Wideband Linear RF Power Amplifier Design

As communication technologies develop, the art of power amplifier design keeps stepping forword, with requirements about the power amplifier's specifications being higher and higher. Focusing on bandwidth, efficiency, power gain,linearity and some other specifications, people have proposed different schemes to improve the amplifier's capability, in the price of complexity of the power amplifier system.Since FM synchronized broadcasting system needs to amplify several channels of FM signals at the same time, linearity level has been estimated,taking account of the specifications of real FM isolator and the national regulations about FM broadcasting as well as some engineering considerations. To satisfy the requirement of the specifications in the power amplifier, theory foundations about power amplifier have being laid ahead of designing. After that, studying the methods of design a wideband power amplifier and researching the linearization technologies of power amplifier go ahead. With the help of ADS, a simulation with BLF175's S2 P model has been made. Based on the simulation, a power amplifier is realized.In the process of design, the tradeoff between the power level and linearity is hard to achieve. The input and output matching network of BLF175 have been designed carefully. Negative feedback loop has been applied in the design, helping reach the goal of linearity. After delicately tuning, the power amplifier finally matched all the specification requirements. With bandwidth covering entire FM band, the repeater can make the engineer's work easier in the field application. The shortage of this design is its low efficiency, costing a rather big amount of power.To higher the efficiency level, a scheme to solve the problem has been proposed in the paper. After analysis and comparison of negative feedback technology, power backoff, predistortion and pre linearization technology etc., a feed forward technology using diode has been chosen. The scheme was simulated in the ADS, using MRF6VS25 L. The simulation indicated that using feedforward technology with diode can improve the efficiency while the high linearity is kept.