Browsing by Subject "Power amplifiers"
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Item Open Access Balancing gain narrowing with self phase modulation: 100-fs, 800-nJ from an all-fiber-integrated Yb amplifier(IEEE, 2013) Pavlov, Ihor; Rybak, A.; Cenel, C.; İlday, F. ÖmerThere is much progress in Yb-fiber oscillator-amplifier systems, which enable generation of high-repetition-rate, microjoule energies and sub-picosecond pulse widths [1,2]. Given the extremely large total gain factors to reach microjoules starting from nanojoules, which is often in the range of 40-60 dB, due to losses, and the impact of mismatched high-order dispersion as temporal stretching and compression of pulses by large factors (30-40 dB) need to be employed. As a result of these challenges, most of the Yb-fiber amplifiers have resulted in pulse durations of several 100 fs or longer. While pulse durations in this range are suited for some applications, there are many cases where 100-fs or shorter pulses in microjoule range are required. Gain narrowing can be effectively countered by self-phase modulation (SPM) [3] by limiting amplification factor in each stage of amplification and through careful optimization of SPM and inversion level along the gain fiber. The conceptual template is readily present in the evolution of the pulse inside the oscillator cavity, where gain factors are often in the 10-50 range per roundtrip. To the extend that the B-integral and the gain distribution along the amplifier can be kept identical to the oscillator by proper scaling of the chirped pulse width and fiber mode area, the original oscillator can be preserved in arbitrary number of amplification stages. Here, we demonstrate a highly fiber-integrated master-oscillator power-amplifier (MOPA) system, from which - 1 μJ pulses are extracted and externally compressed to 100 fs by arranging amplification in each stage as close as possible to the intra-cavity evolution. To our knowledge, these results are the shortest demonstrated from all-fiber-integrated amplifier at the microjoule level. © 2013 IEEE.Item Open Access Design of high power S-band GaN MMIC power amplifiers for WiMAX applications(IEEE, 2011) Cengiz, Ömer; Kelekçi, Özgür; Arıkan, Galip Orkun; Özbay, Ekmel; Palamutçuoǧullari O.This paper reports two different S band GaN MMIC PA designs for WiMAX applications. First PA has a 42.6 dBm output power with a 55%PAE @ 3.5 GHz and 16 dB small signal gain in the 3.2-3.8 GHz frequency range. When two of these MMICs were combined by using off-chip Lange Couplers, 45.3 dBm output power with a 45%PAE @3.5Ghz and 16 dB small signal gain were obtained with less than 0.2 dB gain ripple in the 3.3-3.8 GHz frequency range. © 2011 IEEE.Item Open Access Design of multi-octave band GaN-HEMT power amplifier(IEEE, 2012) Eren, Gulesin; Şen, Özlem A.; Bölükbaş, Basar; Kurt, Gökhan; Arıcan, Orkun; Cengiz, Ömer; Ünal, Sıla T.K.; Durmuş, Yıldırım; Özbay, EkmelThis paper describes design, fabrication and measurement of 6 GHz - 18 GHz monolithic microwave integrated circuit (MMIC) amplifier. The amplifier is realized as coplanar waveguide (CPW) circuit using 0.3 μm-gate Gallium-Nitride (GaN) HEMT technology. The amplifier has a small signal gain of 7 ± 0.75 dB. The output power at 3dB compression is better than 24 dBm with 16%-19% drain efficiency for the whole 6 GHz-18 GHz frequency band under continuous wave (CW) power. © 2012 IEEE.Item Open Access High power K-band GaN on SiC CPW monolithic power amplifier(IEEE, 2014-10) Cengiz, Ömer; Şen, Özlem; Özbay, EkmelThis paper presents a high power amplifier at K-band (20.2-21.2 GHz). The AlGaN/GaN CPW MMIC amplifier is realized with 0.25 μm HEMT process on 2-inch semi-insulating SiC substrate. The amplifier has a small signal gain over 20 dB for Vds=15V and measured output power of over 31 dBm at 20.2 Ghz. PAE of the amplifier is around 22% for desired frequency band. Initial radiation hardness tests indicate a suitable stability of the technology in space. © 2014 European Microwave Association.Item Open Access A large-signal behavioural modeling approach of GaN HEMTs for power amplifier design(Institute of Electrical and Electronics Engineers Inc., 2021-01-10) Yegin, Mustafa Oğuz; Gurdal, Armagan; Ozipek, Ulas; Özbay, EkmelA new method to simulate the large-signal behaviour of GaN HEMTs is presented along with the two 15W X-band MMIC Class AB power amplifier (PA) designs using the same methodology. Proposed modeling approach is based on curve-fitting transistor performance parameters in the load impedance plane, while transistor’s behaviour in the source impedance space is calculated using a virtual source-pull technique. Good agreement with the results of two fabricated GaN PA MMICs demonstrate the accuracy of the method in simulating Pout , Gt and PAE of the amplifiers at any given compression level. This approach is distinguished from conventional modeling methods with its minimal measurement requirements, ease of model development, and generic nature while accurately predicting the large-signal response, thus is suitable to use for PA design, under the lack of a more comprehensive transistor model.Item Open Access Novel predistortion algorithm for OFDMA(IEEE, 2009) Ali, S.; Markarian, G.; Arıkan, ErdalThe RF amplifier in a wireless communication system is usually non-linear in nature. If such an amplifier is used in OFDMA based systems, it will cause serious degradation. This degradation will be both in terms of the reduction in BER and the generation of out of band noise. In this paper we have worked on the linearization method of the amplifier. This work is on a hybrid methodology, in which estimation of the model is performed in frequency domain and compensation is performed in time domain. The downlink preamble of the IEEE802.16e system is used here for the estimation purpose. The results for the suppression of spectra are shown at the end.Item Open Access Performance of edge windowing for OFDM under non-linear power amplifier effects(IEEE, 2017) Göken, Çağrı; Dizdar, OnurEdge windowing is a windowing technique for Orthogonal Frequency Division Multiplexing (OFDM) signals based on the idea of using shorter cyclic prefix (CP) and longer window lengths at the edge subcarriers while keeping the symbol length fixed. In this study, we investigate the performance of OFDM signals with edge windowing under non-linear power amplifier (PA) effects by observing out-of-band (OOB) emission characteristics, average error vector magnitude (EVM) and coded block error rate (BLER) performance. We explore whether the possible gains over conventional windowing in the presence of PA is possible. We show that the edge windowing can still provide improvements over conventional windowing in terms of OOB emission suppression under various PA models at the expense of increased average EVM, whereas the channel coding substantially mitigates the performance loss due to inter-symbol and inter-carrier interference (ISI-ICI) effects arising as a result of shorter CP length at the edge subcarriers.Item Open Access Structural field plate length optimization for high power applications(IEEE, 2014) Toprak, Ahmet; Kurt, Gökhan; Şen, Özlem A.; Özbay, EkmelIn this work, we report GaN high-electron-mobility-transistors (HEMTs) on SiC with field plates of various dimensions for optimum performance. 0.6 μm gate length, 3 μm drain source space AlGaN/GaN HEMTs with field-plate lengths of 0.2, 0.3, 0.5 and 0.7 μm have been fabricated. Great enhancement in radio frequency (RF) output power density was achieved with acceptable compromise in small signal gain. When biased at 35 V, at 3 dB gain compression, a continuous wave output power density of 5.2 W/mm, power-added efficiency (PAE) of 33% and small gain of 11.4 dB were obtained at 8 GHz using device with 0.5 μm field plate length and 800 μm gate width without using via hole technology.Item Open Access Study of the power performance of gaN based HEMTs with varying field plate lengths(North Atlantic University Union, 2015) Kurt G.; Toprak, A.; Sen O.A.; Özbay, EkmelIn this paper, we report the optimum power performance of GaN based high-electron-mobility-transistors (HEMTs) on SiC substrate with the field plates of various dimensions. The AlGaN/GaN HEMTs are fabricated with 0.6 µm gate length, 3 µm drain-source space. And also, the field plate structures with the lengths of 0.2, 0.3, 0.5, and 0.7 µm have been fabricated on these HEMTs. Great enhancement in radio frequency (RF) output power density was achieved with acceptable compromise in small signal gain. A HEMT of 0.5 µm field plate length and 800 µm gate width is biased under 35 V, at 3 dB gain compression, The results showed that we obtained a continuous wave output power of 36.2 dBm (5.2 W/mm), power-added efficiency (PAE) of 33% and a small signal gain of 11.4 dB from this device. We also could achieve a continuous wave output power of 37.2 dBm (5.2 W/mm), poweradded efficiency (PAE) of 33.7% and a small gain of 10.7 dB from another HEMT with 0.5 µm field plate length and 1000 µm gate width. These results were obtained at 8 GHz without using a via hole technology. The results seem very stunning in this respect. © 2015, North Atlantic University Union. All rights reserved.