| With the development of wireless communication technology, the requrements of spetrum utilization and data transfer rate were increasingly high, which lead to many complicated modulation modes(as WCDMA, OFDM), the signal’s Peak-to-Average Power Ratio of these modulation modes is usurally 6-12 d B. For better signal quality, back-off was used to improve the linearity. However, back-off reduced the amplifier efficiency, which caused high power loss and severe heat issues, therefore high Peak-to-Average Power Ratio signals needed higher amplifier efficiency.This issue focus on the problem above, summarized and analyzed kinds of high efficiency power amplifier. Doherty amplifier was widely used on the basis of simple structure, easily implimented, high efficiency and easy to combine with the conventional linearization technique.Then Doherty amplifier’s working method and active load modulation impliment were selectively analized, and AB-C class Doherty amplifier as research object, deduced Doherty amplifier’s characteristics and efficiency.In this paper, AB-C class was the basic structure, applied freescale LDMOS device MRF8S9102 N transistor, utilized ADS software to simulation and design, and debugged and tested finally. Analysed the influence of the delay line and auxiliary amplifier gate voltage for Doherty amplifier. A Doherty amplifier suitable for CDMA system was implimented, whose working frequency was 880 MHz, the output power is more than 45 dBm, the efficiency is greater than 40%, the power gain is greater than 15 dB, three order intermodulation is less than-26 dBc. |
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