abstract: There is an ever-increasing demand for higher bandwidth and data rate ensuing from exploding number of radio frequency integrated systems and devices. As stated in the Shannon-Hartley theorem, the maximum achievable data rate of a communication channel is linearly proportional to the system bandwidth. This is the main driving force behind pushing wireless systems towards millimeter-wave frequency range, where larger bandwidth is available at a higher carrier frequency. Observing the Moor’s law, highly scaled complementary metal–oxide–semiconductor (CMOS) technologies provide fast transistors with a high unity power gain frequency which enables operating at millimeter-wave frequency range. CMOS is the compelling choice for digital and signal processing modules which concurrently offers high computation speed, low power consumption, and mass integration at a high manufacturing yield. One of the main shortcomings of the sub-micron CMOS technologies is the low breakdown voltage of the transistors that limits the dynamic range of the radio frequency (RF) power blocks, especially with the power amplifiers. Low voltage swing restricts the achievable output power which translates into low signal to noise ratio and degraded linearity. Extensive research has been done on proposing new design and IC fabrication techniques with the goal of generating higher output power in CMOS technology. The prominent drawbacks of these solutions are an increased die area, higher cost per design, and lower overall efficiency due to lossy passive components. In this dissertation, CMOS compatible metal–semiconductor field-effect transistor (MESFETs) are utilized to put forward a new solution to enhance the power amplifier’s breakdown voltage, gain and maximum output power. Requiring no change to the conventional CMOS process flow, this low cost approach allows direct incorporation of high voltage power MESFETs into silicon. High voltage MESFETs were employed in a cascode structure to push the amplifier’s cutoff frequency and unity power gain frequency to the 5G and K-band frequency range. This dissertation begins with CMOS compatible MESFET modeling and fabrication steps, and culminates in the discussion of amplifier design and optimization methodology, parasitic de-embedding steps, simulation and measurement results, and high resistivity RF substrate characterization. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

This thesis presents a study and implementation of several measurement procedures used to efficiently generate non-linear measurement-based behavioral models primary for microwave amplifiers. Behavioral models are a solution for representing devices that can present linear and/or non-linear behavior when little or no information about the internal structure is known. Measurement-based behavioral models are an advantage since they can be extracted from a direct measurement of the device. This work addresses some of the challenges of these types of measurements. A set of software modules has been produced that combine several modern techniques to efficiently generate practical models using equipment commonly available in a typical microwave lab. Advanced models using new and more complex equipment are also discussed. Modeling of the non-linear operation of power amplifiers is a common subject of study since it provides a path to improved system simulations. However, the measurement process used for non-linear behavioral modeling of PAs requires either non-linear measurement instrumentation, not yet widely available, or numerous measurements that makes the process tedious and susceptible to errors. Power dependent S-Parameters obtained with a conventional Vector Network Analyzers (VNA) can be used to extract AM-to-AM and AM-to-PM behavior of a device and to generate, simple but useful, behavioral models. A careful analysis of the characteristics of common RF measurement instrumentation combined with knowledge of common non-linear phenomena provides with the conditions under which useful models can be generated. The results of this work are presented as several programs implemented in National Instruments LabVIEW that will sequence through the different measurements required for the generation of measurement-based behavioral models. The implemented models are known as P2D and S2D models available with Agilent Advanced Design System (ADS.) The code will communicate with the measurement instrumentation and decide on the most efficient way to extract the data. Once the data is extracted, the code will put into the appropriate syntaxes required by the model for direct and convenient setup of the generated models in ADS.

<p>In this thesis, a new way of using predisortion for linearization of power amplifiers is evaluated. In order to achieve an adequate power level for the jamming signal, power amplifiers are used in military jamming systems. Due to the nonlinear characteristic of the power amplifier, distortion will be present at the output. As a consequence, unwanted frequencies are subject to jamming. To decrease the distortion, linearization of the power amplifier is necessary. </p><p>In the system of interest, a portion of the distorted power amplifier output signal is fed back. Using this measurement, a predistortion signal is synthesized to allow suppression of the unwanted frequency components. The predistortion signal is updated a number of times in order to achieve a good outcome. Simulations are carried out in Matlab for testing of the algorithm. </p><p>The evaluation of the new linearization technique shows promising results and that good suppression of distortion components is achieved. Furthermore, new predistortion features are possible to implement, such as predistorsion in selected frequency bands. However, real hardware testing needs to be carried out to confirm the results.</p>

<p>The purpose with the report is to show that it is possible to design a class-D amplifier, using a programmable FPGA mounted on a developing card from Xess and a H-bridge. The FPGA was programmed in VHDL which is the language the software from Xilinx use to implement a logical function into the FPGA The logical function corresponds to a modeling of the music signal and the modeling can be described as a comparator which compare the music signal with a triangle wave and as a out signal produce a pulse width modulated (PWM) signal. The report is also a review and evaluating of two different modulating technologies, AD- modeling and BD-modeling. A detailed part about how the H-bridge was designed and how it works. The result of this project is a working audio amplifier to a significant lower price than the products in todays market.</p>

<p>Power-amplifier efficiency is a significant issue for the overall efficiency of most wireless system. Therefore, currently there are different kind of Switched mode power amplifiers are developed which are showing very high efficiency also at higher frequencies but all of these amplifiers are subjected to drive with the constant envelope signals. Whereas, for the increasing demand of high data rate transmissions in wireless communication there are some new modulation schemes are introduced and which are generating no more a constant envelope signal but a high peak to average power signal. Therefore, recently a new technique is proposed called the burst mode operation for operating the switched mode power amplifiers efficiently while driven by a high peak to average power signal.</p><p> </p><p>The purpose of this master thesis work was to review the theory of this burst mode operation and some basic investigations of this theory on switched mode power amplifiers were performed in simulation environments. The amplifiers of class D, inverse D, DE and J are studied. The thesis work was mainly carried out by ADS and partly in MATLAB SIMULINK environment. Since this burst mode operation is a completely new technique therefore a new Harmonic balance simulation setups in ADS and Microwave Office are developed to generate the RF burst signals.</p><p> </p><p>A Class J amplifier based on LDMOS technique is measured by a 16 carrier multi-tone signal having peak to average power ratio of 7 dB and achieved the drain efficiency of 50% with -30 dBc linearity at 946 MHz.</p><p> </p><p> </p>

Active magnetic bearings (AMBs) have become a key technology in industrial applications with a continued drive for cost reduction and an increase in reliability. AMBs require position feedback to suspend the rotor. Conventional contactless position sensors are used to measure the rotor's position. The major disadvantages of conventional position sensors are their cost and that the sensors are viewed as a weak point in an AMB system. A self-sensing sensor is a type of sensor which is cost effective, reduces sensor wire-length and increases reliability, thus ideal for the industry. This type of sensor relies on the current and voltage signals of the AMB's to obtain the rotor position. Due to the rapid and advanced development of digital electronics, it has become more powerful and cheaper, thus self-sensing in mass production will be cost effective. Different self-sensing approaches were developed in the past and can be divided into two main categories: state estimation and amplitude modulation approaches. In this research the focus will be on the amplitude modulation approach. Amplitude modulation makes use of two signals, namely the modulation signal and the carrier signal. In a self-sensing AMB system the carrier can be a high frequency component injected into the system or the switching ripple of the switch mode power amplifier can be used. The modulation signal is the change in rotor position which results in changing inductances. The actuator material introduces nonlinear effects on the estimated position. Due to these nonlinear effects, it is rather difficult to obtain the rotor position. The first industrial application of a self-sensing turbomolecular pump system was implemented in 2005 by S2M. The aim of this thesis is to evaluate existing self-sensing schemes, devise improvements and investigate possible new schemes. Four different demodulation methods and two new self-sensing schemes are evaluated. An AMB transient simulation model which includes saturation, hysteresis, eddy currents and cross-coupling is used to evaluate the schemes in simulation. The self-sensing schemes are implemented in hardware and evaluated on a 7 A rms 500 N AMB. A comparative study was done on the different self-sensing schemes. From the comparative study it was determined that the gain- and phase effects have a direct effect on the sensitivity of the system. It was also proved that self-sensing can be implemented on a coupled AMB with a sensitivity of 10.3 dB. / Thesis (Ph.D. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2009.

Advanced digital modulation schemes used in the wireless applications, result in the modulated RF signals with high peak to average power ratio which requires linear amplification. On the other hand, the demand for a longer talk time with less battery volume and weight, especially in hand-held radio units, necessitate more power efficient methods to be utilized in power amplifier design. But improved linearity and efficiency have always been contradicting requirements demanding innovative power ampli

Radio frequency (RF) communications are limited to a number of frequency bands scattered over the radio spectrum. Applications over such bands increasingly require more versatile, data extensive wireless communications that leads to the necessity of high bandwidth efficient interfaces, operating over wideband frequency ranges. Whether for a base station or mobile device, the regulations and adequate transmission of such schemes place stringent requirements on the design of transmitter front-ends. Increasingly strenuous and challenging hardware design criteria are to be met, especially so in the design of power amplifiers (PA), the bottle neck of the transmitter’s design tradeoff between linearity and power efficiency. The power amplifier exhibits a nonideal behavior, characterized by both nonlinearity and memory effects, heavily affecting that tradeoff, and therefore requiring an effective linearization technique, namely Digital Predistortion (DPD). The effectiveness of the DPD is highly dependent on the modeling scheme used to compensate for the PA’s nonideal behavior. In fact, its viability is determined by the scheme’s accuracy and implementation complexity. Generic behavioral models for nonlinear systems with memory have been used, considering the PA as a black box, and requiring RF designers to perform extensive testing to determine the minimal complexity structure that achieves satisfactory results. This thesis first proposes a direct systematic approach based on the parallel Hammerstein structure to determine the exact number of coefficients needed in a DPD. Then a physical explanation of memory effects is detailed, which leads to a close-form expression for the characteristic behavior of the PA entirely based on circuit properties. The physical expression is implemented and tested as a modeling scheme. Moreover, a link between this formulation and the proven behavioral models is explored, namely the Volterra series and Memory Polynomial. The formulation shows the correlation between parameters of generic behavioral modeling schemes when applied to RF PAs and demonstrates redundancy based on the physical existence or absence of modeling terms, detailed for the proven Memory polynomial modeling and linearization scheme.

The evolution of wireless technology has necessitated the support of multiple communication standards by mobile devices. At present, multiple chipsets/radios operating at predefined sets of modulation schemes, frequency bands, bandwidths and output power levels are used to achieve this objective. This leads to higher component counts, increased cost and limits the capacity to cope with future communication standards. In order to tackle different wireless standards using a single chipset, digital circuits have been increasingly deployed in radios and demonstrated re-configurability in different modulation schemes (multimode) and frequency bands (multiband). Despite efforts and progress made in digitizing the entire radio, the power amplifier (PA) is still designed using an conventional approach and has become the bottleneck in digital transmitters, in terms of low average power efficiency, poor compatibility with modern CMOS technology and limited re-configurability. This research addresses these issues from two aspects. The first half of the thesis investigates signal encoding issues between the modulator and PA. We propose, analyze and evaluate a new hybrid amplitude/time signal encoding scheme that significantly improves the coding efficiency and dynamic range of a digitally modulated power amplifier (DMPA) without significantly increasing design complexity. The proposed hybrid amplitude/time encoding scheme combines both the amplitude domain and the time domain to optimally encode information. Experimental results show that hybrid amplitude/time encoding results in a 35% increase in the average coding efficiency with respect to conventional time encoding, and is only 6.7% lower than peak efficiency when applied to a Wireless Local Area Network (WLAN) signal with a peak to average power ratio equal to 9.9 dB. A new DMPA architecture, based on the proposed hybrid encoding, is also proposed. The second half of this thesis presents the design, analysis and implementation of a CMOS PA that is amenable to the proposed hybrid encoding scheme. A multi-way current mode class-D PA architecture has been proposed and realized in 130 nm CMOS technology. The designed PA has satisfied the objectives of wide bandwidth (1.5 GHz - 2.7 GHz at 1 dB output power), and high efficiency (PAE 63%) in addition to demonstrating linear responses using the proposed digital encoding. A complete digital transmitter combining the encoder and the multi-way PA was also investigated. The overall efficiency is 27% modulating 7.3 dB peak to average power ratio QAM signals.

This thesis addresses the potential of implementing watt-level class-AB Power Amplifier (PA) for WLAN in 65 nm CMOS technology, at 2.4 GHz frequency. In total, five PAs have been compared, where the examined parameters were output power (Pout), linearity, power added efficiency (PAE), and area consumption. Four PAs were implemented using conventional cascode topology with different combination of transistors sizes in 65nm CMOS, and one PA using a high-voltage Extended Drain MOS (EDMOS) device, implemented in the same 65 nm CMOS with no process or mask changes. All schematics were created using Cadence Virtuoso CAD tools. The test benches were created using the Agilent's Advance Design System ( ADS) and simulated with the ADS-Cadence dynamic link. The simulation results show that the EDMOS PA (L=350 nm) has the smallest area, but has harder to reach the required Pout. Cascode no. 3 (L= 500,260 nm) has the best Pout (29.1 dBm) and PAE (49.5 %). Cascode no. 2 (L= 500,350 nm) has the best linearity (low EVM). Cascode no. 1 (L=500,500 nm) has low Pout (27.7 dBm). Cascode no.4 (L=500,60 nm) has very bad linearity. The thesis also gives an overview for CMOS technology, discusses the most important aspects in RF PAs design, such as Pout, PAE, gain, and matching networks. Different PA classes are also discussed in this thesis.