Search

A new concept of pulsed load modulation (PLM) is introduced for efficient power amplification. The proposed technique allows the power amplifier (PA) to maintain maximum efficiency until the output power of the amplifier is backed off by 6 dB. The PLM amplifier contains two pulse-biased PAs connected with a [lambda]/4 transmission line and a high-Q bandpass resonator. For maximum efficiency and linearity, the load impedance of the amplifier is digitally modulated using the switched-resonator concept. A prototype amplifier is implemented using two PAs and a diplexer for the 1.87-GHz band. The measured efficiency of the amplifier at peak output power is 51%. Compared with 25.5% of the conventional class-B amplifier, the PLM amplifier obtains an improved efficiency of 38% at 6-dB output power back-off. Index Terms--Digital control, linear amplifier, load modulation, nonconstant envelope modulation, power efficiency, switched resonator.

The design and analysis of a dual-operating mode laterally diffused metal-oxide semiconductor (LDMOS) power amplifier for code-division multiple-access wireless communication base-station applications is presented in this paper. The amplifier structure consists of four parallelly located single-stage LDMOS amplifier array, the dual-mode input power divider, and output power combiner. In this dual-mode operation, the number of operating power amplifier (either one or four amplifiers) is controlled depending on the required power level. This results in significant improvement in efficiency performance of the amplifier by minimizing unnecessary dc power consumption. In addition to the enhancement of efficiency, the amplifier design approach also provides better overall linearity performance. The proposed dual-operating mode design technique was successfully demonstrated by designing, implementing, and testing an LDMOS power amplifier with Motorola MRF 21030 in this study. Index Terms--Adjacent channel leakage power ratio (ACLR), characteristic impedance, code division multiple access (CDMA), coupled-line coupler, laterally diffused metal-oxide semiconductor (LDMOS), power-added efficiency (PAE), power amplifier.

This letter presents a new technique to enhance the overall efficiency of a two-stage envelope tracking (ET) power amplifier (PA). Because of heavy gain compression, ET amplifiers can suffer from inefficient driver stages. By reducing the supply voltage of the driver amplifier, its efficiency can be improved without degrading the linearity performance of the overall PA system because the final-stage ET PA allows the decrested RF signal as an input. This technique is demonstrated for a single carrier WCDMA signal using a RF PA based on a GaAs HVHBT with a dynamic supply modulator and a driver stage based on a GaN heterojunction field-effect transistor (HFET). The measurement shows that the drain efficiency of the driver amplifier is improved from 25.6 to 41.5% and the overall efficiency of the ET PA system is improved from 46.2 to 48.3% while the efficiency of the final-stage ET PA is maintained at higher than 55%. The average output power is greater than 44.6 dBm, the overall gain is greater than 20 dB, and the adjacent channel leakage ratio is less than −46 and −53 dBc at 5- and 10-MHz frequency offsets, respectively. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:505-507, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26527 [ABSTRACT FROM AUTHOR]

The B(C6F5)3-catalyzed silylative reduction of conjugated nitriles has been developed to afford synthetically valuable β-silyl amines. The reaction is chemoselective and proceeds under mild conditions. Mechanistic elucidation indicates that it proceeds by rapid double hydrosilylation of the conjugated nitrile to an enamine intermediate which is subsequently reduced to the β-silyl amine, thus forming a new C(sp(3))-Si bond. Based on this mechanistic understanding, a preparative route to enamines was also established using bulky silanes., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)