Joao Paulo Martins

A Metric for the Quantification of Memory Effects in Power Amplifiers

This paper presents a quantitative metric for memory effects in power amplifiers (PAs) and applies it to various active device technologies and wireless system contexts. The proposed metric is mathematically founded in the dynamic two-tone distortion response, has a clear physical meaning in the important field of PA linearization and can be easily evaluated from either harmonic balance simulations or measurement data gathered in a microwave laboratory. In addition, a memoryless PA linearizer, optimum for reducing the integrated intermodulation distortion (IMD) power in the operation bandwidth for a two-tone excitation, is derived, providing a rigorous figure-of-merit of PA linearizability under static IMD compensation. The application of this figure-of-merit is then illustrated for three different PA prototypes based on Si LDMOS, InGaP/GaAs heterojunction bipolar transistors, and GaN high electron-mobility transistors, designed for 900-MHz (global system for mobile communications), 2.1-GHz (wideband code division multiple access), and 3.5-GHz (WiMax) wireless systems, respectively

New method for phase characterization of nonlinear distortion products

This paper presents a new method for phase characterization of nonlinear mixing products based on statistical averages of signal windows captured by a synchronous two-channel sampler. Passing some of the signal processing operations, previously performed by complex laboratorial arrangements, to the digital domain, the present method simplifies the measurement bench and allows absolute phase measurements, i.e., not depending on any arbitrarily selected phase reference nonlinearity.

Multitone phase and amplitude measurement for nonlinear device characterization

This paper presents a new setup for nonlinear device characterization. The presented measuring bench allows the characterization of phase and amplitude of correlated and uncorrelated multitone signals. The method presents a simple hardware implementation using only an ordinary scope as the main device. The validity of the technique is confirmed by an experimental test using a two-tone uncorrelated input signal. The experimental values agree with the theoretical results assuring the validity of the proposed technique. Moreover, they confirm the fact that despite the lower and upper intermodulation distortion can have the same amplitude; they could present different relative phases.

Intermodulation Distortion of Third-Order Nonlinear Systems With Memory Under Multisine Excitations

This paper presents a methodology to compute the distortion output of a class of third-order nonlinear dynamic systems from only standard two-tone test results. Closed-form expressions are presented to compute the distortion output and metrics as adjacent channel power ratio and co-channel power ratio/noise power ratio for an arbitrary multisine with N tones. The impact of memory effects in a multisine excitation is also addressed, improving the design of RF components by a careful understanding of memory effects mechanism in real modulated signals. An experimental validation is presented to prove the proposed theory.

Amplitude and phase characterization of nonlinear mixing products

This paper discusses the problem of amplitude and phase characterization of nonlinear mixing products arising from a broad class of nonlinear microwave devices. Realizing that the most difficult problem stands on the phase measurement, it starts by reviewing the most common approaches used for the phase characterization of spectral regrowth components. It is demonstrated that these methods can be viewed as correlation processes, and are so framed in a common theory. This allows a unique and universal definition of the input-output amplitude and phase relations, even for mixing products that fall on frequency positions for which there are no components present at the input, and for those arising from incommensurate excitations. Finally, it shows how that theory can be implemented in a laboratory measurement scheme, thus giving the introduced theoretical variables a practical engineering value

Multi-sine Response of Third Order Nonlinear Systems with Memory Based on Two-tone Measurements

This paper presents a framework that allows the third order response computation of a dynamic nonlinear system to a multi-sine signal input from only standard two-tone test results. A simulation implementation of the methodology is presented for a third order system with memory. The validation test is performed with a five tone uncorrelated input signal and states the feasibility of the method in the intermodulation distortions prediction. The work now presented is a step forward to the understanding of the memory generation mechanisms and in the extrapolation of the usual standard RF test results to the prediction of the dynamic systems output to a multi-sine signal excitation

Hermes: A versatile platform for wireless embedded systems

This paper presents Hermes, a new modular platform that can be used in a variety of scenarios, including the role of body area network coordinator, enabling temperature, movement and heartbeat sensing, local and remote communication, and indoor and outdoor localization. Hermes is based on two main modules that can operate as a single system in a coordinated fashion or individually, depending on the application scenario. One of the modules uses a Telos-inspired architecture, with new processing, communication, sensing, storage and energy subsystems, and executing TinyOS. The other module is designed around a PIC 24F MCU, also supporting communication, sensing, storage, and executing a custom operating system. Both modules have expansion capabilities. The main innovative aspects of the implemented platform are its modularity and its capability to provide device abstraction, which considerably eases application development. The paper addresses the platform motivation, requirements, hardware architecture, implementation details, and performance evaluation.

Practical Higher Order Statistics Signal Characterization

This paper presents a laboratory implementation for the computation of higher order statistics of a RF signal. It states the feasibility of the higher order statistics computation of practical microwave signals with the nowadays available measurement instrumentation, allowing this way the full dimensional signal characterization

Experimentation made easy with the AMazING panel

Experimental testbeds for evaluating solutions in computer networks, are today required as a complement to simulation and emulation. As these testbeds become larger, and accessible to a broader universe of the research community, dedicated management tools become mandatory. These tools ease the complex management of the testbed specific resources, while providing an environment for researchers to define their experiments with large flexibility. While there are currently several management tools, the research community is still lacking tools that smooth the experimentation workflow. These were key aspects that we considered when developing the management infrastructure for our wireless testbed(AMazING). We developed a experimentation support framework supported by an attractive GUI, automation and scripting capabilities, as well as experiment versioning and integrated result gathering and analysis.

Co-channel and adjacent channel distortion in microwave amplifiers presenting memory

This paper studies both for the co-channel and adjacent channel distortion in power amplifiers, PA, presenting long term memory effects. It is proved that the minimization of the adjacent channel distortion, is not equivalent to the minimization of the co-channel distortion in a PA, presenting long term memory effects.