The role of an RF power amplifier (PA), as an integral part of any transmitter system, is to increase the power level of the RF signal. Power efficiency and linearity are two important parameters in the design of an RF PA. The power efficiency is improved when the active device in the PA circuit operates as a switch with minimum power dissipation. But the operation of the active device in switching mode leads to large amount of distortion in the output signal that causes spectral regrowth of the output signal spectrum and thus increases the interference with adjacent channels. In modern communication systems signals with variable envelope such as M-QAM and QPSK are used to improve the signal spectrum efficiency and to optimally exploit the channel capacity. Due to the high peak to average power ratio (PAPR) in these signals, the linearity of the PA becomes crucial. As a result, employing proper linearization technique for improving the linearity of the PA is necessary. A PA with enhanced linearity can operate near its compression point that in turn results in higher power efficiency of the amplifier. In recent years, many linearization techniques have been proposed which among them; the predistortion is relatively simple and low cost. One of the most recent predistortion methods in the baseband digital predistortion is the injection technique that the main idea behind that is to add proper extra components to the baseband signal to eliminate the distortion at the PA output. Injection techniques are consisted of different types such as second harmonic, difference frequency and third order intermodulation components. In this thesis the third order distortion components injection method has been used to linearize an RF power amplifier. The performance of the proposed technique is examined for different non-constant envelope modulations such as 16QAM, 64QAM and QPSK. For this purpose, a cascode 2.5GHz justify; MARGIN: 0cm 0cm 0pt; unicode-bidi: embed; DIRECTION: ltr" Key Words: RF power amplifier, Injection, Digital predistortion, Variable envelope modulation
