C. Cecchetti

State-of-the-art harmonic-balance simulation of forced nonlinear microwave circuits by the piecewise technique

The theoretical foundations and the numerical performance of an advanced nonlinear circuit simulator based on the piecewise harmonic-balance (HB) technique are discussed. The exact computation of the Jacobian matrix for Newton-iteration based HB simulation and the related conversion-matrix technique for fast mixer analysis are formulated in a general form. Convergence problems at high drive levels are solved by a parametric formulation of the device models coupled with an advanced norm-reducing iteration. A physics-based approximation is shown to allow the HB equations to be effectively decoupled in many practical cases, bringing large-sized jobs, such as pulsed-RF analysis, within the reach of ordinary workstations. The exact Jacobian is used in conjunction with an exact formula for the gradient of the objective function, to implement an efficient broadband nonlinear circuit optimization capability. Examples are presented. >

Computer-aided noise analysis of MESFET and HEMT mixers

A numerical approach to the noise analysis of MESFET and HEMT mixers of arbitrary topology is discussed. A qualitative picture of the complex physical mechanisms responsible for the generation of the intermediate frequency (IF) noise is outlined, and the corresponding computational algorithms are presented. The derivation of a noisy nonlinear model for the microwave FET is addressed, and it is shown that a satisfactory solution to this problem can be obtained by combining a conventional time-domain model with standard noise information. The method has been implemented in a computer program designed to work in conjunction with an existing general-purpose harmonic-balance simulator. An application is described in detail to demonstrate the excellent performance of this software tool. >

Numerical optimization of broadband nonlinear microwave circuits

The implementation of extensive optimization capabilities in a general-purpose harmonic-balance simulator is described. Two different optimizers suitable for autonomous and forced circuits, respectively, are discussed in detail, and their merits and limitations are compared. The efficient numerical optimization of nonlinear microwave circuits specified over a finite frequency band is demonstrated. An example is given, showing that the procedure is very efficient, thus opening the way to the straightforward design of some modern monolithic microwave integrated circuit (MMIC) devices such as multioctave distributed mixers and power amplifiers.<<ETX>>

Fast and robust inexact Newton approach to the harmonic-balance analysis of nonlinear microwave circuits

The authors discuss a novel approach to nonlinear microwave circuit simulation by the harmonic-balance (HE) technique. The nonlinear system is solved by an inexact Newton method, and the GMRES iteration is used at each step to find a suitable inexact Newton update. The peculiar structure of the Jacobian matrix allows the basis vectors of the Krylov subspace to be computed mostly by the FFT. The resulting simulation tool is fast and robust, and outperforms conventional HE techniques when applied to large-size nonlinear analysis problems.

A General-Purpose Program for the Analysis of Nonlinear Microwave Circuits Under Multitone Excitation by Multidimensional Fourier Transform

The paper introduces a user-oriented program providing a general-purpose solution to multitone excitation problems of nonlinear microwave circuits. The use of the harmonic-balance technique coupled to multidimensional Fourier transform eliminates any restriction on the possible combinations of fundamental frequencies and results in a frequency-independent simulation cost. The program offers built-in specialized facilities for the special cases of mixer and intermodulation analysis.

Harmonic-balance optimization of microwave oscillators for electrical performance, steady-state stability, and near-carrier phase noise

The numerical optimization of microwave oscillators including specifications on steady-state stability and near-carrier phase noise is demonstrated for the first time. The approach relies on the harmonic-balance technique and is fully general-purpose. Oscillators designed without such constraints may be strongly suboptimal from the noise viewpoint with no substantial improvement of electrical performance.<<ETX>>

Simultaneous thermal and electrical analysis of nonlinear microwave circuits

A software tool for the simultaneous determination of the thermal and electrical steady-state regimes of nonlinear microwave circuits containing temperature-dependent active devices is introduced. The analysis technique is an extension of the classic piecewise harmonic-balance method, and is quite general-purpose. It can be applied to networks operating under multiple-tone excitation, including pulsed-RF regimes. The simulation problem is reduced to a nonlinear algebraic system whose unknowns are electrical and thermal state-variable harmonics. Advanced numerical techniques are used to overcome the difficulties arising from the high degree of nonlinearity and from the very large number of unknowns of the numerical problem. The program incorporates a facility for the evaluation of the thermal constants of multiple finger planar devices starting from geometrical data. >

Numerical optimization of microwave oscillators and VCOs

A novel harmonic-balance (HB) optimization technique for single-frequency oscillators and broadband voltage controlled oscillators (VCOs) is introduced. The objective function is evaluated by a Newton-iteration-based HB analysis, and an exact algorithm for the computation of the gradient is implemented. The optimizable performance in the VCO case includes the linearity of the tuning characteristic. An example of application of the proposed method is presented.<<ETX>>

Frequency Conversion in General Nonlinear Multiport Devices

The conversion matrix of an arbitrary nonlinear multiport, operated in steady-state periodic regime, is defined and computed by a general straightforward approach. The results can be used to analyze the steady state for stability and generation of spurious, and to give a systematic solution to the generalized mixer problem. Some typical examples of application are presented and discussed.

Fast prediction of the performance of wireless links by simulation-trained neural networks

The paper illustrates a technique for fast and accurate prediction of the performance of wireless links while taking into account the nonlinear distortions in the RF/microwave sections. Each simulation is partly carried out by modulation-oriented harmonic balance, and the results are used to generate a specialized neural network which efficiently performs the major part of the task. High accuracy is obtained, and dynamic behavior of wideband modulating signals can easily be included.