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A generalized dual-input digital predistortion (DPD) methodology for supply-modulated (SM) power amplifiers (PAs) is proposed. Contrary to classical approaches, the SM and the radio frequency (RF) signals are treated as separate digital inputs to be jointly predistorted. A multi-objective optimization (MOO) strategy allows to explore the inherent PA performance tradeoffs to jointly optimize the DPD coefficients for improved power-added efficiency (PAE) and higher RF output power, yet guaranteeing a prescribed linearity performance. To avoid dealing with an unbearably high number of experimental acquisitions, MOO is here made feasible by fast simulation of an empirical surrogate model of the PA, which is progressively refined from a reduced set of iterative acquisitions. The proposed technique enables the adoption of a dynamic supply shaping function, and it automatically accounts for the signals' statistics. Eventually, the method outperforms classical SM approaches, yet using a DPD of the same order, as demonstrated by the experimental results on a gallium nitride (GaN) SM PA operating at 3.5 GHz in the presence of orthogonal-frequency-division-multiplexing (OFDM)-like high-peak-to-average power ratio (PAPR) modulated signals with 10- and 20-MHz bandwidths (BWs).

High-voltage GaN switches offer low conduction and commutation losses compared with their Si counterparts, enabling the development of high-efficiency switching-mode DC–DC converters with increased switching frequency, faster dynamics, and more compact dimensions. Nonetheless, the potential of GaN switches can be fully exploited only by means of accurate simulations, optimal switch driving, suitable converter topology, accurate component selection, PCB layout optimization, and fast digital converter control. This paper describes the detailed design, simulation, and implementation of an air-cooled, 7.5 kW, dual active bridge converter exploiting commercial 650 V GaN switches, a compact planar transformer, and low ESL/ESR metal film capacitors. The isolated bidirectional converter operates at a 200 kHz switching frequency, with an output voltage range of 200–500 V at nominal 400 V input voltage, and a maximum output current of 28 A, with a wide full-power ZVS region. The overall efficiency at full power is 98.2%. This converter was developed in particular for battery charging applications, when bidirectional power flow is required.

High-voltage GaN switches can offer tremendous advantages over silicon counterparts for the development of high-efficiency switching-mode power converters at high commutation frequency. Nonetheless, GaN devices are prone to charge-trapping effects that can be particularly relevant in the early-stage development of new technologies. Charge-trapping mechanisms are responsible for the degradation of the dynamic ON-resistance (RON) with respect to its static value: this degradation is typically dependent on the blocking voltage, the commutation frequency and temperature, and is responsible for the reduction of power converter efficiency. The characterization of this phenomenon is very valuable for the development of a new process to compare different technological solutions or for the final assessment of performance. This characterization cannot be made with traditional static or small signal measurements since RON degradation is triggered by application-like dynamic device excitations. In this paper, we propose a technique for the characterization of the dynamic RON of high-voltage GaN switches under real operating conditions: this technique is based on the design of a half bridge switching leg in which the DUT is operated under conditions that resemble its operation in a power converter. With this setup, the characterization of a 600 V GaN switch dynamic RON is performed as a function of variable blocking voltages and commutation frequency. Additionally, this technique allows the separation of thermal and trapping effects, enabling the characterization of the dynamic RON at different temperatures.

This article deals with the characterization of charge trapping dynamics in a novel 100-nm double-heterojunction AlN/GaN/AlGaN-on-Si radio frequency (RF) HEMT process. In order to study the detrapping mechanisms, we perform the wideband acquisitions of the transient behavior by sweeping the pulsed voltages to cover the entire device operating area. The fast acquisition also enables the characterization of the charge capture behavior, a key aspect for RF performance. From the analysis of the drain current transients, time constants are extracted, showing a fundamental release time constant in the order of 0.1-1 ms, and more than one capture constants, the fastest being in the order of 300 ns. To the best of authors' knowledge, this is the first time that trapping dynamics under large-signal regime are characterized for this type of process.

In this paper, we present a high-efficiency transmitter based on an integrated circuit (IC) supply modulator implemented in the same 0.15- $\mu \text{m}$ gallium nitride (GaN)-on-SiC RF process as the power amplifier (PA) monolithic microwave IC. The X-band 10-W two-stage PA is designed for stable operation with minimal drain capacitance, which enables fast supply modulation. The multilevel supply modulator provides eight voltage levels with 3-bit digital control [(power digital-to-analog converter (pDAC)], achieving a state-of-the-art slew rate of 5 kV/ $\mu \text{s}$ . Characterization of the dynamic $R_{\mathrm{\scriptscriptstyle ON}}$ of the GaN switches allows the development of an efficiency model for the pDAC and an investigation of the effects of the pDAC internal resistance on the PA performance, resulting in a comprehensive efficiency model for the supply-modulated PA. The flexible compact transmitter consisting of the PA and pDAC ICs shows high efficiency in backoff for a variety of signals, both for radar and communications. Measured results for amplitude- and frequency-modulated radar pulses show a composite power-added efficiency (CPAE) of 44% with a peak power of 10 W at 9.57 GHz, with simultaneous spectral confinement and 52-dB improvement of the first time sidelobe. For a 20-MHz high peak-to-average ratio LTE signal, the CPAE increases from 11% to 32% compared to a fixed supply voltage transmitter, while linearity under dynamic supply operation is maintained through digital predistortion.

While digital predistortion (DPD) usually targets only the linearity performance of the radio&ndash, frequency (RF) power amplifier (PA), this work addresses more than a single PA performance metric exploiting a multi-objective optimization approach. We present a predistorer learning procedure based on a constrained optimization algorithm that maximizes the RF output power, while guaranteeing a prescribed linearity level, i.e., a maximum normalized mean square error (NMSE) or adjacent-channel power ratio (ACPR). Experimental results on a Gallium Nitride (GaN) PA show that the proposed approach outperforms the classical indirect learning architecture (ILA), yet using the same predistorter structure with predetermined nonlinearity and memory orders.

The stacked power amplifier is a widely adopted solution in CMOS technology to overcome breakdown limits. Its application to compound semiconductor technology is instead rather limited especially at very high frequency, where device parasitic reactances make the design extremely challenging, and in gallium nitride technology, which already offers high breakdown voltages. Indeed, the stacked topology can also be advantageous in such scenarios as it can enhance gain and chip compactness. Moreover, the higher supply voltages and lower supply currents beneficially impact on reliability, thus making the stacked configuration an attractive solution for space applications. This paper details the design of two stacked cells, differing in their inter-stage matching strategy, conceived for space applications at Ka-band in 100 nm GaN-on-Si technology. In particular, the design challenges related to the thermal constraints posed by space reliability and to the electro-magnetic cross-talk issues that may arise at millimeter-wave frequencies are discussed. The best cell achieves at saturation, in simulation, 3 W of output power at 36 GHz with associated gain and efficiency in excess of 7 dB and 35%, respectively.

A Ka -band monolithic low-noise amplifier (LNA) with high gain and high dynamic range (DR) has been designed and implemented in a 100-nm gallium nitride (GaN)-on-Si technology. The LNA is designed as the first stage of a high DR receiver in an frequency modulated continuous wave (FMCW) radar for the detection of small drones. The three-stage monolithic microwave integrated circuit (MMIC) LNA has a linear gain of 26 dB and a noise figure (NF) of 2 dB in the frequency band 33–38 GHz. The output 1-dB compression point (P1dB) and output IP3 at 37 GHz are 20 and 28.4 dBm, respectively. To our knowledge, this combination of NF, gain, and DR performance represents the state of art in this frequency band.

This work presents a performance improvement technique for supply-modulated (SM) power amplifiers (PAs). Differently from the typical solutions, the SM PA is treated as a double-input nonlinear dynamic device, for which a dynamic supply shaping function and an RF digital predistorter are jointly identified by means of a gradient-based multi-objective optimization (MOO) technique. Simulation-based tests show that the MOO-based optimal inputs can greatly enhance the SM PA effectively exploring, in an automatic way, the best compromise between linearity and efficiency.

This paper describes the performance degradation of RF GaN-on-SiC HEMT switches due to the charge trapping, which is triggered by high voltages under operating regimes. A custom measurement setup is used for the characterization of the switching behavior under dynamic control and blocking voltages. It is shown that both small- [i.e., insertion loss (IL)] and large-signal (LS) performances (i.e., switch compression) are affected by traps. Depending on the applied voltages, an increase of the switch IL up to 50% and significant degradation of the switch compression characteristic were measured for a $4 \times 75\,\,\mu \text{m}^{2}$ RF switch in 0.25- $\mu \text{m}$ GaN-on-SiC technology. These mechanisms cannot be observed with conventional static characterization, and they are not described by standard RF switch models. A device model capable to account for the observed characteristics is identified and empirically validated under LS conditions at 10 GHz.

This paper presents a dynamic characterization of a multilevel (ML) Chireix outphasing (ML-CO) power amplifier (PA) with modulated signals. The ML-CO technique combines the advantages of envelope tracking and outphasing architectures by limiting the supply modulation to discrete levels with an efficient power-DAC modulator and using outphasing for fine amplitude control. We describe an experimental test bench that supplies the required phase- and time-aligned modulated signals for outphasing and supply modulation simultaneously. Pulsed characterization is used to design an ML memoryless polynomial DPD. The linearized ML-CO GaN X-band MMIC PA is demonstrated with fixed input drive levels for 9.3-dB peak-to-average power ratio (PAPR), 1.4-MHz and 11.3-dB PAPR, 10-MHz LTE signals with a 9.7-GHz carrier. For both signals, the average total power consumption is reduced by a factor of two when supply modulation is used. An investigation of control signal generation strategies is presented, including combinations of discrete supply and continuous input modulation. A simple exponential function tracks the optimal efficiency trajectory of the ML-CO PA, enabling overall efficiency improvements within 9 and 27 percentage points. This control strategy is applied to radar pulses with amplitude shaping and frequency chirp, with the efficiency improvement of up to 11.8 percentage points compared with constant-supply operation, with 29-dB improvement in spectral confinement.

This work investigates the impact of nonlinear dynamic effects due to charge trapping and other long-memory phenomena on the wideband linearity of power amplifiers (PAs) for 5G communications applications. The proposed method uses the well-known best linear approximation framework (BLA) to estimate the error vector magnitude (EVM) of the amplifier for the class of modulated signals sharing the same probability density function (pdf) and power spectral density (PSD) as the 5G waveform standards. The dependency of the EVM and the BLA on the large-signal operating point (LSOP) of the PA is studied using random phase multisine signals belonging to the same class. In particular, we evaluate the impact of different signal repetition periods in order to excite low-frequency dynamic phenomena across a wide range of time scales. Results, using just standard vector network analyzer (VNA) relative measurements, are reported for a Gallium Nitride (GaN) power amplifier (PA) for two different 5G-FR1-compliant bandwidths of 20 and 100 MHz around 5.5 GHz.

A pulsed characterization of gallium nitride (GaN) high-electron mobility transistors (HEMTs) under a controlled trap and thermal state is performed to evaluate the trapping-induced degradation in the actual operating conditions, corresponding to different classes of power amplifiers (PAs). Two state-of-the-art GaN-on-SiC technologies are evaluated: 0.15- ${\mu }\text{m}$ Qorvo and 0.25- ${\mu }\text{m}$ Wolfspeed HEMTs, with examples relative to class-AB, class-E, and supply modulated operation. It is shown that, in order to get an accurate device characterization, the measurements have to be performed by preconditioning the trap state consistently with the intended application.

GaN HEMT dispersive phenomena due to charge trapping can be effectively characterized by means of pulsed IV measurements. In this work, we exploit the wideband feature of the setup obtaining pulsed S-parameters measurements within narrow pulse widths, in the order of a few hundred ns. Then, we report the single and double-pulsed S-parameters characterization of the 100-nm GaN-on-Si HEMT technology by OMMIC, showing the impact of traps on the small-signal parameters and providing significant data for compact model identification.

This paper describes the linearization of a base-station L-band 500-W GaN Doherty high power amplifier (HPA) driven by OFDM signals. Pre-pulsing characterization is used to extract the gain dispersion of the carrier and peaking PAs due to trap-induced degradation of GaN-on-SiC transistors. Peak drain voltages reached by PA load-lines mainly set the trap states of the carrier and peaking PAs, while the recovery is longer with a dominant time constant of 100µs for this specific GaN technology. When the peak occurrences are below this dominant time constant of 100µs, such as for symbol periods of 16.7 to 66.7µs (i.e., LTE/5G OFDM), the HPA trap-state remains approximately constant in the time interval between voltage peaks, allowing low-complexity linearization of the HPA. With a 10-MHz OFDM signal with peak-to-peak intervals shorter than 100µs, a memory-less digital pre-distortion (DPD) is shown to improve ACLR by 4dB and NRMSE by 1.6 percentage points, as compared to peak-to-peak intervals longer than 100µs when significant trap recovery takes place.

This paper presents a supply modulated $X$ -band 12-W peak power transmitter that maintains an average efficiency greater than 50% for various shapes of amplitude-modulated pulses. The main power amplifier is a two-stage GaN-on-SiC MMIC with a peak efficiency of 65%, while the pulse envelope modulator is a 95% efficient hybrid 3-b power DAC implemented with GaN-on-Si transistor switches. Envelope shaping of a pulsed waveform results in improved spectral confinement of greater than 15 dB for the first sideband compared with constant-envelope pulses, with over 20 points improvement in total efficiency. The combination of supply modulation and digital predistortion is shown to result in high composite (total) efficiency of over 55%, with simultaneous high dynamic range and with flexible digitally programmable pulse shaping.

A MMIC double-balanced subharmonic diode ring mixer was designed for broadband satellite communications exploiting a GaAs pHEMT process. The circuit implements the frequency conversion from Q (43.5–50 GHz) to Ku-K band (17–21.5 GHz). Besides the RF, LO, and IF baluns, the MMIC integrates a buffer amplifier for the local oscillator signal, which is designed between X and Ku bands (11–16.5 GHz), due to the subharmonic operation. The mixer measured conversion loss is between 8 and 12 dB along the bandwidth, with an LO power of 9 dBm. The input p1 dB and IP3 are 2 and 15 dBm, respectively. The balanced structure ensures an LO and 2 × LO leakages at the IF port lower than −25 and −35 dBm, respectively. Other spurious remain below −67 dBc. The chip dimensions are 2.4 × 2.4 mm2.

In this paper, we describe a rigorous theoretical approach to the circuit-level nonlinear design of an entire inductive resonant wireless power transfer (IR-WPT) system, including the transmitter and receiver nonlinear subsystems. Starting from a novel analytical characterization of the inductive resonant link, the system efficiency is parametrically computed as a function of a set of circuital parameters, including the power levels to be transferred. These quantities are then used as design goals inside the nonlinear optimization of the transmitter and receiver blocks. By adopting the last generation miniaturized enhanced-mode AlGaN/GaN-power field-effect transistor and fast Schottky diodes, a Class-D amplifier and a full-bridge rectifier followed by a switching dc–dc Buck converter that acts as load impedance transformer are designed in a single optimization process at 6.78 MHz. Thus, the transmitter and the receiver are directly connected by the IR two-port network, and the system is capable to adapt to variable distances between the resonators of the IR-WPT link. The choice of the Class-D topology for the transmitter and the adaptability of the active receiver enable to get rid of inter-stage matching networks, which can severely reduce the overall efficiency, especially in high power transfer environments. With the proposed IR-WPT system, up to 44 W of transferred power and a peak of 73% dc-to-dc efficiency were obtained with an input dc voltage V = 30 V at a link distance d = 5 cm. Numerical and experimental results are discussed, demonstrating the accuracy of the proposed design procedure.

This paper addresses the efficiency enhancement of microwave power amplifiers (PAs) with discrete-level supply-modulation. We demonstrate an efficient modulator architecture that generates three levels of drain supply voltages from a single dc voltage. Each level is stored in a "flying" capacitor that acts as a temporary voltage supply and is dynamically regulated by feedback through reversal of the PA drain current. A hybrid modulator based on GaN-on-Si technology is tested with a single-stage 2-W X-band MMIC PA with a drain efficiency of 55% at the peak output power. The overall average drain efficiency (PA and modulator) of up to 43% is measured with Gaussian-like pulses for radar and a 5-MHz 6-dB PAPR OFDM signal, and is improved up to 14 percentage points over a constant supply case, with normalized root mean square error below 1.5% when pre-distortion is used.

This paper presents a broadband efficient power amplifier (PA) targeting sub-6-GHz 5G base station applications. Due to the demanding requirements in both peak-to-average power ratio (PAPR) and bandwidth in 5G systems, we employ a combination of both load and supply modulation for efficiency enhancement. Active matching, implemented using an RF-input load-modulated balanced amplifier (LMBA) architecture, enables efficient octave-bandwidth operation. Supply modulation, which is carrier frequency agnostic, is then used to further extend the back-off efficiency. This paper focuses on a study of supply modulation strategies for the load-modulated PA using an efficient GaN eight-level discrete supply modulator. To overcome the bandwidth limitations associated with discrete-level switching, a commutation rate reduction (CRR) filter is applied in digital baseband and its effects are analyzed theoretically and experimentally. The supply-modulated LMBA is characterized across 1.8–3.8 GHz with 100-MHz, 10-dB PAPR signals. An output power of 34 dBm with average composite (total) PAE ranging from 22.4% to 43.9% across the band is demonstrated, with an ACLR of about −50 dBc after digital predistortion.

The detection of Unmanned Aerial Vehicles (UAVs) of micro/nano dimensions, is becoming a hot topic, due to their large diffusion, and represents a challenging task from both the system architecture and components point of view. The Frequency Modulated Continuous Wave (FMCW) radar architecture in a Multi-Input Multi-Output configuration has been identified as the most suitable solution for this purpose, due to both its inherent short-range detection capability and compact implementation. This paper describes the operation and technology challenges inherent to the development of a millimeter-wave FMCW MIMO radar for small UAVs detection. In particular it analyzes the sub-systems specifications and the expected system performance with respect to a chip set designed and developed in GaN at 37.5 GHz applications.

This work presents multi-level supply modulation of a load modulated balanced amplifier (LMBA). The RF-input LMBA employs dynamic active matching for efficient operation over an octave bandwidth. Supply modulation is a natural candidate to further enhance the back-off efficiency of this broadband amplifier due to its independence on RF carrier frequency. In the ET-LMBA prototype demonstrated here, an efficient hybrid multi-level converter (power DAC) produces supply levels from 10 to 30 V to modulate the drain of the balanced amplifier. Digital predistortion is used to linearize the ET-LMBA behavior at discrete steps and over frequency. This system is demonstrated at 2.1, 2.7 and 3.5 GHz with a 20-MHz, 10-dB PAPR signal showing composite efficiency improvement between 9 and 12 percentage points when supply modulation is employed, while maintaining linearity.

Two C-band monolithic high power amplifiers (HPAs) have been designed and implemented exploiting a 0.25-μm AlGaN/GaN HEMT process on an SiC substrate. The circuits have been designed for use in transmit/recevie modules of satellite synthetic aperture radar antennas for Earth observation. The design was accurately focused on the HEMTs' electrical and thermal working conditions in order to guarantee the reliable operation required by space applications. The HPAs operate in pulsed conditions with typical pulsewidth of 50 μs and 10% duty cycle: in that regime, the circuits deliver about 40 W with more than 21-dB associated gain and 40% to 45% power-added efficiency in the 5-5.8-GHz band. The achieved performance clearly demonstrates the very high potentiality of this technology for the replacement of GaAs-based HPAs in new generations of this type of systems.

This paper presents an envelope tracking (ET) transmitter architecture based on the combination of a novel 3-bit $(N = 3)$ supply modulator and digital predistortion (DPD). The proposed power converter is based on a direct digital-to-analog conversion architecture that implements the binary-coded sum of $N$ isolated dc voltages, allowing the synthesis of an output waveform with $L = 2^{N}$ voltage levels, with a binary distribution in the range $\Delta V = V_{M} - V_{O}$ (maximum voltage $V_{M}$ , offset voltage $Vo$ ). This solution provides a better voltage resolution $V_{S} = \Delta V/(2^{N}-1)$ with respect to typical multilevel switched-sources topologies $(V_{S} = \Delta V/N)$ . The improved voltage resolution enables the correction of the residual discretization error in the ET transmitter by means of DPD of the RF signal without the need of an auxiliary linear envelope amplifier. The proposed ET solution has been tested with an L-band 30-W lateral-diffused MOS RF high power amplifier (RF HPA) with 1.4- and 10-MHz long-term-evolution signals. In these conditions the converter demonstrated 92% and 83% efficiency, respectively, whereas the congregate efficiency of the transmitter are 38.3% and 23.9% at 5.5 and 1.9 W of average RF output power, respectively. These performances correspond to an improvement of 17.2 and 17.9 points for the power-added efficiency of the RF HPA and to 13.4 and 13 points of improvement for the efficiency of the entire transmitter with respect to fixed bias operation.

As well as largely exploited for microwave high-power applications, aluminum gallium nitride (AlGaN)/GaN high electron mobility transistor (HEMT) technologies have demonstrated promising results for the design of low-noise, high dynamic range, and highly robust amplifiers. In this manuscript, we describe the design and characterization of a Ku-band monolithic microwave integrated circuit low-noise amplifier for telecom space applications, exploiting an industrial AlGaN/GaN 0.25-µm HEMT on silicon carbide process. In the frequency band 12.75–14.8 GHz, the LNA features over 20 dB linear gain with a noise figure around 1.8 dB. Input and output return losses are nearly 10 dB. Power dissipation is 700 mW in linear operation. An innovative transistor model based on electromagnetic analyses and small-signal and noise measurements has been developed to improve the predictions of the foundry model on source-degenerated devices. A systematic radio frequency (RF) life stress test campaign performed on the designed low-noise amplifier demonstrated a safe operating area of 15 dBm of overdrive input power. Copyright © 2015 John Wiley & Sons, Ltd.

GaN power switches provide remarkable performance in terms of power-density, reduced parasitics, and high-thermal handling capability that enable the realization of very efficient and compact dc/dc converters. Despite exhibiting state-of-the-art channel conductivity, GaN high electron mobility transistor (HEMT) devices are affected by the degradation of the dynamic on -Resistance ( R ON) at increasing off -state voltages and operative temperatures. In this paper, a novel laboratory setup and characterization procedure for the dynamic R ON of GaN HEMT switches in the presence of thermal- and trapping-effects is presented. The proposed setup allows the study of R ON transients after the switching event at variable off -state voltages and temperatures. The use of custom-designed differential amplification stages and a voltage-controlled current source enables the accurate characterization of R ON even on large periphery devices. At first, the proposed setup is tested with a well-established and mature device technology such as a Si MOSFET. Degradation of the R ON up to 120% due to temperature variation is observed with the presented setup. The setup is then used for the characterization of commercial-grade GaN-on-SiC and GaN-on-Si HEMTs. For both technologies dynamic R ON degradations up to 75% and 20% are observed for temperature and off -state voltage variations, respectively. These characterization data are fundamental for the accurate estimation of conduction losses during the design of switching-mode power converters.

This paper describes a complete system for the wireless supply and control of linear motors for industrial automation. DC power is delivered to a set of five linear motors by means of an inductive resonant wireless power link at 6.78 MHz, exploiting a GaN-HEMT full-bridge inverter and PCB high-Q resonant coils. Additional AC/DC and DC/DC converters are used for the direct connection to the power grid and to regulate a 48-V DC-link for the supply of the motor drives. The WPT link feedback control is provided with a Bluetooth connection, which is also exploited for the wireless command of the motors. A dedicated embedded system with two microcontrollers controls the entire plant, regulating the supply WPT link and the motor functionalities. The system can deliver a maximum average transferred power of 150 W, when the free space between the coils is between 15 to 20 cm.

It is well known that the trap-induced performance degradation of microwave GaN-on-SiC HEMTs is proportional to the peak voltages applied at the device's terminals. Considering that RF $\mathbf{GaN}$ switches are subject to high voltages, their characteristics are especially affected by trapping phenomena. This paper describes the GaN switch insertion loss (IL) degradation due to traps. A custom characterization setup is used for the measurement of the switch IL under dynamic voltage stress, typical of the actual operating regime. It is shown that, depending on the applied voltages setting the trap state, an increase of the switch IL up to 60% was measured for a $\pmb{0.25 \mu\mathrm{m}}$ GaN-on-SiC technology.

A technology-independent, inherently nonlinear approach is proposed for the compact modelling of high-frequency noise in microwave transistors under large-signal operating conditions. For the compact nonlinear noise model formulation we assume that noise generation can be described by a suitable set of distributed stochastic processes perturbing a very general, non-quasi-static deterministic description of the electron device, in accordance with the strategies adopted in physics-based methods for the choice and exploitation of microscopic diffusion noise sources. The propagation of the internal distributed noise sources up to the intrinsic device terminals leads to a set of non-stationary, correlated equivalent noise generators, nonlinearly controlled by the instantaneous large-signal working point of the device. Starting from a first formulation for the generators, formally derived from a physics-based description of the noise generation mechanisms widely adopted in distributed numerical modeling, mild approximations provide a fully behavioral representation that can be empirically extracted on the basis of measurement data only, and can be easily implemented into commercial computer-aided design tools by means of conventional, uncorrelated noise sources. As far as small-signal (i.e., linear) bias-dependent operation is concerned, it is shown how well-known, widely applied compact models for high-frequency noise can be considered as linearized special cases of the proposed approach. For a full validation, experimental examples are provided, both in small-and large-signal operation, for a GaAs-pHEMT, by considering the case study of a broad-band low-noise amplifier progressively driven into nonlinear regime by an increasing power interferer. © 2014 IEEE.

The asymmetry between capture and release time constants associated with charge-trapping phenomena observed in the electrical characteristics of microwave gallium-nitride (GaN) field-effect transistors (FETs) introduces distortion in GaN-based power amplifiers (PA). The PAs that operate with supply modulation to increase efficiency are particularly affected by this phenomenon, since the GaN FET trap state exhibits a nonlinear dependence on the voltage applied to the device terminals. In this paper, a measurement approach and the setup are presented for a large-signal characterization of GaN-based PAs operated with dynamic bias supply: a new prepulsing technique is introduced, which enables the characterization of the PA in controlled charge-trapping and thermal states. The characteristics obtained with this technique are shown to give an accurate description of the PA performance in the actual application working conditions. The proposed approach is validated by using the measured data for the direct computation of predistortion functions for the linearization of a 9.7-GHz envelope tracking 10-W GaN monolithic microwave integrated circuit PA for amplitude-modulated pulsed radar transmitters. Additional research on the PA trap-induced performance degradation is also presented and can be explored to predict the PA performance for different parameters of the operative regime or for the formulation of the PA behavioral models.

This work presents the design of three low-phase-noise monolithic voltage controlled oscillators (VCO) with a 2-μm InGaP-GaAs HBT technology for wideband satellite communications at C, X and Ku frequency bands. A large-signal design approach for the minimization of low-frequency noise up-conversion in conjunction with the optimization of the varactor-tuned integrated resonator were adopted for the minimization of phase noise (PN) generation. The C-band circuit implements a fundamental-frequency topology, whereas the X-and Ku-band oscillators are designed with a push-push configuration for PN and bandwidth optimization at higher frequency. The VCOs feature integrated output buffers for higher output power and improved load pulling. In the push-push VCOs, an integrated differential amplifier is used to provide an f 0 /2 prescaler output. Measured VCO frequency range of 3.31–4.17 GHz, 7.38–8.88 GHz, 10–12.28 GHz have been achieved, with maximum phase noise levels at 1 MHz offset from the carrier of −129 dBc/Hz, −124 dBc/Hz and −122 dBc/Hz respectively.

This work presents a dynamic characterization of a multi-level Chireix outphasing (ML-CO) power amplifier (PA) with modulated signals. The ML-CO technique combines the advantages of envelope tracking and outphasing architectures by limiting the supply modulation to discrete levels (enabled by an efficient power DAC modulator) and using outphasing for fine amplitude control. We describe the development of an experimental test bench able to supply phase- and time-aligned modulated signals for outphasing and supply modulation simultaneously. Pulse characterization is used to design a multilevel memory-less polynomial DPD. The linearized ML-CO PA is demonstrated with 1.4 MHz and 10 MHz LTE signals at 9.7 GHz. For both signals, the average total power consumption is reduced by a factor of two when supply modulation is used. For the 9.3 dB PAR, 1.4 MHz signal the PA operates with 38% average drain efficiency at 0.54 W average output power.

A state-space empirical nonlinear model for GaN-based field-effect transistors (FETs) is defined, along with the associated identification procedures based on a recently published double pulse measurement technique. Charge trapping phenomena are dealt with in terms of a nonlinear state equation, which describes the rate of change of the trap state as a function of its actual distance from the corresponding steady state. Model experimental validation is carried out, after on-wafer characterization of a 1-mm AlGaN-GaN on SiC FET, both under strong and mild nonlinear operation.

In this article, an X-band to Ka-band up-converter circuit designed for the transmitting chain of Satcom-on-the-move terminals is presented. The circuit is implemented using a 0.25 µm GaAs pHEMT microwave monolithic integrated circuit commercial process. It operates at fixed LO frequency of 22 GHz, IF input frequency within the band (8–9) GHz and corresponding RF output frequency within (30–31) GHz band. The up-converter circuit is composed of a resistive FET mixer, a K-band LO buffer amplifier, and a Ka-band medium power amplifier at the RF output. The bias operating condition of the entire multifunction chip is Vdd = 2.8 V, Idq = 322 mA, for a power consumption of 900 mW, when the Ka-band high power amplifier (HPA) operates in linear conditions. The chip dimensions are 3.4 × 2.8 mm2. The up-converter provides more than 12 dB conversion gain over the full bandwidth, when operated with LO input power of 0 dBm and IF fixed input power of −5 dBm. It also achieves 25 dBc of LO isolation at the RF output port. The high 1 dB compression point P1dB > 19 dBm, along with an OTOI in excess of 29 dBm, make the circuit suitable to directly drive Ka-band high power amplifiers in very linear operating conditions. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2649–2656, 2014

A laboratory setup, along with a set of measurement and identification procedures, have been developed expressly for the characterization of the thermal behavior of AlGaN/GaN HEMTs, suitable for microwave high power amplifier (HPA) design. The setup allows the measurement of the drain current time-domain dynamic response to positive drain bias pulses, performed at different temperatures and different dissipated power densities. The proposed measurement conditions discriminate thermal phenomena from electrical dispersive effects for this particular technology. Both the thermal resistance and the 'transient thermal resistance' are identified for a single-cell 1-mm device and for a 4-mm power-bar composed of four devices, designed to be used as the final stage of a monolithic $C$-band HPA for pulsed radar application. Transient data allow to compute the device operative channel temperature as a function of the pulsewidth and duty cycle, which is a crucial feature for pulsed HPA applications, typical for the GaN technology. The measured thermal data point out the nonlinearity of the thermal resistance versus dissipated power and base-plate temperature and the consequent critical thermal issue inherent in physically packing together such devices. © 1963-2012 IEEE.

This paper presents the characterization of a multi-level Chireix outphasing PA with a GaN discrete supply modulator MMIC at 9.7GHz. The internal PAs include class-F harmonic terminations, while the Chireix combiner determines the fundamental frequency load modulation. A power-DAC architecture provides 8 supply levels with 3 half-bridges, maintaining more than 85% efficiency. The combination of the two achieves a peak output power of 4.8W, and average total efficiencies for a 6dB PAR QPSK signal of 44.1% and 48.1% with and without considering the supply modulator consumption, respectively, demonstrating the feasibility of this PA architecture with a real discrete supply modulator.

This paper reviews various techniques that allow efficient amplification of amplitude-modulated radar pulses through some type of supply modulation. Examples at S and X-band with GaN PAs will be shown with efficiencies above 50% for 10-W transmitters and greatly reduced spectral sidelobes.

The chip-set for the transmitting power lineup of satellite SAR antenna T/R modules has been designed and implemented exploiting a 2- μm GaInP-GaAs heterojunction bipolar transistor (HBT) technology suitable for space applications. The HBT technology features an integrated emitter ballast resistor that enables high-power density operation without suffering thermal runaway phenomena. Two monolithic microwave integrated circuit (MMIC) driver amplifiers and a MMIC HPA are described: the drivers exhibit small-signal gains exceeding 21 dB and P1 dB output power of about 28 and 29 dBm, respectively, in a 2-GHz bandwidth and CW condition. The HPA delivers more than 40-dBm power at about 2.5-dB gain compression and power-added efficiency (PAE) exceeding 36% in a 700-MHz bandwidth in pulsed operation. Its peak performance at the center of the band are 40.9-dBm output power and 45% PAE. These performance are obtained within tight de-rating conditions for space applications.

In this paper, a new cyclostationary nonlinear low-frequency (LF) noise model for field-effect microwave transistors is presented based on the general theory of the technology-independent Charge-Controlled Nonlinear Noise modeling approach. The model definition, experimental extraction, and validation are described. For model parameter identification, the characterization of the device in terms of both LF noise in quiescent operation and its up-conversion into phase noise under large-signal RF oscillating conditions was performed using in-house developed measurement setups. The model is exploited in the design of a C-band monolithic microwave integrated circuit (MMIC) voltage-controlled oscillator (VCO) developed for space applications. The selected technology is a space-qualified GaAs 0.25-μm pseudomorphic HEMT (pHEMT) process. The large-signal technique adopted for the VCO design is also highlighted. Comparisons between measurements and simulations are provided, which show the validity of the design methodology and demonstrate the accuracy of the proposed cyclostationary noise modeling approach for phase-noise large-signal analyses of pHEMT-based circuits. The MMIC exhibits 350-MHz bandwidth at 7.3 GHz, with 14-dBm output power and -86-dBc/Hz single-sideband phase noise at 100 kHz from the carrier.

Standard dynamic characterization methods based on periodic narrow-pulse low duty-cycle excitation waveforms provide suboptimal I/V curves when used along with GaN field effect transistors (FETs), due to complex nonlinear charge trapping effects. Thus, a double-pulse technique for the dynamic characterization of GaN FETs is here presented. The double-pulsed I/V characteristics are shown to be not only isothermal but also corresponding to a fixed charge trapping state. © 2013 IEEE.

Nonlinear charge-trapping observed in the electrical characteristics of GaN FETs can introduce distortion in GaN-based power amplifiers (PA), especially in supply-modulated (envelope tracking) transmitters. A measurement approach is developed for large signal characterization of GaN-based PAs operated with dynamic bias supplies for efficiency enhancement. A new pre-pulsing technique is introduced which forces the active device to operate in trapping and thermal states close to those found in the actual application. The characteristics obtained with this technique are shown to give an accurate description of the PA performance. The measured data are used for the direct computation of pre-distortion functions for the linearization of a 10-GHz Envelope Tracking (ET) 12-W GaN MMIC PA for amplitude-modulated pulsed radar transmitters. The demonstrated measurement method can be also exploited for the identification of PA behavioral models, which take into account trapping effects.

This paper addresses both experimentally and through simulations the effects of a microwave tone on the lowfrequency noise properties of GaInP/GaAs heterojunction bipolar transistors. The aim is to contribute to the still unsolved controversy on which modulation strategy should be adopted for the low-frequency noise sources when they should face large signal conditions, as in the cases of oscillators and mixers. An approach similar but not equal to the modulated stationary noise model has been adopted for three different kinds of noise source modulation strategy in the frame of a bias-dependent compact low-frequency noise model.

The present contribution summarizes the activities performed towards the realization of a Single-Chip Front-End (SCFE) operating in C Band, integrating the High Power, Low Noise amplification and switching functionalities to be provided in modern T/R modules' Front-Ends for space SAR applications. The technologies adopted in this project are provided by United Monolithic Semiconductors (UMS) and Selex Electronic Systems (SLX), the GH25-10 0.25 µm gate length and the GaN technology featured by 0.5 µm gate length for UMS and SLX respectively. At the completion of the design phase two SCFEs have been designed in the two technologies, each in two slightly different versions, featured by state-of-the-art performance. In particular, in Tx-mode, both are featured by approximately 40 W power output, with 36 dB large-signal gain and 38 % / 27 % PAE for UMS and SLX versions respectively, while in Rx-mode 2.5 dB noise figure resulted, with robust operation. The two dies are featured by 6.9 × 5.4 mm2 and 7.28 × 5.40 mm2 for UMS and SLX versions respectively.

A double-pulse technique for the I/V characterization of GaN-based transistors is adopted for the nonlinear modeling of a 0.25 μm AlGaN/GaN on SiC FET. Experimental validation is provided by means of large-signal PA performance prediction both at low-frequency, in order to outline the role played by the resistive drain current source, and at microwaves. Improved prediction accuracy is demonstrated with respect to the use of standard single-pulse I/V characteristics.