Overview

Cellular base stations serve the function of distributing RF signals within prescribed zones. When transmitting signals to customers, the RF signal must be amplified in order to have sufficient strength to reach hand held terminals up to distances of 15 miles. The boosting of signal strength is performed using RF Power Amplifiers. In the first generation cellular networks utilizing analog technology, a dedicated RF amplifier was used for each customer for the duration of the call. Modern digital second and third generation networks utilize multi-carrier RF Power Amplifiers to obtain significant increase in voice traffic while using the same allocated broadcasting spectrum.

The linearity and efficiency of the RF Power Amplifier are paramount in determining the performance of the base station. Although class A amplifiers are well known to provide excellent linearity, their efficiency is prohibitively low for broadcasting cellular signals because of the relatively high power levels involved. Class B RF Power Amplifiers provide much better efficiency but the degradation in linearity, exhibited by high distortion products, make them unsuitable for cellular base station applications. Consequently, it is common practice to use class AB RF Power Amplifiers as a good compromise between linearity and efficiency.

Using the current generation of RF LD-MOSFETs, the linearity obtained by using the class AB RF Power Amplifier is unsatisfactory. The inter-modulation products, generated when the main RF signal is amplified, interfere with signals in adjacent channels within the cellular network violating FCC regulations. Many linearization schemes have been proposed to reduce the...