Noise Spectral Power Research Articles

Lattice structure, flux dynamics, and low frequency noise in high temperature superconductors

Noise sources associated with the dynamics of motion of the flux bundles and its lattice interactions in YBaCuO high-Tc superconductors (HTS) have been examined. A model is proposed where, in the layered structure of the material, the flux bundles or fluxoids exhibit a continuous crossover from a motion over activation barriers to diffusive transfer between pinning sites. The results of the model were compared to various experimental measurements on thin films YBaCuO with distinct low frequency behavior. In one of the experiments the low frequency 1f noise spectral power could, in general, be reproduced. In another experiment, agreement between measurements and theoretical predictions was achieved when a defect density functional D(n) (where n is the density of defects in a single plane) was derived. In the flux flow regime, D(n) has the simple form D(n) = (δ/ξ)(1n12ξ)δ−1 where ξ is the superconducting coherence length in the Cu-O planes and δ = (UoKT) is the pinning energy of a flux line normalized to its thermal energy. These results are clear indications that the noise frequency dependence is strongly related to the dynamics of motion of free vortices and the number fluctuation of bound vortices.

Anomalous [formula omitted] low frequency noise in high temperature superconductors

A theoretical analysis for the anomalous low frequency noise enhancement with frequency dependence 1 f 2 which was recently measured in micropatterned YBaCuO thin films was carried out. A generalization of the random fluctuation model we developed earlier led to plausible activation energies and accounted simultaneously for the frequency, temperature, and magnetic field dependence of the noise spectral power. In this approach the defect density functional D( n) where n is the density of defects in a single plane was derived. In the flux flow regime, D( n) has the single form D(n) = ( δ ξ ) ( 1 n 1 2 ξ ) δ-1 , where ξ is the superconducting coherence length in the Cu-O planes, and δ= U 0 kT represents the pinning energy of a flux line normalized to its thermal energy. These results are clear indications that the enhancement of noise with 1 f 2 frequency dependence is strongly related to the dynamics of motion of free vortices and the number fluctuation of bound vortices.

Anomalous 1/ φ noise spectrum of potassium-doped bulk C 60 and C 70 in both the normal and superconducting transition region

We have prepared potassium-doped bulk K xC 60,70 and measured noise spectrum power as a function of temperature. We discovered that in the normal state, the magnitude of the normalized noise spectral power density is greater by about eleven orders of magnitude than the value of a normal metal predicted by Hooge's formula. Another unusual findings is the observation of a markedly enhanced peak near the superconducting transition, which cannot be explained by presently available theories.

Lattice structure, flux dynamics and intrinsic noise generation in high-temperature superconductors

We have examined the noise sources associated with the dynamics of motion of the flux bundles and its lattice interactions in YBaCuO high- T c superconductors (HTS). A model is proposed where in the layered structure of the material, the flux bundles or fluxoids exhibit a continuous crossover from a motion over activation barriers to diffusive transfer between pinning sites. For the vortex motion, we define a diffusion coefficient D= L 2 u/ d, where L is the average distance between pinning centers, u is the vortex velocity, and d is the thickness of the thin film. It was found that when D=( U o w/∅ 2(Δζ/ hd), where U 0 is the height of the potential barrier around a pinning center, w is the width of the film, Δ is the order parameter, and ζ is the coherence length in the CuO planes, the vortex motion has mininum contribution to the noise spectral power. While, the noise characteristics are dominated by the thermal fluctuations and entropy flow which are sufficient to produce the observed 1/f power spectrum.

Noise mechanisms of high temperature superconductors as infrared detectors

Different noise mechanisms associated with the transport properties of high temperature superconductors are discussed. A theoretical model to predict the 1 f noise characteristics of high temperature superconductors to infrared excitations is proposed. Noise mechanisms are attributed to the effects of temperature variations on the quasiparticle fluctuations and kinetic characteristics of the superconductor. In the transition region the thermodynamic fluctuations modulate the conductivity of the sample causing voltage variations in the presnece of a bias current contributing to the 1 f noise spectral power. The predictions of the model are compared to recent experimental measurements on YBaCuO epitaxial and single crystal thin films. The theoretical predictions in both cases are in general smaller than the measured values. We attribute the descrapency to the effects of noise sources associated with the flux hopping process and thermally activated flux creep in the lattice structure which are not addressed in the current theory.

The spectrum of GPS measurement errors and the accuracy of airborne gravity measurements

Recent observations (Georgiadou and Kleusberg, 1987; Kleusberg et al., 1989) suggest that errors in GPS carrier phase observations at frequencies within the gravity passband of airborne gravity systems may be due mainly to multipath interference. Further, the power spectral density (PSD) of these errors has been found to fall off rapidly with increase in frequency throughout the anticipated gravity passband, in the manner of a red spectrum rather than a white (which remains constant). It is shown that this implies a much greater allowable error in GPS‐derived altitude reference than would be the case if the PSD of altitude errors (1) was white, (2) had the same shape as that of typical aircraft vertical motion, or (3) was dominated by a sinusoidal wave located near the high frequency limit of the gravity passband. This enhances the feasibility of airborne gravity for regional scale surveys and perhaps explains why actual measurements have been better than predicted. For example, given a uniform [Formula: see text] distribution of spectral noise power and a speed to grid‐width ratio of 60 per hour, an rms altitude error as large as 12 cm will still allow the computation of acceleration correction with an accuracy of 2 mGal. For the same conditions, the allowable rms altitude error given a white distribution of spectral noise power is 1.5 cm.

Weak links, flux creep and magnetic noise limitations on device applications of high temperature superconductors

Magnetic noise sources associated with flux hopping processing due to weak flux pinning in high temperature superconductors were investigated. Ignoring the complex details of collective vortex motion, we provide an explanation for the temperature and magnetic field dependence of the noise spectral power. It was found that the effect of the magnetic field is to minimize the temperature gradient of the critical current density, therefore reducing the noise spectral power at applied field values between 0.5 T and 1.5 T. For fields greater than 4.5 T a slow increase in the noise power is predicted.

Low-noise gallium-arsenide charge-sensitive preamplifiers for low-temperature particle detectors

Charge-sensitive preamplifiers for operation between 1 K and 120 K have been developed and evaluated. They use double-gate GaAs MESFETs selected for their low 1/f noise. These devices are operated with both gates interconnected, emulating single-gate MESFETs of double gate-length, obtaining in this way a value of A/sub f/, (the coefficient of the 1/f noise spectral power density), of 1.7*10/sup -13/ V/sup 2/ at 77 K and 3.8*10/sup -14/ V/sup 2/ at 4 K. The latter is one-fourth of the value exhibited by the original device before modification and two orders of magnitude less than the value measured at 300 K. At the optimum bias, operating point device transconductance is 6 mA/V and the power dissipation 360 mu W. The input capacitance is less than 5 pF, therefore H/sub f/, the 1/f noise characteristic parameter, is lower than 8.5*10/sup -25/ J and 1.9*10/sup -25/ J at 77 K and 4 K respectively. The basic circuit configuration consists of a double-cascade loaded with a bootstrapped current source. In this way, a high gain-bandwidth product is obtained despite the low dynamic output resistance, 3000 Omega , exhibited by the MESFETs at the operating point. >

Gallium-arsenide charge-sensitive preamplifier for operation in a wide low-temperature range

A charge-sensitive preamplifier for temperature operation between 1 and 120 K has been developed and evaluated. It uses double-gate GaAs MESFETs selected for their low 1/ƒ noise. These devices are operated with both gates interconnected emulating single-gate MESFETs of double gate-length, obtaining in this way a value for A ƒ , the coefficient of the 1/ƒ noise spectral power density, of 1.7 × 10 −13 V 2 at 77 K and 3.8 × 10 −14 V 2 at 4 K. The latter is one fourth the value exhibited by the original device before modification and two orders of magnitude less than the value measured at 300 K. At the optimum bias operating point device transconductance is 6 mA/V, input capacitance is less than 5 pF and the power dissipation 360 μW. The circuit configuration consists of a double-cascade loaded with a bootstrapped current source. In this way, a high gain-bandwidth product is obtained despite of the low dynamic output resistance, 3000 Ω, exhibited by the MESFETs at the operating point. Equivalent noise charge was measured for detector capacitances up to 35 pF. Using a semi-Gaussian weighting function minimum values of 58 and 20 rmse − at 77 and 4 K, respectively, were determined. Noise slopes are 4.68 and 3.64 e −/pF at 1 μs shaping time for 77 and 4 K, respectively. A rise time of 20 ns was measured at the receiving-end of a 1 m length 50 Ω coaxial cable terminated at sending-end, when detector capacitance was C D = 35 pF. The total power dissipation of the preamplifier is less than 10 mW.

A 1 K front-end electronics for a cryogenic bolometric detector

Particle bolometric detectors operate at temperatures ranging from a few to hundreds of mK. When the readout thermistor (in thermal contact with the absorbing crystal) presents a high impedance, a front-end electronics located very close to the detector is required. This imposes on the electronic circuit the condition of operating at very low temperature, in our case 1 K. A discussion on the selection of suitable solid-state active devices for operation at such a low temperature, as well as the results of measurements of static characteristic and noise behaviour performed on GaAs MESFETs are presented. After component selection a complete voltage-sensitive preamplifier was constructed and tested. With a closed loop gain of 10, the rise time is 50 ns and the 1/⨍ noise has an A ⨍ coefficient of 1.1 × 10 −11 V 2. The noise spectral power density at 1 MHz is 2.5 × 10 −18 V 2/Hz.

Time measurements of amplitude and bit shift in thin metallic media

Improved models for media noise are a prerequisite for the design of recording Channels that utilize an increased fraction of the information capacity (linear bit density) available to a given head/disk interface. Noise measurement techniques using power spectral density or RMS noise power inherently assume that all noise sources are stationary and, thus, cannot accurately predict the time-varying statistics of a non-stationary noise process. Studies have indicated that noise in metallic thin-film media is localized in the transition regions; hence, it is not a stationary process. Therefore, we have chosen to characterize media noise by direct time measurement of the readback voltage. In this paper we model thin metallic media noise by assuming that the magnetic transitions experience random variations in both position and width. A time measurement technique was employed to estimate the second order statistics of width and position of isolated readback pulses in 3 different samples of metallic thin-film media. The RMS noise estimated from the model and time measurements of the sample statistics accurately predicts the RMS noise measured by a spectrum analyzer, supporting the validity of the proposed model.

Nonlinear mechanism for1fnoise

A phenomenological theory of excess ($\frac{1}{f}$) voltage noise is suggested. The slowly fluctuating variable describing the noise and obeying a local conservation law in a linear approximation is introduced. The breakdown of the conservation law in a nonlinear approximation leads to the singularity ${\ensuremath{\omega}}^{\ensuremath{-}\frac{1}{2}}$ in the spectral noise power as $\ensuremath{\omega}\ensuremath{\rightarrow}0$. At higher frequencies the model reduces to the temperature diffusion model of Voss and Clarke. The theory is compared with experimental data on metals with respect to the magnitude of noise, its temperature variation, and its dependence on the thermal properties of substrates. The relaxation law for fluctuations as a function of their initial amplitudes is investigated.

A review and tutorial discussion of noise and signal-to-noise ratios in analytical spectrometry—I. Fundamental principles of signal-to-noise ratios

This review consists of two parts which discuss signal-to-noise in a tutorial manner. The sources of noise, the mathematical representation of noise, and the major types of noises in emission and luminescence spectrometry are discussed. An extensive treatment of noise and signal-to-noise ratios of paired readings is given using the relation between the auto-correlation function and the spectral noise power. These signal-to-noise expressions under optimized measurement conditions are given in terms of currents and count rates as well as in terms of charge and counts for the cases of d.c. and a.c. measurements; the present treatment is limited to the cases when the background shows only either shot noise or flicker noise. Finally, the consequences of the combination of these noise sources is considered. Signal expressions for optical spectrometry are also given. Tables give the expressions for signal-to-noise ratios in the various cases.

Fluctuations in doubly scattered laser light

Fluctuations in laser light, doubly scattered by brownian particles, were analysed by measuring the spectral noise power of the photodetector current. Scattering took place at two spatially separated systems of spherical particles. Analytic expressions for the field and intensity correlations are derived. The analytic expressions for the spectrum of the intensity fluctuations of the doubly scattered laser light demonstrate that the frequency dependence of the spectrum depends strongly of the geometry of the experimental arrangement. This is not the case for singly scattered light where in good approximation the spatial and temporal correlations can be separated analytically.Our measurements show that the noise spectrum of the doubly scattered radiation may have the same frequency dependence as the spectrum of the singly scattered light. However, there are conditions where the frequency dependence of the noise of the doubly scattered light diverges markedly from that of the singly scattered light.

Current noise in thin discontinuous films

Measurements have been made of the current noise in thin discontinuous platinum films deposited on glass substrates with surface sensitivities in the range 1.5 to 5.0*103 k Omega sq-1. The influence of film temperature and gaseous ambients on the variation of the spectral noise power density current flowing through the film, noise-channel frequency and surface resistance is described. The experimental data are interpreted in terms of a noise model based on quantum mechanical tunnelling through a surface layer containing adsorbed gaseous ions. The relationship between activation energies determined from conductance temperature and noise against temperature plots is investigated and it is shown that for activation energies epsilon >or=kT the noise mechanism is thermally activated.

Measurements of the Noise Spectral Power Density of Photosensitive Materials at High Spatial Frequencies

A new method of measuring the scattered light to determine the noise spectral power density is described The technique is shown to be useful at the high spatial frequencies used in holography, beyond the range of the former methods of noise power measurement. Measurements of the grain noise of several photographic emulsions used for holography are presented; they are consistent with a model of emulsions characterized by a transmission correlation length. The measured correlation length of several of the emulsions fit experimentally observed spatial frequency responses. Data on noise power of several other photosensitive materials suitable for holography are also presented.

Current noise in thin gold films

Measurements have been made of the current noise in gold films deposited on glass substrates with surface resistivities in the range 10 to 104 Ω/sq. The experimental results have shown that the spectral noise power density may be expressed by where I is the direct current flowing through a gold film of surface resistance R at a temperature T, f is the noise-channel frequency, F(T) is a function of T and G(S) is a function of film structure. Observations have also been made on the phenomenon of noise bursts. The experimental data are interpreted in terms of a trap-assisted tunnelling conduction mechanism with a range of barrier widths. Further support is given to the proposed model from current-noise measurements made on cermet films.

Investigations of the Noise Spectra of Avalanche Oscillators

Measured amplitude noise spectra of X-band microwave oscillators rising silicon avalanche diodes are presented and compared with theoretical calculations. It was found that for the investigated diodes, the up-converted low-frequency noise (modulation noise) is the main contribution to the spectrum. In a frequency range extending from 1 kHz to several hundred MHz, the spectral noise power distribution is a sensitive function of the bias network impedance. Improvements in the noise-to-carrier power ratio of 5 to 15 dB were obtained by optimizing the bias network impedance. The dc current dependence of the amplitude noise spectrum is a complicated function of diode and circuit parameters. In general, the noise-to-signal ratio improves with increasing current. At high current densities, a reversal of this behavior may occor due to excess noise generation in the breakdown region and saturation effects of the signal power output. The equivalent rms deviation of the frequency modulation noise spectrum is typically one order of magnitude below that of the RF phase noise contribution due to RF noise sources, The phase noise spectrum of the oscillator is, therefore, not affected by the bias network impedance. Measurements on recent diodes indicate that the noise characteristics can be improved by careful control of the semiconductor device processing.

NOISE STUDIES IN UNIFORM AVALANCHE DIODES

This Letter reports avalanche noise studies on microplasma-free guard-ring avalanche diodes. The low and high frequency approximations of Hines' theory are compared with experimental results at 1 kHz and 3 to 9 GHz, respectively. Good agreement is found between experiment and theory at both low and high frequencies. The open-circuit spectral voltage density is white up to the avalanche frequency ωa and decreases inversely with current. For ω ≫ ωa the spectral noise power density falls off with ω4.

Heterodyne Spectral Noise Analyzer

An electronic heterodyne noise analyzer has been developed with the following properties: (a) Spectral noise power can be measured at any frequency between 10 cps and 1 Mc. (b) Three interchangeable filters (1 cps and higher) are incorporated, the bandwidths of which are independent of the frequency in the whole frequency range covered. They allow for a high resolving power in the whole frequency range concerned and in addition for high accuracy at relatively short measuring times. (c) No response to harmonics of the analysis frequency is found.