A study on Broadband Three-way Asymmetric Doherty Power Amplifier for High Efficiency
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As the wireless communication system is rapidly developing, high efficiency, high linearity, high power and wideband characteristic of the base-station RF power amplifiers (PAs) in the transmitter are increasingly demanding. This dissertation, therefore, proposes the Doherty power amplifier (DPA) for high efficiency, high linearity and broadband characteristic. The DPA has been studied for the promising solution to achieve high efficiency at large backed-off power (BOP). However, in the current wireless communication system, modulated signals such as wide-band code division multiple access (WCDMA) and long-term evolution (LTE) have a high peak to average power ratio (PAPR). The conventional DPA is not suitable for using the modulated signals. In this study, thus, three-way asymmetric DPA structure is presented to enlarge the BOP from saturation power. For the experimental verification, a 2.1-GHz three-way asymmetric DPA using LDMOSFETs with a power ratio of 1:2:2 is implemented and tested using continuous-wave (CW) and LTE signal. The proposed DPA attained >22 % power-added efficiency with the power gain of 7.5 dB is maintained in 100 MHz bandwidth at the output power of 40 dBm, which is 10 dB backed-off power. Also we achieved more than -11 dBc ACLR improvement, under -30 dBc in the 100 MHz using DPD linearization. It is evident that the proposed DPA can be a valuable guideline to evolve the PAs for high efficiency, high linearity and broadband characteristic.