The RF front-end in modern communication systems is faced with variable envelope and large bandwidth signals (including desired signals and large interferers), which require the behavioral model of the amplifying unit (either in Tx or Rx) to accurately account for nonlinear memory effects. Important advancements have been made on the subject; however it is still challenging to derive a model that performs equally well with all possible input stimuli. This paper gives a concise overview of the recent developments that have been made on the continuous-time modeling approach for the behavioral modeling of nonlinear memory in power amplifiers, as opposed to the explicit discrete-time modeling approach.

On the Continuous-Time Model for Nonlinear-Memory Modeling of RF Power Amplifiers

This paper presents a new radio frequency power amplifier behavioral model that is capable of modeling long term memory effects. The proposed model is derived by assuming linear dependence of the parameters of a conventional model to a long term memory parameter, which enables the model to better track the signal-induced changes of the power amplifier electrical behavior. The model is experimentally tested on a 100W Doherty power amplifier, with a signal that has a step-like change in power, representative of a realistic communication system with bursty behavior. Results show that the proposed model is able to improve the normalized mean squared error performance by around 2–3 dB.

http://publications.lib.chalmers.se/records/fulltext/local_159821.pdf

Modeling of long term memory effects in RF power amplifiers with dynamic parameters

The quest for the best compromise between the requirements for battery preservation and system operation linearity in the radio frequency (RF) and microwave front end has been a constant push for research on behavioral modeling of active devices since the early days of satellite communications [1] and has accelerated with the growth of modern mobile communication infrastructures. This focus has resulted today in a vast amount of behavioral model options, especially for the RF power amplifier (PA), in which it is not always simple for a designer to find his or her way as discussed in [2]-[5]. Using the term "behavioral model," we define these models as those derived from the observation of the electrical variables at the block ports (with very little insight on the internal composition of the block) and dedicated to the modeling of baseband/bandpass subsystems. Unlike transistor-level compact modeling, where there are well-established initiatives for model standardization driven by foundries and computer-aided design vendor companies [6], [7], there is, unfortunately, no such comparable effort yet at the subsystem level [8]. This article offers a concise summary of the recent progress on time-domain behavioral modeling with a particular focus on the continuous-time (CT) modeling theory [9].

Progress for Behavioral Challenges: A Summary of Time-domain Behavioral Modeling of RF and Microwave Subsystems

This paper deals with pulsed LSNA measurements of high power AlGaN/GaN transistors performed in a multi-harmonic passive load-pull environment. Time domain waveforms are acquired during a 150 ns window. This measurement window is moved across the 20 mus duration of pulses, the period is 1 ms. Phase and gain drifts of transistor characteristics versus time during the pulses are obtained and discussed.

/pdf/pulse-profiling-for-algan-gan-hemts-large-signal-1to2iiubii.pdf

Pulse Profiling for AlGaN/GaN HEMTs Large Signal Characterizations

A set of monolithic microwave integrated circuits (MMICs) has been successfully developed by using a qualified European GaN HEMT technology. In particular a high power amplifier (HPA), a low noise amplifier (LNA) and a single pole double throw (SPDT) switch have been designed, manufactured and tested. The presented chipset is very suitable for integration in future GaN-based T/R module Frontend for spaceborne X-band SAR applications. In particular, the MMIC HPA integrates two stages of gain in 5.5 × 4.0 mm2 of area. Its measured performance is an output power of 27 W, a PAE of 36% with a linear gain greater than 24 dB from 8.8 GHz to 10.2 GHz. The MMIC LNA integrates three stages of gain in 3.0 × 2.02 mm2 of area. Its measured performance is a small signal gain greater than 23 dB with an associated noise figure of 1.6 dB in the frequency range from 7.4 to 11.4 GHz. Besides, its output power at 1 dB of gain compression is greater than 22 dBm. The MMIC SPDT switch exploits a robust asymmetrical absorptive/reflective topology in 3.0 × 1.0 mm2 of area. The chosen topology allows obtaining different functionalities of each switched branch. In the frequency range from 8.4 GHz to 10.8 GHz its measured performance is an insertion loss lower than 1 dB for both tx and rx path, and tx-mode rx-mode isolations better than 20 dB and 28 dB respectively. Besides, the tx path 1 dB insertion loss compression occurs at nearly 20 W of input power.

A GaN MMIC chipset suitable for integration in future X-band spaceborne radar T/R module Frontends

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.

Behavioral Thermal Modeling for Microwave Power Amplifier Design

This paper presents the development of power MMICs in GaN HEMT technology for X-Band T/R modules. We will focus here specifically on the transmit path, which contains the high power amplifier and its power driver. A step by step description of the tasks in order to design this channel will be done, beginning from a short overview of the epitaxial process to the presentation of its measured and simulated power performances.

http://ieeexplore.ieee.org/iel5/5606058/5613634/05613748.pdf

GaN power MMICs for X-Band T/R modules

This paper presents a behavioral model for RF power amplifiers including load-pull and self-heating effects for radar applications. The model topology combines nonlinear scattering functions with a thermal model. This work focuses on model identification from time domain load-pull measurements and thermal simulations of the power amplifier. Comparisons between model and pulsed measurements, demonstrate its ability to accurately reproduce the signals and temperature for arbitrary load impedances.

Electrothermal behavioral model identification and validation from time domain load pull measurement of a RF power amplifier

This paper presents a behavioral electrothermal model implementation for high RF power amplifiers dedicated to the simulation of radar application in the Scilab/Scicos environment. This model, based on the direct coupling between a behavioral electrical model and a physics-based reduced thermal model, allows to predict nonlinear effects, high-frequency memory effects, and thermal effects due to the amplifier self-heating. System model implementation in Scilab/Scicos platform allows fast time domain simulation with very good convergence properties.

Implementation of electrothermal system-level model for RF power amplifiers in Scilab/Scicos environment

Modélisation électrothermique comportementale d'amplificateur de puissance avec prise en compte de l'effet load pull pour des applications radar à bande étroite

Julie Mazeau

Papers

Behavioral Thermal Modeling for Microwave Power Amplifier Design

GaN power MMICs for X-Band T/R modules

Electrothermal behavioral model identification and validation from time domain load pull measurement of a RF power amplifier

Implementation of electrothermal system-level model for RF power amplifiers in Scilab/Scicos environment

Modélisation électrothermique comportementale d'amplificateur de puissance avec prise en compte de l'effet load pull pour des applications radar à bande étroite