On the combined response of clipper‐amplifier cascade for PAPR reduction of OFDM signals

Orthogonal frequency division multiplexed (OFDM) signals have high peak‐to‐average power ratio (PAPR) which results in excessive nonlinear distortion when amplified by power amplifiers (PA) and hence, reduction in system signal‐to‐noise (SNR) and spectral efficiency. Clipping has been one of the most popular and low‐cost technique for reducing the PAPR of OFDM signals. The overall spectral efficiency of an OFDM system that involves clipping depends on the combined response of the cascade of clipper‐amplifier and not only on the response of the clipper. In this article, the performance of clipped and nonlinearly amplified OFDM signals is studied. The combined response of a clipper‐amplifier cascade is obtained using an orthogonalized behavioral model which enables in‐band and out‐of‐band nonlinear distortions to be accurately predicted without using the Gaussian assumption of signal statistics. Furthermore, different clipping characteristics are studied where it is shown that the overall nonlinear distortion, and hence the overall SNR, is highly dependent on the type of clipping characteristics and the clipping ratio. Simulation results are verified by Simulink measurement model which uses measured amplifier characteristics in a “General Amplifier” block. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:656–664, 2014.     

A straightforward design technique for narrowband multi‐stage low‐noise amplifiers with I/O conjugate match

Low‐noise amplifier (LNA) designers often struggle to simultaneously satisfy gain, noise, stability, and I/O matching requirements. In this article, a novel design technique, tailored for two‐stage low‐noise amplifiers, is presented. The proposed design method is completely deterministic and exploits inductive source degeneration to obtain a two‐stage LNA featuring perfect input and output match together with low noise figure (NF) and a pre‐determined gain, including stability analysis. A novel flowchart is provided together with the corresponding design chart that contains gain, matching, and stability information, therefore addressing all key figures‐of‐merit of a linear amplifier. The design chart is easily implementable in commercial Electronic Design Automation software, to aid designers in the difficult task of selecting the appropriate source degeneration inductor value. The noise performance, on the other hand, is the best possible since the matching networks are designed to provide the input of the two Field Effect Transistors with the optimum termination for noise. The design method is validated with two separate test vehicles operating respectively at Ka‐band (26.5‐31.5 GHz) and K‐band (20.0‐24.0 GHz). The realized Monolithic Microwave Integrated Circuits exhibit 18 dB gain for both versions, NF of 1.5 and 1.2 dB, respectively for the Ka‐band and K‐band version. Input and output matching are typically better than 12 and 15 dB.     

Effects of low‐frequency drain termination and injection on nonlinear amplifier performances

Low‐frequency parameters have important effects on the nonlinear performances of power amplifiers. Injection at the output of a low‐frequency‐voltage device, following the signal envelope, is proposed. Two‐tone simulations, measurements using the principle of a low‐frequency active load‐pull system, and implementation of the technique are presented. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Frequency‐dependent behavioral‐model‐based nonlinear analysis and design of a low‐profile transmit active phased array antenna

Design and behavioral‐model‐based nonlinear analysis of a 3‐GHz active‐phased array antenna (APAA) are presented. Four nonlinear power amplifiers are employed in the output ports of the feeding network (FN) and analyzed based on a 5‐order polynomial model with frequency‐dependent coefficients. The FN is based on 4‐port new Gysel power dividers and combiners arranged in such a way to feed the array with Gaussian‐like amplitude and in‐phase distributions. Beam steering capability is obtained in 2 directions by a new technique including a phase shifter and an amplitude controller (AC). The features result in a low‐profile APAA whose design and fabrication complexity and cost are reduced. Single and 2‐tone power tests are performed to develop analytical expressions in nonlinear region for array factor as a function of the model, FN and the phase and ACs. A similar system with frequency‐independent model is also analyzed for comparison in terms of scan loss, beamwidth, side‐lobe level, beam position, and gain. A microstrip array antenna including the power amplifiers, pre‐amplifiers, AC, delay‐line‐based phase shifters and Gysels is fabricated and measured. The simulation results at the single and dual tones and the intermodulation products are presented which have a good agreement with the measurements.     

Extended theoretical analysis method on the performance of high‐efficiency power amplifiers by solving nonlinear waveform determination process

Classical analysis of high‐efficiency power amplifiers (PA) is usually based on ideal voltage and current waveforms limited to optimal states. A transistor's nonlinear I‐V curves are not usually taken into consideration because of their complexity. With a computer‐aided calculation tool developed herein, a direct waveform determination method involving nonlinear I‐V curves is realized. Using this approach and simplified I‐V curves, a PA's extended theoretical performance from the back‐off region to saturation can be investigated. If using practical dc I‐V curves, this method can also give good performance analysis results even at microwave frequency. Numerical examples of different PA settings are given to verify this method. Nonlinear calculations, harmonic balance simulations, and measurements of a class‐E PA operating at 3 GHz are shown with consistent results to prove this waveform determination method.     

基于Duffing振子的随机共振研究

随机共振是非线性系统中的一种动力学现象.本文对基于Duffing振子的随机共振现象进行研究,研究了Duffing系统噪声强度与信噪比的关系,不同频率正弦信号与信噪比的关系,以及阻尼比参数对随机共振的影响.研究结果表明,Duffing系统的阻尼比参数对随机共振的影响非常重要,阻尼比参数与输出信号信噪比之间存在着一种复杂的非线性关系,并且会随着Duffing系统参数的改变而变化.     

Output feedback control of a class of feedforward nonlinear systems in the presence of sensor noise

We propose an output feedback controller for a class of feedforward nonlinear systems under sensor noise. The sensor noise is any signal whose DC component is finite, which covers not only deterministic signals but also random signals including many practical noises. We introduce a notion of virtual state, then propose a measurement output feedback controller that utilizes a gain scaling factor. The gain scaling factor is commonly employed by the observer and controller. Through analysis, we show that all system states and output remain to be bounded in the presence of sensor noise, and the bound of states except output can be made arbitrarily small. Moreover, if the DC component of sensor noise is zero, the ultimate bound of the states and output can be made arbitrarily small by increasing the gain scaling factor in the presence of sensor noise. Copyright © 2013 John Wiley & Sons, Ltd.     

Output‐feedback control of a class of stochastic nonlinear systems with linearly bounded unmeasurable states

In this paper, the problems of stochastic disturbance attenuation and asymptotic stabilization via output feedback are investigated for a class of stochastic nonlinear systems with linearly bounded unmeasurable states. For the first problem, under the condition that the stochastic inverse dynamics are generalized stochastic input‐to‐state stable, a linear output‐feedback controller is explicitly constructed to make the closed‐loop system noise‐to‐state stable. For the second problem, under the conditions that the stochastic inverse dynamics are stochastic input‐to‐state stable and the intensity of noise is known to be a unit matrix, a linear output‐feedback controller is explicitly constructed to make the closed‐loop system globally asymptotically stable in probability. Using a feedback domination design method, we construct these two controllers in a unified way. Copyright © 2007 John Wiley & Sons, Ltd.     

p‐Times differentiable unbounded functions for robust control of uncertain switched nonlinear systems with tracking constraints

This paper investigates the problem of robust controller design for output‐constrained and state‐constrained uncertain switched nonlinear systems. By using the idea of p‐times differentiable unbounded functions and the backstepping technique, a constructive method is proposed to design effective controllers such that the output of a class of uncertain switched nonlinear systems in lower triangular form can asymptotically track a constant reference signal without violation of the output tracking error constraint. Furthermore, the explored method is applied to the state‐constrained robust stabilization problem for a class of general uncertain switched nonlinear systems. Finally, a simulation example is provided to demonstrate the effectiveness of the developed results. Copyright © 2014 John Wiley & Sons, Ltd.     

New noise‐to‐state stability and instability criteria for random nonlinear systems

This paper investigates the noise‐to‐state stability and instability criteria for random nonlinear affine systems. Firstly, some new noise‐to‐state stability theorems, which weaken the sufficient conditions in the existing stability criteria on random nonlinear systems, are given by means of the uniformly asymptotically stable function. Secondly, the noise‐to‐state instability definitions are introduced and the sufficient conditions of noise‐to‐state instability are provided based on a new established lemma and the uniformly asymptotically stable function. Finally, some examples show the feasibility of theoretical findings.     

Differentially private nonlinear observer design using contraction analysis

Real‐time information processing applications such as those enabling a more intelligent infrastructure are increasingly focused on analyzing privacy‐sensitive data obtained from individuals. To produce accurate statistics about the habits of a population of users of a system, this data might need to be processed through model‐based estimators. Moreover, models of population dynamics, originating for example from epidemiology or the social sciences, are often necessarily nonlinear. Motivated by these trends, this paper presents an approach to design nonlinear privacy‐preserving model‐based observers, relying on additive input or output noise to give differential privacy guarantees to the individuals providing the input data. For the case of output perturbation, contraction analysis allows us to design convergent observers as well as set the level of privacy‐preserving noise appropriately. Two examples illustrate the proposed approach: estimating the edge formation probabilities in a social network using a dynamic stochastic block model, and syndromic surveillance relying on an epidemiological model.     

Improvements and analysis of nonlinear parallel behavioral models

This article performs an analysis of current limitations regarding the extraction of parallel behavioral models to reproduce the power amplifier (PA) nonlinear behavior and its dynamics. To overcome these limitations, a general preprocessing block that clearly improves the identification capabilities shown by classical parallel structures is proposed. It follows the principle of separating both static and dynamic nonlinear behavior of the PA to obtain a better identification performance. A comparison with common parallel configurations using linear estimation is performed, to highlight the benefits of using the preprocessing structure. Furthermore, a new nonlinear parallel structure using sub‐band filtering techniques is also proposed. For the models extraction and comparison, four types of noise‐free simulated data presenting different levels of nonlinearities and memory, as well as a measured signal obtained from a laboratory amplifier have been considered. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Global asymptotic tracking for nonminimum‐phase nonlinear systems in output feedback form

The problem of global asymptotic tracking by output feedback is studied for a class of nonminimum‐phase nonlinear systems in output feedback form. It is proved that the problem is solvable by an n‐dimensional output feedback controller under the two conditions: (a) the nonminimum‐phase nonlinear system can be rendered minimum‐phase by a virtual output; and (b) the internal dynamics of the nonlinear system driven by a desired signal and its derivatives has a bounded solution trajectory. With the help of a new coordinate transformation, a constructive method is presented for the design of a dynamic output tracking controller. An example is given to validate the proposed output feedback tracking control scheme.     

A W‐band RF‐MEMS switched LNA in a 70 nm mHEMT process

This work presents a monolithic integrated reconfigurable active circuit consisting of a W‐band RF micro‐electro‐mechanical‐systems (MEMS) Dicke switch network and a wideband low‐noise amplifier (LNA) realized in a 70 nm gallium arsenide (GaAs) metamorphic high electron mobility transistor process technology. The RF‐MEMS LNA has a measured gain of 10.2–15.6 dB and 1.3–8.2 dB at 79–96 GHz when the Dicke switch is switched ON and OFF, respectively. Compared with the three‐stage LNA used in this design the measured in‐band noise figure (NF) of MEMS switched LNA is minimum 1.6 dB higher. To the authors’ knowledge, the experimental results represent a first time demonstration of a W‐band MEMS switched LNA monolithic microwave integrated circuit (MMIC) in a GaAs foundry process with a minimum NF of 5 dB. The proposed novel integration of such MEMS switched MMICs can enable more cost‐effective ways to realize high‐performance single‐chip mm‐wave reconfigurable radiometer front‐ends for space and security applications, for example. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:639–646, 2015.     

An open‐loop digital predistorter based on memory polynomial inverses for linearization of RF power amplifier

Digital Predistorter is a cost‐effective solution to compensate for the nonlinear distortions appearing in the RF power amplifiers (PAs). The indirect learning scheme is widely implemented because of its flexibility to eliminate the requirement for building a closed‐loop real time system, which dramatically reduces the complexity for measurement setup. However, such scheme is sensitive to the measurement noise that may cause biasing in the coefficients estimation. To minimize the influence of measurement noise and simultaneously enable the open‐loop implementation, we propose a predistortion technique that first model the PA and then generates predistorted signal iteratively through a feedback configured structure to avoid using the noisy signal when performing the inverse model estimation. Unlike the indirect learning which estimates the postinverse of the PA, our predistortion is based on the preinverse of the PA. Both simulations and measurements show that utilizing the proposed predistortion can obtain adjacent channel power ratio (ACPR) improvement in wideband code division multiple access (WCDMA) signal test compared with the conventional memory polynomial predistortion based on indirect learning. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

PVT‐compensated low‐voltage and low‐power CMOS LNA for IoT applications

In this paper, a low‐noise amplifier (LNA) with process, voltage, and temperature (PVT) compensation for low power dissipation applications is designed. When supply voltage and LNA bias are close to the subthreshold, voltage has significant impact on power reduction. At this voltage level, the gain is reduced and various circuit parameters become highly sensitive to PVT variations. In the proposed LNA circuit, in order to enhance efficiency at low supply voltage, the cascade technique with g_m boosting is used. To improve circuit performance when in the subthreshold area, the forward body bias technique is used. Also, a new PVT compensator is suggested to reduce sensitivity of different circuit's parameters to PVT changes. The suggested PVT compensator employs a current reference circuit with constant output regarding temperature and voltage variations. This circuit produces a constant current by subtracting two proportional to absolute temperature currents. At a supply voltage of 0.35 V, the total power consumption is 585 μW. In different process corners, in the proposed LNA with PVT compensator, gain and noise figure (NF) variations are reduced 10.3 and 4.6 times, respectively, compared to a conventional LNA with constant bias. With a 20% deviation in the supply voltage, the gain and noise NF variations decrease 6.5 and 34 times, respectively.     

微伏信号放大系统设计

介绍一种微伏信号放大系统设计方法,该系统主要由放大、滤波以及隔离输出三部分组成。输入部分采用共模抑制比很高小信号放大器;滤波电路由一个四阶低通滤波和一个二阶高通滤波组成的带通滤波器以及陷波器组成,可有效滤除噪声及干扰;中间和末级放大采用常见的同相比例放大器进行信号的进一步放大;隔离输出部分采用线性度很高的光电隔离电路。总体电路放大增益高,对10μV以上信号放大效果良好,可很好地满足后级采集电路的信号输入要求。     

Computer‐aided analysis of near‐carrier noise in RF–microwave frequency converters

The paper presents for the first time a rigorous nonlinear analysis of near‐carrier noise in a frequency converter consisting of a noisy nonlinear circuit driven by noisy sinusoidal source(s). The problem being tackled is the evaluation of the phase and amplitude noise of the up‐ or down‐converted signal starting from the knowledge of the circuit topology, of noisy models for the nonlinear devices, and of the statistical properties of the noisy forcing source(s). Two mixer models of different complexities are treated in depth, i.e., the case of an ideally buffered local oscillator (LO), and the case of a real LO fully described by its circuit topology. In both cases a correct evaluation of the near‐carrier noise is shown to require a perturbative analysis of the noiseless quasiperiodic steady state generated by the intermodulation of the local oscillation with the RF signal. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 449–467, 1999     

微伏信号放大系统设计

介绍一种微伏信号放大系统设计方法，该系统主要由放大、滤波以及隔离输出三部分组成。输入部分采用共模抑制比很高小信号放大器；滤波电路由一个四阶低通滤波和一个二阶高通滤波组成的带通滤波器以及陷波器组成，可有效滤除噪声及干扰；中间和末级放大采用常见的同相比例放大器进行信号的进一步放大；隔离输出部分采用线性度很高的光电隔离电路。总体电路放大增益高，对10μV以上信号放大效果良好，可很好地满足后级采集电路的信号输入要求。