Chapter 9 - RF Power Amplifier Linearization Techniques

Abstract

One of the biggest issues related to radio frequency (RF) power amplifiers in a base station is the linearity requirement. Nonlinearities within the system components of the radio equipment cause distortion of the transmitted signal and result in the generation of signals outside the intended frequency channel or band. These unwanted distortion products are potential interfering sources to other radio users and must be reduced to a level where all radios in a system can operate satisfactorily. Frequency dependent distortion that occurs because of power amplifier circuit design and device linear power capability is termed intermodulation distortion products (IMD). The magnitude of the vector between the desired and actual point is known as error vector magnitude (EVM), which is typically reported as a percentage of the peak signal level. The signal running through the distortion path is passed through a distortion creator. Phase and magnitude adjustments are necessary to allow for the exact desired input signal for the main amplifier. Some of the most powerful digital baseband predistortion techniques use a lookup table (LUT) to produce the predistortion. While different linearization methods are being developed for applications that requires high linearity, digital predistortion techniques hold the most promise for being the most valuable in terms of simplicity, large bandwidth capability, and cost.