Corrado Florian

Theoretical and Numerical Design of a Wireless Power Transmission Link With GaN-Based Transmitter and Adaptive Receiver

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 VDC=30 V at a link distance D=5 cm. Numerical and experimental results are discussed, demonstrating the accuracy of the proposed design procedure.

GaN FET Nonlinear Modeling Based on Double Pulse

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.

{ I}/{ V}

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

Characteristics

C

Characterization of the Nonlinear Thermal Resistance and Pulsed Thermal Dynamic Behavior of AlGaN–GaN HEMTs on SiC

-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.

A C-Band AlGaN-GaN MMIC HPA for SAR

A C-Band MMIC high power amplifier (HPA) has been designed exploiting a 0.25 μm HEMT GaN process on SiC substrate. The HPA is designed for future synthetic aperture radar (SAR) antenna applications. The HPA delivers 16 W output power with PAE over 38% at 6 dB gain compression within a 900 MHz bandwidth around 5.75 GHz. Up to 20 W output power and 40% PAE are obtained at higher gain compression. A comparison with another amplifier, differing only for the layout of the devices in the final stage, points out that the transistor thermal conditions represent the main limitation for this high power density technology.

Design of 40-W AlGaN/GaN MMIC High Power Amplifiers for

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.

C

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.

-Band SAR Applications

In this paper a new active bias network (ABN) for the technology-independent characterization of low-frequency (LF) dispersion in the output impedance and transadmittance of high-power microwave transistors is described. The proposed bias network is capable of synthesizing a high-impedance active DC-feed in the range of 10 Hz-1 MHz, where III-V microwave devices typically exhibit frequency response dispersion due to energy traps and/or self-heating. The input impedance values obtained in such a large bandwidth (five decades) are considerably higher than those that can be achieved with passive resistive and inductive solutions. In fact, these lead to severe limitations in terms of achievable impedance values, calibration accuracy, power handling capabilities, and physical dimensions. The ABN is particularly suitable for the characterization of high-voltage and high-current devices. In particular, here it is used, along with standard laboratory instrumentation, for the characterization of the LF dispersion of an AlGaN/GaN HEMT, suitable for microwave power amplifier applications.

12-W

In the paper the advantages of the push-push oscillator topology in terms of phase noise performance are discussed and experimentally verified by means of measurements on X-band and C-band GaInP-GaAs MMIC VCOs. In particular an analytical approach, based on the frequency sensitivity pushing factor parameter, is used to demonstrate the phase noise improvement of at least 9 dB inherently offered by push-push topology, with respect to a fundamental frequency oscillator. This theoretical analysis is for the first time experimentally validated trough the design and characterization of three different MMIC VCOs, specifically developed for this purpose.