Claude Duvanaud

Electrostatic discharges from charged spheres approaching a grounded surface

Abstract A program based on the boundary element method enabled an accurate computation of the electric field in the gap between a conductive sphere of given charge and a grounded plate. The information on field distribution represented the input data of another program which estimated the dielectric strength of that gap in air at atmospheric pressure. In this way, it was possible to determine the critical conditions (charge, gap length) in which a discharge occurs between spherical objects of various sizes and a grounded surface.

NEW IDENTIFICATION PROCEDURE FOR CONTINUOUS-TIME RADIO FREQUENCY POWER AMPLIFIER MODEL

In this paper, we present a new method for characterization of radio frequency Power Amplifier (PA) in the presence of nonlinear distortions which affect the modulated signal in Radiocommunication transmission system. The proposed procedure uses a gray box model where PA dynamics are modeled with a MIMO continuous filter and the nonlinear characteristics are described as general polynomial functions, approximated by means of Taylor series. Using the baseband input and output data, model parameters are obtained by an iterative identification algorithm based on Output Error method. Initialization and excitation problems are resolved by an association of a new technique using initial values extraction with a multi-level binary sequence input exciting all PA dynamics. Finally, the proposed estimation method is tested and validated on experimental data.

Cancellation of third order intermodulation currents in a two-stages amplifier topology

This paper gives a detailed description of a linearization technique using a two-stage amplifier. The first stage is used to generate third order intermodulation products (IMD3), which will be added to the input signal of the second stage in order to cancel the IMD3 at its output. The technique effectively improves the linearity of the system. To investigate the effect of IMD3 injection, analytical calculations of the drain currents for the fundamental frequencies f/sub 1/ and f/sub 2/ and for the third order intermodulation currents 2f/sub 1/-f/sub 2/ and 2f/sub 1/-f/sub 1/ are established without and with injection of intermodulation components at the input of the power stage. To evaluate the improvement provided by the proposed technique, a two-tone test at carrier frequency of 900 MHz is performed with a GaAs MESFET. The test procedure is described and measurements show a great improvement of IMD3. A carrier to third intermodulation ratio C/I3 of 55 dBc was achieved for a 19 dBm output power, compared with 25 dBc achieved without the first stage.This paper gives a detailed description of a linearization technique using a two-stage amplifier. The first stage is used to generate third order intermodulation products (IMD3), which will be added to the input signal of the second stage In order to cancel the IMD3 at its output. The technique effectively improves the linearity of the system. To investigate the effect of IMD3 injection, analytical calculations of the drain currents for the fundamental frequencies f/sub 1/ and f/sub 2/ and for the third order intermodulation currents 2f/sub 1/-f/sub 2/ and 2f/sub 2/-f/sub 1/ are established without and with injection of intermodulation components at the input of the power stage. To evaluate the improvement provided by the proposed technique, a two-tone test at carrier frequency of 900 MHz is performed with a MESFET. The test procedure is described and measurements show a great improvement of IMD3. A carrier to third intermodulation ratio C/I3 of 55 dBc was achieved for a 19 dBm output power, compared with 25 dBc achieved without the first stage.

A comparison of several gradient based optimization algorithms for PAPR reduction in OFDM systems

The aim of this paper is to evaluate and compare different optimization algorithms for Peak to Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) systems. Based on Tone Reservation (TR) method, we exploit the unused subcarriers of the studied standard to generate the peak canceling signal without data rate loss. Gradient, Conjugate-Gradient with two directions search and QuasiNewton methods have been investigated and evaluated on the basis of spectral regrowth, convergence speed and ability to improve the high peak-to-average reduction in multicarriers systems. As an example, the simulations are performed in the case of Local Area Network WLAN (IEEE 802.11a standard). Simulation results show that a PAPR reduction gain around 3 dB can be achieved.

Analysis of the Doherty technique and application to a 900MHz power amplifier

In this paper, we present the study, the realisation and the measurement of an amplifier at 900 MHz using the Doherty technique. This technique is based on the large signal performance analysis of the active devices under different drive levels. The improvements made by the application of this technique were checked by simulations and measurements on a prototype made with two MESFETs transistors. For a 6 dB backoff, obtaining significant values of Power Added Efficiency was possible thanks to the application of a methodology of design, specific to this technique.

Linearization of RF Power Amplifiers Using Adaptive Kalman Filtering Algorithm

In this paper, a new linearization algorithm of power amplifier (PA), based on Kalman filtering theory is proposed for obtaining fast convergence of the adaptive digital predistortion. The proposed method uses the real-time digital processing of baseband signals to compensate the nonlinearities and memory effects in radio-frequency power amplifier. To reduce the complexity of computing in classical Kalman filtering, a sliding time-window has been inserted which combines offline measurement and online parameter estimation with high sampling time to track the changes in the PA characteristics. The performance of the proposed linearization scheme is evaluated through simulation and experiments. Using digital signal processing, experimental results with commercial power amplifier are presented for multicarrier signals to demonstrate the effectiveness of this new approach.

Kalman filtering algorithm for on-line memory polynomial predistortion

A new adaptive technique for digital predistortion is presented. The proposed method uses the real-time digital processing of baseband signals to compensate the nonlinearities and memory effects in radio-frequency power amplifier. Kalman filtering algorithm with sliding time-window is adapted to track the changes in the PA characteristics. Simulation and measurement results, using digital signal processing, are presented for multicarrier signals to demonstrate the effectiveness of this new approach.

Behavioral Modeling and Digital Predistortion of RF Power Amplifiers

Modeling accurately the nonlinear behavior of radio frequency power amplifiers is a key point in the design and development of linearizer. In this paper we presented a predistorsion technique based on DSP circuit and the identification of continuous time model describing the power amplifier associated to quadrature modulator and demodulator circuits. The model is composed by two blocks, the first uses polynomial functions to model the nonlinear amplitude and phase distortion, the second one is based on a MIMO continuous filter to describe the PA dynamics. Parameters are determined using identification method based on output error technique and a pseudo random binary sequence as signal excitation. Using the previous solution, the non-linear inverse function is calculated and implemented in the DSP. Experimental results of digital predistorsion show an improvement of 10 dB of the ACPR for QPSK and pi/4 DQPSK modulated signals

Modeling and identification of continuous-time system for RF amplfiers

In this paper, we present a new identification procedure for radio frequency power amplifier (PA) in the presence of nonlinear distortion and memory effects. The proposed procedure uses a continuous-time model where PA dynamics are modeled with a multivariable filter and a general polynomial function. Using the baseband input and output data, model parameters are obtained by an iterative identification algorithm. Finally, the proposed estimation method is tested and validated on experimental data by comparison of the quadrature IQ signals in time domain.

Electrostatic discharges from charged cylindrical bodies to grounded or floating surfaces

Most of the studies carried out on the hazards related to the electrostatic discharges (ESD) assume that the breakdown strength of air, at atmospheric pressure, is 30 kV/cm. The authors have developed numerical techniques for a most accurate estimation of the conditions in which a self-sustaining discharge can occur between conductive bodies of different shapes and sizes. An analysis is presented of three ESD events involving charged cylindrical bodies in the proximity of grounded or floating surfaces. The voltage at breakdown, the critical charge that triggers the discharge, the charge exchanged between the two bodies and the energy transferred in the discharge are evaluated as functions of various geometric parameters. The interpretation of the results provide a better understanding of the multitude of factors which determine the probability of a discharge and the relative severity of such an event in various technical systems.