Voltage-controlled oscillators are widely used circle blocks, particularly in phase- locked loops. As CMOS is the technology of choice for many applications, CMOS oscillators with low timing jitter are highly desired. In this thesis, two types of VCO based on differential ring oscillator and relaxation oscillator are proposed. We describes the effect of supply noise on the performance of differential ring and relaxation oscillators. Compared to the conventional VCO, the proposed VCOs have lower sensitivity to noise on the power supply and also provided a high linearity gain (Kvco) which decreases the VCO jitter in the PLL circuit and improve the system stability. Both of VCOs are designed in TSMC 0.35£gm 2P4M Mixed-Signal process technology.

Thesis advisor: Renato Mirollo / There are countless occurrences of oscillating systems in nature. Climate cycles and planetary orbits are a few that humans experience daily. Man has also incorporated, to his benefit, oscillation into his craft; the grandfather clock, for example, can keep track of time with astounding accuracy using the period of a long pendulum. Such systems can range in complexity in a number of ways. The governing equation for a given oscillator could be as simple as a sine curve, or its motion could appear so erratic that oscillatory motion is undetectable to viewers. The number of oscillators in a system can also vary, and oscillators can be coupled; that is, oscillators can be affected by the motion of neighboring oscillators. It is this last case we wish to study. We will briefly look at the case of finitely many oscillators and then move to analyzing a model consisting of infinitely many identical oscillators. Synchrony is the simplest collective behavior. We will study a more complicated pattern called splay states in which oscillators are equally staggered in phase, i.e. phase locked such that the system will return to this pattern if it is disturbed by an arbitrarily small amount. Mathematically, this requires us to find attracting fixed points in the system. We will approximate the local behavior of our model by linearizing the system near its fixed points. We will then apply our findings to a few specific cases of such models including: uniform density, linear distribution, alpha-function pulses, and integrate-and-fire. / Thesis (BS) — Boston College, 2013. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Mathematics.

Future wireless communications (often referred to as 5G) are expected to operate at much higher frequencies compared to today’s wireless systems. During this thesis, we have investigated the option to use high frequency crystal oscillators, which along with a PLL, will generate the RF LO signal in the mmW range. Different topologies that consume low power and deliver low phase noise for better channel capacity have been studied and presented. In this report we provide a detailed analysis of crystal oscillator theory and designand we discuss techniques that we have used to simulate our models. During this project we have encountered various challenges such as parasitic oscillation, start-up behaviour and effects from package modeling. All these issues are discussed in detail while solutions, examples and results are demonstrated. Finally, along with the crystal oscillator we have also proceeded in the design of a buffer for a better input/output isolation. A squarer has been implemented for greater power savings.

This thesis report presents system specification, such as frequency and output power level, and selection topology of an oscillator circuit suitable for a CMOS Integrated Doppler radar application, in order to facilitate short range target detection within 5-15 m range, using a 0.35 μm CMOS process. With this selected CMOS process, the frequency band at 2.45 GHz or 5 GHz, with a maximum output power level of 25 mW (e.i.r.p), is found to be appropriate for the whole system to obtain a good performance. In this thesis work, a Ring VCO with pseudo-differential architecture has been designed and optimised for 2.45 GHz application. However, for 5 GHz application, a differential cross-coupled LC VCO oscillator topology has been suggested and it is so designed that it can be further scaled down to operate at a frequency of 2.45 GHz. The performance of the oscillator circuits has been tested at circuit level and has been presented as simulation results in this report.

This thesis presents a novel current-controlled oscillator (CCO). It charges and discharges a source-coupled capacitor periodically with well-controlled current sources. Its current-to-frequency conversion relies on passive components, which are insensitive to the temperature and process variations. The proposed CCO is compact and area-efficient. Moreover, compared to ring-oscillator and LC-tank oscillator, it exhibits much wider tuning range and better linearity. Therefore, it suits the modern system-on-chip (SoC) design. / text

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A voltage controlled oscillator (VCO), that generates a periodic signal whose frequency is tuned by a voltage, is a key building block in any integrated circuit systems. A sine wave oscillator can be used for a built-in self testing where high linearity is required. A bandpass filter (BPF) based oscillator is a preferred solution, and high quality factor (Q-factor) is needed to improve the linearity. However, a stringent linearity specification may require very high Q-factor, not practical to implement. To address this problem, a frequency harmonic shaping technique is proposed. It utilizes a finite impulse response filter improving the linearity by rejecting certain harmonics. A prototype SC BPF oscillator with an oscillating frequency of 10 MHz is designed and measurement results show that linearity is improved by 20 dB over a conventional oscillator. In radio frequency area, preferred oscillator structures are an LC oscillator and a ring oscillator. An LC oscillator exhibits good phase noise but an expensive cost of an inductor is disadvantageous. A ring oscillator can be built in standard CMOS process, but suffers due to a poor phase noise and is sensitive to supply noise. A RC BPF oscillator is proposed to compromise the above difficulties. A RC BPF oscillator at 2.5 GHz is designed and measured performance is better than ring oscillators when compared using a figure of merit. In particular, the frequency tuning range of the proposed oscillator is superior to the ring oscillator. VCO is normally incorporated with a frequency synthesizer (FS) for an accurate frequency control. In an integer-N FS, reference spur is one of the design concerns in communication systems since it degrades a signal to noise ratio. Reference spurs can be rejected more by either the lower loop bandwidth or the higher loop filter. But the former increases a settling time and the latter decreases phase margin. An adaptive lowpass filtering technique is proposed. The loop filter order is adaptively increased after the loop is locked. A 5.8 GHz integer-N FS is designed and measurement results show that reference spur rejection is improved by 20 dB over a conventional FS without degrading the settling time. A new pulse interleaving technique is proposed and several design modifications are suggested as a future work.

Diverse forms of life have evolved 24-hour or circadian timekeeping systems serving to coordinate internal biological events with the daily solar cycle. The generation of circadian rhythms by this timekeeping system ensures that internal processes occur at the appropriate time of day or night in relation to the environmental cycle and to other functionally-affiliated events. For mammals, endogenous oscillations in gene expression are a prevalent feature of oscillatory cells residing in the suprachiasmatic nucleus (SCN) and non-SCN tissues. To determine whether immortalized cells derived from the rat SCN (SCN2.2) retain the intrinsic rhythm-generating properties of the SCN, oscillatory behavior of the SCN2.2 transcriptome was analyzed and compared to that found in the rat SCN in vivo. In SCN2.2 cells, 116 unique genes and 46 ESTs or genes of unknown function exhibited circadian fluctuations for 2 cycles. Many (35%) of these rhythmicallyregulated genes in SCN2.2 cells also exhibited circadian profiles of mRNA expression in the rat SCN in vivo. To screen for output signals that may distinguish oscillatory cells in the mammalian SCN from peripheral-type oscillators, the rhythmic behavior of the transcriptome in forskolin-stimulated NIH/3T3 fibroblasts was analyzed and compared relative to SCN2.2 cells in vitro and the rat SCN in vivo. Similar to the circadian profiling of the SCN2.2 and rat SCN transcriptomes, NIH/3T3 fibroblasts exhibited rhythmic fluctuations in the expression of the core clock genes and 323 (2.6%) functionally diverse transcripts. Overlap in rhythmically expressed transcripts among these different oscillator models was limited to the clock genes and four genes that function in metabolism or transcription. Coupled with evidence for the rhythmic regulation of the inducible isoform of nitric oxide synthase (Nos) in SCN2.2 cells and the rat SCN but not in fibroblasts, studies examining the effects of antisense oligonucleotide-mediated inhibition of Nos2 suggest that the gaseous neurotransmitter nitric oxide may play a key role in SCN pacemaker function. Thus, our comparative analysis of circadian gene expression in SCN and non-SCN cells has important implications in the selective analysis of circadian signals involved in the coupling of SCN oscillators and regulation of rhythmicity in downstream cells.

Abstract In this research, we intend to develop a sinusoidal VCO with low harmonic distortion. A new sinusoidal VCO is developed with only two OTAs. The number of OTAs is fewer than that previously presented in other papers. The oscillator will be easy to debug and the complexity of the oscillator can be reduced. An AGC control mechanism is applied to the VCO to control the oscillation amplitude and to reduce the harmonic distortion. The oscillation is designed with the frequency around 100MHz and the oscillation amplitude is around 100mV. The simulation results and the problem encountered are discussed.