Study On The Linearization Of Radio Frequency Power Amplifier Based On Predistortion Technology

With the rapid development of wireless communication the linear modulation methods are widely used. Since the envelope of modulated signal fluctuates,these methods generate unwanted intermodulation distortion (IMD) products in a nonlinear Radio Frequency (RF) Power Amplifier (PA). So it is necessary to use linearization technique to reduce the adjacent channel interference (ACI). Predistortion is a widely used linearization technique because of its unique advantage,and the research of predistorting linearizer is becoming the hot research field. The main studying of this dissertation is about cubic analog predistorer,digital predistortion linearizer based on Look-up Table (LUT) technology and feedforward-predistortion linearization system. The original work and valuable results in this dissertation are as follows.1.A novel third-order distortion generator which can suppress the residual second-order intermodulation distortion (IMD2) is presented. This new distortion generator uses a feedback circuit network composed of diodes and resistors to balance the residual IMD2 component. A theoretical study is carried out and basic feature of this generator is analyzed. Compared with common used distortion generator,the cubic predistorters that use this kind of novel generator have a better IMD2 suppression performance and can adaptive the different matching performance of diode pairs. The simulation results show the cubic predistorting linearization system can achieve 46dB third-order intermodulation distortion (IMD3) suppression.2.The indexing method of LUT predistorting linearization system is studied in this dissertation. First the companding function that can realize optimum table spacing is derived,and a new nonlinear indexing method based on LUT technique is putting forward. The advantage of this new indexing method is studied and the practical implementation is present. At last an improved adaptive scheme of the new method is considered. Simulation study shows 2.5dB IMD3 suppression can be improved compared with common polar LUTpredistorting system that has same 64 LUT entries. Besides the studying of indexing technique,the adaptive refresh algorithms of LUT are studied and a new algorithm is obtained.3.A RF PA linearziation system that combines RF predistorting technique and feedforward technique is present. Contrasted with basic feedforward system,the main improvement of new system is the signal feature of error signal path. In new system the error PA can also amplify the original signal,so the performance of whole amplifier system increases. Since RF predistorters used in the new system,the linearity and power efficiency can be enhanced. Considering the nonlinear difference of the gain and phase characteristic in Solid State Power Amplifier (SSPA),a parallel but imbalanced predistorting adjuster is used and the hardware cost can be reduced. The simulation result shows this new kind of linearization system can get 63dB IMD3 suppression.