The Research Of Linearization Technology On Doherty Power Amplifiers

With the development of wireless communication technology, radio frequency(RF) power amplifiers(PAs) are required of high data rates, digital, broadband and high frequency. Because of the simple configuration, easy to implement, low cost, and less effect on the linearity of system, Doherty power amplifiers have become a hot topic for the amplifier designers. To improve the quality of communication, linearization technique has caused the industry take seriously. So, it is a meaningful issue for the linearization of Doherty PAs.The main content of this thesis is to analysis and realize the digital pre-distortion(DPD) for Doherty PA. At the same time, we propose an effective scheme to compensate the nonlinearity and memory effect of the PA. The research is based on a Doherty PA working at 1.7~2.6GHz. Firstly, testing the Doherty PA to obtain its nonlinear distortion character. Then we discuss the algorithm and configuration for the DPD. After that, an effective way to solve the distortion of the Doherty PA is proposed, and we named it the multi-step iterative digital pre-distortion based on vector piecewise decomposition. Compared with the traditional method, this way proposed in this thesis always has better experiment results regardless of how to model of this PA. Vector piecewise decomposition can fit the PA’s behavior character accurately and the configuration based on multi-step iterative can get more precise data to model PA. The DPD with this method can do better in compensating the nonlinearity of PA, especially for Doherty PA.To verify the feasibility of the proposed method, the author set up experimental platform with VSG and VSA. After analyzing the distortion from the test bed, some signal processing techniques are applied to improve the performance of the test system. The experimental results show that the ACPR of the output signal is-34 d Bc~-28 d Bc when testing with WCDMA signal. But the proposed method can improve the ACPR 16.82 d B at least, and the ACPR of the output signal can be dropped below-50 d Bc. Compared with the traditional method, the ACPR has been improved about 4d B.