GaN integrated circuit technologies have dramatically progressed over the recent years. The prominent feature of high-electron mobility transistors (HEMTs), unparalleled output power densities, has created a paradigm shift in established and emerging high-power applications. In this article, we present review on developments prospects amplifiers (PAs). progress including improvements their impo...

Radiofrequency (RF) power amplifiers (PAs) are important elements of modern communication systems. The most components in PAs the transistors, which operated under large-signal regimes such applications. Designing and optimizing challenging tasks that demand highest accuracy on measurements at both device circuit levels. Large-signal transistor characterization demands development utilization h...

The zero-forcing algorithm (min-norm algorithm) is one of the proposed methods for downlink beamforming. This algorithm steers the nulls towards interferers and the main beam towards the desired user provided the angles of arrival of these signals are known to the basestation. However, downlink adaptive arrays use additional power when they are required to include null steering in their beam pa...

OF DOCTORAL DISSERTATION HELSINKI UNIVERSITY OF TECHNOLOGY P.O. BOX 1000, FI-02015 TKK http://www.tkk.fi Author Fernando Hugo Gregorio Name of the dissertation Analysis and compensation of nonlinear power amplifiers effects in multi-antenna OFDM systems Manuscript submitted 08.06.2007 Manuscript revised 27.09.2007 Date of the defence 19.11.2007 Monograph Article dissertation (summary + original...

Advances in silicon processing technology have made CMOS power amplifiers a feasible option for wireless communication applications. Compared to the compoundsemiconductor counterparts, CMOS PAs become increasingly attractive due to their lower cost and higher level of integration. The continued scaling of CMOS technology further extends the cut-off frequency of CMOS devices up to several hundre...

–High power efficiency is an important requirement in cellular transmitter radios. OFDM systems require very linear transmission because of high peak-to-average-power-ratio (PAPR). However, linear power amplifiers (PA) have very low efficiency. To enhance the power efficiency, non-linear PAs are applied and even forced to work near the saturation point. This generates inevitably huge non-linear...

This paper presents a suboptimum custom-tailored (SCT) model for power amplifiers (PAs). Based on the pruned Volterra series, the SCT model is developed by using a recursive optimum-term selecting (ROS) algorithm with an offline characterization process. The proposed model sacrifices accuracy in comparison with the custom-tailored (CT) model derived from the general Volterra series. But the for...

In the present paper, the nonlinear Internal Model Control (IMC) method is introduced and applied to linearize high frequency Power Amplifiers (PAs). The IMC is based on the description of a process model and of a controller. It is shown that baseband frequency descriptions are suitable for the model and the controller. Their description parameters are derived from input and output modulation s...

With the advent of spectrally efficient wireless communication systems employing modulation schemes with varying amplitude of the communication signal, linearization techniques for nonlinear microwave power amplifiers (PAs) have gained significant interest. In this article, a low complexity, direct-learning multilevel lookup table based adaptive digital predistortion technique has been proposed...

The low efficiency of existing power amplifiers (PAs) is causing excessive energy consumption in wireless systems. Improving the PA efficiency is therefore of great environmental and economical importance. This thesis address a wide range of advanced PA design methods and novel PA architectures that all contribute to significantly improve the efficiency of PAs for wireless applications. The fir...