7.1 INTRODUCTION

Over the past two decades, advances in nonlinear simulation techniques have enabled the efficient numerical solution of problems important in the design of new microwave and RF integrated circuits. Some key advances have been the development of modern harmonic balance simulators, and more recently, of transient envelope simulators. Harmonic balance [1] allows the efficient simulation of large-signal steady-state circuits in the frequency domain, achieving great efficiency gains over traditional time-domain simulators like SPICE for steady-state problems with large numbers of frequency components. Such multisine problems are often found in the design of microwave circuits. The recent availability of transient envelope simulators [2, 3] has allowed the efficient simulation of problems for which the typical spectra can be represented by a set of several discrete tones and time-dependent modulation around them. This modulation is a common characteristic of modern communication circuits.

Even so, modern microwave and wireless communications systems are nowadays too complex to permit the complete simulation of the nonlinear behavior at the transistor level of description. The combination of a large number of nonlinear devices the transistors in the circuits and a complex signal modulation mean that the number of nonlinear equations that must be solved at each iteration step in the simulation is prohibitively large. The memory requirements alone discourage all but the most determined (or...