Oscillator phase noise: a tutorial

Linear time-invariant (LTI) phase noise theories provide important qualitative design insights but are limited in their quantitative predictive power. Part of the difficulty is that device noise undergoes multiple frequency translations to become oscillator phase noise. A quantitative understanding of this process requires abandoning the principle of time invariance assumed in most older theories of phase noise. Fortunately, the noise-to-phase transfer function of oscillators is still linear, despite the existence of the nonlinearities necessary for amplitude stabilization. In addition to providing a quantitative reconciliation between theory and measurement, the time-varying phase noise model presented in this tutorial identifies the importance of symmetry in suppressing the upconversion of 1/f noise into close-in phase noise, and provides an explicit appreciation of cyclostationary effects and AM-PM conversion. These insights allow a reinterpretation of why the Colpitts oscillator exhibits good performance, and suggest new oscillator topologies. Tuned LC and ring oscillator circuit examples are presented to reinforce the theoretical considerations developed. Simulation issues and the accommodation of amplitude noise are considered in appendixes

Investigation of pulsed quasi-steady MPD arc jets

Evaluation of magnetohydrodynamic arc thrusters operating in quasi-steady mode with electrode vapor as propellan

Measurements, Models, Systems and Design

531 s.

Metrological characterisation of Low Power Voltage Transformers by using impulse response analysis

this thesis presents a new approach in dealing with characterize LPVT and proposes determining the impulse response of LPVT, purposing to find transfer function (h(t)) which contains most electrical characteristics of LPVTs as a dynamic system

Signal Processing for Caching Networks and Non-volatile Memories

The recent information explosion has created a pressing need for faster and more reliable data storage and transmission schemes. This thesis focuses on two systems: caching networks and non-volatile storage systems. It proposes network protocols to improve the efficiency of information delivery and signal processing schemes to reduce errors at the physical layer as well. This thesis first investigates caching and delivery strategies for content delivery networks. Caching has been investigated as a useful technique to reduce the network burden by prefetching some contents during o˙-peak hours. Coded caching [1] proposed by Maddah-Ali and Niesen is the foundation of our algorithms and it has been shown to be a useful technique which can reduce peak traffic rates by encoding transmissions so that different users can extract different information from the same packet. Content delivery networks store information distributed across multiple servers, so as to balance the load and avoid unrecoverable losses in case of node or disk failures. On one hand, distributed storage limits the capability of combining content from different servers into a single message, causing performance losses in coded caching schemes. But, on the other hand, the inherent redundancy existing in distributed storage systems can be used to improve the performance of those schemes through parallelism. This thesis proposes a scheme combining distributed storage of the content in multiple servers and an efficient coded caching algorithm for delivery to the users. This scheme is shown to reduce the peak transmission rate below that of state-of-the-art algorithms

From Triazines to Heptazines

The first non-metal tricyanomelaminates have been synthesized via metathesis reactions and characterized by means of single-crystal X-ray diffraction and vibrational and solid-state NMR spectroscopy. The crystal structures of [NH4]2[C6N9H] (1) (P21/c, a = 1060.8(2) pm, b = 1146.2(2) pm, c = 913.32(18) pm, β = 112.36(3)°, V = 1027.0(4) × 106 pm3), [C(NH2)3]3[C6N9]·2 H2O (2) (P212121, a = 762.12(15) pm, b = 1333.6(3) pm, c = 1856.6(4) pm, V = 1887.0(7) × 106 pm3) and [C3N6H7]2[C6N9H]·2.5 H2O (3) (P1̄, a = 1029.5(2) pm, b = 1120.3(2) pm, c = 1120.7(2) pm, α = 104.22(3)°, β = 112.74(3)°, γ = 104.62(3)°, V = 1064.8(4) × 106 pm3) are composed of singly protonated (1 and 3) or nonprotonated (2) tricyanomelaminate ions, which, together with the respective counterions, form two-dimensional, layered structures (1 and 3) or a quasi three-dimensional network (2). Particular emphasis has been placed on the elucidation of the thermal reactivity of the three molecular salts by means of thermal analysis and vibrational and NMR spectroscopy, as well as temperature-dependent X-ray powder diffraction. The title compounds were found to be promising candidates as molecular CNx precursors for the synthesis of graphitic carbon nitride materials. Upon being heated, ammonium and guanidinium tricyanomelaminate uniformly pass the crystalline, heptazine (C6N7)-based intermediate melem (C6N7(NH2)3), which decomposes and forms a semi-amorphous CNxHy material with a pronounced layered structure. Identical pyrolysis products are obtained for the melaminium salt, a classical triazine (C3N3)-based CNx precursor, after passing an intermediate, possibly cross-linked phase at low temperatures. Preliminary solid-state NMR investigations of the final products best conform to heptazine-based structure models for g-C3N4 that have commonly been rather disregarded in favor of triazine-based ones

Microprocessor based signal processing techniques for system identification and adaptive control of DC-DC converters

PhD ThesisMany industrial and consumer devices rely on switch mode power converters (SMPCs) to provide a reliable, well regulated, DC power supply. A poorly performing power supply can potentially compromise the characteristic behaviour, efficiency, and operating range of the device. To ensure accurate regulation of the SMPC, optimal control of the power converter output is required. However, SMPC uncertainties such as component variations and load changes will affect the performance of the controller. To compensate for these time varying problems, there is increasing interest in employing real-time adaptive control techniques in SMPC applications. It is important to note that many adaptive controllers constantly tune and adjust their parameters based upon on-line system identification. In the area of system identification and adaptive control, Recursive Least Square (RLS) method provide promising results in terms of fast convergence rate, small prediction error, accurate parametric estimation, and simple adaptive structure. Despite being popular, RLS methods often have limited application in low cost systems, such as SMPCs, due to the computationally heavy calculations demanding significant hardware resources which, in turn, may require a high specification microprocessor to successfully implement. For this reason, this thesis presents research into lower complexity adaptive signal processing and filtering techniques for on-line system identification and control of SMPCs systems. The thesis presents the novel application of a Dichotomous Coordinate Descent (DCD) algorithm for the system identification of a dc-dc buck converter. Two unique applications of the DCD algorithm are proposed; system identification and self-compensation of a dc-dc SMPC. Firstly, specific attention is given to the parameter estimation of dc-dc buck SMPC. It is computationally efficient, and uses an infinite impulse response (IIR) adaptive filter as a plant model. Importantly, the proposed method is able to identify the parameters quickly and accurately; thus offering an efficient hardware solution which is well suited to real-time applications. Secondly, new alternative adaptive schemes that do not depend entirely on estimating the plant parameters is embedded with DCD algorithm. The proposed technique is based on a simple adaptive filter method and uses a one-tap finite impulse response (FIR) prediction error filter (PEF). Experimental and simulation results clearly show the DCD technique can be optimised to achieve comparable performance to classic RLS algorithms. However, it is computationally superior; thus making it an ideal candidate technique for low cost microprocessor based applications.Iraq Ministry of Higher Educatio

Chemistry: Space resources for teachers including suggestions for classroom activities and laboratory experiments

Curriculum supplement to assist general chemistry teachers in updating instruction materials with aerospace development