Showing papers on "Noise (electronics) published in 1995"

BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise

Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >

Stochastic resonance and the benefits of noise: from ice ages to crayfish and SQUIDs

Abstract: Noise in dynamical systems is usually considered a nuisance. But in certain nonlinear systems, including electronic circuits and biological sensory apparatus, the presence of noise can in fact enhance the detection of weak signals. This phenomenon, called stochastic resonance, may find useful application in physical, technological and biomedical contexts.

Calculation of thermal noise in atomic force microscopy

Abstract: Thermal fluctuations of the cantilever are a fundamental source of noise in atomic force microscopy. We calculated thermal noise using the equipartition theorem and considering all possible vibration modes of the cantilever. The measurable amplitude of thermal noise depends on the temperature, the spring constant K of the cantilever and on the method by which the cantilever deflection is detected. If the deflection is measured directly, e.g. with an interferometer or a scanning tunneling microscope, the thermal noise of a cantilever with a free end can be calculated from square root kT/K. If the end of the cantilever is supported by a hard surface no thermal fluctuations of the deflection are possible. If the optical lever technique is applied to measure the deflection, the thermal noise of a cantilever with a free end is square root 4kT/3K. When the cantilever is supported thermal noise decreases to square root kT/3K, but it does not vanish.

On quantum noise

Abstract: We discuss the distribution function for the current noise in Quantum point contacts. Special interest is paid to contact of a superconductor with a normal metal. A new derivation of the Lesovik-Levitov formulae is suggested. It is shown, for the SN point contacts, that the distribution of the noise describes independent processes when charge ±e 0 or ±2e 0 passes through the contact. At low temperature and voltage only processes with double charge transfer are relevant. At zero temperature and low voltage the distribution has a binomial form.

A fundamental limit on delay estimation using partially correlated speckle signals

Abstract: Delay estimation is used in ultrasonic imaging to estimate blood or soft tissue motion, to measure echo arrival time differences for phase aberration correction, and to estimate displacement for tissue elasticity measurements. In each of these applications delay estimation is performed using speckle signals which are at least partially decorrelated relative to one another. Delay estimates which utilize such data are subject to large errors known as false peaks and smaller magnitude errors known as jitter. While false peaks can sometimes be removed through nonlinear processing, jitter errors place a fundamental limit on the performance of delay estimation techniques. The authors apply the Cramer-Rao Lower Bound to derive an analytical expression which predicts the magnitude of jitter errors incurred when estimating delays using radio frequency (RF) data from speckle targets. The analytical expression presented includes the effects of signal decorrelation due to physical processes, corruption by electronic noise, and a number of other factors. Simulation results are presented which show that the performance of the normalized cross correlation algorithm closely matches theoretical predictions. These results indicate that for poor signal to noise ratios (0 dB) a small improvement in signal to noise ratio can dramatically reduce jitter magnitude. At high signal to noise ratios (30 dB) small amounts of signal decorrelation can significantly increase the magnitude of jitter errors. >

Array enhanced stochastic resonance and spatiotemporal synchronization.

Abstract: We enhance the response of a ``stochastic resonator'' by coupling it into a chain of identical resonators. Specifically, we show via numerical simulation that local linear coupling of overdamped nonlinear oscillators significantly enhances the signal-to-noise ratio of the response of a single oscillator to a time-periodic signal and noise. We relate this array enhanced stochastic resonance to the global spatiotemporal dynamics of the array and show how noise, coupling, and bistable potential cooperate to organize spatial order, temporal periodicity, and peak signal-to-noise ratio.

Applying electric field sensing to human-computer interfaces

Abstract: A non-contact sensor based on the interaction of a person with electric fields for human-computer interface is investigated. Two sensing modes are explored: an external electric field shunted to ground through a human body, and an external electric field transmitted through a human body to stationary receivers. The sensors are low power (milliwatts), high resolution (millimeter) low cost (a few dollars per channel), have low latency (millisecond), high update rate (1 kHz), high immunity to noise (>72 dB), are not affected by clothing, surface texture or reflectivity, and can operate on length scales from microns to meters. Systems incorporating the sensors include a finger mouse, a room that knows the location of its occupant, and people-sensing furniture. Haptic feedback using passive materials is described. Also discussed are empirical and analytical approaches to transform sensor measurements into position information.

A 1.8-GHz CMOS low-phase-noise voltage-controlled oscillator with prescaler

Abstract: The implementation of the two high-frequency building blocks for a low-phase-noise 1.8-GHz frequency-synthesizing PLL in a standard 0.7-/spl mu/m CMOS process is discussed. The VCO uses on-chip bondwires, instead of spiral inductors, for low noise and low power. The design of these bondwire inductors is discussed in great detail. A general formula for the theoretical limit of the phase noise of LC-tuned oscillators is presented. The design of a special LC-tank allows a trade-off between noise and power. The realized VCO has a phase noise of -115 dBc/Hz at 200 kHz from the 1.8-GHz carrier and consumes 8 mA from a 3-V supply. The prescaler has a fixed division ratio of 128 and uses an enhanced ECL-alike high-frequency D-flipflop. Its power consumption is 28 mW.

Performance of optimum and suboptimum receivers in the presence of impulsive noise modeled as an alpha-stable process

Abstract: Impulsive noise bursts in communication systems are traditionally handled by incorporating in the receiver a limiter which clips the received signal before integration. An empirical justification for this procedure is that it generally causes the signal-to-noise ratio to increase. Recently, very accurate models of impulsive noise were presented, based on the theory of symmetric /spl alpha/-stable probability density functions. We examine the performance of optimum receivers, designed to detect signals embedded in impulsive noise which is modeled as an infinite variance symmetric /spl alpha/-stable process, and compare it against the performance of several suboptimum receivers. As a measure of receiver performance, we compute an asymptotic expression for the probability of error for each receiver and compare it to the probability of error calculated by extensive Monte-Carlo simulation. >

Non-Dynamical Stochastic Resonance: Theory and Experiments with White and Arbitrarily Coloured Noise

Abstract: We describe the simplest system which shows stochastic resonance. Theoretical results for white and (almost) arbitrarily coloured noise are presented. The new system has new, unique properties which originate from its non-dynamical character; for example, the strength and phase shift of periodic response of the system is independent of the frequency. Experiments have been carried out with the following noise processes: (physical) white noise, (physical) Lorentzian noise and (physical) 1/f noise. With a small extension of the system, its linear-response regime can be significantly increased. As the system is similar to some simple models of neurons, the new results might have not only physical but also biological importance.

Noise-shaped multbit D/A convertor employing unit elements

Abstract: By appropriately selecting the elements used to form each output sample of a multibit digital-to-analogue convertor, the spectrum of the error caused by element mismatch can be noise-shaped. Simulations indicate that first-order, second-order and bandpass noise-shaping are all possible. The technique enables the use of multibit feedback in delta-sigma A/D and D/A convertors.

Effects of undersampling on the proper interpretation of modulation transfer function, noise power spectra, and noise equivalent quanta of digital imaging systems

Abstract: The proper understanding of modulation transfer function (MTF), noise power spectra (NPS), and noise equivalent quanta (NEQ) in digital systems is significantly hampered when the systems are undersampled. Undersampling leads to three significant complications: (1) MTF and NPS do not behave as transfer amplitude and variance, respectively, of a single sinusoid, (2) the response of a digital system to a delta function is not spatially invariant and therefore does not fulfill certain technical requirements of classical analysis, and (3) NEQ loses its common meaning as maximum available SNR2 (signal-to-noise) at a particular frequency. These three complications cause the comparisons of MTF and NEQ between undersampled digital systems to depend on the frequency content of the images being evaluated. A tutorial of MTF, NPS, and NEQ concepts for digital systems is presented, along with a complete theoretical treatment of the above-mentioned complications from undersampling.

Distortion in linearized electrooptic modulators

Abstract: Intermodulation and harmonic distortion are calculated for a simple fiber-optic link with a representative set of link parameters and a variety of electrooptic modulators: simple Mach-Zehnder, linearized dual and triple Mach-Zehnder, simple directional coupler (two operating points), and linearized directional coupler with one and two dc electrodes. The resulting dynamic ranges, gains, and noise figures are compared for these modulators. A new definition of dynamic range is proposed to accommodate the more complicated variation of intermodulation with input power exhibited by linearized modulators. The effects of noise bandwidth, preamplifier distortion, and errors in modulator operating conditions are described. >

Period-doubling cascades and chaos in a semiconductor laser with optical injection

Abstract: We characterize the nonlinear dynamics of a semiconductor laser subject to optical injection. The key characteristics of measured optical spectra are reproduced in calculations based on a single-mode model that includes spontaneous-emission noise. The laser exhibits chaos over a bounded range of injection levels. As the chaotic regime is approached from both lower and higher injection levels, a period-doubling route to chaos is followed, although the route is obscured by spontaneous-emission noise. A new, bounded regime of period-doubling occurs for injection levels well above the region of chaotic dynamics. Optical injection strongly modifies the carrier-field resonance coupling frequency.

Micromechanical resonators for oscillators and filters

Abstract: Fully monolithic, high-Q, micromechanical signal processors are described. A completely monolithic high-Q oscillator, fabricated via a combined CMOS plus surface micromachining technology, is detailed, for which the oscillation frequency is controlled by a polysilicon micromechanical resonator to achieve high stability. The operation and performance of mechanical resonators are modelled, with emphasis on circuit and noise modelling. Micromechanical filter design is described, and a prototype two-resonator bandpass filter is demonstrated. An integrated micro-oven that stabilizes the resonance frequency against temperature variations using only 2 mW of power is reviewed. Brownian motion and mass loading phenomena are shown to have a greater influence on short-term stability and dynamic range in this micro-scale. Scaling strategies are proposed to alleviate potential limitations due to Brownian noise.

Thermally excited vibrations of the mirrors of laser interferometer gravitational-wave detectors.

Abstract: The effect of thermally excited mirror vibrations on length measurements using a laser interferometer gravitational-wave detector is calculated, and the number of vibrational modes which must be included to predict the Brownian motion of the mirror surface relative to its center of mass is estimated. These calculations account for both the full three-dimensional shape of the vibrational modes of the mirrors and the spatial shape of the optical modes of the interferometer. A convergence pattern for the number of modes which must be included in a complete thermal noise estimate is found; all vibrational modes with acoustic wavelengths greater than the laser beam spot size must be considered. When the full geometries of the mirror and the optical mode are taken into account, the thermal noise power in the gravitational-wave frequency bandwidth for mirror and laser parameters relevant to the LIGO (Laser Interferometer Gravitational-Wave Observatory) interferometer is approximately a factor of 6 larger than the noise obtained in earlier estimates which typically considered only the lowest few modes. If mirror vibrational thermal noise were the limiting noise source for the detection of some astrophysical sources, then this difference in noise power would result in a factor of 15 difference in estimated determination rates for these sources.

Statistical models of partial volume effect

Abstract: Statistical models of partial volume effect for systems with various types of noise or pixel value distributions are developed and probability density functions are derived. The models assume either Gaussian system sampling noise or intrinsic material variances with Gaussian or Poisson statistics. In particular, a material can be viewed as having a distinct value that has been corrupted by additive noise either before or after partial volume mixing, or the material could have nondistinct values with a Poisson distribution as might be the case in nuclear medicine images. General forms of the probability density functions are presented for the N material cases and particular forms for two- and three-material cases are derived. These models are incorporated into finite mixture densities in order to more accurately model the distribution of image pixel values. Examples are presented using simulated histograms to demonstrate the efficacy of the models for quantification. Modeling of partial volume effect is shown to be useful when one of the materials is present in images mainly as a pixel component. >

Stochastic resonance in a superconducting loop with a josephson junction

Abstract: A simple superconducting loop with a Josephson junction subject to a time‐sinusoidal magnetic flux embedded in a noise background is considered. Cooperative effects, arising from the interplay between the noise and modulation are described; they manifest themselves in the response, measured as an output signal‐to‐noise ratio. In particular, it is shown that the response displays the stochastic resonance effect, wherein the output signal‐to‐noise ratio passes through a maximum at a critical value of the noise strength. A simple theory, based on the characterization of the superconducting quantum interference device as a bistable switching element, is seen to yield good qualitative agreement with the experimental results.

Enhancement of physiological signals using fractal analysis

Abstract: A technique for the derivation of a pulse oximetry signal using fractal dimension analysis of detected light signals. First and second light sources transmit light through the patient's finger or reflect light off the blood vessels in the patient's finger. A light detector detects light from each of the light sources and generates a measured intensity signal. The measured intensity signal includes the true intensity of light transmitted from each of the light sources as well as noise introduced during the measurement process. A data sample from each of the light sources is digitized and a set of equations developed as a function of a ratio value indicative of oxygen saturation in the patient. The fractal dimension is determined for the set of signal functions over the normal physiological range for the ratio value. Maximum and/or minimum fractal dimension values are calculated to determine the desired ratio values which are possible indicatives of the ratio of true physiological signals or noise signals. The ratio values are subsequently processed to determine the oxygen saturation within the patient.

A frequency and timing period acquisition technique for OFDM systems

Abstract: Symbol Pattern Abstract This paper introduces a frequency and timing period acquisition technique for orthogonal frequency division multiplexing (OFDM) systems. The proposed technique estimates both the frequency and timing pesiod offsets at the time by using only one pilot symbol with its suitable frequency assignment. Pseudo noise (PN) sequences are introduced to assign these frequencies of the pilot symbol so that the acquisition range can be widened. Numerical examples are given to show the estimate variances for both additive white Gaussian noise (AWGN) and multipath fading channels.

Noise analysis applied to electrochemical systems

Abstract: Random fluctuations of the electrical quantities (electrode potential and cell current) in electrochemical systems commonly are referred to as electrochemical noise. The present work descr...

Influence of electron-electron scattering on shot noise in diffusive contacts.

Abstract: Shot noise in contacts with a small elastic mean free path in the presence of electron-electron scattering is calculated using the Boltzmann-Langevin approach and the approximation of effective electron tempreature. In the case of strong electron-electron scattering, the ratio between the shot noise ${\mathit{S}}_{\mathit{I}}$ and its classical value 2e\ensuremath{\Vert}I\ensuremath{\Vert} increases from 1/3 to \ensuremath{\surd}3 /4 owing to an increasing band of partially occupied states. The influence of electron-phonon scattering on the shot noise at finite temperatures is also considered. As this scattering decreases the energy of electron gas, it suppresses the shot noise at high voltages and increases the low-voltage boundary of the shot-noise range at finite temperatures. However, the noise decrease with increasing contact length more slowly than its reciprocal.

Dynamic pattern formation leads to 1/f noise in neural populations.

Abstract: We present a generic model that generates long-range (power-law) temporal correlations, 1/f noise, and fractal signals in the activity of neural populations. The model consists of a two-dimensional sheet of pulse coupled nonlinear oscillators (neurons) driven by spatially and temporally uncorrelated external noise. The system spontaneously breaks the translational symmetry, generating a metastable quasihexagonal pattern of high activity clusters. Fluctuations in the spatial pattern cause these clusters to diffuse. The macroscopic dynamics (diffusion of clusters) translate into 1/f power spectra and fractal (power-law) pulse distributions on the microscopic scale of a single unit.

Mean Switching Frequency Locking in Stochastic Bistable Systems Driven by a Periodic Force

Abstract: The nonlinear response of noisy bistable systems driven by a strong amplitude-periodic force is investigated by physical experiment. The new phenomenon of locking of the mean switching frequency between states of a bistable system is found. It is shown that there is an interval of noise intensities in which the mean switching frequency remains constant and coincides with the frequency of the external periodic force. The region on the parameter plane "noise intensity---amplitude of periodic excitation" which corresponds to this phenomenon is similar to the synchronization (phase locking) region (Arnold's tongue) in classical oscillatory systems.

On the error probability of linearly modulated signals on frequency-flat Ricean, Rayleigh, and AWGN channels

Abstract: The method used in Aghamohammadi and Meyr (1990) for finding the error probability of linearly modulated signals on Rayleigh frequency-flat fading channels has been applied to the more general case of Ricean fading. A signal received on a fading channel is subject to a multiplicative distortion (MD) and to the usual additive noise. Following a compensation of the MD, the signal provided to the detector may be thought to include only a single additive distortion term ("final noise"), which comprises the effects of the original additive noise, the MD, and the error in MD compensation. An exact expression for the probability density function of the final noise is derived. This allows calculation of error probability for arbitrary types of linear modulations. Results for many cases of interest are presented. Furthermore, as special cases of Ricean fading, error probability for Rayleigh fading and non-fading channels are obtained which either match the results or complete the approximate derivations formerly known from the literature. >

Statistical properties of phase-shift algorithms

Abstract: Statistical properties of phase-shift algorithms are investigated for the case of additive Gaussian intensity noise. Based on a bivariate normal distribution, a generally valid probability-density function for the random phase error is derived. This new description of the random phase error shows properties that cannot be obtained through Gaussian error propagation. The assumption of a normally distributed phase error is compared with the derived probability-density function. For small signal-to-noise ratios the assumption of a normally distributed phase error is not valid. Additionally, it is shown that some advanced systematic-error-compensating algorithms have a disadvantageous effect on the random phase error.

Miniature electrical filters for single electron devices

Abstract: In experiments on single electron devices, the electromagnetic noise from parts of the apparatus at temperatures higher than that of the device can dramatically increase the tunnel rates out of the Coulomb‐blocked state and therefore increase the device error rate. The electrical lines must therefore be filtered adequately. We derive simple expressions for calculating the required attenuation coefficient. We describe a wide‐band miniature dissipative filter functioning at cryogenic temperatures. The effective thermalization of an experiment at 30 mK can be obtained by placing four of these filters in series at temperatures ranging from 4 K to 30 mK.

Rectification and signal averaging of weak electric fields by biological cells.

Abstract: Oscillating electric fields can be rectified by proteins in cell membranes to give rise to a dc transport of a substance across the membrane or a net conversion of a substrate to a product. This provides a basis for signal averaging and may be important for understanding the effects of weak extremely low frequency (ELF) electric fields on cellular systems. We consider the limits imposed by thermal and "excess" biological noise on the magnitude and exposure duration of such electric field-induced membrane activity. Under certain circumstances, the excess noise leads to an increase in the signal-to-noise ratio in a manner similar to processes labeled "stochastic resonance." Numerical results indicate that it is difficult to reconcile biological effects with low field strengths.

Low-frequency noise in polysilicon emitter bipolar transistors

Abstract: The low-frequency noise in polysilicon emitter bipolar transistors is investigated. Transistors with various geometries and various properties of the oxide layer at the monosilicon polysilicon interface are studied. The main 1/f noise source proved to be located in the oxide layer. This source causes both 1/f noise in the base current S/sub Ib/ and 1/f noise in the emitter series resistance S/sub re/ The magnitude of the 1/f noise source depends on the properties of the oxide layer. The 1/f noise is ascribed to barrier height fluctuations of the oxide layer resulting in transparency fluctuations for both minority and majority carriers in the emitter, giving rise to S/sub Ib/ and S/sub re/ respectively. It is also shown that a low transparency of the oxide layer also reduces the contribution of mobility fluctuations to S/sub Ib/. >