Showing papers on "Noise (electronics) published in 1976"

Least - squares frequency analysis of unequally spaced data

Abstract: The statistical properties of least-squares frequency analysis of unequally spaced data are examined. It is shown that, in the least-squares spectrum of gaussian noise, the reduction in the sum of squares at a particular frequency is aX22 variable. The reductions at different frequencies are not independent, as there is a correlation between the height of the spectrum at any two frequencies,f1 andf2, which is equal to the mean height of the spectrum due to a sinusoidal signal of frequencyf1, at the frequencyf2. These correlations reduce the distortion in the spectrum of a signal affected by noise. Some numerical illustrations of the properties of least-squares frequency spectra are also given.

The generalized correlation method for estimation of time delay

Abstract: A maximum likelihood (ML) estimator is developed for determining time delay between signals received at two spatially separated sensors in the presence of uncorrelated noise. This ML estimator can be realized as a pair of receiver prefilters followed by a cross correlator. The time argument at which the correlator achieves a maximum is the delay estimate. The ML estimator is compared with several other proposed processors of similar form. Under certain conditions the ML estimator is shown to be identical to one proposed by Hannan and Thomson [10] and MacDonald and Schultheiss [21]. Qualitatively, the role of the prefilters is to accentuate the signal passed to the correlator at frequencies for which the signal-to-noise (S/N) ratio is highest and, simultaneously, to suppress the noise power. The same type of prefiltering is provided by the generalized Eckart filter, which maximizes the S/N ratio of the correlator output. For low S/N ratio, the ML estimator is shown to be equivalent to Eckart prefiltering.

Properties of speckle integrated with a finite aperture and logarithmically transformed

Abstract: When image plane speckle intensity integrated over a finite aperture is submitted to a logarithmic transformation, the noise becomes additive and signal independent. The first- and second-order moments of the probability distribution are derived. It is found that the logarithm of speckle noise approaches a normal distribution much faster than speckle intensity. The properties of speckle noise are different from those of film-grain noise; for example, neither Nutting’s law nor Selwyn’s law is satisfied by speckle.

The relation between intercellular coupling and electrical noise in turtle photoreceptors.

Abstract: 1. Intracellular recordings from cones and rods in the retina of the turtle, Pseudemys scripta elegans, revealed that in darkness the cell voltage fluctuated spontaneously about its mean level. The fluctuations were reduced during bright steady illmination of the cell often to a level close to that obtained with the electrode outside the cell where the noise did not change significantly during illumination. 2. The magnitude of the intrinsic dark noise (voltage variance in darkness minus voltage variance in strong light) varied widely from cell to cell. In the noisiest cones it was about 0-4 mV2 while in quiet cones it was often as low as 0-01 mV2. The noise appeared radom and could be fitted by a Gaussian probability density function. 3. The spread of voltage in the network of coupled photoreceptors was estimated by measuring the spatial profile of the response to a brief flash of constant intensity moved across the retina. For a light stimulus in the form of a long narrow slit, the peak flash response usually decayed exponentially with displacement from the centred position. 4. For maximum responses less than about 5 mV in cones, the length constant of exponential decay, lambda, varied from less than 10 mum to greater than 35 mum, and the values obtained in opposite directions were often unequal. Background illumination did not significantly change lambda. In cells with extremely narrow spatial profiles, an exponential fit to the decay could not be made reliably. 5. Occasionally the spatial profiles had definite secondary peaks. In the most pronounced examples in a red-sensitive cone and in a rod the maxima were separated by about 20 and 50 mum respectively; for each, one peak was approximately as sharp as the optical stimulator while the second was broader. 6. Cones with short length constants displayed high dark noise while cones with long length constants were relatively quiet. 7. Three models of electrical coupling between cells were investigated: one based on a distributed network, one on a discrete square grid arrangement, and one on a discrete hexagonal array. Each model predicts a strong dependence of both noise and input resistance on length constant, and for tightly coupled cells each predicts that voltage variance is proportional to lambda-2. 8. The measured relationship between voltage variance and lambda in a large sample of cones was well described by both discrete models when the average cell spacing was taken to be approximately 15 mum. 9...

Statistical limitations in x-ray reconstructive tomography

Abstract: Statistical fluctuations, or noise, in reconstructed tomograms are analyzed as a function of x-ray energy. The result is essentially constant for energies above 50 keV, assuming constant dose and spatial resolution, and is in close agreement with the actual performance of the EMI-Scanner (water-bag model). The noise is inversely proportional to the square of cell dimensions. For scanners without a water bag, the theoretical noise is approximately 30% less.

Measurement of the conductance of the sodium channel from current fluctuations at the node of Ranvier.

Abstract: Single myelinated nerve fibres of Rana esculenta were investigated under voltage clamp conditions at 13 degrees C. Fluctuations of steady-state membrane current were measured during the last 152 msec of 190-225 msec pulses depolarizing the membrane by 8-48 mV. Noise power spectral densities were calculated in the frequency range of 6-6-6757 Hz. 2. External application of 150 nM tetrodotoxin (TTX) and/or 10 mM tetraethylammonium (TEA) ion reduced the current fluctuations. The difference of current noise spectra measured in the presence and absence of TTX (TEA) was not changed by the presence of TEA (TTX) during both measurements, and was taken as the spectrum of the Na (K) current fluctuations. 3. Residual current noise during application of both TTX and TEA was, except for some excess noise at the low and high frequency ends of the spectrum, similar to the noise measured from a passive nerve model and could be understood in terms of Nyquist noise of the known resistances and the amplifier noise. 4. Na current fluctuation spectra were interpreted as the sum N/f+SNa(f) where SNa(F) represents the spectrum expected for a set of equal, independent Na channels with only two conductance states (open or closed) which follow Hodgkin-Huxley kinetics. With values of hinfinity, tauh and minfinity measured from macroscopic Na currents, the measured spectra were fitted well by optimizing N, SNa(0) and taum. Values of taum obtained by this method were in fair agreement with values found from macroscopic currents. 5. The 1/f component of Na current noise was roughly proportional to the square of the steady-state Na current, I2. The mean value of N/I2 was (1-1 +/- 0-3) X 10(-4). 6. The current carried by a single Na channel was calculated from fitted spectra and steady-state Na currents measured simultaneously with the current fluctuations. The single channel conductance gamma normalized to zero absolute membrane potential was calculated. The average gamma from twelve measurements at depolarizations of 8-40 mV was 7-9 +/- 0-9 pS (S.E. of mean). The apparent value of gamma was smallest with small depolarizations. Variations of the assumed kinetic properties of the model did not drastically affect the single channel conductance. 7. External application of 0-1 mM-Ni ion lengthened taum in the macroscopic currents and in the fluctuation spectra and enhanced both the steady-state Na current and the current fluctuations. In Ni-treated nodes gamma was smaller than in normal nodes.

PSK Performance with Imperfect Carrier Phase Recovery

Abstract: Methods are given to determine the performance loss caused by imperfect or noisy phase recovery and its use in coherent detection of a PSK signal. Numerical results for both binary and quaternary systems are presented so that these results combined with the characteristics of the phase recovery circuit will enable the "best" practical design of a PSK receiver. lt is assumed that the phase noise associated with the recovered carrier can have a nonzero mean and a Gaussian or a truncated Gaussian-type distribution. The static error of the phase noise is mostly due to offset frequency tracking of the phaselocked loop used to recover the carrier, but may also include an equivalent phase error produced by the comparator dead zone. The random component of the phase noise is due to thermal noise present in the recovery circuit and is also due to the random modulation that may be present on the carrier. Two plausible probability density functions are assumed for the random component of the phase noise to study the sensitivity of the detection results to the detailed characteristics of the phase noise. For small values of static error and phase noise variance and for moderate values of signal-to-noise ratio, it is shown that the two models of the probability distribution give essentially the same results. Since the exact method of determining the performance is rather complex, we also present some simple upper bounds.

Performance of GaAs MESFET Mixers at X Band

Abstract: A theoretical analysis and experimental verification of the signal properties of the GaAs MESFET mixer are presented. Experimental techniques for evaluating some of the mixer parameters are described. Experiments performed on GaAs MESFET mixers at X band show that good noise performance and large dynamic range can be achieved with conversion gain. A conversion gain over 6 dB is measured at 7.8 GHz. Noise figures as low as 7.4 dB and output third-order intermodulation intercepts of +18 dBm have heen obtained at 8 GHz with a balanced MESFET mixer.

Asymptotically robust detection of a known signal in contaminated non-Gaussian noise

Abstract: The Tukey-Huber contaminated noise model is used toobtain rain-max detectors in the asymptotic case for known signals inadditive noise. According to this model, the noise density f(x) is defined by f(x) = (1 - \ )g(x) + \varepsilon h(x) for a given \varepsilon and density g(x) , with h(x) an arbitrary density from a large class. A general theorem is obtainedspecifying the most robust detector for additive contaminated noisewith g(x) satisfying certain regularity conditions. As an example,detector structures are derived by the application of the theorem for the case where g(x) belongs to the class of generalized Gaussian densities(parameterized by their rates of exponential decay). The sign detector is shown to be the asymptotically most robust detector when g(x) is a double-exponential density.

Determination of intermittency from the probability density function of a passive scalar

Abstract: The probability density functions of temperature in the intermittent regions of heated jet and wake flows show a strong spike associated with the temperature of the unheated fluid. The fine structure of this spike fits a Gaussian curve quite closely, and the area under this Gaussian gives an accurate measure of 1−γ where γ is the intermittency factor. The standard deviation of the Gaussian is a measure of the noise due to residual temperature fluctuations in the free‐stream and the electronic noise in the measurement system. The accuracy with which the intermittency can be determined is limited by the signal‐to‐noise ratio.

Statistical evaluation of the error rate of the fiberguide repeater using importance sampling

Abstract: Simulation of repeaters for an optical-fiberguide digital-communication system requires the calculation of the statistical error rate of the signal. The calculations of these error rates are difficult because of the non-gaussian nature of the noise in the optical detector. In this paper, statistical techniques are described which are useful for simulating tails of distributions. In particular, the importance-sampling procedure is used to modify the probability densities of the input values in a way that makes simulation possible. Application of this procedure gives more accurate results in reasonable computer times. The method is applied to the calculation of the error rate of a fiberguide repeater. Realistic examples are simulated. Results compare favorably with experimental measurements. The number of samples needed for simulation was reduced by five to six orders of magnitude. An alternative numerical solution to the problem is also developed.

A Feedback Receive Amplifier for Optical Transmission Systems

Abstract: We consider the design and implementation of a lownoise feedback receive amplifier for use in optical communication systems. The feedback amplifier configuration is advantageous in that it offers a wide bandwidth with good signal to noise ratio.

Noise in buried channel charge-coupled devices

Abstract: The authors discuss the noise measured at the output of a buried channel charge-coupled device (BCCD) linear shift register. The measured noise arises from four sources; the electrical insertion of signal charge, the output amplifier, dark current, and bulk state trapping. In making these measurements the concept of correlated double sampling was used in an output circuit which had a noise level which was equivalent to less than 30 noise electrons.

Noise and admittance of the generation—Recombination current involving SRH centers in the space-charge region of junction devices

Abstract: A collective transport-noise theory is given for the effects caused by generation-recombination current via traps in the space-charge region of a p-n junction. Langevin noise sources are added to the standard kinetic equations, which are subsequently solved for the current noise. No hypotheses are made on the coupling of the g-r current to the external circuit. In particular, Ramo's theorem does not apply, though similar transport factors emerge automatically as a consequence of the inclusion of displacement current. With the assumption that the free carrier transit times are very short, exact agreement with Lauritzen's [3] previous results, based on a probabilistic approach, is found. In addition, the admittance is computed from the same equations and is shown to be frequency dependent, contrary to standard assumptions made for the computation of emitter efficiency. Consistency with Nyquist's theorem is obtained for the low and high frequency regime. The noise reduction factors for forward biased junctions are discussed.

Analysis of bilinear noise models in circuits and devices

Abstract: There are a number of applications in which linear noise models are inappropriate. In the paper, the use of bilinear noise models in circuits and devices is considered. Several physical problems are studied in this framework. These include circuits involving varying parameters (such as variable resistance circuits constructed using field-effect transistors), the effect of switching jitter on sampled data system performance and communication systems involving voltage-controlled oscillators and phase-lock loops. In addition, several types of analytical techniques for stochastic bilinear systems are considered. Specifically, the moment equations of Brockett for bilinear systems driven by white noise are discussed, and closed-form expressions for certain bilinear systems (those that evolve an Abelian or solvable Lie groups) driven by white or colored noise are derived. In addition, an approximate statistical technique involving the use of harmonic expansions is described.

Narrow-Band Excitation of a Nonlinear Oscillator

Abstract: A nonlinear oscillator characterized by a hardening-type restoring force is excited by stationary narrow-band noise. The analysis is based on the concept of quasi-static amplitude and phase values which is exactly opposite to the stochastic or Markov approach with its associated Fokker-Planck equation. The approach, in effect, replaces a system with memory with one without memory. The existence of jumps is demonstrated and an expression for the probability of the occurrence of jumps is derived.

An efficient spectroscopic detection system for cathodoluminescence mode scanning electron microscopy (SEM)

Abstract: SUMMARY A detection system for analytical cathodoluminescence (CL) mode scanning electron microscopy (SEM) is described. This incorporates a cold stage, an efficient light collector, a monochromator and a photomultiplier and used the photon counting technique. The efficiency of the component subsystems was optimized and calibrated, and the performance of alternative light collecting and monochromating equipment is compared. The operation of the photon counter is discussed. The digital output of the photon counter was fed into a multichannel scaler and thence to a computer. This was used to correct the observed count rate with the calibrated spectral variations in the performance of the detection system. Spectra obtained at both room temperature and liquid nitrogen temperacure and monochromatic and panchromatic SEM micrographs are given as examples illustrating the value of this technique. The factors governing the performance of the system are discussed. The forms of noise in the signal and in the detection system are described and the means for minimizing, avoiding or correcting for them are dealt with. Sources of spurious signals in the SEM are treated.

Critical assessment of pyroelectric detectors

Abstract: A critical assessment of the pyroelectric detector is given. The response function and noise sources are reviewed and an optimal procedure to reach the practical performance limit defined by material thermal noise is presented. The temperature dependent characteristics of the detector are described and the figure-of-merit of the detector is discussed.

Temperature noise and dielectric loss in pyroelectric detectors

Abstract: It is shown theoretically and experimentally that the presence of thermal conductance between a pyroelectric material and its environment affects significantly its measured dielectric loss. Depending on the details of the heat exchange with the environment, this thermal contribution to the measured dielectric loss tangent can be larger than the intrinsic loss tangent of the material, i.e., loss due to domain wall motion, defects, and impurities. In detectors fabricated from LiTaO3, temperature fluctuations due to this thermal conductance, known as temperature noise, are observed to limit the normalized detectivity (D*).

The vertical array in reflection seismology—some experimental studies

Abstract: There are several advantages in using vertical arrays for recording reflected signal. Signal-to-noise ratio can be controlled to any desired level when the noise is due to scattering from layers shallower than the depth to the array. By the use of vertical arrays, the band width of useable seismic energy can be increased, events can be properly identified, the signal that eventually produces near surface induced multiples can be measured, as well as the direct pulse radiated from the source and its accompanying ghosts. A field test documents these predictions.

Performance of GaAs MESFET's at Low Temperatures (Short Papers)

Abstract: The noise- and s-parameters of a GaAs MESFET with 1-mu m gate Iength are characterized versus temperature. At room temperature, the noise figure measured at 12 GHz is 3.5 dB. At 90 K, the noise figure decreases to 0.8 dB (T/sub e/ = 60 K). The associated gain is 8 dB. The design of a cooled amplifier for the 11.7-12.2-GHz communication band is discussed. At 60 K, the three-stage amplifier exhibits 1.6-dB noise figure (T/sub e/ = 130 K) and 31-dB gain.

Operation of the SUPARAMP at 33 GHz

Abstract: A 9‐mm degenerate parametric amplifier has been constructed using a linear series array of unbiased Josephson junctions as the active nonlinear element. We used a balanced diode mixer as a synchronous detector, with a single source serving both as the pump and as the mixer local oscillator. A stable net gain of 15 dB in an instantaneous bandwidth (FWHM) of 3.4 GHz has been achieved. We measured a system noise temperature of 220±5 K (DSB) with a SUPARAMP contribution of only 20±10 K. Output saturation, however, has been observed. This complicates the interpretation of our noise‐temperature measurements and may render them upper limits. Comparison is made with the results of an earlier 3‐cm SUPARAMP. The data are in substantial agreement with theoretical predictions.

Acoustic liner optimum impedance for spinning modes with mode cut-off ratio as the design criterion

Abstract: The theoretical optimum acoustic impedance for higher order spinning modes was studied in cylindrical ducts with a boundary layer at the outer edge of a uniform flow. All of the propagating modes were considered from highly propagating to nearly cut-off. It was observed that the mode cut-off ratio uniquely determined the optimum wall impedance and maximum possible attenuation for a given boundary layer thickness, Mach number and frequency. The implications of this phenomenon are quite important in noise suppressor design. Instead of the acoustic power distribution among all of the propagating modes, only the power distribution as a function of cut-off ratio needs to be known. Also, the far field radiation pattern is a function of modal cut-off ratio, and much needed information for liner design can be obtained from these more easily obtained data.

Sensor and suspensions for a low‐temperature gravitational wave antenna

Abstract: A dc‐biased resonant capacitor sensor for cylindrical gravitational antennas is discussed. For appropriate tuning and Q, its noise is found to be below the thermal noise of such antennas down to millidegree temperatures. ’’Ring’’ and ’’knife edge’’ suspensions of antennas are also discussed as possible alternates to wire and magnetic suspensions.

Submicron Single-Gate and Dual-Gate GaAs MESFET's with Improved Low Noise and High Gain Performance

Abstract: Microwave performance of single-gate and dual-gate GaAs MESFET's with submicron gate structure is described. Design consideration and device technologies are also discussed. The performance of these GaAs MESFET's exceeds previous performance with regard to lower noise and higher gain up to X band: 2.9-dB noise figure (NF) and 10.0-dB associated gain at 12 GHz for a 0.5-mu m single-gate MESFET, and 3.9-dB NF and 13.2-dB associated gain at the same frequency for a dual-gate MESFET with two 1-mu m gates.

Enhanced fluctuations in radiation scattered by a moving random phase screen

Abstract: We discuss the properties of enhanced non-Gaussian fluctuations that occur in radiation scattered by a moving deep random phase screen (e.g., a perfectly conducting, very rough surface) when the scattering configuration is such that the electric field at the point of observation is composed of relatively few independent randomly phased contributions. Fraunhofer and Fresnel region effects are considered both from the information-content point of view and in the context of unwanted noise in measuring and detection systems.