Research On Behavioral Modeling For Power Amplifiers

Power amplifiers(PA) play an extremely important part in mobile communication system. It’s inherent nonlinear characteristics make linearization and efficiency are contradictory, especially for non-constant envelope modulation signal with high peak average power ratio(PAPR) which is easy to produce nonlinear distortion for entering saturation region. Nonlinear distortion generates new spectrum component causing the out-of-band power leak and in-band spectrum distortion. In the case of spectrum resource scarcity, the problem urgently needs to be solved. Therefore it is necessary to adopt the linearization method to compensate nonlinear characteristics.In this dissertation, author makes a study on power amplifiers’ behavioral model and digital predistortion techniques. Firstly the power amplifiers’ non-linear characteristics are analyzed.Second, starting from the modeling of PA, the performance of different models are analyzed and contrasted. Two carriers WCDMA signal test is done by a VSG-VSA test platform based on a Class AB amplifier employing Freescale’s MRFS21170 H which works at 2.14 GHz. The generalized polynomial model has a better modeling capability through data analysis and modeling contrast of various models, the NMSE value reaches at-50.15 dB.Third, for the power backoff caused by high PAPR signal, this dissertation describes two clipping processing algorithms. The PAPR can be reduced 3dB while ensuring the signal EVM under certain indicators. For the predistortion algorithm validation, we use the LDMOS MHL21336 PA for dual-tone and WCDMA signal test. The experiments show that memory polynomial is the optimum predistortion model considering complexity and performance. The IMD3 of two-tone is improved 25 dB and ACPR of WCDMA signal is improved 15 dB.At last, for carrier aggregation transmitter system, a new dual-band model and a new dual-band predistortion based on iterative feedback is researched. Using Hittite company’s low-noise amplifier HMC374 for correction, the experiments show that dual-band predistortion solution has great advantages compared to traditional single-band solution. The feedback iterative solution improves the ACPR of 20 dB, compared with other methods has a 10 dB improvement.