Cesar Sanchez-Perez

Performance improvement of mobile DVB-H terminals using a reconfigurable impedance tuning network

DVB-H (digital video broadcasting for handheld) is one of the technology standards for the transmission of digital TV to handheld receivers such as mobile phones or PDAs. Antenna design for DVB-H terminals is challenging due to the size limitation and as a result, the antenna presents large mismatches. To address this issue, we propose the use of a reconfigurable tuning network to reduce the mismatch (or the antenna size for a given mismatch) between the antenna and the RF front-end in a DVB-H terminal. This technique offers some advantages over other proposed alternatives and improves the antenna realized gain, as well as the overall efficiency of the DVB-H receiver.

Dynamic Load Modulation With a Reconfigurable Matching Network for Efficiency Improvement Under Antenna Mismatch

This brief presents the application of a reconfigurable matching network (RMN) to improve the efficiency of an RF power amplifier (PA) using dynamic load modulation techniques under different antenna mismatch conditions. By changing the RMN state, a near-optimal output impedance is presented to the PA, achieving high efficiency for all input-driven levels. Simulations show efficiency enhancement, while nonlinear distortion can be mitigated using digital predistortion. It will be also shown that under severe mismatch conditions, using an RMN, significant efficiency and linearity improvements can be achieved.

Synthesis of Hecken-tapered microstrip to Paralell-Strip baluns for UHF frequency band

Microstrip to Parallel-Strip transitions are frequently used for feeding balanced antenna structures, such as dipoles and printed spiral antennas. In this paper, we propose an analytical method to compute the gradual taper using a Hecken approach in order to minimize the return losses and to have continuity. The proposed method is verified experimentally with the aid of three transitions including matching capabilities with different ratios, suitable for spiral antenna structures in, at least, the ranges from 450 MHz to 2 GHz.

Digital predistortion based on Zernike polynomial functions for RF nonlinear power amplifiers

Predistortion linearizer for high nonlinear power amplifiers (PAs) is an important topic of research in wireless applications. Behavioral models based on polynomial functions are widely used for both PAs and predistorters. However, they often suffer from numerical instability problems when we include high nonlinear-order in the mathematical model. In this work, we propose a new predistorter model considering the use of an orthogonal basis. This basis is composed of Zernike polynomials, which are very robust and stable when they are applied to classical identification techniques. Computer simulations in a typical DVB-T OFDM transmission confirm the predistorter computed with the Zernike polynomial model provides improvements in adjacent channel power ratio with stability and moderate complexity in the DPD coefficient estimation.

High Power Amplifier Linearization Using Zernike Polynomials in a LTE Transmission

Digital predistortion (DPD) is a highly cost- effective technique to linearize high power amplifiers (HPAs) in wireless applications. The polynomial-type behavioral models are widely used both for HPAs and predistorters, but they often suffer from the numerical instability when high order nonlinearities are included. In this paper, we propose a new polynomial predistorter model considering the use of a orthogonal polynomial model based on a Zernike polynomial basis which is very robust and stable when classical identification techniques are applied. Computer simulations in a LTE uplink transmission confirm the predistorter computed with the Zernike polynomial model provides improvements in adjacent channel leakage ratio (ACLR) with stability and moderate complexity in the DPD coefficient estimation.

Improving Digital Predistortion Mismatch Sensitivity Using Tunable Matching Networks

Digital predistortion (DPD) is a well-known method to reduce non-linear distortion in RF power amplifiers (PAs). In this paper, we present a study on the sensitivity of this linearization technique under large mismatch conditions, and how this sensitivity can be improved using a tunable matching network (TMN). Under different load conditions, PA behavior may change significantly making more complicated the DPD solution convergence, reducing its performance or even disabling its correct operation. Using a TMN the load impedance variation effect can be reduced, observing improvements in adjacent channel power ratio (ACPR) and regions of DPD convergence in the Smith chart.

Exploring the use of reconfigurable matching networks for efficiency and linearity improvement in RE power amplifiers under load variations

This paper presents the application of a reconfigurable MEMS-based tuning network for the improvement of the linearity and efficiency in RF power amplifiers (PAs) under load variations. Simulations show the performance improvement of the whole system in terms of linearity and efficiency with different loads.

Tunable outphasing for power amplifier efficiency improvement under load mismatch

Load mismatch in RF high power amplifier leads to efficiency reduction or amplifier failure. Instead of impedance tuning, in this paper an outphasing architecture with a tunable non-isolated combiner is used to reduce sensitivity to load variations. Experimental results with two GaN class AB amplifiers at 2.14GHz show it is possible to maintain the efficiency above 50% over a wide range of impedances, while maintaining the output power within a few dB around 20W.

Design of a Varactor-Based Matching Network Using Antenna Input Impedance Variation Knowledge

It is commonly assumed that the antenna input impedance remains static during the transmission and reception process. However, in a real scenery the impedance value is a dynamic parameter, affected by the user and the environment, that can be very different compared to the static situation. With a statistical approach, the impedance variation can be characterized in the matching domain. This information can be very useful for the design of efficient adaptive matching circuits. In this paper, we propose the design and optimization of a varactor-based tunable matching network (VMN) to improve the antenna matching, using the previous knowledge of the antenna input impedance variations. Improvements in power transmission greater than 3 dB for the originally unmatched region, and reduced power losses (under -0.5 dB) in the originally matched area can be achieved using this circuit.

Behavioral Power Amplifier Modeling and Digital Predistorter Design with a Chirp Excitation Signal

Digital predistortion techniques are widely utilized to linearize radio frequency power amplifiers (PAs). In their training process, they commonly use filtered Average White Gaussian Noise (AWGN) or the same signal as the transmitted. In this paper an improved calibration waveform for PA behavioral modeling and baseband digital predistortion is proposed. This signal is suitable for different amplifiers, by modifying their configurable parameters. A reduction of the training time and an enhancement in the out-of-band emission level up to 14 dB are achieved.