Αντικείμενο αυτής της διπλωματικής εργασίας είναι ο σχεδιασμός ενός αναλογικού ενισχυτικού κυκλώματος χαμηλού θορύβου το οποίο θα λειτουργεί σε υψηλές συχνότητες. Ο ενισχυτής αυτός προορίζεται για χρήση στο analog front end κυκλωμάτων τα οποία θα υποστηρίζουν πρωτόκολλα μεταφοράς πληροφορίας σε δίκτυα ισχύος (Power Line Communication, Internet of Things). Για τον σχεδιασμό γίνεται η χρήση της κλασικής θεωρίας μικροηλεκτρονικών κυκλωμάτων αλλά και της μικροκυματικής θεωρίας. Παρουσιάζονται οι διάφορες τοπολογίες των τρανζίστορ BJT, γίνεται μία παρουσίαση των βασικότερων πηγών θορύβου και αναφέρονται βασικές αρχές των S παραμέτρων και της προσαρμογής εμπέδησης. Ο ενισχυτής κοινού εκπομπού απορρίφθηκε καθώς αποδείχθηκε αμφίπλευρος οπότε καταλήξαμε στην επιλογή της cascode τοπολογίας η οποία προσδίδει ευστάθεια, απομόνωση και καλή γραμμικότητα. Η απόλυτη προδιαγραφή που τέθηκε για το θόρυβο δεν επιτεύχθηκε και οπότε αναφέραμε τους λόγους που οδήγησαν σε αυτό και προτείναμε πιθανές λύσεις μέσω άλλων υλοποιήσεων. / The subject of this diploma thesis is the design of a low noise high-frequency analogue amplifier. The amplifier is designed to be used in the analog front end of circuits designed to support protocols that control the transmission of information over power lines (internet of things). To achieve this goal we make use of classic microelectronics theory but also microwave theory. The topologies of the BJT transistors are presented, we also go through the basic noise production reasons and we also make a short reference on the s-parameters and on the basic principles of impedance matching. The common emitter amplifier proved to be bilateral, so the cascode amplifier, which provides stability, isolation and linearity, was preferred. The noise specification was not achieved so we present the basic reasons of this, as well as we propose possible solutions.

In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers.This single-frequency laser technology was used to develop an all-fiber actively Q-switched fiber lasers. A short cavity is used to create large spacing between longitudinal modes. Using this method, we demonstrated the first all-fiber Q-switched fiber laser in the 1 micron region.In addition to creating high peak powers with Q-switched lasers, created even higher powers using fiber amplifier systems. High power fiber lasers typically produce spectral broadening through the nonlinear effects of stimulated Raman scattering, stimulated Brullion scattering, and self-phase modulation. The thresholds for these nonlinearities scale inversely with intensity and length. Thus, we used a short phosphate fiber gain stage to reduce the length, and a large core fiber final stage to reduce intensity. In this way we were able to generate high peak power pulses while avoiding visible nonlinearities, and keeping a narrow bandwidth.The immediate goal of developing these high power fiber laser systems was to generate narrowband terahertz radiation. Two different wavelengths were combined into the final amplifier stage at orthogonal polarizations. These were collimated and directed into a GaSe crystal, which has a very high figure of merit for THz generation. The two wavelengths combined in the crystal through the process of nonlinear difference frequency generation. This produced a narrowband beam of THz pulses, at higher powers than previous narrowband THz pulses produced by eyesafe fiber lasers.

The internet revolution has led to the demand for high speed, low cost solutions for providing high bandwidth to the consumers. Cable and DSL systems address these requirements through sophisticated analog and digital signal processing schemes. A key element of the analog front end of such systems is the line driver which interfaces with the transmission medium such as co-axial cable or twisted pair. The line driver is an amplifier that provides the necessary output current to drive the low impedance of the line. The main requirements for design are high output swing, high linearity, matched impedance to the line and power efficiency. These requirements are addressed by a class AB amplifier whose output impedance can be controlled through feedback. The property of this topology is that when the gain is unity, the output resistance of the driver is matched to the line resistance. Unity gain is achieved for varying line conditions through a tuning loop consisting of peak-to-peak detectors and differential difference amplifier. The design is fabricated in 0.5 micron AMI CMOS process technology. For line variations from 65 to 170 ohms, the gain is unity with an error of 3 % and the impedance matching error is 20 % at the worst-case. The linearity is better than 50 dB for a 1.2 V peak-to-peak signal over the signal bandwidth from 10 kHz to 5 MHz and the line resitance range from 65 to 160 ohms.

The objective of the proposed research is to characterize the safe-operating-area of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) under radiofrequency (RF) operation and extreme environments. The degradation of SiGe HBTs due to mixed-mode DC and RF stress has been modeled for the first time. State-of-the-art 200 GHz SiGe HBTs were first characterized, and then DC and RF stressed. Excess base leakage current was modeled as a function of the stress current and voltage. This physics-based stress model was then designed as a sub-circuit in Cadence, and incorporated into SiGe power amplifier design to predict the DC and RF stress-induced excess base current. Based on these studies, characterization of RF safe-operating-area for SiGe HBTs using devices and circuits is proposed.

Next generation communication systems are reaching 110Gbps rates. At these frequencies, the skin effect and dielectric loss of copper cables cause inter-symbol interference (ISI) and frequency dependent loss, severely limiting the channel bandwidth. In this thesis, different methods for alleviating ISI are explored. The design of the critical blocks of an adaptive channel equalizer with up to two times oversampling are presented. The circuits were fabricated in a 0.13μm SiGe BiCMOS technology. The linear, adaptive equalizer operates up to 70Gbps and its measured S-parameters exhibit a single-ended peak gain of 12.2dB at 52GHz, allowing for 31dB of peaking between DC and 52GHz. Equalization is demonstrated experimentally at 59Gbps for a cable loss of 17.9dB. These results make it the fastest receive equalizer published to date. A retiming flip-flop operating between 72 and 118 GHz, the highest reported in silicon, is also designed and characterized, showing less than 500-fs jitter.

Next generation communication systems are reaching 110Gbps rates. At these frequencies, the skin effect and dielectric loss of copper cables cause inter-symbol interference (ISI) and frequency dependent loss, severely limiting the channel bandwidth. In this thesis, different methods for alleviating ISI are explored. The design of the critical blocks of an adaptive channel equalizer with up to two times oversampling are presented. The circuits were fabricated in a 0.13μm SiGe BiCMOS technology. The linear, adaptive equalizer operates up to 70Gbps and its measured S-parameters exhibit a single-ended peak gain of 12.2dB at 52GHz, allowing for 31dB of peaking between DC and 52GHz. Equalization is demonstrated experimentally at 59Gbps for a cable loss of 17.9dB. These results make it the fastest receive equalizer published to date. A retiming flip-flop operating between 72 and 118 GHz, the highest reported in silicon, is also designed and characterized, showing less than 500-fs jitter.

In this thesis, I have developed a tunable two-color two-stage ultrafast Yb:fiber chirped pulse amplifier for the generation of short-pulse mid-infrared (MIR) radiation in the long-wavelength side of the "molecular fingerprint" (2.5-25 μm) using difference frequency generation (DFG) technique. The two colors called blue and red are in the wavelengths 1.03-1.11 μm and are amplified simultaneously in the same Yb-doped fiber amplifier (YDFA) stages in order to reduce the induced environmental noise on the phase difference of the pulses and to minimize the complexity and system cost. I will present numerical simulations on the two-stage YDFA system to amplify a two-color spectrum in the wavelengths 1.03-1.11 μm. The first and second YDFA called preamplifier and main amplifier are single-clad, single-mode and double-clad, single-mode YDFA respectively. From numerical simulations, the optimal length of the preamplifier to have equal power at two colors centered at 1043 nm and 1105 nm are in agreement with experimental results. It is well known that the power of MIR radiation generated by difference frequency mixing of two wavelengths scales up with the product of mixing powers in a fixed-field approximation. Furthermore, for the gain narrowing effect on the short-wavelength side of the YDFA gain profile, the spectral bandwidth of the blue color decreases resulting in pulse broadening. In addition, for the two colors separated largely, the amplified spontaneous emission is intensified. Considering the cited factors, I will present the modeling results on the two-color, two-stage YDFA system that the product of the power of the two colors is maximized for a maximized wavelength separation between the two mixing colors and a minimized gain narrowing on the blue color in order to build an as broadly tunable and powerful as possible ultrafast mid-infrared source by difference frequency mixing of the two colors. In this research, I achieved a wavelength separation as broad as 71 nm between pulses centered at 1038 nm and 1109 nm from the two-color ultrafast YDFA system. I achieved combined average powers of 2.7 W just after the main amplifier and 1.5 W after compressing the two-color pulses centered at 1041 nm and 1103 nm to nearly Fourier transform limited pulses. From autocorrelation measurements, the full width at half maximum (FWHM) of the compressed two-color pulses with the peak wavelengths of 1041 nm and 1103 nm was ~500 fs. By mixing the tunable two-color pulses in a 1-mm-thick GaSe crystal using DFG technique, I achieved tunable short-pulse MIR radiation. In this research, I achieved short-pulse MIR radiation tunable in the wavelengths 16-20 μm. The MIR tuning range from the lower side was limited to the 16 μm because of the 71-nm limitation on the two-color separation and from the upper side was limited to the 20 μm because of the 20-μm cutoff absorption wavelength of GaSe. Based on measured MIR spectra, the MIR pulses have a picosecond pulse duration in the wavelengths 16-20 μm. The FWHM of measured spectra of the MIR pulses increases from 0.3 μm to 0.8 μm as the MIR wavelength increases from 16 μm to 20 μm. According to Fourier transform theory, the FWHM of the MIR spectra corresponds to the bandwidth of picosecond MIR pulses assuming that the MIR pulses are perfectly Fourier-transform-limited Gaussian pulses. In this research, I achieved a maximum average power of 1.5 mW on short-pulse MIR radiation at the wavelength 18.5 μm corresponding to the difference frequency of the 500-fs two-color pulses with the peak wavelengths of 1041 nm and 1103 nm and average powers of 1350 mW and 80 mW respectively. Considering the gain bandwidth, Ti:sapphire is a main competitor to the YDFA to be used in the two-color ultrafast laser systems. In the past, the broad gain bandwidth of Ti:sapphire crystal has resulted in synchronized two-color pulses with a wavelength separation up to 120 nm. Apart from its bulkiness and high cost, Ti:sapphire laser system is limited to a watt-level output average power at room temperature mainly due to Kerr lensing problem that occurs at high pumping powers. In comparison, YDFA as a laser amplifier has a narrower gain bandwidth but it is superior in terms of average power. Optical parametric generation (OPG) and optical parametric amplification (OPA) techniques are two competitors to DFG technique for the generation of short-pulse long-wavelength MIR radiation. Although OPG offers a tunability range as broad as DFG, the MIR output power is lower because of the absence of input signal pulses. From the OPA technique, the tunability range is not as broad as the DFG technique due to limitations with the spectral bandwidth of the optical elements. Currently, quantum cascade lasers (QCLs) are the state-of-art MIR laser sources. At the present time, the tunability range of a single MIR QCL is not as abroad as that achieved from the DFG technique. More, mode-locked MIR QCLs are not abundant mainly because of the fast gain recovery time. Thus, the generation of widely tunable short-pulse MIR radiation from DFG technique such as that developed in this thesis remains as a persistent technological solution. The application of the system developed in this thesis is twofold: on one hand, the tunable two-color ultrashort pulses will find applications for example in pump-probe ultrafast spectroscopy, short-pulse MIR generation, and optical frequency combs generation. On the other hand, the short-pulse MIR radiation will find applications for example in time-resolved MIR spectroscopy to study dynamical behavior of large molecules such as organic and biological molecules.

This thesis examines the design of high speed transimpedance amplifiers (TIAs) in low cost complimentary metal oxide semiconductor (CMOS) technology. Due to aggressive scaling, CMOS has become an attractive technology for high speed analog circuits. Besides the cost advantage, CMOS offers the potential for higher levels of integration since the analog circuits can be integrated with digital electronics on the same substrate. A 2.5 Gbps transimpedance amplifier fabricated using 0.18 um CMOS technology is presented. The TIA uses a shunt-shunt feedback topology with a cascode gain stage. Measurements of the transimpedance gain, group delay, and common mode rejection ratio are presented for the TIA and show a good match to simulated results. The noise of the TIA was characterized by measuring the noise parameters of the TIA. The noise parameters are then used to determine the input referred noise current spectral density. A 10 Gbps transimpedance amplifier fabricated using 0.18 um CMOS technology is also presented. This TIA uses a shunt-shunt feedback topology with a common source gain stage. In order to achieve the required bandwidth, the TIA uses a bandwidth extension technique called shunt-series inductive peaking. A discussion of the different methods of bandwidth extension using inductive peaking is included, and the optimal configurations for maximally flat responses are shown for shunt inductive peaking,series inductive peaking, and shunt-series inductive peaking. The TIA circuit topology is optimized using a novel noise analysis that uses a high frequency noise model for the transistor. The optimum transistor size and bias current are determined to minimize the amplifier noise. Unfortunately differential measured results are not available due to a stability problem in the amplifier. The cause of this instability is further explored and modifications to solve the problem are discussed. Single-ended results are presented and show reasonable agreement with simulated results. Differences in the results are attributed to poor modelling of the on-chip spiral inductors. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2007-07-16 13:34:41.46

No description available.

No description available.