| With the rapid development of wireless communication technology, more demands are raisedfor power amplifier, such as wide bandwidth, high efficiency, high linearity, high output power andhigh gain. Performance greatly affects the communication quality. A30MHz-108MHz broadbandpower amplifier unite was designed. Because of wide bandwidth, high gain and high efficiency arecritical issues of power amplifiers. Theory involved are described in this paper, such as the basicstructure of power amplifier, broadband matching technology, common linearization technique,theory of the filter, the design scheme of power amplifier unite, standing wave protection circuit andthe main performance index. And we paid attention to some problems during experiments. specifictest methods was described.Finally,We complete the specific design of the power amplifier uniteand the test results are also given.Due to high gain needed, we adopted two-stage amplifications. Philips’ power amplifier chipBLF404was chosen in the driver stage and BLF244in the final stage. In order to improveefficiency, two stage amplifiers are used in a class AB. Comparing the advantages anddisadvantages of linearization techniques and achieving complexity, we adopted negative feedbacktechnology to improve linearity. We balanced linearity and efficiency reasonably by using thebalanced structure of MOS tube in broadband design. The balanced and unbalanced structureconvertion is realized through a transmission line transformer. By ADS software, the input andoutput matching circuit is designed. By S-parameters, the gain, stability and other performanceindex are analyzed. We finally completed each level simulation.In order to filter out harmonic and noise, The power amplifier is followed by4segment lowpass filters. Considering performance demands of amplifier unite and output performance ofamplifier, insertion loss in-band is less than2dB, etc.. Each was passive circuit design.ADSsimulation software is used for simulations and optimizings of the filters.According to PCB layout, lining and EMC principles, Protel is used in the PCB layout designof power amplifier unite. Finally, material object was designed. The schemes are described indetails and The test datum of module and whole system are given. Some theoretical knowledges indesign are demonstrated after debugging. Design process are analyzed in detail.The test resultsshow that, in the whole frequency range, the output power is37dBm, and efficiency is above46%;When the dual signal has a100KHz interval, third-order inter modulation is above33dBc. Addingfilter to amplifier, the second harmonic suppression is more than52dBc, and the third harmonicsuppression is more than60dBc. Other technical indicators have obtained ideal results. The design of the power amplifier meets design criterion.Efficiency, flatness and linearity are demonstratedrather good. |
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