Showing papers on "Noise (electronics) published in 1987"

Low-noise erbium-doped fibre amplifier operating at 1.54μm

Abstract: High gain amplification of up to 28 dB has been observed in a 3m-long erbium-doped fibre. The amplifier has a spectral bandwidth of greater than 300GHz in the region of 1.536µm and a measured sensitivity of -42dBm at a bit rate of 140 Mbit/s.

Non-Gaussian State—Space Modeling of Nonstationary Time Series

Abstract: A non-Gaussian state—space approach to the modeling of nonstationary time series is shown. The model is expressed in state—space form, where the system noise and the observational noise are not necessarily Gaussian. Recursive formulas of prediction, filtering, and smoothing for the state estimation and identification of the non-Gaussian state—space model are given. Also given is a numerical method based on piecewise linear approximation to the density functions for realizing these formulas. Significant merits of non-Gaussian modeling and the wide range of applicability of the method are illustrated by some numerical examples. A typical application of this non-Gaussian modeling is the smoothing of a time series that has mean value function with both abrupt and gradual changes. Simple Gaussian state—space modeling is not adequate for this situation. Here the model with small system noise variance cannot detect jump, whereas the one with large system noise variance yields unfavorable wiggle. To work...

Effect of interbreath fluctuations on characterizing exercise gas exchange kinetics

Abstract: Breathing has inherent irregularities that produce breath-to-breath fluctuations (“noise”) in pulmonary gas exchange. These impair the precision of characterizing nonsteady-state gas exchange kinet...

Radar Detection Prediction in K-Distributed Sea Clutter and Thermal Noise

Abstract: The compound K-distribution model for high resolution seaclutter is extended to cover the addition of thermal noise. Thismodel is not only a good match to real data but also allows thepulse-to-pulse correlation of the clutter returns to be modeled. Thematching of real data and the analysis required for target detectionprediction are described, together with some typical detectionresults.

An Analysis of the Output Spectrum of Direct Digital Frequency Synthesizers in the Presence of Phase-Accumulator Truncation

Abstract: An algorithm is presented for the calculation of the spectrum of direct digital frequency synthesizers (DDFS's) as a result of phase accumulator truncation. This algorithm, which is derived using number theoretic methods, includes a closed form expression relating the magnitude, number, and position of the spurious noise lines in the output spectrum of a DDFS to the read-only memory (ROM) look-up table size, the amount of phase accumulator truncation and the input frequency control command. The combined finite word length effects of the ROM and the Digital-to-Analog converter (DAC) nonlinearities are also examined in the light of these new results and new design guidelines are developed. The spectrums predicted by these closed form expresslons are compared against spectrums generated by a discrete Fourier transform (DFT) and are shown to have comparable accuracy. As a result of obtaining an expression for the magnitude of the spurious the input frequency command word and the ROM table size, the phase noise frequencies, a relationship between the greatest common divisor of accumulator word lengths, and the magnitude of the worst case spur is obtained. This relationship is used as the basis for a novel modification to the conventional phase accumulator structure which results in a 3.922dB reduction in the magnitude of the worst case spurious response. This hardware modification is also shown to average out the error effects of DAC nonlinearities and roundoff in the stored sine ROM samples.

Intensity correction in surface-coil MR imaging

Abstract: The use of surface coils in MR imaging has made it possible to obtain images of superficial structures with improved signal-to-noise ratio relative to conventional circumferential receiver coils [1 -4]. However, the signal intensity distribution in surface-coil images is inherently nonuniform; the decreased sensitivity to signal from more distant regions implies a conresponding decreased sensitivity to noise from those regions. As the total noise detected is uniformly distributed over the image, there is a net increase in the signal-to-noise ratio in the image of regions closer to the coil as compared with the conventional receiver coil [1 , 5]. The resulting range of relative intensity over surface-coil images makes it difficult to display them properly or to analyze them quantitatively. In addition, the local image contrast will decrease proportionally to the average local intensity. We report a method for correcting such surface-coil images so as to produce a uniform relative intensity over the region being imaged.

A Detection Algorithm for Optical Targets in Clutter

Abstract: There is active interest in the development of algorithms for detecting weak stationary optical and IR targets in a heavy opticalclutter background. Often only poor detectability of low signal-to-noise ratio (SNR) targets is achieved when the direct correlation method is used. In many cases, this is partly obviated by using detection with correlated reference scenes [1, 2].This paper uses the experimentally justified assumption that most optical clutter can be modeled as a whitened Gaussian randomprocess with a rapidly space-varying mean and a more slowlyvarying covariance [2]. With this assumption, a new constant falsealarm rate (CFAR) detector is developed as an application of the classical generalized maximum likelihood ratio test of Neyman and Pearson. The final CFAR test is a dimensionless ratio. This test exhibits the desirable property that its probability of a false alarm(PFA) is independent of the covariance matrix of the actual noiseencountered. When the underlying noise processes are complex intime, similar considerations can yield a sidelobe canceler CFARdetection criterion for radar and communications. Performance analyses based on the probability of detection (PD)versus signal-to-noise ratio for several given fixed false alarm probabilities are presented. Finally these performance curves are validated by computer simulations of the detection process which use real image data with artificially implanted signals.

Scaling limits in batch-fabricated silicon pressure sensors

Abstract: The scaling properties of silicon capacitive and piezoresistive pressure sensors are described. An evaluation of the various noise mechanisms and pressure offsets in the scaled devices is presented, including Brownian noise, electrical noise, electrostatic pressure variations and pressure offset due to resistor mismatch. The analysis of diaphragm deflection includes the effects of intrinsic stress and the transition from plate theory to membrane theory. Both ultraminiature and ultrasensitive sensors are considered. Ultraminiature piezoresistive sensors with diaphragms measuring 100 µm in length and resolving 1 mmHg should be possible using present technology as well as ultrasensitive capacitive sensors that resolve 1 µmHg.

The intracellular pupil mechanism and photoreceptor signal: noise ratios in the fly Lucilia cuprina.

Abstract: The function of the intracellular pupil mechanism is examined by comparing the responses of photoreceptors in normal flies with those from white-eyed flies that lack the pupil. In white-eyed flies the response to an intensity increment of fixed contrast decreases at high background intensities. There is a smaller decrease in noise amplitude so that the signal:noise ratio falls. The intensity dependence of the photoreceptor signal:noise ratio fits a simple model in which activated photopigment molecules compete for 3 X 10(4) transduction units. The signal:noise ratio decreases at high intensities because the transduction units are saturated. This model is supported by a noise analysis, which provides three estimates of the number of events generating photoreceptor responses. In white-eyed flies the event number saturates at high background intensities, suggesting that a maximum of 2 X 10(4) events can be simultaneously active. Wild-type flies do not exhibit saturation effects over the range of intensities studied. The signal:noise ratio rises with intensity to reach a stable asymptote, close to the maximum observed for white-eyed flies. Pupil attenuation is calculated from measurements of signal:noise ratio in white-eyed and wild-type flies. The pupil is progressively activated over a two log unit intensity range and when fully closed attenuates the effective intensity by 99%. The threshold of this pupil effect coincides with the threshold of pupil activation measured optically. We conclude that the intracellular pupil attenuates the light flux to prevent receptor saturation and to extend the range of intensities at which fly photoreceptors operate close to their maximum signal:noise ratio. This upper limit is determined by the number of transduction units generating a cell's response.

Performance of DS/SSMA Communications in Impulsive Channels--Part I: Linear Correlation Receivers

Abstract: The performance of digital linear correlation receivers is studied in a multiuser environment. There are assumed to be two types of sources interfering with data transmission: multiple-access interference, and additive channel noise which is attributed to impulsive noise sources in the environment. The contribution of multiple-access interference is examined by considering K asynchronous users transmitting simultaneously over a linear channel using the binary PSK direct-sequence spreadspectrum multiple-access (DS/SSMA) technique. Alternatively, the effects of the non-Gaussian impulsive channel in such a system are studied by modeling the samples of noise after front-end filtering. Errorprobability performance under these conditions is compared to that for additive white Gaussian noise (AWGN) channels. Due to computational complexity, exact analysis is limited here to systems utilizing short spreading sequences. Computationally simple methods are proposed for approximating the average error probability when the length of the signature sequences is large. Furthermore, some asymptotic results are obtained for the case of infinitely long sequences. In all cases, performance variation is examined as the shape of the noise density varies with SNR held constant. The results of this analysis indicate that the presence of impulsive noise can cause significant performance degradation over that predicted from an AWGN model, even when the total noise power does not increase.

Can free energy be transduced from electric noise

Abstract: Recently, it was shown that free energy can be transduced from a regularly oscillating electric field to do chemical or transport work when coupled through an enzyme with appropriate electrical characteristics. Here we report that randomly pulsed electric fields can also lead to work being done, giving rise to speculation as to whether appropriately designed enzymes can extract and convert free energy from the inherent fluctuations in their environment. The paradox is resolved by showing that equilibrium electrical noise resulting from the environment around an enzyme cannot be completely random but is correlated to the state that the enzyme is in. If the noise has the appropriate reciprocal interaction with the enzyme, its potential to serve as a free-energy source disappears. This is shown by Monte Carlo and other numerical calculations and is proven analytically by use of the diagram method. This method also is used to provide an explicit equation showing that, under a range of conditions, our model enzyme will be induced by uncorrelated ("autonomous") noise to undergo net cyclic flux. That work can be transduced from the "random" noise is demonstrated by using numerical methods.

Modulation and detection characteristics of optical continuous phase FSK transmission system

Abstract: The modulation and differential detection characteristics of optical CPFSK transmission systems are investigated both theoretically and experimentally. The error rate expressions of differentially detected CPFSK are derived by considering phase noise of LD's. It is clear that the linewidth requirement is less than 0.68 m percent of the bit rate, where m is modulation index. The performances of CPFSK are then experimentally presented at 400 Mbit/s using external optical feedback DFB LD's as the optical source. A beat spectral linewidth of less than 200 kHz for the transmitter and local oscillator LD's is achieved. The frequency response nonuniformity of frequency modulation efficiency is compensated by electrical circuits within 3 dB and 60°. To reduce IF thermal noise, a resonance-type preamplifier is used, with a 4.8 pA/ \sqrt{Hz} average input noise current density, and a receiver sensitivity 1.3 dB better than the conventional preamplifier. Differential detection of the 400-Mbit/s CPFSK modulation is performed. The generation of CPFSK is confirmed by good correlation between the output spectrum and theory. The average received optical power at a 10-9bit error rate is -49.9 dBm which improves direct detection by 10.3 dB. No additional power penalties due to 290-km transmission exist.

Spectral dependence of 1ƒγ noise on gate bias in n-MOSFETS

Abstract: The modified McWhorter model that has been developed before to explain the 1 ƒ γ noise in Metal-Oxide-Semiconductor-Field-Effect-Transistors was extended to include frequency dependence of the noise power spectrum on operating voltages. Under the assumption of energy and spatial distribution of traps in the oxide, the drain voltage noise spectrum was calculated for MOSFETs operating in the linear region. Experimentally flicker noise measured on n -channel enchancement-mode MOSFETs up to the frequency of 4 kHz. The actual value of the exponent γ in the 1 ƒ γ spectrum was found to increase with gate bias. Furthermore, it was found that the magnitude of the noise power decreased with gate bias. The detail of the calculations and the experimental results are presented.

Dendritic sidebranching in the three-dimensional symmetric model in the presence of noise.

Abstract: The time-dependent behavior of sidebranching deformations in the three-dimensional symmetric model of dendritic solidification is studied within a WKB approximation. Localized wave packets generated by pulses in the neighborhood of the tip are found to grow in amplitude and to spread and stretch as they move down the sides of the dendrite. This behavior is shown to imply that noise in the solidifying medium is selectively amplified in such a way as to produce a fluctuating train of sidebranches in qualitative agreement with experimental observations. A rough estimate indicates that purely thermal noise is probably not quite strong enough to fit the data.

Steady-state analysis of strongly colored multiplicative noise in a dye laser.

Abstract: A new Langevin equation for dye-laser fluctuations below and near threshold is used to obtain the intensity distribution function in closed form. The effect of strongly colored multiplicative pump noise is incorporated by means of an ansatz of Hanggi et al [Ph.ys. Rev. A 32, 695 (1985)] for an effective diffusion coefficient at steady states. Excellent agreement with the measurements of Lett, Short, and Mandel [Phys. Rev. Lett. 52, 341 (1984)] is obtained. I. INTRODUCTION Recent work on dye-laser noise has emphasized the simultaneous presence of additive quantum noise and multiplicative pump noise. Moreover, it has become apparent that the pump noise is not white but colored with a relatively long correlation time. Two experimental approaches have been used to characterize the noise parameters. Steady-state measurements of the normalized variance of the intensity fluctuations and the intensity autocorrelation function, ' and the first-passage-time technique have been used ' to determine these parameters. These measurements have produced refinements in the theoretical description of laser noise in terms of an augmented semiclassical laser model. The time evolution of the complex laser field is described by a Langevin equation containing both additive (spontaneous emission) noise ' and multiplicative (pump) noise. " ' When additive white noise and strongly colored pump noise are simultaneously present it is necessary to perform numerical Monte Carlo simulations in order to deduce the predictions of the theory for comparison with measurements. In this paper we will show that a detailed analysis of the steady-state measurements is possible which avoids time consuming simulations. This is possible because (a) we obtain a novel Langevin equation solely in terms of the laser intensity, which we prove fully describes the behavior of the intensity below, near, and somewhat above threshold, and (b) for steady state we invoke and justify the ansatz of Hanggi et at'. ' for treating Langevin equations containing strongly colored noise. Lett, Short, and Mandel observed a peak in the normalized variance of the intensity fluctuations as a function of mean intensity. They used the Monte Carlo procedure of Sancho et al. ' as applied to the laser problem by Dixit and Sahni, to fit their measurements. We have used our Langevin equation to obtain the steady-state probability distribution for the intensity with which we have also fit their data. This procedure is far simpler to implement than the Monte Carlo simulations. The agreement obtained among measurements, simulations, and our theory strongly supports both the Langevin intensity equation and the ansatz of Hanggi et al. ' for colored noise in steady-state situations.

Problems in Signal-to-Noise Ratio for Attenuation Correction in High Resolution PET

Abstract: In high resolution PET, the number of events required for a high signal-to-noise ratio in the measured attenuation correction is an order of magnitude higlher (50-100 million) than that required for the emission image. This is due to the large number of elements in the attenuation correction sinogram (e.g. 50,000) and the large attenuation factors through the thicker sections of the body (e.g. 50). Another major contribution to noise in high resolution PET is contamination of true coincidences by accidentals and their subtraction from the prompt coincidences. In this work three methods which reduce noise in the measured attenuation are evaluated. The methods are: (1) optimization of energy threshold, (2) processing of random sinogram before subtraction and (3) spatial averaging of the tranismission sinogram before performing attenuation correction.

Low-frequency noise in silicon-gate metal-oxide-silicon capacitors before oxide breakdown

Abstract: Measurements of the fluctuations in the tunneling current It through a thin SiO2 insulating layer, by means of an ultralow noise measurement set, showed that after a first time interval in which its power spectral density is stationary and proportional to I2t, an on‐off modulation of It arises, just before oxide breakdown. This bistable noise seems to be related to localized phenomena controlled by trapping‐detrapping processes within the oxide. Two possible mechanisms which could give rise to this bistable noise are discussed.

Macroscopic potentials, bifurcations and noise in dissipative systems

Abstract: A review is presented of recent work dealing with dissipative dynamical systems weakly perturbed by noise. A free-energy like macroscopic nonequilibrium potential is defined for such systems which determines the stability and mean life-times of the systems' attractors. General properties of the nonequilibrium potential are discussed along with selected applications such as noise in Josephson junctions, in systems near bifurcation points of codimension two, and in systems described by the strange attractor of the Lorenz model.

Flicker (1/f) noise generated by a random walk of electrons in interfaces

Abstract: Flicker noise can be generated by a random walk of mobile electrons in interfaces via interface states. It is proposed that these electrons interact with surface phonons to form polarons, which have very low mobilities. The flicker-noise model is a general one and may be used to explain flicker noise on MOSFET's, clean Si surfaces, metallic resistors, grain boundaries, amorphous layers, electron tubes, metal-insulator-metal junctions, diodes, and transistors. The dependence of the noise intensity is calculated as a function of device parameters such as interface state density, source-drain current, source-drain voltage, gate voltage, oxide layer thickness, grain size, temperature, size of the cathode, diode current, base current, and the surface recombination in the emitter-base area. Hooge's parameter is calculated quantitatively for several devices.

Electromigration and low-frequency resistance fluctuations in aluminum thin-film interconnections

Abstract: Low-frequency noise spectra originating from resistance fluctuations in Al films during electromigration were measured in the absolute temperature and current density intervals 327 \leq T \leq 396 K and 1.34 \times 10^{6} \leq j \leq 2.22 \times 10^{6} A/cm2. The values of S R , the resistance power spectral density, at 20 × 10-3Hz allowed the construction of an Arrhenius plot from which a grain-boundary activation energy value of about 0.6 eV was deduced. This value lies in the range of values found by other authors using different techniques. A first attempt to model the observed dependence of S R on j and T is also described.

Surface mobility fluctuations in metal-oxide-semiconductor field-effect transistors.

Abstract: We have calculated, from first principles, two-dimensional mobility fluctuations in metal-oxide-semiconductor field-effect transistors (MOSFET's) due to scattering between the induced charge carriers and the interfacial traps. The results are used to evaluate the behavior of the 1/${f}^{\ensuremath{\gamma}}$ noise in MOSFET's, particularly the gate-bias dependence of both the functional form and magnitude of the noise power spectrum. Similar to previous calculations that assumed the noise to be due to number fluctuations, the new model accurately accounts for the change of the spectral distribution of noise at different gate biases. However, when the surface mobility fluctuations are included in the noise computation, a much better fit to the experimentally measured noise power magnitude is obtained.

Diversity Combining for Channels with Fading and Partial-Band Interference

Abstract: Diversity combining techniques that employ a ratiothreshold test (RTT) are suggested for communications with fading and partial-band interference. We consider a system with binary orthogonal signaling and noncoherent demodulation. The fading channel is modeled as a group of independent narrow-band channels, each with nonselective Rician fading. We assume that the partial-band interference is Gaussian, and we include additive white Gaussian quiescent noise in the analysis to account for wide-band noise sources. The performance measures we use to evaluate the diversity combining schemes are the narrow-band interference rejection capability and the signal-to-noise ratio requirement over the entire range of partial-band interference duty factors. The performances of the RTT with square-law combining and the RTT with majority logic decoding are compared to each other and to the performance of the optimum diversity combining technique.

Quantitative "local-interference" model for 1/f noise in metal films.

Abstract: Electron scattering calculations by Martin are used to predict the magnitude of resistivity fluctuations in metal films arising from the fluctuating interference of electrons in the local environment of a moving defect. A ''local-interference'' model based on these calculations accounts for the 1/f-noise magnitude observed in irradiated Cu films and in room-temperature metal films. For relatively ordered metal films at room temperature this model predicts larger noise magnitudes than an alternative model based on universal conductance fluctuations, while the latter model predicts larger noise in metals that are sufficiently disordered and/or at lower temperatures.

High resolution imaging doppler interferometer

Abstract: A system for simultaneously locating a plurality of targets and distinguishing the targets from noise which utilizes phase detector techniques to generate complex voltage signals and obtain phase information. Spectral analysis is performed on the complex voltage temporal functions to generate doppler frequency functions. Both spectral phase functions and spectral amplitude functions are generated from the doppler frequency functions. Spectral phase functions are analyzed using interferometry techniques to determine if a potential target has a common locational source from returns of a plurality of sensors. A zenith angle is also generated using interferometry techniques to provide locational information of the multiple targets. Range gating and two frequency range detection methods provide high resolution range information as to the location of the targets. High resolution range information and two dimensional zenith angle information are used to provide an image of the targets. The present invention uses a two-frequency pulse which can be generated simultaneously or sequenced within a pulse in a manner which is phase coherent. The two-frequency pulse eliminates problems associated with range aliasing, zenith angle aliasing, scattering point analysis and allows for range location with high resolution. An error correction factor is also generated which eliminates spectral smearing.

Multichannel intermodulation distortion in high-speed GaInAsP lasers

Abstract: We present an experimental study of intermodulation distortion (IMD) in high-speed, long-wavelength GaInAsP lasers modulated up to 8 GHz. It is found that three-tone distortion products are the dominant contribution to IMD interference when the number of subcarriers is large. These distortion data are used with a simple theory to predict accurately the measured signal/noise ratio for each channel of a multichannel subcarrier system.

Wigner-function Description of Quantum Noise in Interferometers

Abstract: A quantum-statistical description of noise in interferometers is given in terms of the Wigner distribution function. The interferometer may contain an amplifier in one of its arms. The input field can be in a variety of states such as a Fock state, a coherent state or a squeezed coherent state. The Wigner function of the output field at the detector is shown to have a general Gaussian form with non-zero complex field amplitude and with other parameters related to the characteristics of the input field, amplifier and beam splitters, etc. An explicit form of the photon-number distribution is given. Higher-order correlations of the output field can be obtained from the Gaussian property of the Wigner function.

Novel superconducting thermometer for bolometric applications

Abstract: The temperature dependence of the magnetic penetration depth in a superconductor, in the kinetic inductance limit, is proposed as a basis for a sensitive thermometer. Considered as a bolometer, the noise equivalent power from the sum of the Johnson noise and the preamplifier noise can be reduced to about 7×10−20 W/(Hz)1/2, which is approximately four orders of magnitude below currently realized values.

Microwave Noise Characterization of GaAs MESFET's: Evaluation by On-Wafer Low-Frequency Output Noise Current Measurement

Abstract: A simplified noise equivalent circuit is presented for submicron-gate-length MESFET's in the common-source configuration, consisting of five linear circuit elements: the gate-to source capacitance C/sub gs/, the total input resistance R/sub T/, the transconductance g/sub m/, the output resistance R/sub 0/, and a noise current source of spectral density S/sub io/ at the output port. All of these elements can be determined by on-wafer measurements, and the noise current can be measured at a low frequency. The minimum noise figure of the device calculated from this model, as well as the bias and frequency dependence of the noise figure, is shown to be in agreement with microwave noise figure measurements. Thus a technique has been established for determination of the minimum noise figure of a device solely by on-wafer measurements rather than by the usual microwave measurements. The proposed technique can be employed rapidly, conveniently, without the need for tuning, and at the wafer stage of device fabrication.

Low‐frequency excess noise in Nb‐Al2O3‐Nb Josephson tunnel junctions

Abstract: A fabrication technique for Nb‐Al2O3‐Nb Josephson tunnel junctions is described that is an alternative to the trilayer method generally used. At 4.2 K the magnitude of the low‐frequency noise in the critical current I0 of four junctions with areas A ranging from 7.8 to 115 μm2 was characterized by S1/2I0A1/2/I0 =(14±6)pA μm/μA Hz1/2, where SI0 is the spectral density of the excess noise at 1 Hz. The noise power spectrum of one 3×3 μm2 junction exhibited a Lorentzian feature associated with the emptying and filling of a single trap in the barrier. The low level of noise makes these junctions attractive for use in superconducting quantum interference devices.

Black-box identification of MIMO transfer functions : asymptotic properties of prediction error models

Abstract: Identification of multi-input/multi-output (MIMO) transfer functions is considered. The transfer function matrix is parametrized as black-box models which have certain shift properties; no structure or order is chosen a priori. In order to obtain a good transfer function estimate, we allow the order of the model to increase to infinity as the number of data tends to infinity. The expression of asymptotic covariance of the transfer function estimates is derived, which is asymptotic both in the number of data and in the model order. The result indicates that the joint covariance matrix of the transfer function estimates of the process and of the noise filter is proportional to the (generalized) ratio of output noise to imput signal; the factor of proportionality is the ratio of model order to number of data. The result is independent of the particular model structure used. This result is the MIMO extension of the theory of Ljung. The application of this theory for defining the upper bounds of identification errors is highlighted.