Sébastien Mons

A unified approach for the linear and nonlinear stability analysis of microwave circuits using commercially available tools

For the first time, an exhaustive linear and nonlinear stability analysis of multi-transistor MMIC circuits is presented. A key point of the proposed stability analysis lies in that it can be easily implemented on any CAD package. Our straightforward and powerful approach allows both linear and nonlinear stability analysis of any complex circuit submitted or not to large RF signals. Following our novel approach, a MMIC HBT power amplifier was analyzed. Division frequency phenomena and spurious oscillations were detected by simulations and confirmed by measurements.

A pulsed-measurement based electrothermal model of HBT with thermal stability prediction capabilities

In this paper, a new electrothermal non linear model of HBT suitable for CAD purposes is presented. This model is fully determined by pulsed measurement techniques and for the first time, it is shown that the prediction of thermal instabilities (collapse of current gain) is obtained from the CAD model. The model has been validated both by DC and RF load-pull measurements.

Hot small-signal S-parameter measurements of power transistors operating under large-signal conditions in a load-pull environment for the study of nonlinear parametric interactions

This paper presents a setup that enables wide-band (in-band and out-of-band) measurements of hot small-signal S-parameters of nonlinear devices driven by a large-signal single tone (namely, the pump signal). A load-pull characterization is performed at the pump frequency (F/sub 0/), while hot small-signal S-parameters are measured with a perturbating signal at a frequency (f) by the use of a probe tone. Basically, the frequency of the probe tone is swept over a wide bandwidth (at the present time from 300 MHz up to F/sub 0//2). A higher frequency range, from near dc to KF/sub 0/, will be implemented in a similar manner. The measurement setup reported here is applied to on-wafer measurements of S-band HBTs. Hot small-signal S-parameter measurements versus large-signal load impedance and pump level will be shown. An application to the prediction of parametric oscillations will be demonstrated. A parametric oscillation predicted at 373 MHz is confirmed by spectrum measurements.

A novel behavorial model of power amplifier based on a dynamic envelope gain approach for the system level simulation and design

This paper presents a novel and non quasi static behavioral ( black box) model of power amplifiers. It takes into account nonlinear memory effects for an accurate prediction of signal distortions and power budget in communication systems. The model topology and the model extraction procedure are described. The model proposed in this paper can be derived either from envelope simulation results of a PA circuit design or from time domain envelope measurements of a PA driven by modulated stimuli. Examples of new measurements (i.e. : dynamic AM/AM conversion characteristics) highlight nonlinear memory of SSPAs. The behavioral model proposed is very well suited for an efficient implementation in system level software packages because it consists of an extension of the complex envelope gain function. The proposed complex gain which depends on the input envelope and its first time derivatives provides a great enhancement as compared to the memoryless static complex gain derived from classical AM/AM and AM/PM conversion characteristics.

Efficient nonlinear Stability Analysis of Microwave Circuits using Commercially Available Tools

In this paper, two techniques for checking stability of multi-transistor MMIC circuits are analyzed. The two approaches allow both linear and nonlinear stability analysis of any complex circuit fed by small or large signals. The agreement found gives a unified way to propose a fast and efficient tool to ensure stability of a design during the design step using commercially available software. An example is given to evidence the suitability of the approach. It concerns a MMIC HBT power amplifier, which exhibited a frequency division phenomena that has been detected by simulations and confirmed by measurements.

EM/Circuit Mixed Simulation Technique for an Active Antenna

Todays increase of functions, improvement of performance, and cost reductions required on an active electronically scanned array (AESA), associated to the limited amount of available areas and volumes to implement the equipment, drive an approach leading to directly connect power amplifiers (PAs) to the antennas array without placing an isolator/circulator between them. In this letter, an electromagnetic/radio frequency (EM/RF) circuit mixed simulation technique will be theoretically introduced and experimentally demonstrated on transmission (Tx) chains to deal with the proposed challenge.

An accurate modeling technique for antennas and nonlinear RF power amplifier mixed simulation

The design of agile active antennas requires an efficient modeling methodology in order to quantify the impact of other components on the array radiation pattern, and especially the influence of power amplifiers (PA). Therefore, the performance prediction of PA on TX chains is of prime importance. This article describes two different approaches for active antenna applications. The first one concentrates on PA macro-modeling, which takes into account a large output load impedance mismatch with a voltage standing wave ratio up to 4:1. A PA behavioral model based on nonlinear scattering functions was developed and extracted from CW measurements. The model validity was checked by comparison with the measured data. The second one describes a novel technique for synthesizing a given radiation pattern, whereas taking into account the mutual coupling and calculated matching impedances (ZL =50 V) of each antenna in the array according to frequency and pointing angle.

LTV Circuit Modelling Techniques for System Simulation. Application to a MMIC K-Band I-Q Signal-Modulator

A technique for modelling LTV circuits with frequency-translation such as mixers and signal modulators is presented. The time and frequency-domain simulations of these comp lex circuits can be very expensive in terms of computational resources. A black-box reduced modelling approach for system simulation is proposed. The model consists of an equivalent linearized low-pass filter followed by a memoryless multiplication. The reduced model provides a noticeable decrease of simulation time, with a slight loss of accuracy. The modelling technique has been applied to a MMIC QPSK signal-modulator in K band and implemented in a standard simulation tool. The simulation results of the reduced model and the complete modulator equivalent circuit have been compared, obtaining good agreement.

Design of a 55 W packaged GaN HEMT with 60% PAE by internal matching in S-band

This paper reports a package synthesis method in order to ensure good performances in PAE, output power and bandwidth. The internal matching circuits of the optimized package enable to reach the best impedance pre-matching at fundamental frequencies and also to confine the harmonic impedances seen by the internal GaN power bar into safe-efficiency regions whatever the external impedances presented to the package at second harmonic frequencies. In a 50Ω environment, the packaged GaN HEMT delivers 55 W output power associated with 60% PAE and 13.3 dB power gain at 2.7 GHz. By optimizing source and load impedances at the fundamental frequencies, the packaged GaN HEMT demonstrates more than 58% PAE from 2.6 GHz to 3.0 GHz.

Mixed simulation approach for direct connection between power amplifiers and antenna arrays without the use of isolators

This paper describes a mixed simulation approach of electromagnetic (EM) macromodel and nonlinear circuit bilateral model to correct the output signal for a power amplifier (PA) and obtain an optimal radiation pattern for an active antenna array transmit (TX) chain. Various experimental results show the reliability of EM, nonlinear PA models and mixed simulation approach as well. The originality of this work is the elimination of isolators between PAs and antennas while maintaining a matched PA and a correct radiation pattern in regards to the antennas high impedance mismatch.