Emmanuel Gatard

Behavioral Thermal Modeling for Microwave Power Amplifier Design

System-level models simplify the analysis of complex RF systems, such as transmission-reception modules, by expressing global input-output relationships. However, the development of high RF power models for nonlinear subsystems requires the prediction of the distortion induced by low-frequency memory effects such as self-heating effects. In this framework, we present a new electrothermal behavioral model for power amplifiers. This global model is based on the coupling between a behavioral electrical model derived from the transistor-level description of the amplifier and a thermal reduced model. This model, implemented into a circuit simulator, allows to predict the impact of the thermal effects in pulsed RF mode thanks to an envelope transient analysis. This approach has also been validated by measurements.

An Improved Physics-Based Formulation of the Microwave p-i-n Diode Impedance

An improved formulation of the frequency-dependent impedance for p-i-n diodes from physical and geometrical parameters is presented. This work is addressed to diode designers and allows them to evaluate quickly and accurately the diode impedance. It comes in parallel with existing SPICE p-i-n diode model used in CAD software. Under forward bias conditions, important recombinations occur in the heavily doped end regions of thin p-i-n diodes that seriously affects the diode impedance. This effect is taken into account to increase the accuracy of existing numerical models and to extend their validity domain to any I-region thicknesses. This improvement has been validated by measurement results on a 5-mum I-region width silicon p-i-n diode

Nonlinear Thermal Reduced Model for Power Semiconductor Devices

The challenge in terms of accurate prediction of electrical behavior, reliability and thermal management of semiconductor power devices goes through the coupling of multi physics analysis and especially through the coupling of nonlinear thermal models with nonlinear electrical models. In order to obtain a precise nonlinear thermal model which can be implemented as an equivalent SPICE (simulation program integrated circuits especially) subcircuit in circuit simulators, we present a methodology based on a model order reduction technique applied to a three dimensional finite element thermal description. This reduction method is based on the Ritz vector approach. In order to take into account the nonlinear thermal properties of materials, an extension of the method based on the Kirchoff transformation and an interpolation formula is proposed. This method, theoretically suitable only for homogeneous structures, exhibits in practice a very good accuracy for heterogeneous structures. Another improvement in the nonlinear transient response relies on the self consistent calculation of a coefficient related to the thermal conductivity approximation law. Thus, obtaining directly in time domain a nonlinear thermal reduced model for inhomogeneous structure is possible. The complete model has been successfully implemented in circuit simulator for several power devices and for various nonlinear materials such as GaAs, GaN or silicon. The nonlinear behavior has been validated on a wide range of input power and baseplate temperature. The influence of the interpolation formula is discussed for strongly nonlinear materials. Thermal infrared and electrical measurements have been performed to validate the simulation results

Multiharmonic Volterra Model Dedicated to the Design of Wideband and Highly Efficient GaN Power Amplifiers

This paper presents a complete validation of the new behavioral model called the multiharmonic Volterra (MHV) model for designing wideband and highly efficient power amplifiers with packaged transistors in computer-aided design (CAD) software. The proposed model topology is based on the principle of the harmonic superposition introduced by the Agilent X-parameters, which is combined with the dynamic Volterra theory to give an MHV model that can handle short-term memory effects. The MHV models of 10- and 100-W packaged GaN transistors have been extracted from time-domain load-pull measurements under continuous wave and pulsed modes, respectively. Both MHV models have been implemented into CAD software to design 10- and 85-W power amplifiers in L- and S-bands. Finally, the first power amplifier exhibited mean measured values of 10-W output power and 65% power-added efficiency over 36% bandwidth centered at 2.2 GHz, while the second one exhibited 85-W output power and 65% drain efficiency over 50% bandwidth centered at 1.6 GHz.

High power S band limiter simulation with a physics-based accurate nonlinear PIN diode model

This paper deals with the simulation and the design of an active dual stage high power S band limiter. The contribution of this work relies on an accurate nonlinear PIN diode model that has been used to predict the limiter performances. This model takes into account recombination phenomenon in the heavily doped region and include junctions effects. In the first section, the model is presented and validated by measurement results on two thin diodes. In the second section, the limiter output power and isolation characteristics are validated by power measurements up to +55 dBm and by spectrum measurements.

New electrothermal system level model for RF power amplifier

This paper considers a new approach for nonlinear system level models dedicated to high RF power amplifiers. The constant increase of power density imposes to take into account of thermal effects. In this framework, a new electro-thermal behavioral model based on the coupling between a behavioral electrical model and a thermal reduced model predicting the operating temperature of the amplifier is expressed for radar application. This model has been successfully implemented into the Agilent Advanced Design System (ADS) circuit simulator. The transient thermal effects have been simulated thanks to an envelope transient analysis.

A multi-harmonic model taking into account coupling effects of long- and short-term memory in SSPAs

This paper presents a new macro modeling methodology for solid-state power amplifiers (SSPAs) and packaged transistors used in communication systems. The model topology is based on the principle of harmonic superposition recently introduced by Agilent Technologies’ X-parameters combined with dynamic Volterra theory. The resulting multi-harmonic bilateral model takes into account the coupling effects of both shortand long-term memory in SSPAs. In this work, the behavioral model was developed from time-domain load pull and used to simulate the amplifier’s response to a 16-QAM signal with specific regards to ACPR and IM3.

A new Multi-Harmonic Volterra model dedicated to GaN packaged transistor or SSPA for pulse application

This paper presents a new macro modeling methodology for solid-state amplifiers (SSAs) and packaged transistors used in radar systems. The model topology is based on the principle of the harmonic superposition recently introduced by the Agilent X-parameters(TM) combined with dynamic Volterra theory. In this work, we focus on a pulsed identification method which has been made from time domain load pull measurement performed on a packaged transistor. The model has been validated by pulsed RF measurement in the optimum area for several frequencies.

A Physics-Based Nonlinear Model of Microwave P-I-N Diode for CAD

A p-i-n diode model for switching and limiting applications is presented. The model allows to simulate the I-region store charge effect that governs the impedance-frequency characteristic of the diode. The model also includes recombination phenomenon in the heavily doped region and junctions effects. The diode model has been implemented in a commercial circuit simulator and validated with a good agreement by measurement results