Modulation of load impedance is an effective way to maintain efficient power amplifier (PA) operation over high dynamic range modulated signals. For high efficiency, a load modulation approach can be applied to inherently efficient classes of PAs such as those with harmonic tuning: class J, class F, and inverse class F. This paper presents an analysis of harmonically tuned amplifiers operating under load modulation conditions, deriving the optimal loading trajectories for these multiple classes of operation. Because these load trajectories are complex, it is then shown-through a series of analysis, simulations and measurements-that harmonically tuned amplifiers are better suited for outphasing systems, than conventional amplifiers such as class B. A design methodology is proposed and validated through design and measurement of a 900 MHz outphasing system, comprising of two Gallium Nitride (GaN) class J branch PAs, delivering 44.6 dBm with 75% PAE at saturation, while mantaining PAE above 60% over a 7 dB output power back-off.
The design and implementation of a high efficiency Class-J power amplifier (PA) for basestation applications is reported. A commercially available 10W GaN HEMT device was used, for which a large-signal model and an extrinsic parasitic model were available. Following Class-J theory, the needed harmonic terminations at the output of the transistor were defined and realised. Experimental results show good agreement with simulations verifying the class of operation. Efficiency above 70% is demonstrated with an output power of 39.7dBm at an input drive of 29dBm. High efficiency is sustained over a bandwidth of 140MHz.
This study investigates the feasibility of ambient radio frequency (RF) energy harvesting for powering low-power electronic devices, in domestic environments. An RF spectrum survey was carried out in a variety of locations around the city of Bristol, UK between 500 MHz and 6 GHz. Locations are limited to indoor residential environments, and as a comparison an office. The measurement setup consists of an omnidirectional, broadband, discone antenna and a handheld spectrum analyser. On the basis of the measured power consumption of a number of low-power electronic devices and the analysed results, the required harvesting time to power each device is calculated. The results show that in order to harvest enough energy to power-up a small calculator (2 μW) for 1 s, an antenna array covering 1.7-2.5 GHz with effective area of 1 m 2 requires on average about 10 min of harvesting.
The effect of time misalignment between the radiofrequency (RF) input and tunable matching network control signal in dynamically load-modulated power amplifiers (Pas) is investigated in theory and practice. Moreover, the impact of different input signal statistics is considered. A simple amplifier model is used for the study, based on which the impact on output power, efficiency, and linearity is explored with various generic multi-tone signals. Furthermore, to experimentally verify the results, a 10 W dynamically load-modulated RF PA is measured. As expected, proper synchronization of the signals is crucial, especially as channel bandwidth increases. Additionally, it is shown that the input signal characteristics, such as the amplitude distribution, are important. Moreover, the prototype RF PA is measured with a 1.4 MHz long-term evolution (LTE) signal delivering an average output power of 33.9 dBm with 46% efficiency. Finally, high efficiency and linearity is maintained over output power by scaling the drain supply voltage.
This paper presents an experimental investigation of the effect of bandwidth reduction for baseband control signals used in dynamic load-modulated (DLM) amplifiers. Using a low-power reactively DLM architecture operating at 2.35GHz the effect of control signal filtering on efficiency, output power and adjacent channel power ratio (ACPR) of the system is shown for various signal bandwidths. The method is applied on WCDMA and LTE signals showing a degradation of 2-4 percentage points (pp) in efficiency, 0.5dB lower output power and similar ACPR performance for reducing the bandwidth of the control signal by 70%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.