Analysis And Design Of L-band Linear Power Amplifier

RF power amplifiers are the hard-core of the transmitter. The performance of the power amplifiers has already restricted the capability of the whole communication system. Especially in recent years, wireless telecommunication system is developing towards adding channel capability, multi-carrier, linear modulation, multi-level, widening the frequency and high PAR. Under the background, linear modulation techniques are widely used. Because linear modulated techniques have the characteristic of varying envelop, modulated signals with varying envelop will generate intermodulation distortion. The distortion results in errors in the magnitude and the phase of the modulated vector signal, enlarging the spectrum, disturbing the adjacent-channel, worsening the error-code-rate and so on. Thereby, linear RF power amplifier has been a hot spot of research.The dissertation discusses the design of L-band linear power amplifier. First of all, it analyses the principle of power amplifier and linearization techniques. Secondly, the RF predistortion linear three stages power amplifier that work in the 1.90GHz—2.0GHz band is designed. The amplifier is simulated to test its performance. The simulation results demonstrate that the amplifier has a good linearity and high output power.The main contents and innovation of the dissertation are as follow:①Through analyzing the theory of power amplifier, the design scheme of three stages amplifiers cascade is confirmed, in order to meet high output power and great gain of the power amplifier.②Because of unavailable large signal S parameters and different operating state& performance among the amplifiers, pre-stage and driver stage amplifiers are designed by the method of small signal S parameters, while last stage amplifier by load-pull design method. The cascade amplifier has 34.143dBm output power, greater than 30dB gain, and less than 1dB gain flatness. All of these performances are superior to design index.③In order to improve the linearity of the amplifier, the plan based on the cubic law predistortion is confirmed by comparing lots of linearization techniques. And the innovative improve of the cubic law predistorter include: 1) Using the 1800 quadrature coupler instead of T-type resistance network. 2) Inserting balance resistance network to correct the asymmetry of the antiparallel diode pair. It great improves the predistorter performances. At the same time, 3dB Wilkinson power dividers/combiners, attenuator and analog phase shifter are also designed. The result shows that, when the output power of the amplifier is 35dBm, the IMD3 can be less than -60dBc by the effect of the predistortion system. The predistortion system can improve IM3 27dBc. It improves the power amplifier linearity effectively.