A Novel Load and Source Tuning System for Balanced and Unbalanced WCDMA Power Amplifiers

The recent large-scale introduction of spread spectrum techniques for personal communications (PCS) in the USA, Japan and Europe is an enormous stimulus for innovation [1]. The varieties and dynamics of spread spectrum based systems such as: frequency hopping, time domain hopping, multi carrier CDMA and the direct sequence spread spectrum technique have complicated and altered the design paradigm [2]. This diversity has confronted designers with the non-trivial task of rapidly responding to the vagaries of the mobile communication business. Complex digital communications signals with broad bandwidth, varying rectified envelope power and a relatively large crest factor have rendered inadequate traditional verification methods based on the use of CW signals [3]. The attendant demands on cost, efficiency and system constraints and the growing use of balanced circuits in broadband wireless applications has increased the need for accurate modeling and characterization of the nonlinear behavior of active devices. Since the input and output terminations of these devices dictate their large signal behavior, complete device characterization including the determination of constant output power contours requires the use of source and load tuning. Furthermore, proper verification entails simulation and test at both software and hardware levels using the same stimuli [2]. This paper offers a comprehensive, automatic tuner based solution suitable for balanced and unbalanced devices driven by WCDMA based signals.