CMOS RLC and crystal oscillators based on current conveyors

Analysis and design of RLC and crystal oscillators based on current conveyors, in 1.5 μm CMOS integrated technology, are described. Maximal operating frequencies are 350 and 50 MHz, respectively     

Computer aided design of quartz crystal oscillators

The latest development of a simulation program designed for quartz crystal oscillator analysis is presented in this paper. The simulator being developed uses the full nonlinear Barkhausen criterion method. It consists of finding the frequency ω₀ and the amplitude u₀ which nullify both the real and imaginary parts of a characteristic complex polynomial P(u,jω) describing the oscillator behavior. Most of the nonlinearities come from the amplifying transistor described by using large signal admittance parameters y(u) obtained by means of an analog circuit simulator (SPICE). This paper presents the method used to derive and code the characteristic polynomial coefficients. This method has been successfully implemented for a Colpitts oscillator and is currently being used to build an oscillator library covering the most widely used structures. The validity and the predictive power of the model have been checked experimentally and the comparison between experimental results and simulation is presented and discussed     

Dispersion-compensating photonic crystal fiber with wavelength tunability based on a modified dual concentric core structure

We present a 5-layer air-hole dispersion-compensating photonic crystal fiber (PCF) with a modified dual concentric core structure, based on central rod doping. The finite element method (FEM) was used to investigate the structure numerically. If the structural parameters remain unchanged, a high degree of linear correlation between the central rod refractive index and the operating wavelength can be achieved in the wavelength range of 1.5457–1.5857 μm, which suggests that the operating wavelength can be determined by the refractive index of the centre rod. A negative dispersion coefficient between –5765.2 ps/km/nm and –6115.8 ps/km/nm was obtained by calculation and within the bandwidth of 108 nm (1.515–1.623 μm) around 1.55 μm, a dispersion coefficient of –3000 ps/km/nm can be ensured for compensation. In addition, this proposed PCF also has the advantage of low confinement loss, between 0.00011 and 0.00012 dB/m, and ease of fabrication with existing technology. The proposed PCF has good prospects in dispersion-compensating applications.     

ALC crystal oscillators based pressure and temperature measurement integrated circuit for high temperature oil well applications

An application specific integrated circuit for the pressure and temperature measurement at the high temperature oil well bottom conditions is presented in this paper. The circuit is mainly composed of three high performance automatic level controlled (ALC) oscillator circuits, which drive three external crystals (the sensitive elements), as well as mixing and filtering stages. The integrated circuit was successfully tested up to 220 degrees C, showing a frequency resolution of 0.0003 ppm (0.0007 psi, for the pressure measurement) and a drift of 1.5 Hz/month (0.5 psi/month) concerning, respectively, the short- and long-term measurement stability. A drastic reduction of the whole measurement tool size and cost was then allowed by means of this application specific BiCMOS integrated circuit.     

Modeling of quartz crystal oscillators by using nonlinear dipolar method

A quartz crystal oscillator can be thought of as a resonator connected across an amplifier considered as a nonlinear dipole the impedance of which depends on the amplitude of the current that flows through it. The nonlinear amplifier resistance and reactance are obtained by using a time domain electrical simulator like SPICE (Simulation Program with Integrated Circuit Emphasis): the resonator is replaced with a sinusoidal current source of the same frequency and a set of transient analyses is performed by giving the current source a larger amplitude. A Fourier analysis of the steady-state voltage across the dipolar amplifier is performed to calculate both real and imaginary parts of the dipolar impedance as a function of the current amplitude. From these curves, it is then possible to accurately calculate the oscillation amplitude and frequency without having to perform unacceptably long transient analyses needed by a direct oscillator closed loop simulation. This method implemented in the Analyse Dipolaire des Oscillateurs a Quartz or Quartz Crystal Oscillators Dipolar Analysis (ADOQ) program calculates the oscillation start-up condition, the oscillation steady-state features (oscillation amplitude and frequency), and the oscillator sensitivity to various parameters. The oscillation nonlinear differential equation is solved by using the slowly varying function method so that the program quickly and accurately calculates the current amplitude and frequency transients. Measurements performed on an actual amplifier show a very good agreement with the results obtained by the simulation program.     

Long-term performance of precision crystal oscillators in a near-Earth orbital environment

The Navy Navigation Satellite System (NNSS) uses precision quartz crystal oscillators to provide time and frequency in the orbiting spacecraft. The frequency changes for multiple oscillators, which were observed for 28 years of operational service in the orbital environment, are discussed. The primary frequency changes are believed to be caused by mass transfer to and from the resonator, stress relief in the resonator mounting structure and electrodes, and ionizing radiation of the quartz resonator. Observations to a resolution of 10- 13 have been made from 1963 to 1991 on 20 operational satellites in near-Earth orbit. No oscillator failures have occurred during the entire program life of nearly 30 years. One oscillator provided continuous operational service for over 21 years, and several have served more than 15 years. No oscillator changed frequency more than two parts in 107 while in operational service. One of the best performing oscillators had a predictable drift rate of 9x10(-13)+/-1x10(-13) per day after three years of service.     

Investigation on terahertz parametric oscillators using GaP crystal with a noncollinear phase-matching scheme

Terahertz parametric oscillator (TPO) using GaP as gain medium with a noncollinear phase-matching scheme is investigated. Frequency-tuning characteristics of the terahertz wave (THz-wave) by varying the phase-matching angle and pump wavelength are analyzed. Gain and absorption characteristics of the THz-wave are investigated. The characteristics of GaP and LiNbO₃ (LN) are compared when the two crystals are used as gain medium for TPO. The analyses indicate that GaP is more suitable than LN to be used as gain medium for TPO.     

High-frequency properties of high-T c Josephson junctions and mixing experiments in the W-band

We report on the high frequency properties of high-T_c superconductor (HTS) Josephson junctions using mixing experiments in the frequency range 78 GHz-119 GHz. Experiments with YBa₂Cu₃O₇ (YBCO) step-edge (SEJ) and bicrystal junctions on LaAlO₃ and MgO substrates have been performed. In order to achieve optimal junction properties we performed an oxygen plasma treatment. Junctions with RSJ-like current voltage characteristics were mounted into a heterodyne mixing setup. We obtained conversion efficiencies around-40 dB and heterodyne mixing response above 1 THz. For SEJs we observed mixing response related to a second junction in series. We also investigated self-mixing properties.     

Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite

Multiwalled carbon nanotubes (MWCNTs) reinforced epoxy based composites were fabricated by using an innovative ultrasonic dual mixing (UDM) process consists of ultrasonic mixing with simultaneous magnetic stirring. The effect of addition of varying amount of MWCNTs on thermal stability and tensile properties of the epoxy based composite has been investigated. It is found that the thermal stability, tensile strength and toughness of the epoxy base improves with the increase of MWCNTs addition up to 1.5 wt.% and UDM processing at certain capacity of the system. Tensile tests and thermal gravimetric analysis (TGA) were performed on each group of composites containing different amount of MWCNTs to determine their mechanical and thermal properties respectively. The dispersion of 1.5 wt.% MWCNTs fillers in epoxy nanocomposites was studied by transmission electron microscopy (TEM) as well as by field emission scanning electron microscopy (FESEM) applied on their tensile fracture surface.     

Effects of crystal phase mixing on the electrical properties of InAs nanowires

We report a systematic study of the relationship between crystal quality and electrical properties of InAs nanowires grown by MOVPE and MBE, with crystal structure varying from wurtzite to zinc blende. We find that mixtures of these phases can exhibit up to 2 orders of magnitude higher resistivity than single-phase nanowires, with a temperature-activated transport mechanism. However, it is also found that defects in the form of stacking faults and twin planes do not significantly affect the resistivity. These findings are important for nanowire-based devices, where uncontrolled formation of particular polytype mixtures may lead to unacceptable device variability.     

基于Duffing振子的天然气管道泄漏检测方法

针对天然气管道泄漏因泄漏声波信号信噪比(SNR)过低而难于检测的问题,研究了基于Duffing振子的天然气管道泄漏检测方法。该方法将待检测数据输入Duffing振子系统,以振子系统的状态转化实现非周期信号中周期信号的检测。为了更好地提高Duffing振子的检测性能,在Duffing振子设计阶段,以随机共振的有关理论为基础,通过对系统输出信噪比的优化来实现Duffing振子的参数设计。基于实际天然气管道泄漏数据的测试结果表明,所提出方法可在低信噪比(-68dB)的情况下有效检测出泄漏,具有较好的检测性能。     

Femtosecond optical parametric oscillators based on periodically poled lithium niobate

Abstract

We describe two configurations of collinearly pumped femtosecond optical parametric oscillator based on periodically poled lithium niobate and tunable in the infrared from 975 nm to 4.98 μm. Maximum output powers of 240 mW for the signal and 106 mW for the idler were recorded with 25 mW of average power measured at 4.88 μm. An overall conversion efficiency of 35% and slope efficiencies for the signal of 46% at a wavelength of 1.04 μm and 70% at 1.1 μm were measured. Interferometric autocorrelations of the signal and idler pulses at various wavelengths within the tuning range have been obtained and imply nearly transform-limited pulse durations of about 140fs for the signal and about 190fs for the idler.     

A controllable chaotic system based on inductively coupled bistable oscillators

A mathematical model of a new controllable autooscilatory chaotic system based on inductively coupled Chua’s oscillators is described. Numerical simulations show that, using a chaotizing feedback algorithm, chaotic oscillations in this system can be excited in regimes where only regular oscillations are generated otherwise.