Frequency Precision of Oscillators Based on High-Q Resonators

We present a method for analyzing the phase noise of oscillators based on feedback driven high quality factor resonators. Our approach is to derive the phase drift of the oscillator by projecting the stochastic oscillator dynamics onto a slow time scale corresponding physically to the long relaxation time of the resonator. We derive general expressions for the phase drift generated by noise sources in the electronic feedback loop of the oscillator. These are mixed with the signal through the nonlinear amplifier, which makes them {cyclostationary}. We also consider noise sources acting directly on the resonator. The expressions allow us to investigate reducing the oscillator phase noise thereby improving the frequency precision using resonator nonlinearity by tuning to special operating points. We illustrate the approach giving explicit results for a phenomenological amplifier model. We also propose a scheme for measuring the slow feedback noise generated by the feedback components in an open-loop driven configuration in experiment or using circuit simulators, which enables the calculation of the closed-loop oscillator phase noise in practical systems

Pulse shaping approach to PAPR reduction for OFDM communication systems

One of the main drawbacks of the OFDM communication system is the high peak-to-average-power ratio (PAPR) of the transmitted signal. In this thesis: (i ) Optimal pulse shaping filter design is proposed to reduce the PAPR of the OFDM signal; (ii ) The level crossing rate theorem is used to derive an upper bound for the CCDF of PAPR of OFDM signal with pulse shaping; (iii ) The multiple filter design is proposed to reduce the PAPR of multiuser OFDM signal

Analysis of two coupled NLTL-based oscillators

A system of two coupled oscillators based on nonlinear transmission lines (NLTL) is proposed for pulsed-shaping applications. The maximum propagation frequency through the NLTL is calculated and optimized with a realistic numerical method. With additional design considerations, this is used to increase the waveform steepening capabilities of the NLTL and obtain an oscillator based on the shockwave concept. Coupling two of these oscillators with slightly different characteristics various pulse shapes can be achieved through composition of the individual waveforms. The coupled-system behavior is understood with the aid of a new reduced-order formulation, which takes into account the differences between the oscillator elements. The formulation is extended for stability and phase-noise analysis. It provides valuable insight into the impact of the individual oscillator characteristics on the coupled-system dominant poles and unsymmetrical stable phase-shift range. It also explains the variation of the spectral density with the phase shift, as well as the mechanisms for the phase noise corners observed when increasing the offset frequency. A more realistic analysis of the coupled system is also carried out with the conversion-matrix approach, using cyclostationary noise sources. The analysis and design techniques have been applied to several prototypes at 0.8 GHz.This work was supported by the Spanish Ministry of Science and Innovation under project TEC2011-29264-C03-01