The rapid development of the RF power electronics requires the introduction of wide bandgap material due to its potential in high output power density, high operation voltage and high input impedance GaN-based RF power devices have made substantial progresses in the last decade This paper attempts to review the latest developments of the GaN HEMT technologies, including material growth, processing technologies, device epitaxial structures and MMIC designs, to achieve the state-of-the-art microwave and millimeter-wave performance The reliability and manufacturing challenges are also discussed

GaN-Based RF Power Devices and Amplifiers

Gallium-nitride power transistor (GaN HEMT) and integrated circuit technologies have matured dramatically over the last few years, and many hundreds of thousands of devices have been manufactured and fielded in applications ranging from pulsed radars and counter-IED jammers to CATV modules and fourth-generation infrastructure base-stations. GaN HEMT devices, exhibiting high power densities coupled with high breakdown voltages, have opened up the possibilities for highly efficient power amplifiers (PAs) exploiting the principles of waveform engineered designs. This paper summarizes the unique advantages of GaN HEMTs compared to other power transistor technologies, with examples of where such features have been exploited. Since RF power densities of GaN HEMTs are many times higher than other technologies, much attention has also been given to thermal management-examples of both commercial “off-the-shelf” packaging as well as custom heat-sinks are described. The very desirable feature of having accurate large-signal models for both discrete transistors and monolithic microwave integrated circuit foundry are emphasized with a number of circuit design examples. GaN HEMT technology has been a major enabler for both very broadband high-PAs and very high-efficiency designs. This paper describes examples of broadband amplifiers, as well as several of the main areas of high-efficiency amplifier design-notably Class-D, Class-E, Class-F, and Class-J approaches, Doherty PAs, envelope-tracking techniques, and Chireix outphasing.

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A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs

A television schedule system and method for displaying television schedule information on a television screen includes a program guide having a schedule information area that depicts the programs that are being presented on each channel at each time during the day. An input device allows the viewer to browse through the schedule information area and/or obtain more information about programs of particular interest. In one aspect, the viewer may watch a program on the currently-tuned channel, while browsing through the other channels on a portion of the television screen. In another aspect, the viewer may watch programs currently being shown on the television, while he or she browses through the program guide. In yet another aspect, the system includes a database, a processor and associated software for automatically customizing the television schedule guide to an individual viewer or a group of viewers, e.g., a family, to facilitate use of the television schedule.

System and method for using television schedule information

A 175-to-350 V hard-switched boost converter was constructed using a high-voltage GaN high-electron-mobility transistor grown on SiC substrate. The high speed and low on-resistance of the wide-band-gap device enabled extremely fast switching transients and low losses, resulting in a high conversion efficiency of 97.8% with 300-W output power at 1 MHz. The maximum efficiency was 98.0% at 214-W output power, well exceeding the state of the art of Si-based converters at similar frequencies.

A 97.8% Efficient GaN HEMT Boost Converter With 300-W Output Power at 1 MHz

Wide-bandgap semiconductors are expected to be applied to solid-state lighting and power devices, supporting a future energy-saving society. While GaN-based white LEDs have rapidly become widespread in the lighting industry, SiC- and GaN-based power devices have not yet achieved their popular use, like GaN-based white LEDs for lighting, despite having reached the practical phase. What are the issues to be addressed for such power devices? In addition, other wide-bandgap semiconductors such as diamond and oxides are attracting focusing interest due to their promising functions especially for power-device applications. There, however, should be many unknown phenomena and problems in their defect, surface, and interface properties, which must be addressed to fully exploit their functions. In this review, issues of wide-bandgap semiconductors to be addressed in their basic properties are examined toward their ?full bloom?.

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Wide-bandgap semiconductor materials: For their full bloom†

An RF power amplifier circuit for amplifying an RF signal over a broad range of power with improved efficiency includes a carrier amplifier for amplifying an RF signal over a first range of power and with a power saturation level below the maximum of the broad range of power is disclosed. A plurality of peak amplifiers are connected in parallel with the carrier amplifier with each of the peak amplifiers being biased to sequentially provide an amplified output signal after the carrier amplifier approaches saturation. The input signal is applied through a signal splitter to the carrier amplifier and the plurality of peak amplifiers, and an output for receiving amplified output signals from the carrier amplifier and the plurality of peak amplifiers includes a resistive load R/2. The split input signal is applied through a 90° transformer to the carrier amplifier, and the outputs of the peak amplifiers are applied through 90° transformers to a output load. When operating below saturation, the carrier amplifier delivers power to a load of 2R and the carrier amplifier delivers current to the load, which is one-half the current at maximum power when the amplifier is saturated. In one embodiment with the output having an impedance, Z, the carrier amplifier and each peak amplifier is connected to the output through an output-matching network presenting an output impedance of less than Z to each amplifier and with each output-matching network having selected phase length to reduce reactance of the output impedance.

N-way rf power amplifier circuit with increased back-off capability and power added efficiency using selected phase lengths and output impedances

A systematic and consistent approach to the thermal modeling and measurement of GaN on SiC HEMT power transistors is described. Since the power density of such multilayered wide bandgap structures and assemblies can be very high compared with other transistor technologies, the application of such an approach to the prediction of operating channel temperatures (and hence product lifetime) is important. Both CW and transient (i.e. pulsed and digitally modulated) thermal resistances are calculated for a range of transistor structures and sizes as a function of power density, pulse length and duty factor and compared with measured channel temperatures and RF parameters. The resulting thermal resistance values have then been imported into new “self-heating” large signal models so that transistor channel temperatures and the resulting effects on RF performance such as gain, output power and efficiency can be determined during the amplifier design phase. Some practical examples are included in the paper including the temperature rises in the carrier and peaking transistors of a high power Doherty amplifier.

Thermal analysis and its application to high power GaN HEMT amplifiers

The linearity of a transistor amplifier comprising a plurality of transistors operating parallel is improved by reducing the odd order transconductance derivatives of signals generated by the transistors. The transistors can be provided in groups with each group having a different bias voltage applied thereto or each group of transistors can have a different input signal applied thereto. The groups of transistors can have different physical parameters such as the width to length ratio of gates in field effect transistors and threshold voltages for the transistors.

RF transistor amplifier linearity using suppressed third order transconductance

A high-power amplifier using two 288-mm-periphery GaN HEMTs was demonstrated with all matching components inside the package When biased at 55 V, a power bandwidth of 33-36 GHz was obtained, with 550-W peak output, 125-dB associated gain and 66% drain efficiency at 345 GHz

Simon Wood

Papers

A Review of GaN on SiC High Electron-Mobility Power Transistors and MMICs

N-way rf power amplifier circuit with increased back-off capability and power added efficiency using selected phase lengths and output impedances

Thermal analysis and its application to high power GaN HEMT amplifiers

RF transistor amplifier linearity using suppressed third order transconductance

An Internally-matched GaN HEMT Amplifier with 550-watt Peak Power at 3.5 GHz