Tuning space mapping: The state of the art

The electromagnetic (EM)‐simulator‐based tuning process for rapid microwave design can combine EM accuracy with circuit‐design speed. Our own approach is based on the intuitive engineering idea of “space mapping.” In this article, we explain the art of microwave design optimization through “tuning space mapping” procedures. We list various appropriate types of models (called “surrogates”). We demonstrate the implementation of these surrogates through a simple bandstop filter. We provide application examples using commercial simulation software. Our purpose is to help microwave engineers understand the tuning space mapping methodology and to inspire new implementations and applications. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 639–651, 2012.     

EM‐simulation‐driven design optimization of compact microwave structures using multi‐fidelity simulation models and adjoint sensitivities

Reliable design of miniaturized microwave structures requires utilization of full‐wave electromagnetic (EM) simulation models because other types of representations such as analytical or equivalent circuit models are of insufficient accuracy. This is primarily due to considerable cross‐coupling effects in tightly arranged layouts of compact circuits. Unfortunately, high computational cost of accurate EM analysis makes the dimension adjustment process challenging, particularly for traditional methods based on parameter sweeps, but also for conventional numerical optimization techniques. In this article, low‐cost simulation‐driven designs of compact structures were demonstrated using gradient search with adjoint sensitivities as well as multi‐fidelity EM simulation models. The optimization process was arranged sequentially, with the largest steps taken at the level of coarse‐discretization models. Subsequent fine tuning was realized with the models of higher fidelity. Switching between the models was realized by means of adaptively controlled termination conditions. This allowed for considerable reduction of the design cost compared with single‐level optimization. The approach was illustrated using a compact microstrip rat‐race coupler with two cases considered, that is, (i) bandwidth enhancement, and (ii) minimization of the structure size. In both cases, the optimization cost corresponded to a few high‐fidelity EM simulations of the coupler structure. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:442–448, 2016.     

EM‐based yield optimization exploiting trust‐region optimization and space mapping technology

Design centering is a design problem which looks for nominal values of circuit parameters that maximize the probability of satisfying the design specification (yield function). Direct yield optimization of electromagnetic (EM)‐based circuits is obstructed by the high expense of EM simulations required in the yield estimation process. Also, the absence of any gradient information represents an obstacle against the optimization process. In this article, a new approach for design centering and yield optimization of EM‐based circuits is introduced. In the proposed approach, the generalized space mapping (SM) technique is incorporated with a derivative‐free trust region optimization method (NEWUOA). Moreover, a variance reduction sampling technique is implemented in the yield estimation process. Two techniques suitable for the microwave circuit design centering process are introduced. The first technique exploits the surrogate developed using any circuit optimizer, for example, minimax optimizer, in the yield maximization process. While the second technique iteratively constructs and updates an SM surrogate during the yield optimization process. Our novel approach is illustrated by practical examples showing its efficiency. One of the examples is entirely designed within the sonnet em environment. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:474–484, 2015.     

Rapid design and size reduction of microwave couplers using variable‐fidelity EM‐driven optimization

In this article, fast electromagnetic (EM) simulation‐driven design optimization of compact microwave couplers is addressed. The main focus is on explicit reduction of the circuit footprint. Our methodology relies on the penalty function approach, which allows us to minimize the circuit area while ensuring equal power split between the output ports and providing a sufficient bandwidth with respect to the return loss and isolation around the operating frequency. Computational efficiency of the design process is achieved by exploiting variable‐fidelity EM simulations, local response surface approximation models, as well as suitable response correction techniques for design tuning. The technique described in this work is demonstrated using two examples of compact rat‐race couplers. The size‐reduction‐oriented designs are compared with performance‐oriented ones to illustrate available design trade‐offs. Final design solutions of the former case illustrate ～92% of miniaturization for both coupler examples (with corresponding fractional bandwidths of 16%). Alternative design solutions pertaining to the latter case show a lesser size reduction (～90% for both examples), but present a much wider bandwidths (～25% for both couplers). The overall computational cost of the design procedure corresponds to about 20 and 10 high‐fidelity coupler simulations for the first and second design example, respectively. Numerical results are also validated experimentally. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:27–35, 2016.     

Robust control of T‐S fuzzy systems with time‐varying delay using new approach

This paper aims to design a controller to robustly stabilize uncertain nonlinear systems with time‐varying delay and norm bounded uncertainties via Takagi–Sugeno (T‐S) fuzzy model. The stabilization conditions are given in the form of linear matrix inequalities using a single Lyapunov–Krasovskii functional (LKF) combining the introduction of some relaxation matrices and only one tuning parameter. In comparison with the existing techniques in the literature, the proposed approach has two major advantages. The first is the reduction of computational complexity when the number of IF‐THEN rules, r, is big. The second concerns the conservatism reduction. Several examples are given to show the effectiveness and the merits of the design procedure. Copyright © 2009 John Wiley & Sons, Ltd.     

Switching linear parameter‐varying control with improved local performance and optimized switching surfaces

This paper presents a novel approach to designing switching linear parameter‐varying (SLPV) controllers with improved local performance and an algorithm for optimizing switching surfaces to further improve the performance of the SLPV controllers. The design approach utilizes the weighted average of the local L₂‐gain bounds (representing the local performance) as the cost function to be minimized, whereas the maximum of the local L₂‐gain bounds (representing the worst‐case performance over all subsets) is bounded with a tuning parameter. The tuning parameter is useful for taking the trade‐off between the local performance and the worst‐case performance. An algorithm based on the particle swarm optimization is introduced to optimize the switching surfaces of an SLPV controller. The efficacy of the proposed SLPV controller design approach and switching surface optimization algorithm is demonstrated on both a numerical example and a physical example of air‐fuel ratio control of an automotive engine.     

Design and optimization of a tunable W‐band subharmonic cavity based Gunn diode oscillator using computer‐aided design technique

In this work, a systematic computer‐aided design technique is proposed to minimize the fabrication iteration for the design and development of W‐band subharmonic Gunn diode oscillator with wideband tunable bandwidth at W‐band. Gunn diode based single diode oscillator structure was divided into passive and active parts to facilitate the modeling of the component on appropriate simulation environment. Resonating structure and package of Gunn diode are modeled as passive circuit in high frequency structure simulator (HFSS). To satisfy the oscillator design equation, disc‐post resonating structure is tuned in HFSS and its S‐parameters are collaborated with the model of Gunn diode in advanced design system. Magnitude and phase of reflection coefficient (S11) is observed to ascertain the desired frequency of oscillation. Proper tuning of disc‐post structure is done on simulation platform, which reduces the fabrication complexity and cost as well. The measurement results validate the models designed using EM and circuit simulator. The measured maximum stable RF power without any fabrication iteration is 14.2 dBm. A tunable bandwidth of 4 GHz with power output ripple of ±1 dB is measured by using a movable backshort.     

Low‐cost multiband compact branch‐line coupler design using response features and automated EM model fidelity adjustment

Design closure of compact microwave components is a challenging problem because of significant electromagnetic (EM) cross‐couplings in densely arranged layouts. A separate issue is a large number of designable parameters resulting from replacement of conventional transmission line sections by compact microstrip resonant cells. This increases complexity of the design optimization problem and requires employment of expensive high‐fidelity EM analysis for reliable performance evaluation of the structure at hand. Consequently, neither conventional numerical optimization algorithms nor interactive approaches (e.g., experience‐driven parameters sweeps) are capable of identifying optimum designs in reasonable timeframes. Here, we discuss application of feature‐based optimization for fast design optimization of dual‐ and multiband compact couplers. On one hand, design of such components is difficult because of multiple objectives (achieving equal power split and good matching and port isolation for all frequency bands of interest). On the other hand, because of well‐defined shapes of the S‐parameter responses for this class of components, feature‐based optimization seems to be well suited to control multiple figures of interest as demonstrated in this work. Two‐level EM modeling is used for further design cost reduction. More importantly, we develop a procedure for automated determination of the low‐fidelity EM model coarseness that allows us to find the fastest possible model that still ensures sufficient correlation with its high‐fidelity counterpart, which is critical for robustness of the optimization process. Our approach is illustrated using two dual‐band compact couplers. Experimental validation is also provided.     

Design,analysis, and modeling of miniaturized multi‐band patch arrays using mushroom‐type electromagnetic band gap structures

Novel designs of miniaturized multi‐band 1 × 2 patch antenna array with electromagnetic band gap (EBG) for wideband operation are presented in this article. The proposed patch array is composed of three unequal arms fed by CPW‐to‐slotline transitions to widen the impedance bandwidth with multiple resonances. By adding two conventional mushroom‐type EBG (CMT‐EBG) structures on both sides of 100 Ω slotline transitions, the compact wideband patch array (first design) is obtained. This proposed design with CMT‐EBG includes two bands with the measured ranges (S₁₁ ≤ ?10 dB) of 6.65‐6.95 GHz (C‐band) and 8.57‐11.53 GHz (X‐band). Moreover, the proposed 1 × 2 patch array with the 3 × 3 CMT‐EBG array on the one side of the structure (second design) operates at multi‐bands with the measured ?10 dB impedance bandwidths of 5.80‐5.98 GHz, 6.25‐6.47 GHz, and 8.48‐11.52 GHz. The second design compared to the first design introduces a considerable size reduction with more resonance tuning capability. The performance of the proposed designs is analyzed based on the EBG band gap properties near the slotline transitions. These designs with the EBGs indicate prominent features like resonance tuning capability, acceptable miniaturization, and enhanced impedance bandwidth with low‐fabrication cost. In this study, an equivalent circuit model of the proposed first design with EBG is also offered to describe the properties of multi‐band operation.     

Robust H∞ deconvolution filtering for uncertain singular Markovian jump systems with time‐varying delays

The problem of H_∞ deconvolution filter design for a class of singular Markovian jump systems with time‐varying delays and parameter uncertainties is considered in this paper. By constructing a more comprehensive stochastic Lyapunov‐Krasovskii functional, novel delay‐dependent conditions are established to guarantee the filtering error system is not only stochastically admissible, but also satisfies a prescribed H_∞‐norm level for all admissible uncertainties. The desired filter parameters can be obtained by solving a set of strict linear matrix inequalities. Two examples and an electrical RLC circuit example are employed to verify the effectiveness and usefulness of the proposed methods in the paper. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal floating point multiplication processor for signal processing

The design of a floating point matrix- vector multiplication processor array for VLSI, which has an optimal area-time complexity product, is presented. This processor array is capable of performing the function (where n = 1,…, N) and can be applied in many digital signal processing applications, by simply changing the matrix coefficients stored in that array. Each N-bit mantissa, M-bit exponent (N, M) processor element of the array comprises a mantissa multiplier/adder circuit and hardware to handle the floating point control. The multiplier/adder circuit is implemented by a new optimal algorithm, which is regular, recursive and fast. Secondly, the algorithm offers a highly local and regular interconnection network, which is a fundamental requirement in VLSI circuit design methodology.     

A digitally driven pixel circuit with current compensation for AMOLED microdisplays

A novel digitally driven pixel circuit for active‐matrix organic light‐emitting diode (OLED) microdisplays is proposed and evaluated. This circuit supports both pulse width modulation and pulse density modulation digital drive approaches. Only three transistors and one capacitor are required per pixel for the proposed circuit. A current mirror is used to compensate for the pixel current changes that occur because of the degradation of the OLEDs over time. The compensation current depends on the potential of the common cathode, the properties of the current mirror, and the Width/Length (W/L) ratio of the drive transistor. The proposed digital pixel circuit also has advantages in circuit layout compared with analog pixel circuits.     

AN LMI APPROACH TO ROBUST H∞ CONTROL FOR UNCERTAIN CONTINUOUS‐TIME SYSTEMS

This paper investigates the problems of robust H∞ control for uncertain continuous‐time systems with time‐varying, norm‐bounded uncertainties in all system matrices. Necessary and sufficient conditions for the above problems are proposed. All conditions are represented in the form of linear matrix inequalities (LMIs). The robust H∞ controller can be easily designed from the solutions of the LMI conditions. Unlike earlier works, the proposed method does not involve any parameter tuning. Thus the robust H∞ optimization control problem, which has not been discussed in earlier reports, can be dealt with using this newly proposed method.     

Robust observer–controller compensator design using the loop shaping design procedure and the algebraic method

This paper investigates robust observer‐controller compensator design using Vidyasagar's structure (VS). VS has a unit matrix parameter H similar to the Q parameter for the Youla–Kucera parameterization. VS can be designed based on the left coprimeness of the central controller in the H_∞‐loop shaping design procedure (H_∞‐LSDP) and therefore can preserve the intrinsic properties of the H_∞‐LSDP. This paper introduces algebraic methods to simplify the design of H in the VS controller by solving specific algebraic equations. In particular, the algebraic design of H can achieve two things. First, a dynamic H adjusts the tracking performance and yields the integral action. Second, a dynamic H rejects the input and output sinusoidal disturbances with known frequencies. These attributes are indications of the flexibility of the proposed method since the output‐feedback controller design of the H_∞‐LSDP cannot easily deal with such conditions. This paper discusses the achieved loop and the closed‐loop behavior of the system with VS, and also gives two numerical examples. The first example shows that the proposed method results in a better design in many aspects than the resulting from H_∞‐LSDP. The second example shows the application of the proposed method to rejecting input and output step disturbances, and input and output multiple sinusoidal disturbances, for which the H_∞‐LSDP can hardly be used. Copyright © 2009 John Wiley & Sons, Ltd.     

Vt Compensated voltage‐data a‐Si TFT AMOLED pixel circuits

Abstract— Active‐matrix organic light‐emitting‐diode (AMOLED) displays are now entering the marketplace. The use of a thin‐film‐transistor (TFT) active matrix allows OLED displays to be larger in size, higher in resolutions and lower in power dissipation than is possible using a conventional passive matrix. A number of TFT active‐matrix pixel circuits have been developed for luminance control, while correcting for initial and electrically stressed TFT parameter variations. Previous circuits and driving methods are reviewed. A new driving method is presented in which the threshold‐voltage (V_t) compensation performance, along with various circuit improvements for amorphous‐silicon (a‐Si) TFT pixel circuits using voltage data, are discussed. This new driving method along with various circuit improvements is demonstrated in a state‐of‐the‐art 20‐in. a‐Si TFT AMOLED HDTV.     

H∞ Guaranteed Cost Control for LPV Systems Subject to The Gain Constraint

This paper deals with the problem of H_∞ guaranteed cost control for linear parameter varying (LPV) systems subject to the gain constraint. Specifically, our main goal is to design a controller such that the closed‐loop system is exponentially stable with the H_∞ performance index, the quadratic performance index, and the gain within the desired constraints over the entire parameter region. In order to achieve this goal, less conservative and more practical sufficient conditions for the existence of the state feedback controller are proposed by introducing the parameter dependent Lyapunov function and many extra freedom degrees in terms of linear matrix inequalities and a free parameter matrix. The parameter matrix aspecially can regulate the gain freely without the influence of the desired performance to meet the additional design criteria enhancing the practicability and the design flexibility. As a special case, relevant results are extended to design a static output feedback controller. One numerical example is used to show advantages of the proposed approach.     

L∞ Observer for Uncertain Linear Systems

In this paper, an L_∞ observer design method is proposed for linear system subject to parameter uncertainty and bounded disturbance. The proposed L_∞ observer, which satisfies a peak‐to‐peak disturbances attenuation performance, is designed to overbound the estimation error. Moreover, sufficient conditions for the design of L_∞ observer are derived and expressed in terms of linear matrix inequalities (LMIs). The novelty of the proposed method is that we develop an L_∞ observer that not only can attenuate bounded disturbance but also provides an upper bound of estimation error norm. Simulation results are presented to illustrate the effectiveness of the proposed method.     

A frame‐based EM‐simulation for design of LC oscillator with MoM capacitor banks

This article presents a simulation method for the design of a digitally controlled oscillator (DCO). Electromagnetic (EM) simulations are essential and inevitable for modern LC oscillator design. Although EM‐simulators provide high accuracy, the EM‐simulation time is very long when metal‐oxide‐metal (MoM) capacitors are present. The proposed frame‐based EM‐simulation can significantly reduce the EM‐simulation time even in the presence of MoM capacitors without influencing the accuracy. To verify the proposed method, a DCO was fabricated using a 55‐nm CMOS process. Measurements of the DCO are in good agreement with the frame‐based post‐layout simulation results. In addition, the DCO has good performances with a low power consumption of approximately 0.68 mW.     

Identification and robust control for systems with ellipsoidal parametric uncertainty by convex optimization

In this paper, sufficient conditions for robust output feedback controller design for systems with ellipsoidal parametric uncertainty are given in terms of solutions to a set of linear matrix inequalities (LMIs) Performance specifications are in terms of combined pole placement with sensitivity function shaping in the H₂ or H_∞ norm. Furthermore, an optimal input design technique for parameter estimation that is integrated into the robust control design is employed in this paper. This means that performance specifications on the closed‐loop transfer functions are translated into the requirements on the input signal spectrum. The simulation results show the effectiveness of the proposed method. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

State feedback control synthesis for networked control systems with packet dropout

This paper is concerned with the problem of H_∞ controller design for networked control systems (NCSs) with time delay and packet dropout. A combined switching and parameter uncertainty‐based method is proposed to deal with time‐varying delay. The proposed method can avoid the high computational complexity of the delay switching‐based method and introduce less conservatism than the parameter uncertainty‐based method. An active varying sampling period method is proposed to make full use of network bandwidth, and a multi‐objective optimization methodology in terms of linear matrix inequalities is used to deal with H_∞ controller design for NCSs with active varying sampling period. The simulation results illustrate the effectiveness of the proposed active varying sampling period method and the less conservatism of the combined switching and parameter uncertainty‐based method. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society