4.1 INTRODUCTION

As modern wireless systems continue to improve their performance and expand their level of functionality, the nonlinear circuit simulators experience greater and greater difficulties in handling the design of these complex and heterogeneous systems. Until very recently we could partition these systems into various manageable and cascadable blocks in which the circuit types were clearly differentiated. Now, such an attempt would be destined for failure.

The increasing capacity of modern wireless systems demands higher speeds in the baseband processing and digital control circuits, which consequently require bandwidths or switching speeds that can extend well into the microwave range. The RF front ends are benefitting from the advances in digital signal processing technologies and are incorporating more and more digital system concepts. A few years ago the traditional RF and baseband circuitry of a wireless transceiver could be readily identified, separate from the digital circuitry. These days, even the last remaining microwave module the power amplifier (PA) is being augmented by highly complex digital technology to improve the power-added efficiency, using dynamic switching dc power supplies [1], and to improve the distortion performance using digital predistortion linearizer techniques [2].

The consequence of this challenging scenario is that either circuit and system designers assume the risk of relaxing analysis accuracy, by relying on system level simulations of behavioral (or black-box) models with extremely reduced levels of detail, or they accept the need to...