Francesco Scappaviva

A New Approach to Microwave Power Amplifier Design Based on the Experimental Characterization of the Intrinsic Electron-Device Load Line

This paper presents a new original approach to power amplifier design, which is mainly based on low-frequency nonlinear empirical electron device (ED) characterization. The proposed technique enables the same level of accuracy provided by expensive load-pull measurement systems to be obtained through a relatively simple and low-cost setup. Moreover, ED currents and voltages related to reliability issues can be directly monitored. Different experimental examples based on power GaAs and GaN field-effect transistors are provided to demonstrate the validity of the proposed approach.

GaN HEMT Noise Model Based on Electromagnetic Simulations

This paper presents a new approach for the definition and identification of a transistor model suitable for low-noise amplifier (LNA) design. The resulting model is very robust to layout modifications (i.e., source degeneration) providing accurate predictions of device noise-performance and small-signal parameters. Moreover, the described procedure is very robust since it does not require any numerical optimization, with possibly related problems like local minima and unphysical model parameters. The adopted model topology is based on a lumped element parasitic network and a black-box intrinsic device, which are both identified on the basis of full-wave electromagnetic simulations, as well as noise and S-parameter measurements. The procedure has been applied to three GaN HEMTs having different peripheries and a Ku-band LNA has been designed, demonstrating a very good agreement between measurements and predicted results.

Improvement of PHEMT intermodulation prediction through the accurate modelling of low-frequency dispersion effects

Large-signal dynamic modelling of III-V FETs cannot be simply based on de i/v characteristics, when accurate performance prediction is needed. In fact, dispersive phenomena due to self-heating and/or traps (surface state densities and deep level traps) must be taken into account since they cause important deviations in the dynamic drain current. In this paper, a recently proposed large-signal i/v measurement setup is exploited to extract an empirical model for lowfrequency dispersive phenomena in microwave electron devices. This i/v model is then embedded into a microwave large-signal PHEMT model. Eventually, a Ka-band highly linear power amplifier, designed by Ericsson using the Triquint GaAs 0.25pm PHEMT process, is used for model validation. Excellent intermodulation distortion predictions are obtained with different loads despite the extremely low power level of IMD products involved. This entitles the proposed model to be also used in the PA design process instead of conventional loadpull techniques whenever the high-linearity specifications play a major role.

X-Band GaN Power Amplifier for Future Generation SAR Systems

A X-band GaN monolithic microwave integrated circuits (MMIC) High Power Amplifier (HPA) suitable for future generation Synthetic Aperture Radar systems is presented. The HPA delivers 14 W of output power, more than 38% of PAE in the frequency bandwidth from 8.8 to 10.4 GHz. Its linear gain is greater than 25 dB. For the first time an MMIC X-band HPA has been designed by directly measuring the transistor behavior at the current generator plane. In particular, optimum device load-line has been selected according to the chosen performance tradeoffs.

A new approach to Class-E power amplifier design

An innovative, recently introduced, methodology for microwave power amplifier design, is here extended to switching-mode Class-E amplifier operation. Such a technique is based on a complete and accurate electron device (ED) characterization, which is provided by both direct large-signal low-frequency I/V measurements, performed by means of a relatively simple low-cost setup, and a model-based description of nonlinear reactive effects related to ED capacitances. In order to verify the proposed design methodology, a Class-E power amplifier (PA) has been designed.

10 Watt High Efficiency GaAs MMIC Power Amplifier for Space Applications

This paper describes the design of a GaAs monolithic high power amplifier at Ku band. The chip delivers about 40 dBm of saturated output power, in CW operating conditions, at 11.7 GHz central frequency, with 17% of bandwidth. The saturated power gain is 12.4 dB with 2 dB gain flatness across the application bandwidth while the chip power added efficiency is estimated between 33% to 47%. The amplifier is designed to be used as final stage of a downlink satellite transmitter for Tracking Telemetry & Command system. A commercial power p-HEMT process capable of handling a power density higher than 1 W/mm has been selected for the MMIC design. Due to the space application, special attention must be put on the process and MMIC reliability: to this aim performances must be guaranteed in de-rated conditions respect to the process maximum ratings and, in addition, the channel temperature of the active devices must be kept within the value established by Space Requirements and carefully controlled. This makes the design objective very tight. The MMIC power amplifier design and some measurement results are presented in the paper.

“Hybrid” approach to microwave power amplifier design

A new “hybrid” approach to microwave power amplifier design is presented which is based both on experimental large-signal low-frequency I/V load-line characterization and a model-based description of the device capacitances. Such a technique allows to get the same information obtained through nonlinear measurement setups operating at microwave frequencies. Several simulated and experimental data are proposed, based on GaN technology, in order to prove the effectiveness of the methodology.

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

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.

Hybrid High Power Amplifiers for L-Band Space Application

This paper describes the design and implementation of 2 hybrid high power amplifiers at L band for a space application. Indeed, the amplifiers represent prototype test vehicles for a larger hybrid amplifier to be used as the final power stage in the transmitting chain of a T/R module of an L-band SAR antenna for earth observation. The amplifiers described in this paper exploit a discrete bar of a commercial 0.35 mum pHEMT process as active device. The first amplifier, featuring a single discrete device, delivers 12 Watts with 56.5% PAE and 12.3 dB gain at 2 dB compression. The second amplifier exploits 4 discrete pHEMT bars using input/output microstrip splitter/combiner and lumped wire bonding/ceramic MIM capacitor output matching networks. It delivers 42 watts with 50% PAE and 13 dB gain at 2.5 dB compression. Since it is a space application, these performances have been achieved with the required de-rating on break-down voltages, current densities and operating channel temperature. The latter has been evaluated by means of a 3-D device model implemented in the framework of a finite differences numerical thermal simulator. In spite of the constraints due to space de-rating rules, the obtained output power densities are 1 W/mm and 0.875 W/mm for the single-discrete and the 4-discrete amplifiers, respectively, which represent a value very close to the state of the art for pHEMT processes.

GaN HEMT modelling through 50-Ω NF measurements

In this paper a small-signal and noise transistor model with the associated extraction procedure is proposed. The model is based on an equivalent circuit, extracted from electromagnetic simulations and noise measurements using an automatic analytical procedure. This identification procedure ensures high robustness to layout modifications, making the model suitable for low-noise amplifier design. An equivalent temperature approach is exploited for noise modelling: every passive element of the equivalent circuit is considered at room temperature, except for the intrinsic drain conductance. Its equivalent temperature is extracted by simply fitting the noise figure for a 50 Ω source termination. The proposed technique allows a very good accuracy of the noise parameter predictions for degenerated devices, avoiding expensive and time consuming noise parameter characterization.