Based On Pre-distortion Power Amplifier Linearization Techniques

Power amplifiers are key components in wireless communication systems, whose linearity and efficiency are always the emphases. Linear modulation technology is widely adopted in the third generation mobile communication systems (e.g. WCDMA, CDMA2000). However, the distortion will be generated when the non-constant evelope signals with high peak-average-ratio (PAR) are amplified by a non-linear power amplifier. These distored signals will result in the spectrum growth and interfere with adjacent channels. If we simply back-off the input signal to achieve the linearity required for the power amplifier, the power amplifier efficiency will be very low for high PAR signals. Therefore, the linearization methods are needed to improve the linearity, thus reducing the interference and improving the efficiency.There are several PA linearization methods available which can be classified mainly as feedback, feedforward, cross cancellation and predistortion. This dissertation deals mainly with analog predistortion.The nonlinearity characteristics and parameters of power amplifers are firstly introduced. The principle of memory effect of power amplifier is analyzed. Then, several linearization methods are analyzed and compared in simple way. Meanwhile, the adavantages of analog predistortion are presented compared with other methods. The analog predistorters are specially discussed for the system. The schottky-diodes-based predistorter and the FET-based predistorter are analyzed, simulated and compared for system scheme. Meanwhile, the loop structures of analog predistortion are analyaed, including single-loop, dual-loops and multi-loops. Through the analysis and comparison, the FET-based analog predistorter with dual-loops is adopted for this design.Based on the detailed analysis of the analog predistortion system, the 16 Watts power amplifier of WCDMA repeaters is designed for validating the characteristics of the designed analog predistorter. The results indicate the ACPR is improved by 5~8dB within 60MHz bandwidth to different extents and the efficiency is over than 15%. In a word, both the linearity and the efficiency of the power amplifier are improved by this adopted perdistorter.