A Study And Design Of Pulsed Power Amplifier Based On LDMOS Transistor

Power amplifier, which is the core component of modern communication system, plays a vital role in the communication, radar, navigation system and so on. The performance of power amplifier determines the performance of the whole system above. Thus, the power amplifier with larger output power, higher efficiency, higher gain and wider bandwidth is always the much anticipated. The appearance of LDMOS transistor meets the demand of it at some extent. Power amplifier which is designed with LDMOS transistor have been widely used for its performance of better linearity, higher efficiency and lower budget, especially in the wireless communication system. And the technique of power combination primely makes up the disadvantage of which the output power of single solid device is limited, which solve the problem of high output power.Firstly, this paper introduces the basic theory and some main design index of power amplifier. In addition, the main content of design of power amplifier is summarized and the technique of power combination is simply described.Secondly, since the LDMOS transistor mainly applies to RF band and wideband power divider and combiner is obliged to the technique of wideband power combination, the technique of planar artificial transmission line(ATL) is applied to miniaturize the wideband power divider. A wideband miniaturized power divider has been proposed with two–step ATL equivalence of quarter wavelength impedance transformer by carefully analyzing ATL. Simulation results of HFSS show that the divider which operates from 0.5GHz to 1.5GHz performs well.Finally, wideband PA based on LDMOS transistor is designed in this paper. At first,a wideband power combiner with three-step quarter wavelength Chebyshev impedance transformer have been proposed with good simulation result. The input and out impedance of LDMOS transistor are gained by load-pull and source-pull method. Matching networks are designed with the conjugate match method. In addition, simulation results of wideband power divider and combiner are guided into ADS software and the whole circuit of power amplifier is fabricated and simulated. Simulation results show that the designed PA which operates from 0.5GHz to 1.4GHz achieves more than 15.5d B small signal gain and good stability. The lay-out of PA is gained according to the simulated schematic diagram and physical of PA is achieved and tested. Measurement results with pulse wave of PA show that: maximum gain of 19.8d B within the band, maximum output power of 42.7d Bm, maximum drain efficiency of 52.2%.This paper shows some guideline for designing wideband pulse power amplifier.