Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Limiting amplifiers are employed in electronic warfare (EW) systems requiring a high measure of amplitude control. These EW systems employ sensitive signal processing components that are unable to accept the full dynamic range of input signals the system must face. The limiting amplifier, however, offers the unique capability of reducing the received signal spectrum to a suitable dynamic range. A typical application of the limiting amplifier is in the instantaneous frequency measurement (IFM) receiver where the limiting amplifier allows the receiver to accurately measure pulsed signals over a wide input dynamic range The aim of this study is the design and analysis of a broadband limiting amplifier. Focus is placed on the design of a socalled backbone limiting amplifier (BLA) which forms an integral part of a proposed modular design approach for realizing a design with improved input dynamic range. A designed BLA is discussed in this thesis while insight is given as to the intricacies associated with its mechanism of operation. Over its 45 dB (- 40 to + 5 dBm) input dynamic range, the designed 2-18 GHz limiting amplifier offers a typical saturated output power of 7.5 dBm while harmonic suppression of better than 8.6 dBc is achieved. The BLA design was based on an existing limiting amplifier design, the so-called baseline limiting amplifier, employing alternating amplifiers and attenuators. Evaluation of the baseline limiting amplifier design allowed for formulation of a design hypothesis for realizing the BLA design. Physical measurements on the BLA were then used to scrutinize and validate the formulated design hypothesis. The requirements for realizing the BLA design were the establishment of a thorough radio frequency (RF) amplifier design capability, an understanding of the nonlinear phenomena associated with the RF amplifier and the utilization and control thereof within the limiting amplifier. Different RF amplifier designs that were carried out are discussed in this thesis, while it is shown how they were used to further investigate important design considerations for application in the BLA design. The computer-aided design packages namely MultiMatch and Microwave Office (MWO) were successfully used in realizing the desired broadband RF amplifier designs and the eventual BLA design. / AFRIKAANSE OPSOMMING: Beperker versterkers word gebruik in elektroniese oorlogvoering (EO) stelsels waar ’n redelike mate van amplitude beheer noodsaaklik is. Sensitiewe seinverwerking komponente, wat nie die volle dinamiese bereik van intreeseine kan hanteer nie, maak deel uit van hierdie EO stelsels. Die beperker versterker bied egter die unieke eienskap om die ontvangde seinspektra te reduseer tot ’n gepaste dinamiese bereik. ’n Tipiese toepassing vir die beperker versterker is as deel van die oombliksfrekwensie- meting ontvanger waar die beperker versterker die ontvanger toelaat om akkurate meting van gepulsde seine te doen oor ’n wye intree dinamiese bereik. Die doel van hierdie studie is die ontwerp en analise van ’n wye-band beperker versterker. Fokus word geplaas op die ontwerp van ’n sogenaamde kruks beperker versterker wat ’n integrale deel uitmaak van ’n voorgestelde modulêre ontwerpsbenadering, wat ten doel het om ’n verbeterde intree dinamiese bereik daar te stel. Oor die 45 dB (- 40 tot + 5 dBm) intree dinamiese bereik, bied die ontwerpte 2-18 GHz beperker versterker ’n tipiese versadigde uittreedrywing van 7.5 dBm terwyl harmonieke onderdrukking van beter as 8.6 dBc verkry is. Die ontwerp van hierdie komponent word in hierdie tesis bespreek terwyl belangrike aspekte oor die werking daarvan uitgelig word. Die ontwerp van die kruks beperker versterker is gebaseer op ’n bestaande beperker versterker ontwerp, of sogenaamde basis ontwerp, wat gebruik maak van afwisselende versterkers en attenuators. Evaluering van die basis ontwerp het toegelaat vir die formulering van 'n ontwerpshipotese om die kruks beperker versterker te realiseer. Fisiese metings op die kruks beperker versterker is gebruik om die ontwerpshipotese krities te evalueer. Om die kruks beperker versterker te realiseer moes die nodige RF versterker ontwerpsvaardigheid daargestel word, ’n begrip vir die nie-liniêere verskynsels in die RF versterker en die gebruik en beheer daarvan in die beperker versterker moes daargestel word. Verskeie RF versterkers wat ontwerp is word in hierdie tesis bespreek, terwyl getoon word hoe hierdie ontwerpe gebruik is om belangrike ontwerpsaspekte te ondersoek wat uiteindelik toegepas is in die kruks beperker versterker ontwerp. Die ontwerpspakkette naamlik MultiMatch en Microwave Office is suksesvol gebruik vir die realisering van die nodige wye-band RF versterkers en die uiteindelike kruks beperker versterker ontwerp.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / Modern day digital modulation techniques in communication systems produce large peak-to-average ratios. To maintain linearity, power amplifiers have to operate at backed-off levels. This results in low efficiency with consequences such as high power consumption, short battery life and excessive heat in power amplifiers. A Doherty amplifier is an efficiency enhancement technique which increases an amplifier’s efficiency at backed-off levels. This thesis presents a design procedure for a Classical Doherty amplifier. A method where Sparameter measurements from a transistor are used to predict the transistor’s transmission phase response for varying input power is presented. This method is found to be accurate by comparing it to measurements done on a non-linear network analyser. The measured S-parameters are also used to design the Doherty amplifier at its predicted peak output power. Two Classical Doherty amplifiers are designed, manufactured and characterised. The measurements are performed on a custom measurement setup using in-house developed Matlab code to automate the measurements. The first Doherty amplifier used small-signal Siemens CFY30 GaAs FETs and the second Doherty amplifier used 10W Motorola MRF282 LDMOS transistors. The performance of both amplifiers is compared to similar balanced amplifiers and shows improvements in their efficiency. The improvement in efficiency for the 10W Doherty power amplifier in relation to a balanced amplifier is compared to results found in the literature and a good correspondence between the measured and published results were obtained.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The thesis details the design, construction and experimental evaluation of 30W, 35W and 250W L-Band LDMOS Radar amplifiers. Each amplifier module contains an integrated high speed power supply in order to optimize RF pulse repeatability and to improve radar MTI factor (Moving Target Indication.) As part of the work, a pulsed RF measurement system for measuring the dynamic I-V curves of a power FET was developed. Work was also done on low impedance S-parameter measurement test fixtures for the characterisation of power FETs. These measurement systems generated design information which was used in the development of the L-Band power amplifiers / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwerp, bou en experimentele evaluering van „n 30W, 35W en 250W L-band LDMOS radarversterker. Elke versterker bevat ook „n geintegreerde hoë-spoed kragbron om optimum RF pulsherhaalbaarheid te verseker en die radar se „MTI (Moving Target Indication)‟ te verbeter. „n RF-pulsmetingstelsel is ook ontwikkel om die dinamiese I-V kurwes van „n hoë-krag FET te meet. Verder is daar ook gewerk aan „n toetsopstelling vir lae-impedansie S-parameters om hoë-krag FETs te karakteriseer. Hierdie toetsopstelling is gebruik om ontwerpsdata te genereer wat gebruik is in die ontwerp van die L-band kragversterkers.

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

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The effects of radiation on an operational amplifier were investigated through simulation. The μA 741 was simulated using Spice. Under normal conditions the 741 had the following properties: offset Voltage (Vos) of 0.8 mV, bias current (IB) of 27 nA, offset current (Ios) of 1 nA, and an open loop gain (A0.1.) of 112 dB. When exposed to neutron fluence of 5 x 10¹³ n/cm², these parameters changed to offset voltage of 45 mV, bias current of 1500 nA, offset current of 500 nA, and an open loop gain of 66 dB. A new circuit is proposed that provides improvements in the above parameters. The modified circuit gives a Vos of 3 mV, IB of 200 nA, Ios of 34 nA and A0.1. of 93 dB following exposure to a neutron fluence of 5 x 10¹³n/cm².

Cladding pumped single-frequency Yb3+-doped fiber amplifiers at 976 nm were investigated. Over 4 W output power was obtained and further power scaling can be achieved by reducing the cladding diameter of the Yb3+-doped fiber.

Lin Pui-Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 103-105). / Abstracts in English and Chinese. / Acknowledgement / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Nonlinear Phenomenon of Power Amplifier --- p.5 / Chapter 2.1. --- AM-AM and AM-PM Distortion --- p.5 / Chapter 2.2. --- Intermodulation Distortion --- p.7 / Chapter Chapter 3 --- Linearization Techniques --- p.10 / Chapter 3.1. --- Power Backoff --- p.11 / Chapter 3.2. --- Feedback --- p.12 / Chapter 3.3. --- Predistortion --- p.12 / Chapter 3.4. --- Feedforward --- p.14 / Chapter 3.5. --- Other Linearization Techniques --- p.15 / Chapter Chapter 4 --- Analysis of Feedforward Power Amplifier --- p.17 / Chapter 4.1. --- Feedforward Efficiency --- p.18 / Chapter 4.2. --- Design Criteria of the Auxiliary Amplifier --- p.20 / Chapter 4.3. --- Sensitivity Analysis --- p.21 / Chapter 4.3.1. --- Phase and Amplitude Mismatch --- p.22 / Chapter 4.3.2. --- Delay Mismatch --- p.23 / Chapter 4.3.3. --- Combined Effect --- p.25 / Chapter 4.3.4. --- Practical Consideration --- p.27 / Chapter 4.4. --- Other Design Criteria --- p.28 / Chapter Chapter 5 --- Adaptive Control Networks for FFPA --- p.29 / Chapter 5.1. --- Basic Principles of the Adaptive Control Network --- p.30 / Chapter 5.1.1. --- Lookup Table --- p.30 / Chapter 5.1.2. --- Power Minimization Vs. Correlation --- p.31 / Chapter 5.2. --- Analog Vs Digital Implementation of the Adaptive Control Network --- p.34 / Chapter 5.3. --- Techniques for Improving the Convergence Behaviour at the Distortion Cancellation Loop --- p.35 / Chapter 5.4. --- Important Notes on the Control Networks --- p.38 / Chapter Chapter 6 --- Novel Analysis of Adaptive FFPA --- p.40 / Chapter 6.1. --- Gradient algorithm --- p.40 / Chapter 6.2. --- Dual Loop Adaptive FFPA --- p.41 / Chapter 6.2.1. --- System Modeling --- p.42 / Chapter 6.2.2. --- Adaptation Behavior of the Distortion Extraction Loop --- p.44 / Chapter 6.2.3. --- Adaptation Behavior of the Distortion Cancellation Loop --- p.48 / Chapter 6.2.4. --- Accuracy Requirement of the Control Signals --- p.50 / Chapter 6.2.5. --- Effect of Delay Mismatch on the Convergence Accuracy --- p.51 / Chapter 6.2.6. --- Convergence Behaviors for Two Tone Input Signal --- p.52 / Chapter 6.2.6.1. --- Distortion Extraction Loop --- p.53 / Chapter 6.2.6.2. --- Distortion Cancellation Loop --- p.55 / Chapter 6.2.6.3. --- Simulation Results --- p.57 / Chapter 6.2.7. --- Convergence Behaviors for Digital Modulated Test signal --- p.60 / Chapter 6.2.7.1. --- Distortion Extraction Loop --- p.61 / Chapter 6.2.7.2. --- Distortion Cancellation Loop --- p.66 / Chapter 6.2.7.3. --- Simulation Results --- p.68 / Chapter 6.2.8. --- Comparison for the Adaptation Performance with Two Tone and Digital Modulated Test Signal --- p.70 / Chapter 6.3. --- Triple Loop Adaptive FFPA --- p.71 / Chapter 6.3.1. --- Adaptation Performance of the Additional Loop --- p.73 / Chapter 6.3.2. --- Adaptation Performance of the Distortion Cancellation Loop --- p.75 / Chapter 6.3.3. --- Improvement in Bias Error at the Distortion Cancellation Loop --- p.76 / Chapter 6.3.4. --- Effect of Delay Mismatch --- p.77 / Chapter 6.3.5. --- Simulation Results --- p.79 / Chapter Chapter 7 --- Implementation and Measured Performance of Triple Loop Adaptive FFPA --- p.85 / Chapter 7.1. --- Hardware Design --- p.85 / Chapter 7.1.1. --- Vector Modulator --- p.87 / Chapter 7.1.2 --- Complex Correlator --- p.88 / Chapter 7.2. --- Experimental Setup and Measured Results --- p.90 / Chapter Chapter 8 --- Conclusion --- p.95 / Appendix I Matlab Program for Simulation of Dual Loop Adaptive FFPA --- p.97 / Appendix II Matlab Program for Simulation of Triple Loop Adaptive FFPA --- p.100 / Reference --- p.103 / Author's Publication --- p.106

<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>

No description available.