Alessandro Lipparini

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. >

General-purpose harmonic balance analysis of nonlinear microwave circuits under multitone excitation

A powerful software tools for the simulation of nonlinear microwave circuits under single- or multiple-frequency excitation is described. The program operates in a truly general-purpose fashion, both circuit topology and active-device equivalent circuits being arbitrarily established by the user at the data entry level. Built-in facilities based on the multidimensional Fourier transform allow a straightforward and unrestricted treatment of mixer and intermodulation problems. The capabilities of the program are illustrated by a number of practical examples. >

Computer-aided optimization of nonlinear microwave circuits with the aid of electromagnetic simulation

This paper discusses some modern trends in nonlinear (NL) microwave circuit optimization based on electromagnetic (EM) simulation. In order to keep the CPU time required for a typical design within acceptable limits, the number of expensive EM analyses must be kept under tight control. This may be obtained by resorting to a systematic implementation of some modern algorithmic concepts such as space mapping, domain partitioning, and neural-network modeling of the passive subnetwork and/or of its most critical parts. Although these techniques are well established for linear microwave circuit design coupled with EM analysis, their extension to the NL case is not trivial, and deserves a specialized treatment. Several examples are presented in order to give a feeling of the state-of-the-art of NL/EM optimization.

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.

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. >

A fully automatic domain partitioning technique for the efficient circuit-level simulation of large nonlinear microwave subsystems

The domain partitioning concept is applied to the circuit-level simulation of complex nonlinear microwave subsystems of arbitrary topology, such as entire front-ends. The subsystem is described as a whole at the data entry level, but is automatically split into the interconnection of a near-optimal number of nonlinear blocks at run time. Nonlinear analysis is based on a scattering-matrix version of Krylov-subspace harmonic balance (HB) in order to avoid Y-matrix singularities in the decomposition process. This leads to high numerical efficiency and allows an excellent tradeoff between the piecewise and nodal HB approaches to be established.

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.

Modulation-oriented harmonic balance based on Krylov-subspace methods

The paper introduces a new approach to the circuit-level analysis of nonlinear RF/microwave (sub)systems driven by digitally modulated carriers. The circuit is simulated by a sequence of modified harmonic-balance analyses based on a Krylov-subspace method driven by an inexact Newton loop. In this way, problems with many million nodal unknowns may be efficiently tackled at the workstation level.

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.

Three-dimensional computation of the thermal parameters of multiple-gate power FETs

The paper discusses a 3D numerical approach to the computation of the thermal parameters of multiple-finger semiconductor devices. The analysis relies upon an electrical analogy of the temperature field and makes use of the actual physical dimensions of all electrodes. The thermal nonlinearity of real devices is taken into account. The numerical results are supported by comparison with the results of an infrared thermal scanning of a 2 mm MESFET.