either the analytical description or the identification of the output impedance of the source converter and the input admittance of the load converter. However, this methodology is restricted by the small-signal conditions, which are usually violated in this kind of systems due to the high variability imposed by the renewable energy sources. In nonlinear systems, the stability analysis usually consists on the definition of the region of attraction around a stable equilibrium point. In the literature, the analysis of nonlinear systems is almost exclusively applied to analytical systems, where all the details are known. This paper proposes a black-box methodology to obtain the region of attraction of the equilibrium point of commercial off-the-shelf dc-dc converters working in power distribution systems. First, optimization algorithms are used to identify the parameters of a predefined structure, such that it is able to reproduce the dynamic behavior of the system. The parameters identified can be used to create a switching equivalent model that accounts for the nonlinearities produced by the switching process of the converters. Second, the bisection method is implemented to minimize the number of simulations needed to determine the region of stability accurately. The proposed methodology has been validated both with simulations and with an experimental setup.

Distributed Small-Signal Stability Conditions for Inverter-Based Unbalanced Microgrids

The proliferation of inverter-based generation and advanced sensing, controls, and communication infrastructure have facilitated the accelerated deployment of microgrids. A coordinated network of microgrids can maintain reliable power delivery to critical facilities during extreme events. Low-inertia offered by the power-electronics interfaced energy resources, however, can present significant challenges to ensuring stable operation of the microgrids. In this work, distributed small-signal stability conditions for inverter-based microgrids are developed that involve the droop-controller parameters and the network parameters (e.g. line impedances, loads). The distributed closed-form parametric stability conditions derived in this paper can be verified in a computationally efficient manner, facilitating the reliable design and operations of networks of microgrids. Dynamic phasor models have been used to capture the effects of electromagnetic transients. Numerical results are presented, along with PSCAD simulations, to validate the analytical stability conditions. Effects of design choices, such as the conductor types, and inverter sizes, on the small-signal stability of inverter-based microgrids are investigated to identify interpretable stable/unstable region estimates.

X‐parameter modelling of GaN HEMT based on neural network

Currently, S-parameters are commonly used in the design, measurement, and modelling of microwave circuits, but it is only suitable for linear small-signal conditions and not suitable for large-signal conditions. X-parameter is more accurate than the S-parameter in characterising the non-linearity of the device or the microwave circuit, and the artificial neural network has significant advantages in predicting the non-linearity of the system. Based on theoretical analysis, this article selects the GaN HEMT device CGH40010F for X-parameter modelling. Using X-parameter generator of ADS software, the X-parameters of the device were obtained. An X-parameter model based on BP neural network was built using MATLAB neural network box. The accuracy of the model was verified by comparing the test data with the model prediction data.

Input Offset Estimation of CMOS Integrated Circuits in Weak Inversion

This brief studies the current mismatch of MOS transistors operating in weak inversion region. Explicit formulas are derived from the drain-current relationship of a long-channel MOS transistor. By referring the drain-current variance to the gate terminal under the small-signal conditions, the dependence of the gate–source voltage on the design parameters and sources of mismatch can be considered. This will help designers to choose the optimum sizes and the efficient $gm/I_{\text {D}}$ ratio for current offset reduction of transistors that their mismatch affects the circuit performance, significantly. In order to confirm the accuracy of the calculated drain-current variance, the hand analysis results are compared with MATLAB simulator outputs. In addition, the input offset of a conventional folded-cascode amplifier is estimated by hand analysis, and the results are compared with SPICE simulator outputs through Monte Carlo analysis.

Codesign of Compact III–V Millimeter-Wave Wavelet Transmitters With On-Chip Antennas

Monolithically integrated millimeter-wave wavelet transmitters are presented and analyzed in this paper. Two designs that include compact dielectric resonator antennas with either inductive or self-resonant input characteristics are compared. The efficient transmitter front-end core consists of a resonant tunneling diode oscillator that is quenchable by a transistor switch. A physical diode model is used to formulate small-signal matching criteria and study codesign conditions. Fabricated transmitters provide up to 11-dBm equivalent isotropically radiated power in down to 80-ps wideband wavelets at $V$ -band carrier frequencies. Analyses of the radiated waveform envelope and time-frequency characteristics give insight in the circuit operation.

Nonlinear Optical Angle Modulation for Suppression of RF Interference

A new optical technique for suppression of electronic interference is detailed theoretically and experimentally. The method is based on operating an angle-modulated photonic link in its nonlinear regime, where Bessel functions govern the response. This novel signal-processing technique is analyzed for optical intensity and phase modulation. Experimental results demonstrate suppression of continuous-wave, pulsed, and chirped signals at levels ranging from at least 30 dB to upwards of 70 dB relative to small-signal conditions.

High-Frequency Behavioral Ring Core Inductor Model

The switching of the power semiconductors in static converters is the main source of electromagnetic interferences (EMI). To meet with electromagnetic compatibility standards, it is necessary to reduce the level of the conducted emissions. This reduction can be achieved by different techniques including the EMI filters whose design is mainly based on the use of ring core inductors. This element is a key point for designing efficient EMI filters, requiring then accurate inductor high-frequency (HF) models. Therefore, this paper deals with the development of an HF behavioral model of inductors, based on electrical equivalent circuit, for an implementation in circuit simulation software. The aim is to provide a robust and adjustable model under small-signal operating conditions for frequencies up to 100 MHz. The proposed model considers the frequency-dependent properties of the magnetic core material and also includes the parameterization of the electrical equivalent circuit elements with the number of winding turns and dimension of the magnetic core. Simulations results using the obtained inductor model are validated by impedance measurements with two types of magnetic materials: ferrite and nanocrystalline.

Modulation–Frequency Analysis of an Electrically Pumped Plasmonic Amplifier

Frequency of variations of surface plasmon intensity at the input of a plasmonic amplifier is called modulation–frequency. High modulation–frequency behavior of a Schottky junction-based plasmonic amplifier has been in the focus of this paper. Both small signal and large signal conditions have been considered. In small signal condition, an analytical solution of the rate equations of the electrons and photons has been presented which its results are in accordance with the simulation results of a harmonic balance method. For an amplifier of 100 μm length, the small signal gain has been 14.62 dB from both methods. Large signal behavior has been described by IIP2 and IIP3 in a two tone test which has been implemented by the harmonic balance method. IIP2 and IIP3 of the plasmonic amplifier of this work at 1 GHz are –21.2 and –19.95 dBm, respectively, and their values increase with frequency.

A Unified Approach to the Sensitivity and Variability Physics-Based Modeling of Semiconductor Devices Operated in Dynamic Conditions. Part II—Small-Signal and Conversion Matrix Sensitivity

We present here and in Part I a general framework for the modeling of semiconductor device variability through the physics-based analysis of the small-change sensitivity. While Part I focuses on the sensitivity of the device terminal currents in periodic large-signal (LS) operation, we extend here the analysis to the linearized device representations, i.e., to the sensitivity of the small-signal (SS) admittance matrix (SS sensitivity) and the conversion admittance matrix (SS-LS sensitivity). The proposed technique is based on the linearization of a physical device model around a nominal process parameter, and on the evaluation of relevant Green’s functions linking the parameter variations to the terminal performance. This provides, for the first time, a unified and computationally efficient simulation framework for the device physics-based sensitivity in dc, SS, LS, and SS-LS conditions. To highlight the accuracy of the approach when compared with the incremental evaluation, we discuss two case studies, concerning the SS-LS sensitivity of a class A GaAs MESFET-based amplifier and the SS sensitivity of an AlGaN/GaN microwave HEMT.

Si/SiC-based DD hetero-structure IMPATTs as MM-wave power-source: a generalized large-signal analysis

A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (∼ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 106 S/m2), susceptance (10.4 × 107 S/m2), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (> 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.

Noise figure of microwave photonic links operating under large-signal modulation and its application to optoelectronic oscillators.

The noise performance of intensity-modulation direct-detection microwave photonic links (MWPL) operating under large-signal conditions has been studied in this paper. A sinusoidal signal plus narrowband white Gaussian noise is applied at the radio frequency input of the link, and the output spectrum is derived using a nonlinear analytical approach. We show that the output SNR can be severely affected by the interaction of signal and noise due to the nonlinearity of the MWPL combined with the large input modulating signal. It is shown that the large-signal noise figure (NF) of an MWPL depends on the input power, a dependence that is not readily apparent under small-signal conditions, due to two unavoidable issues appearing in the large-signal conditions: (1) the link power gain is a function of its input power, and (2) the link power gain is not the same for the signal and noise due to the capture effect. We also have observed that if shot noise or laser relative intensity noise (RIN) is the dominant source of noise, link large-signal NF increases as the input signal power increases. We have shown that, when the MWPL is operating in the linear regime, our theoretical predictions approach the already published results on small-signal NF, which are verified by experimental data. We have shown that large-signal NF affects the noise performance of optoelectronic oscillators because they contain MWPLs at saturation.