Based On Feedforward Technology High Linear Power Amplifier Design

As our material life level unceasing enhancement, the demand for wireless communication also become increasingly strong that led directly to the rapid development of all kinds of communication systems, the new type of linear modulation technology such as QAM, QPSK also gradually moving towards the appiication. A(?) of the RF communication systems are required to reduce their out-of-band interference. The requirement about linearity of the RF system becomes a more and more serious problem. The power amplifier is a key component of modern radio frequency systems. The linearity, efficiency, and power of the power amplifiers affect the overall wireless systems seriously. Therefore, it has the important actual meaning to linearizer of the power amplifiers.The amplifiers that used for communication systems usually work in the big signal state, which is1dB area. At this time, the power amplifiers are very close to the saturated zone, so the nonlinear distortion will become more serious, such as intermodulation distortion (IMD), harmonic distortion (THD), AM-AM, AM-PM and so on.When multi-carrier signal input, the third order intermodulation distortion is the most serious impact on the amplifier. Therefore, in order to ensure the linearity of the amplifier, the output is set far away from the point, it will certainly affect the amplifier, the specific performance is the low output power and efficiency. Therefore, the linearization of the amplifier is very meaningful and important.In this paper, the basic technical indicators, the nonlinear characteristics, and the methods of analyzing the nonlinear characteristics of power amplifiers are introduced firstly. The author introduces the basic principles of the various power amplifier linearization methods (power back-off, feedforward, feedback, pre-distortion, etc).comparisons are made of various linerization techniques. Then the author focuses on feedforward system, for the deficiencies of the traditional feedforward system, the adaptive feedforward system is introduced. As the efficiency of the traditional feedforward is quite low, so in this paper the efficiency increase technology-Doherty structure is used in the main PA of adaptive feedforward system, and the author introduces the basic working principles of Doherty amplifier.Finally, based on the feedforward technical the author uses the Agilent’s ADS software to simulate and design a feedforward power amplifier. Results are given for a series of two tones inter-modulation distortion measurements and the IM3is about-49dBc. It shows that about a19dB improvement in the inter-modulation margin can be achieved when the amplifier’s output is about46dBm, achieves the expected goal, and meets the communication requirement.