Characterization of Microwave Transistors for Robust Receivers and High Efficiency Transmitters

The next generation of integrated transceiver front-ends needs both robust low noise amplifiers and high power amplifiers on a single-chip. The Aluminium Gallium Nitride / Gallium Nitride (AlGaN/GaN) High Electron Mobility Transistors (HEMT) is a suitable semiconductor technology for this purpose due to its high breakdown voltage and high electron mobility. In this thesis the AlGaN/GaN HEMT’s thermal properties, noise and survivability have been characterized for the intended use in robust high power transceivers. Furthermore, a new characterization setup for load modulated high efficiency power amplifiers have been developed. The thermal properties of AlGaN/GaN HEMTs have been carefully investigated considering self-heating and its effect on small-signal parameters and high frequency noise. Self-heating is a severe problem for a high power transistor on any semiconductor material, including GaN. In addition to reliability problems, the performance of the operating HEMT degrades with temperature. The access resistances showed a large temperature dependence, which was also verified with TLM measurements. Due to the large self-heating, the temperature dependence of the access resistances has to be taken into account in the modeling of the AlGaN/GaN HEMT. A temperature dependent small-signal noise model was derived and verified through fabricated amplifiers. Design strategies for robust low noise amplifiers are discussed and implemented using the derived model. The new characterization setup gives new possibilities to characterize the performance of load modulated amplifiers. Recent results on load modulated amplifiers show promising efficiency improvements in back-off operation. Therefore a new measurement setup was developed that performs dynamic load modulation at the transistor terminals. This method should be useful to further improve the performance of load modulated amplifiers for high efficiency operation. The measurement setup is based on an active load-pull setup, where a modulated input signal is used to synthesize a time varying output power. The load impedance is dynamically controlled with the envelop of the input signal, following an optimum efficiency load trajectory. This gives better insight into device operation and possible improvements

Novel power amplifier design using non-linear microwave characterisation and measurement techniques

This thesis, addresses some aspects of the well-known, problem, experienced by designer of radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is focused on finding and documenting solution to linearity problem than can be used to advance the performance of radio frequency (RF) and microwave systems used by the wireless communication industry. The research work, this was undertaken by performing a detailed investigation of the behaviour of transistors, under complex modulation, when subjected to time varying baseband signals at their output terminal: This is what in this thesis will be referred to as “baseband injection”. To undertake this study a new approach to the characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as transistors, designated as device-under-test (DUT), subjected to time varying baseband signals at its output terminal, was implemented. The study was focused on transistors that are used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear device under test (NL-DUT) is a generalisation to include transistors and other nonlinear devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations the device is perturbed by multi-tone modulated RF signals of different complexities. The wireless communication industry is very familiar with these kinds of devices and signals. Also familiar to the industry are the effects that arise when these kind of signal perturb these devices, such as inter-modulation distortion and linearity, power consumption/dissipation and efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects. While the concept of using baseband injection to linearize RFPAs is not new the mathematical framework introduced and applied in this work is novel. This novel approach NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK ABSTRACT vi has provided new insight to this very complex problem and highlighted solutions to how it could be a usable technique in practical amplifiers. In this thesis a very rigorous and complex investigative mathematical and measurement analysis on RFPA response to applied complex stimulus in a special domain called the envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal waveforms by using special control keys with which to provide solution to some of the problems highlighted above is presented. The formulation is based on specific background principles, identified from the result of both mathematical theoretical analysis and detailed experimental device characterisation

Hardware Solutions for High Data Rate Modems

The exponentially-growing mobile data traffic imposes significant demands on the capacity of the mobile network. Fiber optic and microwave links are two main solutions for the mobile backhaul network, which provides connectivity between radio base station (RBS) sites and the switch sites. As compared to fiber, a microwave solution is much easier to deploy, however, its capacity is lower. This thesis is devoted to the design and implementation of modems supporting high data rate transmission. This thesis includes the design and implementation of one MMIC-based on- /off- keying (OOK) modem and two FPGA-based differential phase shift keying (D-QPSK) modems. The OOK modem is designed for short-distance applications. The D-QPSK modems are made for high capacity microwave radio applications. The OOK modulator is implemented in a heterojunction bipolar transistor (HBT) process, and is capable of transmitting data at rate of 14 Gbps. The OOK demodulator is implemented in a metamorphic high electron mobility transistor (mHEMT) process with a detection range of 10 to 60 GHz. An OOK link is set up and 10 Gbps transmission is achieved. For the D-QPSK scheme, a 2.5 Gbps and a 5 Gbps D-QPSK modem are implemented with FPGAs and microwave components. Modifications at the modulator and demodulator are explained, which doubles the data rate of the D-QPSK modem. It also enables the possibility of scaling up to even higher data rates. A point-to-point radio is demonstrated by using such a modem and commercial E-band RF front-end components, which achieves 5 Gbps full-duplex data transmission

Concepts for Short Range Millimeter-wave Miniaturized Radar Systems with Built-in Self-Test

This work explores short-range millimeter wave radar systems, with emphasis on miniaturization and overall system cost reduction. The designing and implementation processes, starting from the system level design considerations and characterization of the individual components to final implementation of the proposed architecture are described briefly. Several D-band radar systems are developed and their functionality and performances are demonstrated

Distributed Circuit Analysis and Design for Ultra-wideband Communication and sub-mm Wave Applications

This thesis explores research into new distributed circuit design techniques and topologies, developed to extend the bandwidth of amplifiers operating in the mm and sub-mm wave regimes, and in optical and visible light communication systems. Theoretical, mathematical modelling and simulation-based studies are presented, with detailed designs of new circuits based on distributed amplifier (DA) principles, and constructed using a double heterojunction bipolar transistor (DHBT) indium phosphide (InP) process with fT =fmax of 350/600 GHz. A single stage DA (SSDA) with bandwidth of 345 GHz and 8 dB gain, based on novel techniques developed in this work, shows 140% bandwidth improvement over the conventional DA design. Furthermore, the matrix-single stage DA (M-SSDA) is proposed for higher gain than both the conventional DA and matrix amplifier. A two-tier M-SSDA with 14 dB gain at 300 GHz bandwidth, and a three-tier M-SSDA with a gain of 20 dB at 324 GHz bandwidth, based on a cascode gain cell and optimized for bandwidth and gain flatness, are presented based on full foundry simulation tests. Analytical and simulation-based studies of the noise performance peculiarities of the SSDA and its multiplicative derivatives are also presented. The newly proposed circuits are fabricated as monolithic microwave integrated circuits (MMICs), with measurements showing 7.1 dB gain and 200 GHz bandwidth for the SSDA and 12 dB gain at 170 GHz bandwidth for the three-tier M-SSDA. Details of layout, fabrication and testing; and discussion of performance limiting factors and layout optimization considerations are presented. Drawing on the concept of artificial transmission line synthesis in distributed amplification, a new technique to achieve up to three-fold improvement in the modulation bandwidth of light emitting diodes (LEDs) for visible light communication (VLC) is introduced. The thesis also describes the design and application of analogue pre-emphasis to improve signal-to-noise ratio in bandwidth limited optical transceivers