Noise Plateau Research Articles

Micromagnetic Study of Media Noise Plateau in Heat-Assisted Magnetic Recording

The relationship between integrated media noise power and linear density in heat-assisted magnetic recording (HAMR) is discussed. A noise plateau for intermediate recording density has been observed in HAMR, similar to that found in perpendicular magnetic recording (PMR). Here, we show, by changing the temperature profile of the heat spot in HAMR, that we can tune the noise plateau regions to different recording densities. The heat spot with sharp temperature gradient favors a plateau at high recording density, while the heat spot with gradual temperature gradient favors a plateau at low recording density. This effect is argued to be a consequence of the competition between transition noise and remanence noise in HAMR.

Spatial power spectral density estimation using a multitapered coprime sensor array minimum processor.

A coprime sensor array (CSA) is a sparse array geometry that interleaves two spatially undersampled uniform linear arrays (ULAs) with coprime undersampling factors. The CSA Min processor achieves an asymptotically unbiased spatial power spectral density (PSD) estimate while approaching the variance of a ULA conventional beamformer. Nonstationary underwater sonar environments often preclude the number of snapshots required to achieve a desirable PSD variance. The multitaper method improves PSD variance by O(K) at the expense of resolution without additional snapshot cost by averaging uncorrelated PSD estimates obtained using a set of K orthogonal tapers. This paper proposes the multitapered Min processor to achieve unambiguous PSD estimates with desirable variance properties for passive beamforming scenarios. The probability density function and the first two moments of the MT-Min processor's PSD estimate are derived in closed-form for spatially white Gaussian processes. Simulations verify the variance reduction predicted by the analytical derivation for white processes and, by extension, for non-white processes. The multitaper method is then extended to an ad hoc mixture of Min and Product processors under constant noise plateau normalization that attenuates the spurious peaks occurring in the CSA PSD estimates in the presence of multiple planewave arrivals.

Adaptive logical stochastic resonance in time-delayed synthetic genetic networks.

In the paper, the concept of logical stochastic resonance is applied to implement logic operation and latch operation in time-delayed synthetic genetic networks derived from a bacteriophage λ. Clear logic operation and latch operation can be obtained when the network is tuned by modulated periodic force and time-delay. In contrast with the previous synthetic genetic networks based on logical stochastic resonance, the proposed system has two advantages. On one hand, adding modulated periodic force to the background noise can increase the length of the optimal noise plateau of obtaining desired logic response and make the system adapt to varying noise intensity. On the other hand, tuning time-delay can extend the optimal noise plateau to larger range. The result provides possible help for designing new genetic regulatory networks paradigm based on logical stochastic resonance.

Pulsar timing noise and the minimum observation time to detect gravitational waves with pulsar timing arrays

The sensitivity of pulsar timing arrays to gravitational waves is, at some level, limited by timing noise. Red timing noise - the stochastic wandering of pulse arrival times with a red spectrum - is prevalent in slow-spinning pulsars and has been identified in many millisecond pulsars. Phenomenological models of timing noise, such as from superfluid turbulence, suggest that the timing noise spectrum plateaus below some critical frequency, $f_c$, potentially aiding the hunt for gravitational waves. We examine this effect for individual pulsars by calculating minimum observation times, $T_{\rm min}(f_c)$, over which the gravitational wave signal becomes larger than the timing noise plateau. We do this in two ways: 1) in a model-independent manner, and 2) by using the superfluid turbulence model for timing noise as an example to illustrate how neutron star parameters can be constrained. We show that the superfluid turbulence model can reproduce the data qualitatively from a number of pulsars observed as part of the Parkes Pulsar Timing Array. We further show how a value of $f_c$, derived either through observations or theory, can be related to $T_{\rm min}$. This provides a diagnostic whereby the usefulness of timing array pulsars for gravitational-wave detection can be quantified.

Superlinear growth of Rayleigh scattering-induced intensity noise in single-mode fibers.

Rayleigh scattering generates intensity noise close to an optical carrier that propagates in a single-mode optical fiber. This noise degrades the performance of optoelectronic oscillators and RF-photonic links. When using a broad linewidth laser, we previously found that the intensity noise power scales linearly with optical power and fiber length, which is consistent with guided entropy mode Rayleigh scattering (GEMRS), a third order nonlinear scattering process, in the spontaneous limit. In this work, we show that this behavior changes significantly with the use of a narrow linewidth laser. Using a narrow linewidth laser, we measured the bandwidth of the intensity noise plateau to be 10 kHz. We found that the scattered noise power scales superlinearly with fiber length up to lengths of 10 km in the frequency range of 500 Hz to 10 kHz, while it scales linearly in the frequency range of 10 Hz to 100 Hz. These results suggest that the Rayleigh-scattering-induced intensity noise cannot be explained by third-order nonlinear scattering in the spontaneous limit, as previously hypothesized.

High-finesse cavity external optical feedback DFB laser with hertz relative linewidth

We report hertz level relative linewidth distributed feedback diode lasers with external optical feedback from a high finesse F-P cavity, and demonstrate the efficient phase noise suppression and laser linewidth reduction of the optical feedback technique. The laser phase noise is dramatically suppressed throughout the measurement frequency range. Especially at the Fourier frequency of 17 kHz, approximately the linewidth of the F-P reference cavity, the laser phase noise is significantly suppressed by more than 92 dB. Above this Fourier frequency, the noise maintains a white phase noise plateau as low as -124.4 dBc/Hz. The laser's FWHM linewidth is reduced from 7 MHz to 4.4 Hz, and its instantaneous linewidth is 220 mHz in the Lorentzian fitting.

Characterization of timing jitter in a 5 GHz quantum dot passively mode-locked laser

The timing jitter performance of a 5 GHz quantum dot passively mode-locked laser is investigated at different harmonics in the RF spectrum. The necessity of measuring the phase noise at relatively large harmonic numbers is motivated experimentally in the context of determining the corner frequency, its correlation to the RF linewidth, and the related white noise plateau level. The single-sideband phase noise with an integrated timing jitter of 211 fs (4-80 MHz) is reported. An all-microwave technique has been used to determine a pulse-to-pulse rms timing jitter of 96 fs/cycle. This low timing jitter value makes the chip-scale quantum dot mode-locked laser an attractive source for low noise applications such as optical clocking and sampling.

Micromagnetic Study of Medium Noise Plateau

Medium noise characteristics and transition jitter in perpendicular magnetic recording are explored using micromagnetic simulation. A noise plateau for intermediate recording densities is observed for a recording layer of typical magnetization. The plateau is replaced by a normal linear dependence of noise on recording density for a low magnetization recording layer. We show analytically that a source of the plateau is similar to that producing the non-linear transition shift of signal. In particular, magnetostatic effects are predicted to produce positive correlation of jitter and thus negative correlation of noise at the densities associated with the plateau.

Monte Carlo Simulation of Schottky Diodes Operating Under Terahertz Cyclostationary Conditions

We report Monte Carlo simulations of the current response and noise spectrum in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) operating under periodic large-signal conditions in the forward bias region. Due to the rather thin depletion region and heavy doping of these diodes, we find that the returning carrier resonance is shifted well above the terahertz region, so that the low-frequency noise plateau extends over the terahertz region. Here, frequency multiplication and mixing can take place at noise levels equal or below than that of full shot noise. We show that the signal-to-noise ratio of these SBDs is definitely superior to that of bulk semiconductors exploiting velocity-field nonlinearity.

Electron valence-band tunneling-induced Lorentzian noise in deep submicron silicon-on-insulator metal–oxide–semiconductor field-effect transistors

In this article, the impact of several electrical and technological parameters on a particular type of Lorentzian noise, occurring in deep submicron silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors with an ultrathin gate dielectric is described and a semi-empirical model is proposed that captures the main features of the experimental behavior. It is shown that the noise takes place in both n- and p-channel partially depleted SOI transistors. The excess Lorentzians are also found in the n-channel fully depleted devices studied, whereby the noise plateau amplitude [SI(0)] increases for a more negative back-gate bias, putting the back interface into stronger accumulation. The dependence of the characteristic time constant τ and SI(0) on transistor length, drain, front- and back-gate bias is reported, where from a first-order model is derived. The latter is based on the idea that the excess Lorentzian noise originates from filtered shot noise induced by majority carriers, that are injected in the floating body of the transistors by electron valence-band tunneling across the ultrathin (2.5 nm) gate oxide.

Phase noise contribution of the phase∕frequency detector in a digital PLL frequency synthesiser

A theoretical basis for the figure of merit method used to quantify the phase noise plateau of a PLL frequency synthesiser is described. Analyses are developed both to calculate the in-band phase noise of a given synthesiser architecture and to predict the figure of merit from the phase/frequency detector parameters. A range of experimental results is provided to validate the theory.

FICKIAN DIFFUSION AND NEWTONIAN COOLING: A CONCEPT FOR NOISE INDUCED CLIMATE VARIABILITY WITH LONG-TERM MEMORY?

Observed near surface air and soil temperature time series reveal a long-term memory, which is associated with a power-law scaling of the frequency spectra, S(ω) ~ ω- β with β ~ 0.6, lying between white and flicker noise, 0 < β < 1. As this power law scaling is not consistent with the Brownian motion concept of climate variability, Fickian diffusion is added to a Newtonian cooling relaxation to provide a more suitable analog of climatic fluctuations: (i) Diffusive plus random heat fluxes parametrise the turbulent mixing by synoptic scale eddy life cycles, affect tropospheric and near surface temperatures and excite a long-term memory regime with a β ~ 0.5 scaling. (ii) Newtonian cooling describes the near surface temperatures relaxing towards a global mean deep soil temperature and stabilises the system to a white noise response at very low frequencies. The long-term memory regime emerges from the high frequency scaling (β ~ 1.5), once temperatures become correlated in space due to diffusion, so that spatially averaged fluctuations correlate for times beyond the diffusion time scale. The long-term memory regime disappears into a white noise plateau (β ~ 0), when low frequencies exceed the damping time scale of Newtonian cooling. This system may be interpreted as a diffusive system relaxing towards the deep soil restoration temperature with an almost infinitely large time scale.

DC measurement errors due to auto-zeroed amplifier noise

An empirical fit to the noise voltage source spectrum of an auto-zeroed operational amplifier is used to calculate the variance in the measurement of the amplifier's dc input voltage or its input offset voltage. Convenient closed-form solutions for the variance and hence the normalized standard error are obtained. This allows the selection of the integration time required to achieve a desired accuracy in the measurement of the dc voltage if the low-frequency noise plateau is known or to measure the low-frequency noise plateau using a simple circuit and dc voltage measurements.

Noise performance of bound-to-miniband transition III-V quantum-well infrared photodetectors

Dark current noise measurements between 10 and 105 Hz were carried out at T=77 K on three different types of III-V quantum-well infrared photodetectors designed for 8–12 μm IR detection. These devices have superlattice barriers leading to miniband transport in the extended conduction band. For frequencies between 102 and 104 Hz, noise plateau levels stemming from the trapping and detrapping of electrons in the quantum-well bound states are observed. From the measured noise data the low-bias electron diffusion length, the bias-dependent noise gain, the electron trapping probability, and the thermal electron generation rate are calculated.

Effect of mucosal halides on Ca(2+)-blockable currents through the skin of Rana ridibunda

The present study deals with the interaction of mucosal anions with apical Ca(2+)-blockable cation channels of the skin of Rana ridibunda. The intracellular potential was depolarized by exposing the basolateral membranes to K2SO4 Ringer solution. The apical bathing medium consisted of nominal Ca(2+)-free K+ or Na+ solutions with SO4(2-), Cl-, Br-, or I- as the major anion. The effects of mucosal anion substitutions were studied by analyzing 1) the fluctuation in K+ current across the apical membrane driven by imposed transepithelial clamping potentials and 2) alterations of the transepithelial current (It) and conductance (Gt) as well as the Lorentzian parameters in response to anion substitution in the mucosal bathing solution. It and current noise spectra were recorded at different transepithelial potentials (Vt). A Lorentzian component was present in the power density spectrum when Vt was clamped at mucosa-positive voltages. Such noise components were never observed with mucosa-negative potentials. These findings suggest a rectifying behavior of the transepithelial cation currents. The Lorentzian noise component and the inward-oriented cation currents were depressed by the addition of micromolar concentrations of Ca2+ to the apical solutions as well as by replacing mucosal K+ or Na+ by N-methyl-D-glucamine. The Ca(2+)-blockable current and Lorentzian noise plateau (So) were gradually increased by raising Vt. Both parameters, as well as the corner frequency (fc), depended strongly on the major anion species in the apical solution; replacing mucosal SO4(2-) by one of the halides tested reduced fc and elevated So, It, and Gt considerably.

Temperature and field dependences of the generation-recombination noise and the thermal emission rates at the gold acceptor center in silicon

The corner frequencies of the noise power spectra of gold doped silicon MOS field-effect transistors are used to evaluate the fluctuation time constants and the sum of the thermal emission rates of electrons and holes at the gold acceptor center as a function of sample temperature and electric field normal to the silicon-silicon dioxide interface. The sums of the thermal emission rates observed are in good agreement with those obtained more directly from dark and photo current and capacitance transient measurements reported earlier. (8) An attempt to separate the electron and hole emission rates from the noise corner frequency data and from the low frequency noise plateau is not successful due to a number of approximations and uncertainties in the device noise theory which is used to evaluate the observed noise spectra, such as the strong electric field and hence the spatial dependences of the thermal emission rates, the field and temperature dependences of the carrier mobility near the surface, and the depletion approximation assumed in the surface space layer when computing the noise.