Multiband doherty RF power amplifier

In era of exploding energy consumption and thus equipment operating cost as well as the parallel environmental need to reduce the carbon footprint, energy efficient mobile radio is a very important issue and future challenge. Additionally, increased number of standards, frequency bands and applications require flexible and sustainable solutions. On both fields the power amplifier constitutes one of the setscrews to be addressed. On the one hand, the power amplifiers cause up to 60 % of the power dissipation of a base station, on the other hand it constitutes a bottleneck concerning transmit bandwidth. The following paper presents a very promising concept of a highly efficient Doherty which supports multiband capability in order to enable future efficient, flexible and sustainable mobile radio applications. The basic functionality of the proposed concept is verified by simulation and promising simulated results, based on AlGaN/GaN-HEMTs from FhG-IAF (Fraunhofer Freiburg) indicate the benefits of the new concept compared to conventional Class-AB and Doherty amplifiers

Carbon sequestration potential of hydrothermal carbonization char (hydrochar) in two contrasting soils; results of a 1-year field study

Soil amendment with hydrochar produced by hydrothermal carbonization of biomass is suggested as a simple, cheap, and effective method for increasing soil C. We traced C derived from corn silage hydrochar (δ13C of −13‰) added to “coarse” and “fine” textured soils (δ13C of −27‰for native soil C (SOC)) over two cropping seasons. Respiration rates increased in both soils (p<0.001) following hydrochar addition, and most of this extra respiration was derived from hydrochar C. Dissolved losses accounted for ~5 % of added hydrochar C (p<0.001). After 1 year, 33±8 % of the added hydrochar C was lost from both soils. Decomposition rates for the roughly two thirds of hydrochar that remained were very low, with half-life for less estimated at 19 years. In addition, hydrochar-amended soils preserved 15±4 % more native SOC compared to controls (negative priming). Hydrochar negatively affected plant height (p<0.01) and biomass (p<0.05) in the first but not the second crop grown on both soils. Our results confirm previous laboratory studies showing that initially, hydrochar decomposes rapidly and limits plant growth. However, the negative priming effect and persistence of added hydrochar C after 1 year highlight its soil C sequestration potential, at least on decadal timescales

AlGaN/GaN-based power amplifiers for mobile radio applications: A review from the system supplier's perspective

This paper gives a summarized overview on the progress and achievements on AlGaN/GaN high electron mobility transistors (HEMT)-based power amplifiers (PAs) for mobile radio applications which have been achieved within two national funded German projects during a period of six years. Starting with a first 34 dBm (2.5 W, peak) amplifier in 2003 the impressive progress toward highly efficient S-band mobile radio PAs with up to .50 dBm (100 W) peak output power is described by means of some selected single- and multiband amplifier demonstrators. This progress has been mainly enabled by clear progress on GaN technology, device packaging, and PA design. Targeting at highly efficient single-band amplifier applications, a 2.7 GHz symmetrical Doherty amplifier with up to 45% drain efficiency at close to 45 dBm average output power under single-carrier W-CDMA (Wideband Code Division Multiple Access) operation using digital predistortion can be highlighted. In case of multiband capable amplifiers addressing software-defined radio applications, a class-AB-based demonstrator covering a frequency range from 1.8 to 2.7 GHz was realized. The amplifier showed .30% drain efficiency up to 2.5 GHz as well as up to 40 dBm average output power under single-carrier W-CDMA operation using proprietary digital predistortion. Finally, Alcatel-Lucent's activities on envelope tracking for future efficiency improved GaN-based amplifiers are described