· · · Institutional Repository

Vanwege vertrouwelijke informatie of andere redenen is slechts een deel van de publicatie opgenomen in de repository. Due to confidential information or other reasons only a part of the publication is presented in the repository. Doherty Power Amplifier (DPA) is employed to improve the efficiency when operated with complex modulated signals. Due to its simplicity and high efficiency performance, it has become the preferred choice of industry. However, practical implementations of DPA only provide limited RF bandwidth, especially at high power level. The traditional narrow band device matching network, required phase shift for proper load modulation and impedance inverter seriously limit the bandwidth of DPA. In this work, the frequency behavior of the ideal 2-way symmetrical DPA is analyzed in detail, followed by the introduction of two new impedance inverters used to improve the bandwidth of DPA. In order to fully exploit the wideband potential of the new impedance inverters, the phase relation between the main and peak amplifier should be adjusted according to the power level at every frequency, which can be stored in a lookup table. Based on a previous wideband 20W DPA with mixed-signal input drive, in which the device output capacitance is incorporated into the impedance inverter, a modified DPA using the idea of compensated impedance inverter is designed and simulated. The prototype DPA design is implemented with NXP LDMOS bare die device. Simulation results have shown more than 50% 6dB back off efficiency from 1.5GHz to 2.2GHz, compared with the original case whose 50% efficiency bandwidth is from 1.9GHz to 2.3GHz. Since the prototype DPA is implemented at a low power level with bare die devices and mixed-signal input drive, it cannot be used for the practical base station applications. Traditional high power discrete DPA design method is introduced and the frequency behavior is analyzed. It is found that for the high power DPA, the matching network and the offset line are more important than the impedance inverter for the narrow bandwidth of DPA. A new DPA structure was proposed for wideband operation. Simulation results show smaller gain and power added efficiency spread in a 200MHz frequency band from 2.04GHz to 2.24GHz than the traditional DPA.

New generations wireless communication systems require linear efficient RF power amplifiers for higher data transmission rates. However, conventional RF power amplifiers are normally designed for peak efficiency under maximum output power condition. Consequently, when the power is backed-off from its maximum point, the amplifier efficiency drops sharply. As a result, the mean amplifier efficiency is much lower than the efficiency at peak power level. The Chireix outphasing power amplifier is one of the most promising techniques that can simultaneously provide high efficiency and high linearity. Such approach was the origin of the term LINC (LInear amplification using Nonlinear Components), a technique that allows the power amplifiers to continuously operate at their peak power efficiency while providing an almost undistorted output signal. In this project, a Chireix outphasing amplifier for 2.14 GHz with load compensation has been fabricated using GaN HEMTs delivered by CREE. A considerable efficiency improvement has been achieved. The simulation result shows that the drain efficiency of 74% is obtained at 49 dBm peak output power, and the efficiency is kept above 55% over 10 dB power back-off range. The drain efficiency of 70% is measured at 48.5 dBm output power. To meet an increasing demand for wireless communication terminals to handle multi-band multi-mode operation, multi-band multi-mode power amplifiers are urgently needed. An investigation into how to implement multi-band Chireix's outphasing amplifiers has been carried out. Two proposals for implementing potential dual-band Chireixâs amplifiers have been presented. In addition, a comparison of the efficiency under the condition of static load modulation has been made between GaN HEMT devices and LDMOS devices. The result of the comparison is that GaN HEMT devices conspicuously outperform LDMOS devices in terms of drain efficiency under static load modulation.