Showing papers on "Noise (electronics) published in 1997"

Signal-to-noise measurements in magnitude images from NMR phased arrays.

Abstract: A method is proposed to estimate signal-to-noise ratio (SNR) values in phased array magnitude images, based on a region-of-interest (ROI) analysis. It is shown that the SNR can be found by correcting the measured signal intensity for the noise bias effects and by evaluating the noise variance as the mean square value of all the pixel intensities in a chosen background ROI, divided by twice the number of receivers used. Estimated SNR values are shown to vary spatially within a bound of 20% with respect to the true SNR values as a result of noise correlations between receivers.

Errors in elliptical gaussian fits

Abstract: Elliptical Gaussian fits are used in astronomy for accurate measurements of fundamental source parameters such as central position, peak flux density, and angular size. The full value of a noise-limited image can be realized only if the effects of noise on the fitted parameters are estimated accurately. This paper presents the equations of error propagation for two-dimensional elliptical Gaussian fits in the presence of Gaussian noise plus a new method that simplifies the use of a priori size constraints to reduce amplitude errors.

The MICROMIXER: a highly linear variant of the Gilbert mixer using a bisymmetric Class-AB input stage

Abstract: This paper outlines the basic theory of a development of the Gilbert mixer. The bipolar junction transistor (BJT) differential pair widely used as the RF input stage is replaced by a bisymmetric Class-AB topology based on translinear principles. It does not have inherent gain compression, affording a greatly extended signal capacity. The linearity of variants of the basic form is excellent, providing two-tone intermodulation intercepts as high as +30 dBm, without the expenditure of high bias currents. It can operate on supplies as low as 2.2 V, with a power consumption of under 5 mW. The input impedance of this mixer is accurately controllable (typically 50 /spl Omega/) and provides a true broadband match. The noise figure depends on design details and is generally not as low as in mixers specifically optimized for noise performance, although acceptable for many receiver applications. Inductively degenerated variants can be tuned to a narrowband match at microwave frequencies and provide full-mixing SSB noise figures as low as 6.5 dB, Practical realizations are in use in applications to 1.9 GHz.

Empirical and theoretical investigation of the noise performance of indirect detection, active matrix flat-panel imagers (AMFPIs) for diagnostic radiology

Abstract: Noise properties of active matrix, flat-panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin-film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x-ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency-dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x-ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 153631920 pixels at a pixel pitch of 127 mm. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI:Tl intensifying screen can be optimized to provide detective quantum efficiency ~DQE! superior to existing screen-film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a-Si:H imagers, DQE performance approaching that of the best x-ray image intensifier systems may be possible. The results of this analysis suggest strategies for future improvements of this imaging technology. © 1997 American Association of Physicists in Medicine.@S0094-2405~97!01401-6#

Autonomous stochastic resonance in bursting neurons

Abstract: Noise-induced firing is studied in two major classes of bursting neuron models in the absence of periodic input. In the biologically relevant subthreshold regime where no deterministic firing occurs, additive noise induces spiking limit cycles. This noise makes the output firing patterns sensitive to the characteristics of autonomous subthreshold oscillations, which can change in response to various physicochemical stimuli. The nonmonotonic behavior with increasing noise of the phase locking between spikes and subthreshold oscillations, measured using spectral signal-to-noise ratios and line shape characteristics, are a manifestation of autonomous stochastic resonance in these systems. The type of bifurcation giving rise to bursting activity determines the behavior with noise of the mean firing frequency, interspike interval histogram, spike train power spectrum, and phase locking. In particular, it is shown that a saddle-node bifurcation is not required to see stochastic resonance ~SR! without periodic input when there exists a stable deterministic subthreshold oscillation. This paper also studies SR in a detailed ionic neuron model, an approach that leads to tests of hypotheses regarding the nature of noise in real neurons. @S1063-651X~97!12001-3#

Ultrasensitive laser measurements without tears

Abstract: Several easily implemented devices for doing ultrasensitive optical measurements with noisy lasers are presented. They are all-electronic noise cancellation circuits that largely eliminate excess laser intensity noise as a source of measurement error and are widely applicable. Shot-noise-limited optical measurements can now easily be made at baseband with noisy lasers. These circuits are especially useful in situations where strong intermodulation effects exist, such as current-tuned diode laser spectroscopy. These inexpensive devices ~parts cost ’$10! can be optimized for particular applications such as wideband or differential measurements. Although they cannot eliminate phase noise effects, they can reduce amplitude noise by 55‐70 dB or more, even in unattended operation, and usually achieve the shot-noise limit. With 1-Hz signal-to-noise ratios of 150‐160 dB, they allow performance equal or superior to a complex heterodyne system in many cases, while using much simpler dual-beam or homodyne approaches. Although these devices are related to earlier differential and ratiometric techniques, their noise cancellation performance is much better. They work well at modulation frequencies from dc to several megahertz and should be extensible to ’100 MHz. The circuits work by subtracting photocurrents directly, with feedback applied outside the signal path to continuously adjust the subtraction for perfect balance; thus the excess noise and spurious modulation ideally cancel at all frequencies, leaving only the shot noise. The noise cancellation bandwidth is independent of the feedback bandwidth; it depends only on the speeds of the photodiodes and of the bipolar junction transistors used. Two noise-canceled outputs are available; one is a high-pass filtered voltage proportional to the signal photocurrent and the other is a low-pass filtered voltage related to the log ratio of the signal and comparison photocurrents. For reasonable current densities, the noise floors of the outputs depend only on the shot noise of the signal beam. Four variations on the basic circuit are presented: low noise floor, high cancellation, differential high power, and ratio-only. Emphasis is placed on the detailed operation and design considerations, especially performance extension by compensation of the nonideal character of system components. Experience has shown that some applications advice is required by most users, so that is provided as well. © 1997 Optical Society of America

Optical interference produced by artificial light

Abstract: Wireless infrared transmission systems for indoor use are affected by noise and interference induced by natural and artificial ambient light. This paper presents a characterisation (through extensive measurements) of the interference produced by artificial light and proposes a simple model to describe it. These measurements show that artificial light can introduce significant in-band components for systems operating at bit rates up to several Mbit/s. Therefore it is essential to include it as part of the optical wireless indoor channel. The measurements show that fluorescent lamps driven by solid state ballasts produce the wider band interfering signals, and are then expected to be the more important source of degradation in optical wireless systems.

Signal-to-noise measurements in magnitude images from NMR phased arrays

Abstract: A method is proposed to estimate signal-to-noise ratio (SNR) values in phased array magnitude images, based on a region-of-interest (ROI) analysis. It is shown that the SNR can be found by correcting the measured signal intensity for the noise bias effects and by evaluating the noise variance as the mean square value of all the pixel intensities in a chosen background ROI, divided by twice the number of receivers used. Estimated SNR values are shown to vary spatially within a bound of 20% with respect to the true SNR values as a result of noise correlations between receivers.

Stochastic resonance in non-dynamical systems without response thresholds

Abstract: The addition of noise to a system can sometimes improve its ability to transfer information reliably. This phenomenon--known as stochastic resonance--was originally proposed to account for periodicity in the Earth's ice ages, but has now been shown to occur in many systems in physics and biology. Recent experimental and theoretical work has shown that the simplest system exhibiting 'stochastic resonance' consists of nothing more than signal and noise with a threshold-triggered device (when the signal plus noise exceeds the threshold, the system responds momentarily, then relaxes to equilibrium to await the next triggering event). Here we introduce a class of non-dynamical and threshold-free systems that also exhibit stochastic resonance. We present and analyse a general mathematical model for such systems, in which a sequence of pulses is generated randomly with a probability (per unit time) that depends exponentially on an input. When this input is a sine-wave masked by additive noise, we observe an increase in the output signal-to-noise ratio as the level of noise increases. This result shows that stochastic resonance can occur in a broad class of thermally driven physico-chemical systems, such as semiconductor p-n junctions, mesoscopic electronic devices and voltage-dependent ion channels, in which reaction rates are controlled by activation barriers.

An integrated analog/digital random noise source

Abstract: An integrated noise source (INS) has been fabricated in a standard 1.2 /spl mu/m digital CMOS technology. Wideband white noise is generated from the amplified thermal noise of large resistors, which in turn is coupled into a comparator to generate a random digital bit stream. The INS generates 100 mV rms of analog output noise over a bandwidth of 3.2 MHz and operates from a single 5 V power supply with a quiescent current of 7.4 mA. The circuit has an area of 2.92 mm/sup 2/. Potential applications of the INS include data encryption, mathematical simulation, and circuit test and measurement.

Coherence resonance at noisy precursors of bifurcations in nonlinear dynamical systems

Abstract: A general mechanism of coherence resonance that occurs in noisy dynamical systems close to the onset of bifurcation is demonstrated through examples of period-doubling and torus-birth bifurcations. Near the bifurcation of a periodic orbit, noise produces the characteristic peaks of ``noisy precursors'' in the power spectrum. The signal-to-noise ratio evaluated at these peaks is maximal for a certain optimal noise intensity in a manner that resembles a stochastic resonance.

A New Type

Abstract: The areal density of magnetic disk is expected to grow to over 20Gb/in 2 by the end-1990s. In the INTERMAG'96, the authors demonstrated high areal density of 5Gbit/in 2 with PR4ML channel. The thermal instability can not be neglected at higher areal density than 5Gb/in 2 . It indicates the necessity to use the code which expand bit length such as (1,7) RLL code. We consider the best combination of (1,7) RLL code and a partial response channel. The partial response system of the polynomial (1+D)(1-D 2 ) called modified E 2 PR4(MEEPR4) exhibits the best performance. We performed this partial response simulation model with white noise and media - noise and examined the architectural consideration in the design of the experimental prototype.

Robust nonlinear H/sub /spl infin// synchronization of chaotic Lur'e systems

Abstract: We propose a method of robust nonlinear H/sub /spl infin// master-slave synchronization for chaotic Lur'e systems with applications to secure communication. The scheme makes use of vector field modulation and either full static state or linear dynamic output error feedback control. The master-slave systems are assumed to be nonidentical and channel noise is taken into account. Binary valued continuous time message signals are recovered by minimizing the L/sub 2/-gain from the exogenous input to the tracking error for the standard plant representation of the scheme. The exogenous input takes into account the message signal, channel noise and parameter mismatch. Matrix inequality conditions for dissipativity with finite L/sub 2/-gain of the standard plant form are derived based on a quadratic storage function. The controllers are designed by solving a nonlinear optimization problem which takes into account both channel noise and parameter mismatch. The method is illustrated on Chua's circuit.

Theory of stochastic resonance in signal transmission by static nonlinear systems

Abstract: A deterministic periodic signal plus a stationary random noise is applied to a static nonlinearity taking the form of a monovariable arbitrary function on real numbers. The property of noise-enhanced signal transmission through stochastic resonance is studied for this class of static nonlinear systems. A theory is developed that provides expressions for the output autocorrelation function, power spectral density, signal-to-noise ratio, and input-output phase shift, in the presence of a periodic input, a noise distribution, and a static nonlinearity, all three being arbitrary. Both white and colored input noises are successively considered. For white input noise, exact expressions are derived in a discrete-time framework directly confrontable to simulations or experiments. The theory is applied to describe stochastic resonance in various examples of static nonlinear systems, for instance, a diode nonlinearity. In addition, confrontations with experiments and simulations are given that support the theory. In particular, interesting effects are reported such as a signal-to-noise ratio larger at the output than at the input or stochastic resonance at zero frequency. Finally, the validity of the theory is extended to dynamic nonlinear systems that can be decomposed into a static nonlinearity followed by an arbitrary dynamic linear system. @S1063-651X~97!12002-5#

Stochastic resonance in models of neuronal ensembles

Abstract: Two recently suggested mechanisms for the neuronal encoding of sensory information involving the effect of stochastic resonance with aperiodic time-varying inputs are considered. It is shown, using theoretical arguments and numerical simulations, that the nonmonotonic behavior with increasing noise of the correlation measures used for the so-called aperiodic stochastic resonance ~ASR! scenario does not rely on the cooperative effect typical of stochastic resonance in bistable and excitable systems. Rather, ASR with slowly varying signals is more properly interpreted as linearization by noise. Consequently, the broadening of the ‘‘resonance curve’’ in the multineuron stochastic resonance without tuningscenario can also be explained by this linearization. Computation of the input-output correlation as a function of both signal frequency and noise for the model system further reveals conditions where noise-induced firing with aperiodic inputs will benefit from stochastic resonance rather than linearization by noise. Thus, our study clarifies the tuning requirements for the optimal transduction of subthreshold aperiodic signals. It also shows that a single deterministic neuron can perform as well as a network when biased into a suprathreshold regime. Finally, we show that the inclusion of a refractory period in the spike-detection scheme produces a better correlation between instantaneous firing rate and input signal. @S1063-651X~97!01102-1#

Multi-mode noise analysis of cantilevers for scanning probe microscopy

Abstract: A multi-mode analysis of micro-cantilever dynamics is presented. We derive the power spectral density of the cantilever displacement due to a thermal noise source and predict the cantilevers’s fundamental resonant frequency and higher harmonics. The first mode in the multi-mode model is equivalent to the traditional single-mode model. Experimental results obtained with a silicon nitride cantilever at 300 K are in excellent qualitative agreement with the multi-mode model. The multi-mode model may be used to obtain accurate values of the cantilever properties such as the elastic modulus,effective mass, thickness and moment of inertia.

Additive noise effect in digital phase detection

Abstract: The characteristic polynomials associated with the algorithms used in digital phase detection are used to investigate the effects of additive noise on phase measurements. First, it is shown that a loss factor η can be associated with any algorithm. This parameter describes the influence of the algorithm on the global signal-to-noise ratio (SNR). Second, the variance of the phase error is shown to depend mainly on the global SNR. The amplitude of a modulation of this variance at twice the signal frequency depends on a single parameter β. The material presented here extends previously published results, and as many as 19 algorithms are analyzed.

CMB mapping experiments: a designer's guide

Abstract: We apply state-of-the art data analysis methods to a number of fictitious cosmic microwave background (CMB) mapping experiments, including $1/f$ noise, distilling the cosmological information from time-ordered data to maps to power spectrum estimates, and find that in all cases the resulting error bars can be well approximated by simple and intuitive analytic expressions. Using these approximations, we discuss how to maximize the scientific return of CMB mapping experiments given the practical constraints at hand, and our main conclusions are as follows. (1) For a given resolution and sensitivity, it is best to cover a sky area such that the signal-to-noise ratio per resolution element (pixel) is of order unity. (2) It is best to avoid excessively skinny observing regions, narrower than a few degrees. (3) The minimum-variance map-making method can reduce the effects of $1/f$ noise by a substantial factor, but only if the scan pattern is thoroughly interconnected. (4) $1/f$ noise produces a $1/\mathcal{l}$ contribution to the angular power spectrum for well-connected single-beam scanning, as compared to virtually white noise for a two-beam scan pattern such as that of the MAP satellite.

Noise Resistance Applied to Corrosion Measurements II. Experimental Tests

Abstract: Electrochemical noise (EN) measurements have been carried out on several corroding systems, utilizing the technique of simultaneous recording of current and voltage fluctuations, and calculating the frequency dependent spectral noise impedance R{sub sn}(f) as the square root of the ratio of the power spectral densities (PSD) of the voltage to current noise. The results are compared with the theoretical predictions stemming from an analysis of the technique, which is presented in the preceding paper. It is shown that, over a quite large range of conditions, R{sub sn}, coincides with the impedance modulus of the electrodes under study. From the relationship between R{sub sn} and the noise resistance R{sub n}, which is usually obtained calculating the ratio of the standard deviations of the voltage and current fluctuations, it is shown that the latter quantity can be equal to the zero frequency limit of the impedance only if certain conditions are satisfied.

A time-over-threshold machine: the readout integrated circuit for the BABAR Silicon Vertex Tracker

Abstract: A low-noise, mixed-signal, 128-channel CMOS integrated circuit containing the complete readout electronics for the BABAR Silicon Vertex Tracker has been developed. The outstanding feature of the present implementation is the ability to perform simultaneously low-level signal acquisition, derandomizing data storage, sparsification and data transmission on a single monolithic chip. The signals from the detector strips are amplified, shaped by a CR-RC/sup 2/ filter with digitally selectable peaking time of 100 ns, 200 ns, 300 ns, or 400 ns, and then presented to a time-over-threshold processor to implement a compression type analog-to-digital conversion. The digital information is stored, sparsified and read out through a serial link upon receipt of a command. The digital section operates from a 60 MHz incoming clock. Noise measurements at 200 ns peaking time and 3.5 mW total power dissipation per channel yield an equivalent noise charge of 600 el. rms at 12 pF added source capacitance. The chip measures 5.7 mm/spl times/8.3 mm and contains 330 k transistors. The first full-scale prototype was fabricated in a radiation soft 0.8 /spl mu/m, 3-metal CMOS process. The same circuit is now being fabricated in an analogous radiation hard technology.

Kinetic roughening in slow combustion of paper.

Abstract: Results of experiments on the dynamics and kinetic roughening of one-dimensional slow-combustion fronts in three grades of paper are reported. Extensive averaging of the data allows a detailed analysis of the spatial and temporal development of the interface fluctuations. The asymptotic scaling properties, on long length and time scales, are well described by the Kardar-Parisi-Zhang (KPZ) equation with short-range, uncorrelated noise. To obtain a more detailed picture of the strong-coupling fixed point, characteristic of the KPZ universality class, universal amplitude ratios, and the universal coupling constant are computed from the data and found to be in good agreement with theory. Below the spatial and temporal scales at which a crossover takes place to the standard KPZ behavior, the fronts display higher apparent exponents and apparent multiscaling. In this regime the interface velocities are spatially and temporally correlated, and the distribution of the magnitudes of the effective noise has a power-law tail. The relation of the observed short-range behavior and the noise as determined from the local velocity fluctuations is discussed.

Active EMI filter for switching noise of high frequency inverters

Abstract: In high frequency inverter fed AC motor systems, high frequency leakage current generated by high dv/dt at switching times flows to the ground wire through the stray capacitor between motor windings and core. This paper proposes an active EMI filter to compensate common mode current using high frequency transistors as active elements and a high frequency common mode CT. It works just as a power active filter in the harmonic compensation in the power system. The leakage current is actively suppressed to under 1/50 of the uncompensated circuit. The proposed method is also effective to decrease the EMI more than 40 dB/spl mu/V.

Performance analysis of direct-detection optical asynchronous CDMA systems with double optical hard-limiters

Abstract: Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed under the assumption of Poisson shot noise model for the receiver photodetector where the noise due to the detector dark currents exists. Optical orthogonal codes (OOC's) are employed as signature sequence codes. In the analysis, chips are assumed to be synchronous among users, that is, the chip synchronous case, because the effect of the interference is largest in the chip synchronous case and thus the performance in the chip synchronous case results in the upper bounds on the performance of the asynchronous system. The performance is evaluated under average power and bit rate constraints. The results show that, differing from the optical synchronous CDMA systems with double optical hard-limiters, the optical asynchronous CDMA systems with double optical hard-limiters have good performance even when the number of simultaneous users is large.

A CMOS channel-select filter for a direct-conversion wireless receiver

Abstract: A highly selective and linear switched-capacitor channel-select filter is fabricated in 1-/spl mu/m CMOS for a direct-conversion wireless receiver operating in the 902-928 MHz ISM band. The filter selects a 230-kHz wide channel and attenuates by at least 50 dB from 320 kHz to 57 MHz. The input IP3 is +30 dBm, the input-referred noise in the passband is 70 nV//spl radic/Hz, and the circuit takes 4.6 mA from a 3.3 V supply. Direct subsampling of the 915 MHz RF input signal by the filter front-end is also demonstrated with only a small degradation in linearity. The input noise voltage is halved in a redesign while keeping the current drain unchanged.

Stochastic Resonance in Ensembles of Nondynamical Elements: The Role of Internal Noise

Abstract: While many examples of noise-induced signal enhancement have been reported, the role of internal noise has received little attention. Here we study aperiodic stochastic resonance in parallel arrays of nondynamical elements with internal noise. Ensembles of both threshold and threshold-free elements are studied, and the model is applied to two-state ion channels. In finite systems where the input signal controls the probability of discrete events, we demonstrate that the internal noise is modulated by both the applied signal and the external noise. We also show that the internal noise plays a constructive role in information transfer through such systems via an increase in external noise.

Active electronic noise suppression system and method for reducing snoring noise

Abstract: A system for attenuating noise which can be sensed by the auditory nerve comprising a microphone positioned in a first sound region for sensing noise present in the first sound region for creating a first electrical signal having a frequency and amplitude corresponding to the noise sensed in the first sound region. Circuitry is provided for processing the first electrical signal to create a second electrical signal having the same frequency but of opposite amplitude and sign of the first electrical signal. A speaker is provided for converting the second electrical signal to anti-noise for attenuation of the sensed noise in a second sound region spaced from the first sound region. A microphone is disposed in the second sound region for detecting any noise above a predetermined noise level in the second sound region to provide an error correction signal. Circuitry is provided responsive to the error correction signal to modify the second electrical signal to bring the noise in the second sound region so that it is below a predetermined noise level.

Direct temperature sensing of a semiconductor device semiconductor device

Abstract: An apparatus and method for directly measuring the operating temperature of a semiconductor device. A temperature sensor is placed directly on the substrate containing the device whose temperature is of interest. The circuitry used to process the sensor signals is on a separate substrate. Because the sensor is on the same substrate as the device of interest, noise is produced in the sensor signals as a result of electrons injected into the substrate by the device. The present invention includes methods for cancelling the noise and error in the temperature measurements to provide a very accurate determination of the device's operating temperature.

Four-wave mixing in semiconductor optical amplifiers: a practical tool for wavelength conversion

Abstract: Four-wave mixing in semiconductor optical amplifiers is used to produce wavelength conversion. We report an extended study on the dependence of efficiency and noise on device length, pump power, operation wavelength and conversion interval. The use of longer active regions is a good way to obtain performance as good as requested by the most advanced telecommunication systems.