TO achieve high level of integration in order to reduce cost, heterodyne architecture has made way for low-IF and zero-IF (direct conversion) receiver architectures. However, a very serious issue in implementing both zero and low-IF receiver is of local oscillator (LO) pulling. Another challenge is on-chip generation of high-precision quadrature LO signals for image-rejection. We have addressed both these issues in this thesis. Regarding the first problem, we have developed a lowpower frequency multiplication technique which uses a low frequency ring oscillator and multiplies its frequency in power e cient way to generate the desired frequency. We then use this differential LO signal to generate high-precision quadrature phases by using polyphase filter and an injection-locked quadrature oscillator. Design examples are presented for 2.4 GHz band of IEEE 802.15.4 standard which is a low-data rate WPAN standard. The standard o ers relaxed performance specifications in order to help achieve low power of operation. Contributions in the thesis • The problem of local oscillator (LO) pulling can be addressed by running LO at a much reduced frequency and use a frequency multiplier (FM) to generate the desired frequency. Also, use of low-frequency LO saves power in VCO and helps eliminate first few dividers leading to significant power savings. In addition, the entire frequency synthesizer can be run at a lower supply voltage saving additional power. The frequency multiplier involves combining edges from the lower frequency ring oscillator. It improves upon the prior work by proposing a new lower-power edge-combiner. The overall power is reduced by exploiting the relaxed phase noise specification of IEEE 802.15.4 standard. Simulations using SpectreRF show that the circuit consumes only 550 ｵW of power in 0.13 ｵm RF-CMOS technology with 1.2 V supply voltage, and provides 950 VP-P sinusoidal output with phase noise of -85.5 dBc/Hz at 1 MHz offset. • An injection-locking based quadrature desensitization circuit is designed for precision quadrature generation. The differential (two phase) output of the frequency multiplier is fed to a polyphase filter to generate nearly quadrature signals. Output of polyphase filter is in turn fed to the desensitizer circuit to obtain high-precision quadrature signals. Designed for 2.4 GHz band in 0.13 µm RF-CMOS technology, it achieves a phase error of 0.5 for 1% mismatch in LC tanks. It achieves a phase noise of -84.3 dBc/Hz at 1 MHz o set and provides quadrature sinusoids of 475 mV amplitude while consuming 1.56 mW of power. • We have analyzed the popular cross-coupled LC-VCOs to generate quadrature sinusoids. In practical LC-oscillators built using low/moderate quality factor on-chip inductors, the actual frequency of oscillation is a little less than 1/2pvLC . This is known as Groszkowski effect. On the other hand, in quadrature oscillator topologies, consisting of two, cross-coupled, negative resistance LC-VCOs using parallel coupling transistors, an upward shift in frequency of oscillation from the free-running frequency of each LC-VCO is observed. This is because in order to satisfy the Barkhausen’s criteria, the LC-tanks have to operate at a frequency away from the frequency of resonance. This e ect called as quadrature detuning effect results in higher phase noise and reduced amplitude. We have shown that the old treatment given in literature is quite inaccurate for practical LC oscillators that are built using low/mo derate Q on-chip inductors. Also the prior work ignores Groszkowski effect which could be significant for low Q LC tanks. We have provided simple, accurate and closed-form expressions of associated frequency-shifts and amplitude of oscillation including both the effects. Our results show excellent match with results obtained from SpectreRF and Matlab simulations.

Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.

The competitive market of wireless communication devices demands low power and low cost RF solutions. A quadrature local oscillator (LO) is an essential building block for most transceivers. As the CMOS technology scales deeper into the nanometer regime, design of a low-power low-voltage quadrature LO still poses a challenge for RF designers. This dissertation investigates a new quadrature LO topology featuring a transformer-based voltage controlled oscillator (VCO) stacked with a divide-by-two for low-power low-voltage wireless applications. The transformer-based VCO core adopts the Armstrong VCO configuration to mitigate the small voltage headroom and the noise coupling. The LO operating conditions, including the start-up condition, the oscillation frequency, the voltage swing and the current consumption are derived based upon a linearized small-signal model. Both linear time-invariant (LTI) and linear time-variant (LTV) models are utilized to analyze the phase noise of the proposed LO. The results indicate that the quality factor of the primary coil and the mutual inductance between the primary and the secondary coils play an important role in the trade-off between power and noise. The guidelines for determining the parameters of a transformer are developed. The proposed LO was fabricated in 65 nm CMOS technology and its die size is about 0.28 mm2. The measurement results show that the LO can work at 1 V supply voltage, and its operation is robust to process and temperature variations. In high linearity mode, the LO consumes about 2.6 mW of power typically, and the measured phase noise is -140.3 dBc/Hz at 10 MHz offset frequency. The LO frequency is tunable from 1.35 GHz to 1.75 GHz through a combination of a varactor and an 8-bit switched capacitor bank. The proposed LO compares favorably to the existing reported LOs in terms of the figure of merit (FoM). More importantly, high start-up gain, low power consumption and low voltage operation are achieved simultaneously in the proposed topology. However, it also leads to higher design complexity. The contributions of this work can be summarized as 1) proposal of a new quadrature LO topology that is suitable for low-power low-voltage wireless applications, 2) an in-depth circuit analysis as well as design method development, 3) implementation of a fully integrated LO in 65 nm CMOS technology for GPS applications, 4) demonstration of high performance for the design through measurement results. The possible future improvements include the transformer optimization and the method of circuit analysis. / Ph. D.

This work deals with a design of the microwave transverter for 5 760 MHz to 146 MHz. It is divided to a few parts. The first one is focused to design of the local oscillator which generates the signal at frequency f = 116.9583MHz. The oscillator is designed like a crystal oscillator. Its output signal is multiplied and amplified in a second part. The next parts deal with design of the band pass filters. There I chose the design of the filters and did the measurements. The microwave receiver and transmitter circuits are designed with the modern monolithic circuits. The main job of this part is to design low noise amplifier and the power amplifier. At the end of this work I do the measurements and the comparison with the simulations.

Photonics and Optical techniques have advanced recently by a great extend to play an important role in Microwave and Radar applications. Antenna array of modern active phased array radars consist of multiple low power transmit and receive mod- ules. This demands distribution of the various Local Oscillator(LO) signals for up conversion of transmit signals and down conversion of receive signals during various modes of operation of a radar system. Additionally, these receivers require control and clock signals which are digital and low frequency analog, for the synchronization between receive modules. This is normally achieved through RF cables with complex distribution networks which add significantly higher additional weight to the arrays. During radar operations, radio frequency (RF) transmit signal needs to be distributed through the same modules which will in turn get distributed to all antenna elements of the array using RF cables. This makes the system bulky and these large number of cables are prone to Electromagnetic Interference (EMI) and need additional shielding. Therefore it is very desirable to distribute a combination of these RF, analog and digital signals using a distribution network that is less complex, light in weight and immune to EMI. Advancements in Optical and Microwave photonics area have enabled carrying of higher datarate signals on a single fiber due to its higher bandwidth capability including RF signals. This is achieved by employing Wavelength Division Multi- plexing (WDM) that combine high speed channels at different wavelengths. This work proposes, characterizes and evaluates an optical Wavelength Division Multiplexed(WDM) distribution network that will overcome the above mentioned problems in a phased array radar application. The work carries out a feasibility analysis supported with experimental measurements of various physical parameters like am- plitude, delay, frequency and phase variation for various radar waveforms over WDM links. Different configurations of optical distribution network are analyzed for multipoint distribution of both digital and RF signals. These network configurations are modeled and evaluated against various parameters that include power level, loss, cost and component count. A configuration which optimizes these parameters based on the application requirements is investigated. Considerable attention is paid to choose a configuration which does not provide excess loss, which is economically viable, compact and can be realized with minimum component count. After analysing the link configuration, multiplexing density of the WDM link is considered. In this work, since the number of signals to be distributed in radar systems are small, a coarse WDM(CWDM) scheme is considered for evaluation. A comparative study is also performed between coarse and dense WDM (DWDM) links for selection of a suitable multiplexing scheme. These configurations are modeled and evaluated with power budgeting. Even though CWDM scheme does not permit the utilisation of the available bandwidth to the fullest extent, these links have the advantage of having less hardware complexity and easiness of implementation. As the application requires signal distribution to thousands of transmit-receive modules, amplifiers are necessary to compensate for the reduction of signal level due to the high splitting ratio. Introduction of commonly available optical amplifiers like Erbium Doped Fiber Amplifier (EDFA), affect the CWDM channel output powers adversely due to their non-flat gain spectrum. Unlike DWDM systems, the channel separation of CWDM systems are much larger causing significantly high channel gain differences at the EDFA output. So an analysis is carried out for the selection of a suitable wavelength for CWDM channels to minimize the EDFA output power variation. If the gain difference is still significant, separate techniques needs to be implemented to flatten the output power at the antenna end. A CWDM configuration using C-band and L-band EDFAs is proposed and is supported with a feasibility analysis. As a part of evaluation of these links for radar applications, a mathematical model of the WDM link is developed by considering both the RF and digital sig- nals. A generic CWDM system consisting of transmitters, receivers, amplifiers, multiplexers/ demultiplexers and detectors are considered for the modeling. For RF signal transmission, the transmitters with external modulators are considered. Mod- eling is done based on a bottom-top approach where individual component models are initially modeled as a function of input current/power and later cascaded to obtain the link model. These models are then extended to obtain the wavelength dependent model ( spectral response) of the hybrid signal distribution link Further mathematical analysis of the developed link model revealed its variable separable nature in terms of the input power and wavelength. This led to significant reduction in the link equation complexity and development of some approximation techniques to easily represent the link behavior. The reduced form of the link spectral model was very essential as the initially developed wavelength model had a lot of parametric dependency on the component models. This mathematical reduction process led to simplification of the spectral model into a product of two independent functions, the input current and wavelength. It is also noticed that the total link power within specific wavelength range can be obtained by the integrating these functions over a specific link input power. After the mathematical modelling, an experimental prototype physical link is set up and characterized using various radar signals like continuous wave (CW) RF, pulsed RF, non linear frequency modulated signal (NLFM) etc. Additionally a proof of concept Radio-Over-Fiber (RoF) link is established to prove the superior transmission of microwave signal through an optical link. The analysis is supported with measurements on amplitude, delay, frequency and phase variations. The NLFM waveforms transmissions are further analysed using a matched _ltering process to confirm the side lobe requirement. Further a prototype WDM link is built to study the performance when digitally modulated channels are also multiplexed into the link. The link is again validated for signal levels, delay, frequency and phase parameters. Since amplitude and delay are deterministic, it is proposed that these parameter variations can be compensated by using suitable components either in the electrical or the optical domain. Radar systems use low frequency digital signals of different duty-cycles for synchronization and control across various transmit-receive modules. In the proposed link, these digital signals also modulate a WDM channel and hence the link is called a hybrid system. As the proposed link has EDFA to compensate for the splitting losses, there are chances of transient effects at the EDFA output for these low bitrate channels. Owing to the long carrier lifetime, low bitrate digital channels are prone to EDFA transient effects under specific signal and pump power conditions. Additionally, the synchronization signals used in radar application vary the duty-cycle over time, which is found to introduce variations in transient output. This practical challenge is further studied and the thesis for the first time, includes an analysis of EDFA transient e_ects for variable duty-cycle pulsed signals. The analysis is carried out for various parameters like bitrate, input power, pump power and duty-cycle. Investigations on EDFA transients on variable duty-cycle signals help in proposing a viable method to predict the lower duty-cycle transients from higher duty-cycle transients. The predicted transients were again validated against simulated transients and experimental results. As these transient effects are not desirable for radar signals, we propose a novel transient suppression techniques in optical and electrical domain which are validated with simulation and experimental measures. One suppression technique tries to avoid transient effect by keeping the optical input to EDFA always constant by feeding an inverted version of the original pulse into the EDFA along with the actual pulse. It is observed that as the wavelength of the inverted pulse is closer to the original input pulse, the transient effect settles faster. These EDFA transients are evaluated with WDM link configurations, where both high and low bitrate signals are co-propagated. Another challenging aspect of the link operation is the non-at gain spectrum of EDFA. i.e., EDFA provides unequal power level for various signals at WDM link output. This is especially true in the case of local oscillator signals, where it is preferable to have the same amplitude signals before feeding it to the mixer stages. But in the radar applications, this will require additional hardware circuits to equalize the signal level within a phased array antenna. This work also proposes some of the power equalization methods that can be used along with the WDM links. This part of the work is also supported with simulation model and experimental results. The analytical and experimental study of this thesis aids the evaluation process of a suitable optical Wavelength Division Multiplexed(WDM) distribution network that can be used for the distribution of both RF and digital signals. The optical WDM links being superior with its light weight, less loss and EMI/ EMC immunity provides a better solution to future class of radars.

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