Donald F. Kimball

Bio: Donald F. Kimball is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Amplifier & RF power amplifier. The author has an hindex of 27, co-authored 79 publications receiving 2869 citations. Previous affiliations of Donald F. Kimball include University of California & Space and Naval Warfare Systems Center Pacific.

An Improved Power-Added Efficiency 19-dBm Hybrid Envelope Elimination and Restoration Power Amplifier for 802.11g WLAN Applications

Abstract: A comparison of envelope elimination and restoration (EER) and envelope tracking (ET) is discussed and a "hybrid" wideband EER power amplifier (PA) for the WLAN 802.11g system is proposed. A 60% efficiency (the output envelope signal power/input dc power) DC-20-MHz wideband envelope amplifier is designed for wideband EER and wideband ET (WBET) applications. A design method is developed to optimize the efficiency of the envelope amplifier for a given peak-to-average ratio and average slew rate of the envelope signal. An experimental "hybrid" Class-E EER system shows an overall efficiency (modulated RF output power/envelope amplifier dc input power) of 36% and power-added efficiency (the modulated RF output power/envelope amplifier dc input power plus RF input power) of 28% for a WLAN 802.11g signal at 19-dBm (80 mW) output power at 2.4 GHz. Digital predistortion, time alignment, and memory effect mitigation are implemented. The measured 3% error vector magnitude exceeds the 802.11g specification for 5% for a 54-Mb/s modulation signal

High-Efficiency Envelope-Tracking W-CDMA Base-Station Amplifier Using GaN HFETs

Abstract: A high-efficiency wideband code-division multiple-access (W-CDMA) base-station amplifier is presented using high-performance GaN heterostructure field-effect transistors to achieve high gain and efficiency with good linearity For high efficiency, class J/E operation was employed, which can attain up to 80% efficiency over a wide range of input powers and power supply voltages For nonconstant envelope input, the average efficiency is further increased by employing the envelope-tracking architecture using a wide-bandwidth high-efficiency envelope amplifier The linearity of overall system is enhanced by digital pre-distortion The measured average power-added efficiency of the amplifier is as high as 507% for a W-CDMA modulated signal with peak-to-average power ratio of 767 dB at an average output power of 372 W and gain of 100 dB We believe that this corresponds to the best efficiency performance among reported base-station power amplifiers for W-CDMA The measured error vector magnitude is as low as 174% with adjacent channel leakage ratio of -510 dBc at an offset frequency of 5 MHz

A Monolithic High-Efficiency 2.4-GHz 20-dBm SiGe BiCMOS Envelope-Tracking OFDM Power Amplifier

Abstract: A monolithic SiGe BiCMOS envelope-tracking power amplifier (PA) is demonstrated for 802.11g OFDM applications at 2.4 GHz. The 4-mm2 die includes a high-efficiency high-precision envelope amplifier and a two-stage SiGe HBT PA for RF amplification. Off-chip digital predistortion is employed to improve EVM performance. The two-stage amplifier exhibits 12-dB gain, <5% EVM, 20-dBm OFDM output power, and an overall efficiency (including the envelope amplifier) of 28%.

Digital Predistortion for Envelope-Tracking Power Amplifiers Using Decomposed Piecewise Volterra Series

Abstract: Due to dynamic changes of supply voltage, envelope-tracking (ET) power amplifiers (PAs) exhibit very distinct characteristics in different power regions. It is very difficult to compensate the distortion induced by these amplifiers by employing conventional digital predistortion techniques. In this paper, by introducing a new piecewise Volterra model based on a vector threshold decomposition technique, we first set several thresholds in the input power level according to the PA characteristics, and decompose the input complex envelope signal into several sub-signals by using these thresholds. We then process each sub-signal separately by employing the dynamic deviation reduction-based Volterra series, and finally recombine them together to produce the predistorted output. Experimental results show that by using this new decomposed piecewise digital predistorter model, the distinct characteristics of the ET system at different signal power levels can be accurately modeled, and thus, the distortion, including both static nonlinearities and memory effects, caused by the amplifier nonlinear behavior can be effectively compensated.

Envelope tracking power amplifier with pre-distortion linearization for WLAN 802.11g

Abstract: This paper presents a power amplifier based on envelope tracking (ET) with application to the WLAN 802.11g system. Baseband pre-distortion is implemented to improve the linearity. A high-efficiency wide-bandwidth envelope amplifier and a GaAs MESFET class AB RFPA are designed and implemented for the system. An overall system drain efficiency of 30% is obtained for an OFDM output power of 20 dBm at 2.4GHz.

GaN-Based RF Power Devices and Amplifiers

Abstract: 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

State of the Art in 60-GHz Integrated Circuits and Systems for Wireless Communications

Abstract: This tutorial presents an overview of the technological advances in millimeter-wave (mm-wave) circuit components, antennas, and propagation that will soon allow 60-GHz transceivers to provide multigigabit per second (multi-Gb/s) wireless communication data transfers in the consumer marketplace. Our goal is to help engineers understand the convergence of communications, circuits, and antennas, as the emerging world of subterahertz and terahertz wireless communications will require understanding at the intersections of these areas. This paper covers trends and recent accomplishments in a wide range of circuits and systems topics that must be understood to create massively broadband wireless communication systems of the future. In this paper, we present some evolving applications of massively broadband wireless communications, and use tables and graphs to show research progress from the literature on various radio system components, including on-chip and in-package antennas, radio-frequency (RF) power amplifiers (PAs), low-noise amplifiers (LNAs), voltage-controlled oscillators (VCOs), mixers, and analog-to-digital converters (ADCs). We focus primarily on silicon-based technologies, as these provide the best means of implementing very low-cost, highly integrated 60-GHz mm-wave circuits. In addition, the paper illuminates characterization techniques that are required to competently design and fabricate mm-wave devices in silicon, and illustrates effects of the 60-GHz RF propagation channel for both in-building and outdoor use. The paper concludes with an overview of the standardization and commercialization efforts for 60-GHz multi-Gb/s devices, and presents a novel way to compare the data rate versus power efficiency for future broadband devices.

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

Abstract: 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.

Wireless Information and Power Transfer: Energy Efficiency Optimization in OFDMA Systems

Abstract: This paper considers orthogonal frequency division multiple access (OFDMA) systems with simultaneous wireless information and power transfer. We study the resource allocation algorithm design for maximization of the energy efficiency of data transmission (bits/Joule delivered to the receivers). In particular, we focus on power splitting hybrid receivers which are able to split the received signals into two power streams for concurrent information decoding and energy harvesting. Two scenarios are investigated considering different power splitting abilities of the receivers. In the first scenario, we assume receivers which can split the received power into a continuous set of power streams with arbitrary power splitting ratios. In the second scenario, we examine receivers which can split the received power only into a discrete set of power streams with fixed power splitting ratios. For both scenarios, we formulate the corresponding algorithm design as a non-convex optimization problem which takes into account the circuit power consumption, the minimum data rate requirements of delay constrained services, the minimum required system data rate, and the minimum amount of power that has to be delivered to the receivers. By exploiting fractional programming and dual decomposition, suboptimal iterative resource allocation algorithms are developed to solve the non-convex problems. Simulation results illustrate that the proposed iterative resource allocation algorithms approach the optimal solution within a small number of iterations and unveil the trade-off between energy efficiency, system capacity, and wireless power transfer: (1) wireless power transfer enhances the system energy efficiency by harvesting energy in the radio frequency, especially in the interference limited regime; (2) the presence of multiple receivers is beneficial for the system capacity, but not necessarily for the system energy efficiency.

GaN Transistors for Efficient Power Conversion

Abstract: This timely second edition has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements. Acknowledging that GaN transistors are not one-to-one replacements for the current MOSFET technology, this book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and applications. Included are discussions on the fundamental physics of these power semiconductors, layout and other circuit design considerations, as well as specific application examples demonstrating design techniques when employing GaN devices.