Le Convertisseur Analogique Numérique (CAN) est une brique essentielle de la ré- ception et du traitement des données à très haut débit. L’architecture de type "flash" effectue la quantification en comparant simultanément le signal analogique d’entrée à l’ensemble des références du codeur, ce qui en fait, par construction, l’architecture la plus rapide de CAN. Par le passé, cette architecture a démontré des capacités de codage supérieures à 20GS/s dans les conditions de Nyquist. Cependant, cette capac- ité à travailler à très haute vitesse a donné le jour à des réalisations très consommantes (plusieurs Watts) donc peu efficaces énergétiquement. Cette thèse explore différentes approches d’optimisation de l’efficacité énergétique des CAN "flash". Afin de min- imiser la consommation du CAN, il n’y a pas d’Echantillonneur-Bloqueur (EB) en tête du circuit. Les étages d’entrée du codeur sont ainsi exposés à la pleine bande passante du signal, à savoir DC-10GHz. Ceci impose des contraintes très strictes sur la précision temporelle de la détection et de la quantification du signal. L’essentiel de cette thèse est donc concentré sur l’analyse des effets hautes frèquences impactant la conception des éléments frontaux du CAN. La validité et l’efficacité des méthodes présentées sont démontrées par des mesures autour d’un CAN 6 bit 20 GS/s. En em- pruntant les techniques de conception des circuits ultra-rapides et en exploitant le po- tentiel haute-fréquence de la technologie à l’état de l’art SiGe BiCMOS, un circuit complètement analogique a ainsi pu être réalisé. Ce CAN est mono-voie et n’a besoin d’aucune calibration ou correction, ni d’assistance digitale. Avec à peine 1W, ce cir- cuit atteint un record d’efficacité énergétique dans l’état de l’art des CAN rapides non entrelacés. / High speed Analog-to-Digital Converters (ADC) are essential building blocks for the reception and processing in high data rate reception circuits. The flash ADC archi- tecture performs the digitization by comparing the analog input signal to all refer- ence levels of the quantization range simultaneously and is thus the fastest architecture available. In the past the flash architecture has been employed successfully to digitize signals at Nyquist rates beyond 20 GS/s. However the inherent high speed operation has led to power consumptions of several watts and hence to poor energy efficien- cies. This thesis explores approaches to optimize the energy efficiency of flash ADCs. In particular, no dedicated track-and-hold stage is used at the high speed data input. This imposes very stringent requirements on the timing accuracy and level accuracy in the high speed signal distribution to the comparators. The comparators need to ex- hibit a very high speed capability to correctly perform the quantization of the signal against the reference levels. The main focus of this thesis is hence the investigation of design relevant high frequency effects in the analog ADC frontend, such as the bandwidth requirement of overdriven comparators, the data signal distribution over a passive transmission line tree and the dynamic linearity of emitter followers. The correctness and efficacy of the presented methods is demonstrated by measurement results of a 6 bit 20 GS/s Nyquist rate flash ADC fabricated within the context of this work. The demonstrator ADC operates without time interleaving, no calibration or correction whatsoever is needed. By employing design techniques borrowed from high speed analog circuits engineering and by exhausting the high speed potential of a state-of-the-art SiGe BiCMOS production technology, a flash ADC with a record energy efficiency could be realized.

The research conducted in this dissertation studies the issues regarding the improvement of phase noise performance in a BiCMOS Silicon Germanium (SiGe) cross-coupled differential-pair voltage controlled oscillator (VCO) in a narrowband application as a result of a tail-current shaping technique. With this technique, low-frequency noise components are reduced by increasing the signal amplitude without consuming additional power, and its effect on overall phase noise performance is evaluated. The research investigates effects of the tail-current as a main contributor to phase noise, and also other effects that may influence the phase noise performance like inductor geometry and placement, transistor sizing, and the gain of the oscillator. The hypothesis is verified through design in a standard 0.35 μm BiCMOS process supplied by Austriamicrosystems (AMS). Several VCOs are fabricated on-chip to serve for a comparison and verify that the employment of tail-current shaping does improve phase noise performance. The results are then compared with mathematical models and simulated results, to confirm the hypothesis. Simulation results provided a 3.3 dBc/Hz improvement from -105.3 dBc/Hz to -108.6 dBc/Hz at a 1 MHz offset frequency from the 5 GHz carrier when employing tail-current shaping. The relatively small increase in VCO phase noise performance translates in higher modulation accuracy when used in a transceiver, therefore this increase can be regarded as significant. Parametric analysis provided an additional 1.8 dBc/Hz performance enhancement in phase noise that can be investigated in future works. The power consumption of the simulated VCO is around 6 mW and 4.1 mW for the measured prototype. The circuitry occupies 2.1 mm2 of die area. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

This research looks into the design of an integrated in-phase/quadrature (I/Q) VCO operating at 5 GHz. The goal is to design a phase shifter that is implemented at the LO used for RF up conversion. The target application for the phase shifter is towards phased array antennas operating at 5 GHz. Instead of designing multiple VCOs that each deliver a variety of phases, two identical LC-VCOs are coupled together to oscillate at the same frequency and deliver four outputs that are 90 ° out of phase. By varying the amplitudes of the in-phase and quadrature signals independently using VGAs before adding them together, a resultant out-of-phase signal is obtained. A number of independently variable out-of-phase signals can be obtained from these 90 ° out-of-phase signals and this technique is better known as the vector sum method of phase shifting. Control signals to the inputs of the VGAs required to obtain 22.5 ° phase shifts were designed from simulations and are generated using 16-bit DACs. The design is implemented and manufactured using a 0.35 µm SiGe BiCMOS process and the complete prototype IC occupies an area of 2.65 × 2.65 mm2. The I/Q VCO with 360 ° variable phase outputs occupies 1.10 × 0.85 mm2 of chip area and the 16-bit DAC along with its decoding circuitry occupies 0.41 × 0.13 mm2 of chip area. The manufactured quadrature VCO was found to oscillate between 4.12 ~ 4.74 GHz and consumes 23.1 mW from a 3.3 V supply without its buffer circuitry. A maximum phase noise of -78.5 dBc / Hz at a 100 kHz offset and -108.17 dBc / Hz at a 1 MHz offset was measured and the minimum VCO figure of merit is 157.8 dBc / Hz. The output voltages of the 16 bit DAC are within 3.5 % of the design specifications. When the phase shifter is controlled by the 16 DAC signals, the maximum measured phase error of the phase shifter is lower than 10 %. / Dissertation (MEng)--University of Pretoria, 2009. / Electrical, Electronic and Computer Engineering / unrestricted

A 5 GHz continuous unlicensed bandwidth is available at millimeter-wave (mm-wave) frequencies around 60 GHz and offers the prospect for multi gigabit wireless applications. The inherent atmospheric attenuation at 60 GHz due to oxygen absorption makes the frequency range ideal for short distance communication networks. For these mm-wave wireless networks, the low noise amplifier (LNA) is a critical subsystem determining the receiver performance i.e., the noise figure (NF) and receiver sensitivity. It however proves challenging to realise high performance mm-wave LNAs in a silicon (Si) complementary metal-oxide semiconductor (CMOS) technology. The mm-wave passive devices, specifically on-chip inductors, experience high propagation loss due to the conductivity of the Si substrate at mm-wave frequencies, degrading the performance of the LNA and subsequently the performance of the receiver architecture. The research is aimed at realising a high performance mm-wave LNA in a Si BiCMOS technology. The focal points are firstly, the fundamental understanding of the various forms of losses passive inductors experience and the techniques to address these issues, and secondly, whether the performance of mm-wave passive inductors can be improved by means of geometry optimising. An associated hypothesis is formulated, where the research outcome results in a preferred passive inductor and formulates an optimised passive inductor for mm-wave applications. The performance of the mm-wave inductor is evaluated using the quality factor (Q-factor) as a figure of merit. An increased inductor Q-factor translates to improved LNA input and output matching performance and contributes to the lowering of the LNA NF. The passive inductors are designed and simulated in a 2.5D electromagnetic (EM) simulator. The electrical characteristics of the passive structures are exported to a SPICE netlist which is included in a circuit simulator to evaluate and investigate the LNA performance. Two LNAs are designed and prototyped using the 13μ-m SiGe BiCMOS process from IBM as part of the experimental process to validate the hypothesis. One LNA implements the preferred inductor structures as a benchmark, while the second LNA, identical to the first, replaces one inductor with the optimised inductor. Experimental verification allows complete characterization of the passive inductors and the performance of the LNAs to prove the hypothesis. According to the author's knowledge, the slow-wave coplanar waveguide (S-CPW) achieves a higher Q-factor than microstrip and coplanar waveguide (CPW) transmission lines at mm-wave frequencies implemented for the 130 nm SiGe BiCMOS technology node. In literature, specific S-CPW transmission line geometry parameters have previously been investigated, but this work optimises the signal-to-ground spacing of the S-CPW transmission lines without changing the characteristic impedance of the lines. Optimising the S-CPW transmission line for 60 GHz increases the Q-factor from 38 to 50 in simulation, a 32 % improvement, and from 8 to 10 in measurements. Furthermore, replacing only one inductor in the output matching network of the LNA with the higher Q-factor inductor, improves the input and output matching performance of the LNA, resulting in a 5 dB input and output reflection coefficient improvement. Although a 5 dB improvement in matching performance is obtained, the resultant noise and gain performance show no significant improvement. The single stage LNAs achieve a simulated gain and NF of 13 dB and 5.3 dB respectively, and dissipate 6 mW from the 1.5 V supply. The LNA focused to attain high gain and a low NF, trading off linearity and as a result obtained poor 1 dB compression of -21.7 dBm. The LNA results are not state of the art but are comparable to SiGe BiCMOS LNAs presented in literature, achieving similar gain, NF and power dissipation figures. / Dissertation (MEng)--University of Pretoria, 2012. / Electrical, Electronic and Computer Engineering / unrestricted