Phase oscillators are a common starting point for the reduced description of many single neuron models that exhibit a strongly attracting limit cycle. The framework for analysing such models in response to weak perturbations is now particularly well advanced, and has allowed for the development of a theory of weakly connected neural networks. However, the strong-attraction assumption may well not be the natural one for many neural oscillator models. For example, the popular conductance based Morris-Lecar model is known to respond to periodic pulsatile stimulation in a chaotic fashion that cannot be adequately described with a phase reduction. In this paper, we generalise the phase description that allows one to track the evolution of distance from the cycle as well as phase on cycle. We use a classical technique from the theory of ordinary differential equations that makes use of a moving coordinate system to analyse periodic orbits. The subsequent phase-amplitude description is shown to be very well suited to understanding the response of the oscillator to external stimuli (which are not necessarily weak). We consider a number of examples of neural oscillator models, ranging from planar through to high dimensional models, to illustrate the effectiveness of this approach in providing an improvement over the standard phase-reduction technique. As an explicit application of this phase-amplitude framework, we consider in some detail the response of a generic planar model where the strong-attraction assumption does not hold, and examine the response of the system to periodic pulsatile forcing. In addition, we explore how the presence of dynamical shear can lead to a chaotic response.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / With the development of the airborne telemetry technique, it will be demanded that the transmitting sets on the missiles are more reliable and smaller. A frequency modulation (FM) oscillator stabilized with a dielectric resonator (DR), which can operates in the S-band directly, is presented. The FM oscillator is of simple circuit, reliable operation in the stabilization, small size, light weight and low cost. It will have a certain prospect of application in the airborne telemetry transmitting sets.

No description available.

As CMOS processes size continues to shrink, a number of factors limit the ability of analog circuit performance to scale with the process. These issues include smaller transistor intrinsic gains and lower supply voltages. However, scaling continues to increase the speed and decrease the power of digital circuits. In this thesis, an active time-based integrator is proposed to replace amplifiers. The integrator, implemented using highly digital ring oscillators, seeks to take advantage of benefits offered by technology scaling while negating the issues of low gain and low supply voltages. The proposed integrator topology is used in a 20MHz 4th order continuous-time analog filter. Designed in a 90nm CMOS process, the time-based continuous-time filter achieves superior noise and linearity performance compared to state-of-the-art conventional active RC filters in simulations. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from June 17, 2011 - June 17, 2012

Researches in spintronics, especially those remarkably classified in the current induced spin-transfer torque (STT) framework, circumvent challenges with different materials and geometries. Perpendicular magnetic anisotropy (PMA) materials are showing capability of holding promise to be employed in STT based spintronics elements, e.g. spin-torque oscillators (STOs), STT-magnetoresistive random access memories (STT-MRAMs) and current induced domain wall motion elements. This dissertation presents experimental investigations into developing sputter deposited Co/Ni multilayers (MLs) with PMA and employs these materials in nano-contact STOs (NC-STOs) based on giant magnetoresistance (GMR) effect and in pseudo-spin-valve (PSV) structures. The magnetostatic stray field coupling plays an important role in perpendicular PSVs. The temperature dependent coupling mechanism recommends that this coupling can be tailored, by i) the saturation magnetization and coercivity of the individual layers, ii) the coercivity difference in layers, and iii) the GMR spacer thickness, to get a well decoupled and distinguishable switching response. Moreover, this thesis focused on the implementation and detailed characterization of NC-STOs with strong PMA Co/Ni ML free layers and in-plane Co reference layers as orthogonal (Ortho) magnetic geometry in so-called Ortho-NC-STOs. The primary target of reaching record high STO frequencies, 12 GHz, at close to zero field, 0.02 Tesla, was achieved. However, in large external fields, &gt;0.4 Tesla, an entirely new magnetodynamic object, a “magnetic droplet”, theoretically predicted in 1977, was discovered experimentally. Detailed experiments, combined with micromagnetic simulations, demonstrate the formation of a magnetic droplet with a partially reversed magnetization direction underneath the NC, and a zone of large amplitude precession in a region bounding the reversed magnetization. The magnetic droplet exhibits a very rich dynamics, including i) auto-modulation as a combine of droplet frequency with a slow time evolution (few GHz) of un-centering the droplet mode under the NC, ii) droplet breathing as reversible deformation of droplet mode with ½ droplet frequency. All observation of droplet opens a new mechanism of excitation for future fundamental studies as well as experiments especially for domain wall electronics and nano-scopic magnetism. / <p>QC 20121119</p>

In modern telecommunications, there is a need for quadrature oscillator exhibiting an accurate and stable phase relation. For example, identical two mutually coupled relaxation oscillator can generate identical quadrature signals, and have extremely accurate and stable phase relation. In this thesis, we propose a current cross-coupled relaxation oscillator with quadrature outputs. The oscillator consists of two identical current relaxation oscillators and a current comparator. The circuit takes the high frequency advantage of current mode circuit. Because of cross-coupled feedback, this oscillator have highly accurate ( <1¢X) and stable quadrature outputs. It is implemented by using TSMC 0.35£gm 2P4M CMOS technology.

Sinusoidal oscillator is intensively used in many applications, such as built-in-self-testing and ADC characterization. An innovative medical application for skin cancer detection employed a technology named bio-impedance spectroscopy, which also requires highly linear sinusoidal-wave as the reference clock. Moreover, the generated sinusoidal signals should be tunable within the frequency range from 10kHz to 10MHz, and quadrature outputs are demanded for coherent demodulation within the system. A design methodology of sinusoidal oscillator named digital-harmonic-cancellation (DHC) technique is presented. DHC technique is realized by summing up a set of square-wave signals with different phase shifts and different summing coefficient to cancel unwanted harmonics. With a general survey of literature, some sinusoidal oscillators based on DHC technique are reviewed and categorized. Also, the mathematical algorithm behind the technique is explained, and non-ideality effect is analyzed based on mathematical calculation. The prototype is fabricated in OnSemi 0.5um CMOS technology. The experimental results of this work show that it can achieve HD2 is -59.74dB and HD3 is -60dB at 0.9MHz, and the frequency is tunable over 0.1MHz to 0.9MHz. The chip consumes area of 0.76mm2, and power consumption at 0.9MHz is 2.98mW. Another design in IBM 0.18um technology is still in the phase of design. The preliminary simulation results show that the 0.18um design can realize total harmonic distortion of -72dB at 10MHz with the power consumption of 0.4mW. The new design is very competitive with state-of-art, which will be finished with layout, submitted for fabrication and measured later.

The study of the in vitro circadian oscillator of the cyanobacterium Synechococcus elongatus has uncovered a complex interplay of its three protein components. Synchronization of the clock's central oscillatory component, KaiC, has been thought to be achieved through subunit shuffling at specific intervals during the clock’s period. By utilizing an established fluorescence-based analysis on completely phosphorylated and dephosphorylated mutants as well as wild-type KaiC, this study has shown that shuffling rates are largely unaffected by phosphorylation state. These findings conflict with previous reports and hence revise our understanding of this oscillator.

In this thesis, voltage-controlled oscillators (VCOs) with improved phase noise are designed and implemented. In the design of the resonant circuit varactor diodes are employed. In practice, a real VCO has to be packaged. The parasitic effect of the package may generate crosstalk inside the VCO and result in frequency shifting. To obtain an accurate prediction, a full wave model is developed. A simulation procedure is established combining High Frequency Structure Simulator (HFSS) with Advance Design System (ADS) software to predict the frequency response at the initial stage of the VCO design. Prototypes have been constructed and the characteristics measured. The simulation agrees with the measured results well. The obtained result show that our study can be used to cut the development time and cost.

A novel CMOS tunable bandpass filter and a novel voltage controlled oscillator are proposed. Both circuits are designed using the UMC 0.5£gm CMOS process parameters. The CMOS tunablebandpass filter is realised by using the intrinic parasitic capacitance of the MOS transistor. This filter has neither on-chip planar inductor nor poly-capacitance; therefore, the chip area is reduced. Simulation results show that the bandpass filter is tunable in the range between 190MHz and 347MHz. Therefore, the filter is suitable for the IF filter application that is between 200MHz and 300MHz. The Q-factor is also tunable and has a maximum value of 983. Applying the circuit of the bandpass filter, a second order voltage controlled oscillator is designed. Simulation results show that the voltage controllable oscillator is tunable in the range between 444MHz and 746MHz.