| People’s increasing demand for wireless Internet access promotes the rapid development of modern mobile communications technology. Communication technology is the basis of today’s social development. After several years of development, many different new techniques are proposed to improve the performances of PA. In these techniques, the structure of Doherty power amplifier is one of very good techniques. The advantage of the structure of Doherty power amplifier is to improve the performance of PA’s linearity in a simple structure, which can also ensure high efficiency. This structure can meet the demand of high peak to average power ratio(PAPR) of communication technology. Transfering large data need a wide Communication system. 4G, even the future 5G, need high data transmission, so broadband power amplifier design is a hot research topic.To meet the high performances of communication technology, Doherty amplifier is further improved to meet these requirements in this thesis. For different needs of power amplifiers and different requirements for the performances of power amplifier, this thesis designed a two power-modulated Doherty power amplifier and a wideband high efficiency Doherty power amplifier.In order to further improve efficiency of PA, a new method of envelope tracing(ET) technology combining Doherty technology is proposed. This method is to improve efficiency of Doherty power amplifier at low input. At low input power, only the main amplifier of Doherty power amplifier work, so envelope tracing technology can change the drain voltage of the main amplifier to improve efficiency. A Doherty power amplifier with a modulation main amplifier power is designed in this thesis, with operating frequency range from 2110 MHz to 2170 MHz, Output power 43 dBm and efficiency higher than 50%. Linearity better than-30 dBc, efficiency compared to the conventional Doherty amplifier by an average of about 9% at low input. If the efficiency of high amplifier power increased by 9%, it can save a lot of energy, so it is worth researching.In order to meet the broadband requirement of mobile communication technology, a broadband Doherty power amplifier with high-efficiency is designed in this thesis. Limitation of design of broadband Doherty amplifier is λ/4 impedance conversion line. Theoretical analysis bandwidth of broadband Doherty power amplifier has a certain relationship with impedance conversion ratio of λ/4 impedance conversion line. Impedance transformation ratio is inversely proportional to the bandwidth of λ/4 impedance conversion line. Therefore, a new structure is proposed to reduce impedance conversion ratio so that it can adapt the broadband design. A new segment-harmonic tuning technology is proposed to improve efficiency of main PA and auxiliary PA, while ensuring their broadband requirements. Doherty power amplifier with new Doherty structure and new harmonic tuning technique is designed, operating in the 2.1GHz-2.7GHz, with 43 dBm output power, 35% output average efficiency and nearly 60% saturation efficiency. |
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