Linearization Techniques for RF Power Amplifiers

Abstract

For both spectrally efficient transmission and robustly combating multipath fading transmission, orthogonal frequency division multiplexing (OFDM) with high-order modulation formats of M-ary QAM adopted by many wireless standards are widely used in modern wireless communication systems. These kinds of modulated signals naturally behave with non-constant envelope characteristics and have a very high peak-to-average power ratio (PAPR), which demands that radio frequency (RF) transmitter power amplifiers (PAs) operate with high back-off power from their P1dB point to perform linearly, resulting, however, in very low power or energy efficiency. If its back-off power is not high enough, or if it operates close to its P1dB point, a PA causes spectral regrowth, which leads to adjacent channel interference. Meanwhile, it also causes in-band signal distortion, which degrades the bit error rate (BER) performance. It is commonly known that achieving spectrum efficiency is controversial to having energy efficiency. To obtain high energy efficiency to reduce severe distortion caused by PA non-linearity, pre-distortion or linearization techniques have been widely used in applications. Generally, it is classified as digital baseband or RF analog pre-distortion, according to the operating domain.