Showing papers on "Noise (radio) published in 1999"

Design issues in CMOS differential LC oscillators

Abstract: An analysis of phase noise in differential cross-coupled inductance-capacitance (LC) oscillators is presented. The effect of tail current and tank power dissipation on the voltage amplitude is shown. Various noise sources in the complementary cross-coupled pair are identified, and their effect on phase noise is analyzed. The predictions are in good agreement with measurements over a large range of tail currents and supply voltages. A 1.8 GHz LC oscillator with a phase noise of -121 dBc/Hz at 600 kHz is demonstrated, dissipating 6 mW of power using on-chip spiral inductors.

Noise in GPS coordinate time series

Abstract: We assess the noise characteristics in time series of daily position estimates for 23 globally distributed Global Positioning System (GPS) stations with 3 years of data, using spectral analysis and Maximum Likelihood Estimation. A combination of white noise and flicker noise appears to be the best model for the noise characteristics of all three position components. Both white and flicker noise amplitudes are smallest in the north component and largest in the vertical component. The white noise part of the vertical component is higher for tropical stations (+23 o latitude) compared to midlatitude stations. Velocity error in a GPS coordinate time series may be underestimated by factors of 5-11 if a pure white noise model is assumed.

Jet Mixing Noise from Fine-Scale Turbulence

Abstract: It is known that turhulent mixing noise from high-speed jets consists of two components. They are the noise from large turbulent structures in the form of Mach wave radiation and the less directional fine-scale turbulence noise. The Mach wave radiation dominates in the downstream direction. The fine-scale turbulence noise dominates in the sideline and upstream directions. A semiempirical theory is developed for the prediction of the spectrum, intensity, and directivity of the fine-scale turhulence noise. The prediction method is self-contained. The turbulence information is supplied by the k-e turhulence model. The theory contains three empirical constants beyond those of the k-e model. These constants are determined by best fit of the calculated noise spectra to experimental measurements. Extensive comparisons between calculated and measured noise spectra over a wide range of directions of radiation,jet velocities, and temperatures have heen carried out. Excellent agreements are found. It is believed that the present theory offers significant improvements over current empirical or semiempirical jet noise prediction methods in use. There is no first principle jet noise theory at the present time.

Boundary-layer instability noise on aerofoils

Abstract: An experimental and theoretical investigation has been carried out to understand the tonal noise generation mechanism on aerofoils at moderate Reynolds number. Experiments were conducted on a NACA0012 aerofoil section in a low-turbulence closed working section wind tunnel. Narrow band acoustic tones were observed up to 40 dB above background noise. The ladder structure of these tones was eliminated by modifying the tunnel to approximate to anechoic conditions. High-resolution flow velocity measurements have been made with a three-component laser-Doppler anemometer (LDA) which have revealed the presence of strongly amplified boundary-layer instabilities in a region of separated shear flow just upstream of the pressure surface trailing edge, which match the frequency of the acoustic tones. Flow visualization experiments have shown these instabilities to roll up to form a regular Karman-type vortex street. A new mechanism for tonal noise generation has been proposed, based on the growth of Tollmien–Schlichting (T–S) instability waves strongly amplified by inflectional profiles in the separating laminar shear layer on the pressure surface of the aerofoil. The growth of fixed frequency, spatially growing boundary-layer instability waves propagating over the aerofoil pressure surface has been calculated using experimentally obtained boundary-layer characteristics. The effect of boundary-layer separation has been incorporated into the model. Frequency selection and prediction of T–S waves are in remarkably good agreement with experimental data.

Using a Broadband ADCP in a Tidal Channel. Part II: Turbulence

Abstract: A four-transducer, 600-kHz, broadband acoustic Dopple current profiler (ADCP) was rigidly mounted to the bottom of a fully turbulent tidal channel with peak flows of 1 m s−1. Rapid samples of velocity data are used to estimate various parameters of turbulence with the covariance technique. The questions of bias and error sources, statistical uncertainty, and spectra are addressed. Estimates of the Reynolds stress are biased by the misalignment of the instrument axis with respect to vertical. This bias can be eliminated by a fifth transducer directed along the instrument axis. The estimates of turbulent kinetic energy (TKE) density have a systematic bias of 5 × 10−4 m2 s−2 due to Doppler noise, and the relative statistical uncertainty of the 20-min averages is usually less than 20%–95% confidence. The bias in the Reynolds stress due to Doppler noise is less than ±4 × 10−5 m2. The band of zero significance is never less than 1.5 × 10−5 m2 s−2 due to Doppler noise, and this band increases with incre...

2.5-THz GaAs monolithic membrane-diode mixer

Abstract: A novel GaAs monolithic membrane-diode (MOMED) structure has been developed and implemented as a 2.5-THz Schottky diode mixer. The mixer blends conventional machined metallic waveguide with micromachined monolithic GaAs circuitry to form, for the first time, a robust, easily fabricated, and assembled room-temperature planar diode receiver at frequencies above 2 THz. Measurements of receiver performance, in air, yield at T/sub receiver/ of 16500-K double sideband (DSB) at 8.4-GHz intermediate frequency (IF) using a 150-K commercial Miteq amplifier. The receiver conversion loss (diplexer through IF amplifier input) measures 16.9 dB in air, yielding a derived "front-end" noise temperature below 9000-K DSB at 2514 GHz. Using a CO/sub 2/-pumped methanol far-infrared laser as a local oscillator at 2522 GHz, injected via a Martin-Puplett diplexer, the required power is /spl ap/5 mW for optimum pumping and can be reduced to less than 3 mW with a 15% increase in receiver noise. Although demonstrated as a simple submillimeter-wave mixer, the all-GaAs membrane structure that has been developed is suited to a wide variety of low-loss high-frequency radio-frequency circuits.

Two-dimensional imaging of soot volume fraction in laminar diffusion flames.

Abstract: A technique for acquiring two-dimensional soot-volume-fraction measurements in laminar flames has been demonstrated. The technique provides a map of very low noise concentration over a range of wavelengths (250-1100 nm). A noise level of 0.0007 in extinction and a spatial resolution of 30-40 microm for soot concentration were achieved with an arc lamp source that was filtered to provide greater spatial coherence and a CCD detector. The broadband arc lamp source also allowed us to avoid the added noise resulting from speckle with coherent laser sources. Beam steering, due to refractive-index gradients in the flame, was measured and compared with theoretical predictions. The optical arrangement to minimize the effect of beam steering is described. As a result the beam steering had no effect on the soot measurements in the flames examined. Flame-transmission maps obtained with this system in an ethylene/air laminar diffusion flame are presented. Tomographic analysis from use of an Abel inversion of the line-of-sight data to obtain radial profiles of soot concentration is described.

A generation mechanism for chorus emission

Abstract: . A chorus generation mechanism is discussed, which is based on interrelation of ELF/VLF noise-like and discrete emissions under the cyclotron wave-particle interactions. A natural ELF/VLF noise radiation is excited by the cyclotron instability mechanism in ducts with enhanced cold plasma density or at the plasmapause. This process is accompanied by a step-like deformation of the energetic electron distribution function in the velocity space, which is situated at the boundary between resonant and nonresonant particles. The step leads to the strong phase correlation of interacting particles and waves and to a new backward wave oscillator (BWO) regime of wave generation, when an absolute cyclotron instability arises at the central cross section of the geomagnetic trap, in the form of a succession of discrete signals with growing frequency inside each element. The dynamical spectrum of a separate element is formed similar to triggered ELF/VLF emission, when the strong wavelet starts from the equatorial plane. The comparison is given of the model developed using some satellite and ground-based data. In particular, the appearance of separate groups of chorus signals with a duration 2-10 s can be connected with the preliminary stage of the step formation. BWO regime gives a succession period smaller than the bounce period of energetic electrons between the magnetic mirrors and can explain the observed intervals between chorus elements. Key words. Magnetospheric physics (Energetic particles · trapped). Space plasma physics (wave-particle interactions; waves and instabilities)

Ultrasensitive frequency-modulation spectroscopy enhanced by a high-finesse optical cavity: theory and application to overtone transitions of C 2 H 2 and C 2 HD

Abstract: The sensitivity of FM spectroscopy can be dramatically enhanced by location of the sample in a high-finesse cavity, for example, ∼5 orders of magnitude in this study. To avoid conversion of laser frequency noise into amplitude noise by the cavity, we choose the rf modulation frequency to match the cavity’s free spectral range. In this way small frequency fluctuations produce no additional noise, and a pure FM dispersion signal is recovered in transmission. We present a systematic study of the detection sensitivity, signal line shape and size, and slope at the central tuning. Experimentally, using a weakly absorbing gas such as C2H2 or C2HD placed inside an external high-finesse resonator, we obtained an integrated absorption sensitivity of 5×10-13(1×10-14/cm) for the gas’s weak near-IR molecular overtone transitions. As an interesting application, a Nd:YAG laser was well stabilized on the P(5) line of the C2HD(ν2+3ν3) band by this technique. The high attainable sensitivity permitted selection of slow molecules with low power and gas pressure to give a linewidth 13 times below the room-temperature transit-time limit.

A new look at impact ionization-Part II: Gain and noise in short avalanche photodiodes

Abstract: For Part I see R.J. McIntyre, ibid., vol.46, no.8, pp.1623-31 (1999). In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric field and the new one. A systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses is also presented. It is demonstrated that there is a definite "size effect" for thin multiplication regions that is not well characterized by the local-field model. The new theory, on the other hand, provides very good fits to the measured gain and noise. The new ionization coefficient model has also been validated by Monte Carlo simulations.

Anomalous jumping in a double-well potential.

Abstract: Noise-induced jumping between metastable states in a potential depends on the structure of the noise. For an $\ensuremath{\alpha}$-stable noise, jumping triggered by single extreme events contributes to the transition probability. This is also called Levy flights and might be of importance in triggering sudden changes in geophysical flow and perhaps even climatic changes. The steady-state statistics is also influenced by the noise structure leading to a non-Gibbs distribution for an $\ensuremath{\alpha}$-stable noise.

1/3-shot-noise suppression in diffusive nanowires

Abstract: We report low-temperature shot-noise measurements of short diffusive Au wires attached to electron reservoirs of varying sizes. The measured noise suppression factor compared to the classical noise value $2e|I|$ strongly depends on the electric heat conductance of the reservoirs. For small reservoirs injection of hot electrons increases the measured noise, and hence the suppression factor. The universal $1/3$ suppression factor can only asymptotically be reached for macroscopically large and thick electron reservoirs. A heating model based on the Wiedemann-Franz law is used to explain this effect.

Phase noise measurements of ultrastable 10 GHz harmonically modelocked fibre laser

Abstract: Measurements are presented of the lowest timing jitter reported to date for a harmonically modelocked Er fibre laser. Phase detection noise measurements demonstrate a timing jitter of <10 fs over a frequency range of 100 Hz-1 MHz.

Towards true crosstalk noise analysis

Abstract: Accurate noise analysis is currently of significant concern to high-performance designs, and the number of signals susceptible to noise effects will certainly increase in smaller process geometries. Our approach uses a combination of temporal and functional information to eliminate false transition combinations and thereby overcome insufficiencies in static noise analysis. A similar idea arises in timing analysis where functional and timing information is used to eliminate false paths. The goal of our work is to develop an algorithm, software tool, and noise analysis flow that provide an accurate and conservative approach to noise analysis. In particular, this paper proposes an approach to identifying a pair of vectors that exercises the maximum crosstalk noise.

Harmony: static noise analysis of deep submicron digital integrated circuits

Abstract: As technology scales into the deep submicron regime, noise immunity is becoming a metric of comparable importance to area, timing, and power for the analysis and design of very large scale integrated (VLSI) systems. A metric for noise immunity is defined, and a static noise analysis methodology based on this noise-stability metric is introduced to demonstrate how noise can be analyzed systematically on a full-chip basis using simulation-based transistor-level analysis. We then describe Harmony, a two-level (macro and global) hierarchical implementation of static noise analysis. At the macro level, simplified interconnect models and timing assumptions guide efficient analysis. The global level involves a careful combination of static noise analysis, static timing analysis, and detailed interconnect macromodels based on reduced-order modeling techniques. We describe how the interconnect macromodels are practically employed to perform coupling analysis and how timing constraints can be used to limit pessimism in the analysis.

Noise-Sustained Pulsating Patterns and Global Oscillations in Subexcitable Media

Abstract: The constructive role of noise in an excitable activator-inhibitor medium is analyzed. Noise acts parametrically on the excitation threshold of the system, and is seen to support the existence of pulsating spots in the subexcitable regime. Increasing values of the noise intensity in this regime lead to a collective state in which all the elements of the system fire synchronously. The spectral characteristics of the resulting global oscillations are also studied as a function of the noise intensity, showing the typical fingerprint of stochastic resonance.

Noise Driven Avalanche Behavior in Subexcitable Media

Abstract: The interaction of noise with a subexcitable chemical system gives rise to spatiotemporal behavior with novel statistical properties. Wave behavior in a photosensitive Belousov-Zhabotinsky reaction with imposed noise is monitored and statistically analyzed. Waves are initiated at sites where the accumulation of subthreshold perturbations induces local excitations, and waves propagate through the medium by a facilitated percolation process. Statistical analysis of the coherent spatiotemporal structures reveals power-law relations that indicate the system has no intrinsic length or time scale. [S0031-9007(98)08304-5]

Detection of radio transmitter turn-on transients

Abstract: The use of a fractal dimension measure in conjunction with a Bayesian step change detector for the detection of radio transmitter turn-on transients is described. Fractal dimensions from radio transmission samples are calculated. The Bayesian change detector is then used to detect the change in the fractal trajectory in order to locate the transition point from channel noise to the start of a transient.

High sensitivity radio receiver

Abstract: The invention relates to a high sensitivity receiver installed outdoors which may be used in a base station of a mobile communication system, for example. A received radio frequency signal is converted into a signal in a desired frequency band by a reception bandpass filter RXF3, is subject to a low noise amplification to a desired level by a low noise reception amplifier LNA4, and the amplified signal is converted into an optical signal by a laser diode LD5. RXF3, LNA4 and LD5 are confined in a heat shielding box. LD5 is cooled by cooling means to the order of critical temperature where RXF3, for example, assumes a superconducting state, whereby the dynamic range is increased and stabilized.

Long-period seafloor seismology and deformation under ocean waves

Abstract: The deformation of the seafloor under loading by long-period ocean waves raises vertical component noise levels at the deep seafloor by 20 to 30 dB above noise levels at good continental sites in the band from 0.001 to 0.04 Hz. This noise substantially limits the detection threshold and signal-to-noise ratio for long-period phases of earthquakes observed by seafloor seismometers. Borehole installation significantly improves the signal-to-noise ratio only if the sensor is installed at more than 1 km below the seafloor because the deformation signal decays slowly with depth. However, the vertical-component deformation signal can be predicted and suppressed using seafloor measurements of pressure fluctuations observed by differential pressure gauges. The pressure observations of ocean waves are combined with measurements of the transfer function between vertical acceleration and pressure to predict the vertical component deformation signal. Subtracting the predicted deformation signal from pressure observations can reduce vertical component noise levels near 0.01 Hz by more than 25 dB, significantly improving signal-to-noise ratios for long-period phases. There is also a horizontal-component deformation signal but it is smaller than the vertical-component signal and only significant in shallow water (

Teleseismic shear wave splitting measurements in noisyenvironments

Abstract: SUMMARY High noise levels hamper teleseismic shear wave splitting measurements, which bandpass filtering does not always help. To investigate how robust splitting measurements are to noise, we analysed a set of synthetic records with known splitting parameters and added fixed levels of noise. In the presence of weak anisotropy, single-waveform splitting measurements are unreliable when operating with noisy data sets. A practical rule in terms of S/N ratio and splitting delay time parameters is that splitting is confidently detectable at S/N>8, regardless of the wave’s original polarization orientation. However, for the evidence of weak anisotropy to be detectable and measurable at an S/N value of 4, the backazimuth separation of the phases from the fast polarization direction needs to be higher than 20°. Stacks of individual measurements consistently yield reliable results down to S/N values of 4. Applying stacking to data from DSB (Dublin, Ireland), the fast polarization direction w and lag time dt are 58° and 0.95 s. This orientation reflects surface trends of deformation in the area, as found elsewhere in the UK. Our result thus reinforces the proposed model that the detected anisotropy in the British Isles originates from lithospheric coherent deformation preserved from the last main tectonic episode.

Transition from sub-Poissonian to super-Poissonian shot noise in resonant quantum wells

Abstract: We investigate the transition from sub-Poissonian to super-Poissonian values of the zero-temperature shot noise power of a resonant double barrier of macroscopic cross section. This transition occurs for driving voltages, which are sufficiently strong to bring the system near an instability threshold. It is shown that interactions in combination with the energy dependence of the tunneling rates dramatically affect the noise level in such a system. Interaction-induced fluctuations of the band bottom of the well contribute to the noise and lead to a new energy in the Fano factor. They can enhance the noise to super-Poissonian values in a voltage range preceding the instability threshold of the system. At low voltages, interactions may either enhance or suppress the noise compared to the noninteracting case.

Noise Measurements in Supersonic Jets Treated with the Mach Wave Elimination Method

Abstract: We report noise measurements for perfectly expanded coaxial jets composed of a supersonic primary stream at velocity of 920 m/s and a coflow stream at conditions designed to prevent formation of Mach waves. Both the primary and secondary streams consisted of helium-air mixtures to simulate approximately the conditions of hot flows, The resulting sound field was compared to that emitted by a single jet at the conditions of the primary stream. Overall sound pressure levels (OASPL) and noise spectra were obtained at many radial and azimuthal positions around the jet exit. Equal-thrust comparisons were made by using geometric scaling. At equal thrust, Mach wave elimination reduced the near-field OASPL by 11 dB and the far-field OASPL by 5 dB. The mid-to-high-frequency region of the spectrum, which is most pertinent to aircraft noise, was reduced by 20 dB in the near field and by 9 dB in the far field. It is shown that Mach waves account for at least 85 % of the sound field most relevant to aircraft noise.

Amplitude squeezing of light by means of a phase-sensitive fiber parametric amplifier

Abstract: We experimentally demonstrate generation of bright sub-Poissonian light by means of parametric deamplification in a phase-sensitive fiber amplifier that is based on a balanced nonlinear Sagnac interferometer. On direct detection, the photocurrent noise falls below the shot-noise limit by 0.6±0.2 dB (1.4 dB when corrected for detection losses). To observe the noise reduction we employed a scheme that used two orthogonally polarized pulses to cancel the noise that arises from the predominantly polarized guided-acoustic-wave Brillouin scattering in the fiber. We also present a simplified semiclassical theory of quantum-noise suppression by this amplifier, which is found to be in good agreement with the experimental results.

Low avalanche noise characteristics in thin InP p/sup +/-i-n/sup +/ diodes with electron initiated multiplication

Abstract: We have performed electron initiated avalanche noise measurements on a range of homojunction InP p/sup +/-i-n/sup +/ diodes with "i" region widths, w ranging from 2.40 to 0.24 /spl mu/m. In contrast to McIntyre's noise model a significant reduction in the excess noise factor is observed with decreasing w at a constant multiplication in spite of /spl alpha/, the electron ionization coefficient being less than /spl beta/, the hole ionization coefficient. In the w=0.24 /spl mu/m structure an effective /spl beta///spl alpha/ ratio of approximately 0.4 is deduced from the excess noise factor even when electrons initiate multiplication, suggesting that hole initiated multiplication is not always necessary for the lowest avalanche noise in InP-based avalanche photodiodes.