A Data-Based Nested LUT Model for RF Power Amplifiers Exhibiting Memory Effects

In this letter, a new model is proposed for radio frequency power amplifiers exhibiting memory effects. The model is based on nested look-up tables that compute the estimated amplifier output signal, based on the current input sample and the preceding ones. The model is validated experimentally, using input and output waveforms of a high-power LDMOS based amplifier driven by a multicarrier WCDMA signal. It is shown that the performance of the proposed model is comparable to that of the conventional memory polynomial model. However, the nested look-up table based model significantly reduces the complexity of the identification of the model's parameters, as well as the computational complexity in calculating the estimated output signal.     

Design Optimization and DPD Linearization of GaN-Based Unsymmetrical Doherty Power Amplifiers for 3G Multicarrier Applications

In this paper, a design optimization approach for gallium-nitride (GaN)-based Doherty power amplifiers (PAs) is proposed to enhance linearizability and maximize the power-added efficiency (PAE) for multicarrier wideband code division multiple access (WCDMA) applications. This is based on the use of an input offset line at the peaking amplifier path to compensate, at a given backoff level, for the bias and power-dependant phase variation through the carrier and peaking paths. At a 6-dB output power backoff (OPBO), measurement results of the unsymmetrical unlinearized Doherty amplifier using a four-carrier WCDMA signal achieved results of close to 50% for the PAE and about -30 dBc for the adjacent channel leakage ratio. Linearization of the designed Doherty PA using a baseband digital predistortion technique led to quasi-perfect cancellation of spectrum regrowth. At an OPBO equal to the input signal's peak-to-average power ratio, -63- and -53-dBc adjacent channel power ratios were obtained when the Doherty amplifier was driven by single- and four-carrier WCDMA signals, respectively. To the best of the authors' knowledge, this represents the best reported results for PAE and linearity for GaN-based Doherty PAs linearized over 20 MHz of instantaneous bandwidth.     

Digital subband filtering predistorter architecture for wireless transmitters

In this paper, a new architecture for baseband digital predistortion dedicated to wide-band transmissions is presented. The proposed predistorter consists of a cascade of a static lookup-table-based predistorter and a subband filtering block. The subband filtering technique is used to improve the correction bandwidth limitation of conventional architectures. The cases of four- and eight-subband decomposition were considered and compared to the case where the full-band signal is processed. This revealed that the subband processing results in a better sensitivity and an independent tuning ability of the predistorter at each subband. In addition, it was shown that, in the proposed predistorter, the computational complexity and the required processing speed are reduced proportionally to the number of subbands. Moreover, in an adaptive digital predistortion context, a quicker convergence can be achieved. Experimental validation of the subband-based predistortion concept was successfully carried on a 100-W peak envelop power lateral double diffused metal-oxide semiconductor power amplifier.     

Numerical improvement of thin tubes hydroforming with respect to ductile damage

Fully coupled constitutive equations, formulated in the framework of the thermodynamics of irreversible processes with state variables, accounting for isotropic hardening as well as the isotropic ductile damage are used to simulate numerically, by the finite element analysis, 3D metal hydroforming processes with damage occurence. An implicit integration scheme for local time integration of the constitutive equations and a dynamic explicit resolution scheme to solve the associated dynamic equilibrium problem are used. The effects of friction coefficient, material ductility and hydro bulging condition, on the hydroformability of various thin tubes are discussed.     

Magnesium chloride precipitation from mixed salt solution using 1,4-dioxan

This paper deals with the preparation of magnesium chloride hydrate from a mixed salt solution containing, besides MgCl₂, substantial quantities of undesired substances such as alkali metal chlorides and magnesium sulphate. Magnesium chloride extraction was done using dioxan. In particular, it was found that this salt precipitate as the ternary compound MgCl₂·6H₂O·C₄H₈O₂. Reaction equilibrium is reached after 40 min. It was shown that solid phase MgCl₂·6H₂O·C₄H₈O₂ conversion into MgCl₂·6H₂O is feasible by a drying carried out at constant temperature chosen in the range (70-110 °C). Physico-chemical properties of the final product are determined using XRD, complexometry, potentiometry, gravimetry and FAAS. Prepared MgCl₂·6H₂O purity is upper than 99%. Its X-ray diffractogram is impurity free.     

On The Sensitivity of RF Transmitters' Memory Polynomial Model Identification to Delay Alignment Resolution

In this letter, the effects of delay alignment between the input and output baseband waveforms on the performance of a radio frequency transmitters' memory polynomial based model are studied. A 100-W average power transmitter is characterized; various delay values are applied to align the input and output data; and, a model is derived for each delay value. The models' performances, evaluated for these delay values both in time and frequency domains, demonstrate that the memory polynomial model is sensitive to delay overestimation but not to delay underestimation. It is established that a delay underestimation by up to one sampling period does not affect the performance of the identified model. This overcomes the need for the signal oversampling required for high-resolution delay alignment. Consequently, the computational complexity of the digital signal processing algorithm employed for delay estimation and alignment is considerably reduced.     

Design and performance analysis of mismatched Doherty amplifiers using an accurate load-pull-based model

An active load-pull-based large-signal modeling approach, suitable for designing and optimizing load modulated amplifiers such as Doherty or linear amplification using nonlinear components based amplifiers, is proposed. A Doherty amplifier was designed by optimizing the dynamic loads seen by the amplifier's transistor using a large-signal load-pull-based behavior model built into computer-aided-design software. Simulation and measurement results showed good agreement, while results obtained using an empirical model of this transistor demonstrated discrepancies. The load-pull-based model was then used to study performance degradation of the Doherty amplifier when load impedance was moved out from the perfect 50 /spl Omega/. It has been shown that the load mismatch can greatly affect the linearity and efficiency performance of the amplifier unless its phase is controlled and kept within a specific range. A load mismatch system level compensator scheme, capable of restituting the linearity loss and maintaining the power-added efficiency close to its maximum range, is proposed.     

Systematic and Adaptive Characterization Approach for Behavior Modeling and Correction of Dynamic Nonlinear Transmitters

This paper proposes a comprehensive and systematic characterization methodology that is suitable for the forward and reverse behavior modeling of wireless transmitters (Txs) driven by wideband-modulated signals. This characterization approach can be implemented in adaptive radio systems since it does not require particular signal or training sequences. The importance of the nature of the driving signal and its average power on the behavior of radio-frequency Txs are experimentally investigated. Critical issues related to the proposed characterization approach are analytically studied. This includes a new delay-estimation method that achieves good accuracy with low computational complexity. In addition, the receiver linear calibration and its noise budget are investigated. To demonstrate the accuracy and robustness of the proposed method, a full characterization (including the memoryless nonlinearity and the memory effects) of a 100-W Tx driven by a multicarrier wideband code-division multiple-access signal is carried out, and its forward and reverse models are identified. Cascading the identified reverse model derived using the proposed methodology and the Tx prototype leads to excellent compensation of the static nonlinearities and the memory effects exhibited by the latter. Critical issues in implementing this approach are also discussed.     

Glassy-like Metal Oxide Particles Embedded on Micrometer Thicker Alginate Films as Promising Wound Healing Nanomaterials

Micrometer-thicker, biologically responsive nanocomposite films were prepared starting from alginate-metal alkoxide colloidal solution followed by sol-gel chemistry and solvent removal through evaporation-induced assembly. The disclosed approach is straightforward and highly versatile, allowing the entrapment and growth of a set of glassy-like metal oxide within the network of alginate and their shaping as crake-free transparent and flexible films. Immersing these films in aqueous medium triggers alginate solubilization, and affords water-soluble metal oxides wrapped in a biocompatible carbohydrate framework. Biological activity of the nano-composites films was also studied including their hemolytic activity, methemoglobin, prothrombin, and thrombine time. The effect of the films on fibroblasts and keratinocytes of human skin was also investigated with a special emphasis on the role played by the incorporated metal oxide. This comparative study sheds light on the crucial biological response of the ceramic phase embedded inside of the films, with titanium dioxide being the most promising for wound healing purposes.