This report discusses the design, development and the fabrication of a power hybrid. Foldback current limiting which is self reseting is used whereby withstanding indefinitely a short circuit. Thermal design considerations and thermal analysis are described as well as stability analysis. The maximum current capability of this design is four amperes and forty watts can be dissipated in the power transistors over a wide range of temperatures.

As 3G handset manufacturers add more and more features such as multimedia applications, color displays, video cameras, web browsing, gaming, WLAN, and MP3 players, the current consumption of a handset is ever increasing. Of the many components, the RF power amplifiers receive the most attention as they draw significant battery current and continue to represent the largest power load on the battery. In order to improve the overall efficiency of a power amplifier, it is important to know the operating uplink transmit power levels of a mobile phone in the WCDMA network. The work in this thesis makes two major contributions. First is the characterization of uplink transmit power in WCDMA networks based on current network data (collected in AT&T's WCDMA network) and realistic usage scenarios. Second is an investigation of the relationship between the battery life and the probability distribution function of the transmit power. Another important finding is that the talk time estimates using field tests, lab testing and theoretical expressions all give results to within 5%. Based on these data, design goals for WCDMA power amplifiers (in order to improve the talk times significantly) are suggested. The output power levels where the PA efficiencies have to be improved in order to significantly increase the battery life of WCDMA handsets are presented. / Master of Science

<p>Background:</p><p>The task of this thesis is to investigate the possibility of using non-linear high efficiency switching power amplifiers with spectrally efficient varying envelope modulation schemes and, if possible, further investigate such a solution on a high level.</p><p>The thesis focuses on the theory necessary to understand the technical issues related to power amplifiers and the procedures behind simulating and measuring the characteristics of different power amplifier configurations. The thesis also covers basic theory behind Delta-Sigma-modulators. The theory is needed to draw conclusions about the feasibility of using a Delta-Sigma-modulator as input to a switching amplifier.</p><p>Results:</p><p>Using a Delta-Sigma-modulated input to a switching amplifier inherently degrades the performance, mainly because of poor coding efficiency and high switching activity. However, by merely using a switching amplifier as a mixer it is shown to be possible to transmit a non-constant envelope signal, with digital logic. The resulting circuit is, however, not an amplifier and it should not be seen as the final result. As already mentioned: the result lies in the investigation of a using Delta-Sigma-modulator as input to a switching amplifier.</p><p>Conclusion:</p><p>From this investigation we believe that the widely known technique: pulse width modulation (PWM), together with a tuned switching amplifier and some linearization technique, for example pre-distortion, is a better way to go. Much effort should be put in understanding the fundamental limits and possibilities of an efficient tuned switching power amplifier.</p>

Power amplifiers (PAs) are important components of communication systems and are inherently nonlinear. When a non-constant modulus signal goes through a nonlinear PA, spectral regrowth (broadening) appears in the PA output, which in turn causes adjacent channel interference (ACI). Stringent limits on the ACI are imposed by regulatory bodies, and thus the extent of the PA nonlinearity must be controlled. PA linearization is often necessary to suppress spectral regrowth, contain adjacent channel interference, and reduce bit error rate (BER). This dissertation addresses the following aspects of power amplifier research: modeling, linearization, and spectral regrowth analysis. We explore the passband and baseband PA input/output relationships and show that they manifest differently when the PA exhibits long-term, short-term, or no memory effects. The so-called quasi-memoryless case is especially clarified. Four particular nonlinear models with memory are further investigated. We provide experimental results to support our analysis. The benefits of using the orthogonal polynomials as opposed to the conventional polynomials are explored, in the context of digital baseband PA modeling and predistorter design. A closed-form expression for the orthogonal polynomial basis is derived. We demonstrate the improvement in numerical stability associated with the use of orthogonal polynomials for predistortion. Spectral analysis can help to evaluate the suitability of a given PA for amplifying certain signals or to assist in predistortion linearization algorithm design. With the orthogonal polynomials that we derived, spectral analysis of the nonlinear PA becomes a straightforward task. We carry out nonlinear spectral analysis with digitally modulated signal as input. We demonstrate an analytical approach for evaluating the power spectra of filtered QPSK and OQPSK signals after nonlinear amplification. Many communications devices are nonlinear and have a peak power or peak amplitude constraint. In addition to possibly amplifying the useful signal, the nonlinearity also generates distortions. We focus on signal-to-noise-and-distortion ratio (SNDR) optimization within the family of amplitude limited memoryless nonlinearities. We obtain a link between the capacity of amplitude-limited nonlinear channels with Gaussian noise to the SNDR.

Hybrid Digital/RF Envelope Predistortion Linearization for High Power Amplifiers in Wireless Communication Systems Wangmyong Woo 151 Pages Directed by Dr. J. Stevenson Kenney The objective of this research is to implement a hybrid digital/RF envelope predistortion linearization system for high-power amplifiers used in wireless communication systems. It is well known that RF PAs have AM/AM (amplitude modulation) and AM/PM (phase modulation) nonlinear characteristics. Moreover, the distortion components generated by a PA are not constant, but vary as a function of many input conditions such as amplitude, signal bandwidth, self-heating, aging, etc. Memory effects in response to past inputs cause a hysteresis in the nonlinear transfer characteristics of a PA. This hysteresis, in turn, creates uncertainty in predictive linearization techniques. To cope with these nonlinear characteristics, distortion variability, and uncertainty in linearization, an adaptive digital predistortion technique, a hybrid digital/RF envelope predistortion technique, an analog-based RF envelope predistortion technique, and a combinational digital/analog predistortion technique have been developed. A digital adaptation technique based on the error vector minimization of received PA output waveforms was developed. Also, an adaptive baseband-to-baseband test system for the characterization of RF PAs and for the validation of linearization algorithms was implemented in conjunction with the adaptation technique. To overcome disadvantages such as limited correction bandwidth and the need for a baseband input signal in digital predistortion, an adaptive, wideband RF envelope predistortion system was developed that incorporates a memoryless predistortion algorithm. This system is digitally controlled by a look-up table (LUT). Compared with conventional baseband digital approaches, this predistortion architecture has a correction bandwidth that is from 20 percent to 33 percent wider at the same clock speeds for third to fifth order IMDs and does not need a digital baseband input signal. For more accurate predistortion linearization for PAs with memory effects, an RF envelope predistortion system has been developed that uses a combination of analog-based envelope predistortion (APD) working in conjunction with digital LUT-based adaptive envelope predistortion (DPD). The resulting combination considerably decreases the computational complexity of the digital system and significantly improves linearity and efficiency at high power levels.

Background: The task of this thesis is to investigate the possibility of using non-linear high efficiency switching power amplifiers with spectrally efficient varying envelope modulation schemes and, if possible, further investigate such a solution on a high level. The thesis focuses on the theory necessary to understand the technical issues related to power amplifiers and the procedures behind simulating and measuring the characteristics of different power amplifier configurations. The thesis also covers basic theory behind Delta-Sigma-modulators. The theory is needed to draw conclusions about the feasibility of using a Delta-Sigma-modulator as input to a switching amplifier. Results: Using a Delta-Sigma-modulated input to a switching amplifier inherently degrades the performance, mainly because of poor coding efficiency and high switching activity. However, by merely using a switching amplifier as a mixer it is shown to be possible to transmit a non-constant envelope signal, with digital logic. The resulting circuit is, however, not an amplifier and it should not be seen as the final result. As already mentioned: the result lies in the investigation of a using Delta-Sigma-modulator as input to a switching amplifier. Conclusion: From this investigation we believe that the widely known technique: pulse width modulation (PWM), together with a tuned switching amplifier and some linearization technique, for example pre-distortion, is a better way to go. Much effort should be put in understanding the fundamental limits and possibilities of an efficient tuned switching power amplifier.

Emerging wireless standards are designed to be spectrally efficient to address the high cost of licensing wireless spectra. Unfortunately, the resulting signals have a high peak-to-average ratio that reduces the base station power amplifier efficiency at the back-off power level. The wasted energy is converted to heat that degrades the device reliability and increases the base-station’s carbon footprint and cooling requirements. In addition, these new standards place stringent re- quirements on the amplifier output power, linearity, efficiency, and bandwidth. To improve the back-off efficiency, a Doherty amplifier, which uses two device in parallel for back-off efficiency enhancement, is deployed in a typical base station. Unfortunately, the conventional Doherty amplifier is narrowband and thus cannot satisfy the bandwidth requirement of the modern base station that needs to support multiple standards and backward compatibility. In this thesis, we begin by studying the class F/F−1 high efficiency mode of operation. To this end, we designed a narrowband, harmonically-tuned 3.3 GHz, 10 W GaN high efficiency amplifier. Next, we investigate how to simultaneously achieve high efficiency and broad bandwidth by harnessing the simplified real frequency technique for the broadband matching network design. A 2 to 3 GHz, 45 W GaN amplifier and a 650 to 1050 MHz, 45 W LDMOS amplifier were designed. Finally, we analyze the conventional Doherty amplifier to determine the cause of its narrow bandwidth. We find that the narrow bandwidth can be attributed to the band-limited quarter-wave transformer as well as the widely adopted traditional design technique. As an original contribution to knowledge, we propose a novel Doherty amplifier configuration with intrinsically broadband characteristics by analyzing the load modulation concept and the conventional Doherty amplifier. The proposed amplifier uses asymmetrical drain voltage biases and symmetrical devices and it does not require a complex mixed-signal setup. To demonstrate the proposed concept in practice, we designed a 700 to 1000 MHz, 90 W GaN broadband Doherty amplifier. Moreover, to show that the proposed concept is applicable to high power designs, we designed a 200 W GaN broadband Doherty amplifier in the same band. In addition, to show that the technique is independent of the device technology, we designed a 700 to 900 MHz, 60 W LDMOS broadband Doherty amplifier. Using digital pre-distortion, the three prototypes were shown to be highly linearizable when driven with wideband 20 MHz LTE and WCDMA modulated signals and achieved excellent back-off efficiency. Lastly, using the insights from the previous analyses, we propose a novel mixed-technology Doherty amplifier with an extended and reconfigurable back-off level as well as an improved power utilization factor. The reconfigurability of the proposed amplifier makes it possible to customize the back-off level to achieve the highest average efficiency for a given modulated signal without redesigning the matching networks. A 790 to 960 MHz, 180 W LDMOS/GaN Doherty amplifier demonstrated the extended bandwidth and reconfigurability of the back-off level. The proposed amplifier addresses the shortcomings of the conventional Doherty amplifier and satisfies the many requirements of a modern base station power amplifier.

Emerging wireless standards are designed to be spectrally efficient to address the high cost of licensing wireless spectra. Unfortunately, the resulting signals have a high peak-to-average ratio that reduces the base station power amplifier efficiency at the back-off power level. The wasted energy is converted to heat that degrades the device reliability and increases the base-station’s carbon footprint and cooling requirements. In addition, these new standards place stringent re- quirements on the amplifier output power, linearity, efficiency, and bandwidth. To improve the back-off efficiency, a Doherty amplifier, which uses two device in parallel for back-off efficiency enhancement, is deployed in a typical base station. Unfortunately, the conventional Doherty amplifier is narrowband and thus cannot satisfy the bandwidth requirement of the modern base station that needs to support multiple standards and backward compatibility. In this thesis, we begin by studying the class F/F−1 high efficiency mode of operation. To this end, we designed a narrowband, harmonically-tuned 3.3 GHz, 10 W GaN high efficiency amplifier. Next, we investigate how to simultaneously achieve high efficiency and broad bandwidth by harnessing the simplified real frequency technique for the broadband matching network design. A 2 to 3 GHz, 45 W GaN amplifier and a 650 to 1050 MHz, 45 W LDMOS amplifier were designed. Finally, we analyze the conventional Doherty amplifier to determine the cause of its narrow bandwidth. We find that the narrow bandwidth can be attributed to the band-limited quarter-wave transformer as well as the widely adopted traditional design technique. As an original contribution to knowledge, we propose a novel Doherty amplifier configuration with intrinsically broadband characteristics by analyzing the load modulation concept and the conventional Doherty amplifier. The proposed amplifier uses asymmetrical drain voltage biases and symmetrical devices and it does not require a complex mixed-signal setup. To demonstrate the proposed concept in practice, we designed a 700 to 1000 MHz, 90 W GaN broadband Doherty amplifier. Moreover, to show that the proposed concept is applicable to high power designs, we designed a 200 W GaN broadband Doherty amplifier in the same band. In addition, to show that the technique is independent of the device technology, we designed a 700 to 900 MHz, 60 W LDMOS broadband Doherty amplifier. Using digital pre-distortion, the three prototypes were shown to be highly linearizable when driven with wideband 20 MHz LTE and WCDMA modulated signals and achieved excellent back-off efficiency. Lastly, using the insights from the previous analyses, we propose a novel mixed-technology Doherty amplifier with an extended and reconfigurable back-off level as well as an improved power utilization factor. The reconfigurability of the proposed amplifier makes it possible to customize the back-off level to achieve the highest average efficiency for a given modulated signal without redesigning the matching networks. A 790 to 960 MHz, 180 W LDMOS/GaN Doherty amplifier demonstrated the extended bandwidth and reconfigurability of the back-off level. The proposed amplifier addresses the shortcomings of the conventional Doherty amplifier and satisfies the many requirements of a modern base station power amplifier.

The main purpose of this theses is to design a pre-power for WiMAX in the 5.65 GHz frequency range. The pre-power amplifier main features are moderate linearity and output power. Another goal of the theses is to design the phisical layout of the amplifier for PCB presentation.The described power amplifier is designed to operate as a pre-amplifier, class AB and at 5.65 GHz with a gain of around 10 dB with an approximate bandwidth of 300 MHz. / -

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy