Showing papers on "Noise (electronics) published in 1975"

Potassium and sodium ion current noise in the membrane of the squid giant axon.

Abstract: 1. The spectral density of current noise power from 20 mm segments of giant axons of the squid Loligo vulgaris has been measured under space-clamp and voltage-clamp conditions. From 4 to 1000 Hz the measured noise is larger by several orders of magnitude than the theoretical thermal noise. The amplifier's noise, which may yield appreciable contributions above 200 Hz, could be evaluated and subtracted from the total noise using direct measurements of the membrane impedance...

Signal-to-noise ratio of electron micrographs obtained by cross correlation.

Abstract: The signal-to-noise ratio of electron micrographs can be determined by two-dimensional digital cross correlation even though neither signal nor noise can be analysed separately. Such measurements suggest how best to make use of the electron microscope.

Measurement of the Short-Term Stability of Quartz Crystal Resonators and the Implications for Crystal Oscillator Design and Applications

Abstract: A new technique is presented which makes it possible to measure the inherent short-term stability of quartz crystal resonators in a passive circuit. Comparisons with stability measurements made on crystal controlled oscillators indicate that noise in the electronics of the oscillators very seriously degrades the inherent stability of the quartz resonators for times less than 1 s. A simple model appears to describe the noise mechanism in crystal controlled oscillators and points the way to design changes which should improve their short-term stability by two orders of magnitude. Calculations are outlined which show that with this improved short-term stability it should be feasible to multiply a crystal controlled source to 1 THz and obtain a linewidth of less than 1 Hz. In many cases, this improved short-term stability should also permit a factor of 100 reduction in the length of time necessary to achieve a given level of accuracy in frequency measurements.

Noise in the rf SQUID

Abstract: This paper presents the results of an extensive study of the sensitivity-limiting noise sources in rf-biased SQUID flux detectors. Our investigation has included both experiments with point contact and thin-film SQUIDs and digital computer simulations. The paper begins with a discussion of rf SQUID operation, with special emphasis on those aspects that determine flux detector sensitivity. We then discuss the origin and consequences of intrinsic device noise in rf SQUID systems. We describe a straightforward technique for determining intrinsic noise amplitude directly from SQUID rf I–V characteristics. Deviations in the measured intrinsic noise of many devices from the Kurkijarvi-Webb prediction are attributed to departures from the ideal Josephson sinusoidal current-phase relation in the SQUID weak link. Kurkijarvf's SQUID tank circuit noise analysis is reviewed and we show how SQUID sensitivity can be maximized by an optimal coupling between SQUID ring and tank circuit. This optimal coupling depends upon circuit parameters, ring inductance, and weak-link properties. The analysis reveals that variations in the current-phase relation can result in a difference of as much as a factor of ten in the attainable sensitivity of two otherwise identical SQUID systems. We also suggest efforts in circuit design that are most likely to lead to further improvements in flux detector sensitivity. Finally, other factors, including external magnetic noise and underdamping of the SQUID ring, are discussed.

Correlation analysis of electrical noise in lipid bilayer membranes: kinetics of gramicidin A channels.

Abstract: If a membrane contains ion-conducting channels which form and disappear in a random fashion, an electric current which is passed through the membrane under constant voltage shows statistical fluctuations. Information on the kinetics of channel formation and on the conductance of the single channel may be obtained by analyzing the electrical noise generated in a membrane containing a great number of channels. For this purpose the autocorrelation function of the current noise is measured at different concentrations of the channel-forming substance. As a test system for the application of this technique we have used lipid bilayer membranes doped with gramicidin A. From the correlation time of the current noise generated by the membrane, the rate constants of formation (kR) and dissociation (kD) of the channels could be determined. In addition, the mean square of the current fluctuations yielded the single-channel conductance Λ. The values ofkR,kD, and Λ obtained from the noise analysis agreed closely with the values determined by relaxation measurments and single-channel experiments.

Study of a field‐ionization source for microprobe applications

Abstract: Operating parameters for a field‐ionization source have been measured. Sensitivities of 5×10−5 A sr−1 Torr−1 were found at 77 K. Angular distributions are uniform near ϑ=0° and show the beam to be confined to ±20°. The beam signal‐to‐noise ratio was found to increase with increasing current. Calculations based on parameters of lenses in use indicate a resolution of 0.1 μm at ≳10−10 A is possible.

Surface potential equilibration method of setting charge in charge-coupled devices

Abstract: A method of setting charge in a charge-coupled device (CCD) is described whereby the input diode is suitably pulsed and an amount of charge is retained in a potential well under the first transfer electrode. It is shown that, within limits defined by the operating potentials of the device, the sizes of the generated charge packets are linearly dependent on the voltage difference between the first transfer electrode and the input gate. They are also independent of threshold voltage. The method has important applications in all CCD's where it is necessary to obtain a linear low noise charge input that is uniform from one device to another. The linearity has been demonstrated with a 64-element CCD which with a sinusoidal input shows second and third harmonics to be 40 dB down from the fundamental. Measured rms input noise was above the minimum theoretically achievable value but was still 80 dB down from the peak signal level. The electrode area was 2000 μm2. For a comprehensive review on CCD's and input circuits, see [10].

Correction functions for optimizing the reconstructed image in transverse section scan.

Abstract: Two correction functions are derived for one- and two-dimensional convolution methods for reconstructing a section image from multiple projections. The functions are optimized to yield a maximum 'signal-to-noise power ratio' for a given RMS resolution width, where 'signal power' is the integrated squared line spread function (signal power regarding one-dimensional position information per count) and 'noise power' is the variance of the image density at the centre of a locally uniform source. The point spread function of the reconstructed image is Gaussian, and the standard deviation of noise associated with a locally uniform image is found to be proportional to D-32/, where D is the RMS resolution width. The autocovariance function for uniform noise is also given.

Ultrasonic method and apparatus for imaging and characterization of bodies

Abstract: Method and apparatus are provided for the determination of the Raylographic information of a body part which is ensonified by acoustical energy pulses by a particularly precisely focused acoustical focusing system to produce acoustical energy echo pulses which are detected in coherent manner Fourier transformation of the pulses from the time to the frequency domain enables frequency domain deconvolution to provide the impulse response with minimization of mathematical instabilities and distortion of the frequency domain impulse response Noise extraction and spatial deconvolution filtering are included to respectively maximize signal to noise ratio and minimize distortive effects of body part surface non-orthogonality and combine with the above to provide for particular stability in the overall results and attendant increase in the axial resolution of Raylographic display and in the overall resolution of body part image displays

Coupling considerations for SQUID devices

Abstract: Most applications of superconducting quantum interference devices (SQUID’s) involve use of a coupling coil. There are two classes of such applications: magnetometry (magnetic field, field gradient) and voltage or current measurements. We have analyzed the factors which determine the ultimate sensitivity, and present a guide for optimization of signal/noise in each of the two cases. It is found that a single figure of merit, involving both the equivalent input noise of the SQUID and the effectiveness of the coupling to the coil, is applicable to either type of measurement. We propose that this figure of merit be used in evaluating the performance of new SQUID designs.

Applications of electrical noise

Abstract: The omnipresent noise in electronic circuits and devices is generally considered undesirable. This paper describes some of the applications to which it has been put. Short descriptions of a wide variety of applications are given together with references for further details. The applications fall in four categories: applications in which noise is used as a broad-band random signal; measurements in which the random noise is used as a test signal; measurements in which noise is used as a probe into microscopic phenomena; and the applications where noise is a conceptual or theoretical tool. Many examples of applications in each of these categories are given. Some of the applications included are only of historical interest now, and a few are, as yet, only proposals.

Noise characteristics of current mirror sinks/sources

Abstract: General expressions of the limiting and excess noise currents generated by a current mirror sink/source are derived. The analysis, restricted to low and audio frequencies, shows the effect of the transistor base resistance and the noise reduction due to the external emitter degeneration. By means of a computer-aided design (CAD) analysis, spectral density frequency plots are computed, and the total noise content in the audio band calculated for the case of a typical 1/f excess noise generator. The noise characteristics of other current source topologies are compared and shown to be quite similar to the basic current mirror. Noise measurements of current mirrors implemented with IC transistor pairs showed a good correlation with the previous analytical and CAD results.

Spectral damping in Barkhausen noise

Abstract: The spectral amplitude damping of Barkhausen noise is determined theoretically and experimentally as a function of distance inside the sample itself. Power spectra for noise amplitude and its time derivative are measured in some steel specimens over a wide frequency range. Some examples of the influence of the sample microstructure on the power spectra are also examined. The results, including spectral damping, suggest that the nature of Barkhausen noise changes continuously from nonrandom to random either with the thickness of the sample (0.1-5 mm) or with increasing magnetizing frequency (10-2-102Hz). This phenomenon as a whole is explained in terms of the clustering of elementary magnetization transitions.

Excess electrical noise during current flow through porous membranes separating ionic solutions.

Abstract: Spectral analysis of electrical noise from various artificial membrane systems suggests that excess noise of anf −n spectral form, wheren is approximately unity, is not primarily a bulk phenomenon simply dependent on the number of charge carriers. Measurements from aqueous and nonaqueous electrolytic resistors, comprised of several different ionic species, show only flat power density spectra under applied currents, even at extreme dilutions. Excess noise off −n form is observed under applied d-c current in single pore membranes, as previously reported, but is also seen in multipore and polymer mesh membranes. Calculations based on single pore membrane noise data are in significant variance with the bulk charge carrier model proposed by Hooge. These observations suggest that such excess noise occurs in conjunction with anisotropic constraints to ion flow.

Stability Considerations of Low-Noise Transistor Amplifiers with Simultaneous Noise and Power Match

Abstract: Microwave transistor amplifiers may be simultaneously matched for optimum noise and input/output VSWR This paper demonstrates a combination of mapping techniques, computer optimization and stability considerations through two amplifier designs (70 MHz and 4000 MHz) to achieve these goals

Responses of single units in the cochlear nucleus of the cat to cosine noise.

Abstract: The response of single cells in the cochlear nucleus of the cat to noise with a cosinusoidal power spectrum (cosine noise) was studied. Cosine noise is obtained by adding white noise to the same noise delayed over a time τ; maxima in the spectrum occur at n/τ (n=0,1,2,⋅⋅⋅). The spike rate of a unit was continuously registered as a function of τ (τ diagram). This registration shows a periodic fluctuation having maxima at τ=n/CF and troughs at τ= (n+1/2)/CF, with a decreasing peak–trough ratio for increasing n (CF is the characteristic frequency of the unit). For the majority of the units investigated, a maximal peak–trough ratio was observed not for n=0 but for about n=3. This is ascribed to lateral inhibition. By introducing the mathematical concept of a weighting function in the frequency domain, a quantitative relation with the response of the unit to a pure tone in white noise (iso‐intensity curve) could be established. The results are compared with psychophysical results on the internal representation...

Digital matched filtering with pipelined floating point fast Fourier transforms (FFT's)

Abstract: A special floating point arithmetic technique for fast Fourier transform (FFT) processors has been developed. The implementation of a high-speed pipeline FFT matched filter using the method employs significantly fewer components than a fixed-point processor with an equivalent performance level. The special floating point process avoids the nonlinear effects of fixed-point processors while achieving performance levels of traditional floating point arithmetic. Computer simulations were used to examine the performance of the system for linear FM pulse compression under a variety of conditions. In a specific case, with 8 bits plus sign quantization of the complex I- and Q-mantissa words in the processor and a 12-stage (4096-coefficient) FFT convolver, the mean square error (MSE) of the sidelobes relative to the peak from a single point target was less than -70 dB. Changes in waveform duration and sampling rate had negligible effect on the error level. This error characteristic can be treated as a computational or self noise, added to the input thermal noise of the radar receiver. Quantization artifacts or noise peaks which occur at levels consistent with the mantissa quantization are below levels (-50 dB for 8 bits plus sign) which would normally cause difficulty in an operational system.

Introducing signal at low noise level to charge-coupled circuit

Abstract: The first potential well of a charge-coupled device (CCD) register is initially filled from a source diffusion and then the effective depth of this well is reduced and the excess charge removed. The depth reduction and charge removal may be concurrently accomplished by changing the relative potential between the source diffusion and the electrode or electrodes producing the first potential well in a sense to cause this diffusion to operate as a drain for the excess charge. The charge remaining in the first potential well is relatively noise free, that is, it is at a predictable and reproducible level.

A Gaussian sum approach to phase and frequency estimation

Abstract: In this paper, a theory of optimal nonlinear estimation from sampled data signals where the a posteriori probability densities are approximated by Gaussian sums is adapted for application to phase and frequency estimation in high noise. The nonlinear estimators (demodulators) require parallel processing of the received signal. In the limit as the number of parallel processors becomes infinite the FM demodulators become optimum in a minimum mean square error sense and the PM demodulators become optimum in some well defined sense. For the clearly suboptimal case of one processor, the demodulators can be readily simplified to the familiar phase-locked loop. On the other hand, for the intermediate case, significant extension of the phaselocked loop threshold is achieved where (say) six parallel processors are involved.

Analog transversal filtering and correlation with progressive summation of analog signals

Abstract: "Progressive summation" of analog signals with a parallel-in/serial-out (P/I/SO) CCD structure replaces the conventional "simultaneous summation" of analog signals in serial-in/parallel-out (SI/PO) structured systems. Gain non-uniformities presented by buffer circuits and caused in part by threshold non-uniformities are avoided; on-chip power consumption is reduced, thereby avoiding a source of further exaggeration of gain non-uniformities of buffer circuits. Transversal filtering and correlation systems in accordance with the invention accordingly are achieved with these problems of prior art circuits avoided. Reduced power consumption on-chip also maintains more reasonable and constant operating temperature levels, avoiding deleterious effects of temperature increases on dynamic range of CCD systems due to leakage current levels which sharply increase with increased temperature, contributing noise and reducing the maximum charge potential of the CCD wells available for signal.

Optimum direct detection for digital fiber-optic communication systems

Abstract: We report on optimum direct detection of digital data signals that are transmitted over optical fibers. Direct detection is provided by a photodetector whose output current is modeled as a noisy filtered Poisson stream of pulses. In this model, the time-varying pulse arrival rate is proportional to a linearly distorted version of the modulating signal. We show how the photodetector output is processed to derive the minimum probability-of-error receiver. Special attention is given to certain practical limiting cases. When the average energy in the response of the photodetector to an individual photon is small compared to the additive thermal noise, the optimum detector is shown to be linear except for the use of precomputed bias terms. At the other extreme are the photomultiplier and the avalanche photodiode where the average energy in the response of the photodetector to a single photon is large compared with the additive noise. In this situation, we show that the optimum detector estimates the photon arrival times and then uses these estimates in a weighted counter. In both limiting cases, the detectors are specialized to one-shot M-ary and synchronous multilevel pulse-amplitude modulated (pam) signals with intersymbol interference. For pam signaling, we demonstrate that finite system memory allows application of dynamic programming to provide a detector implementation whose computational complexity does not increase with time.

Impulsive Noise in Noncoherent M-ary Digital Systems

Abstract: This concise paper analyses the performance of noncoherent M -ary digital systems in presence of a generalized stationary Poisson impulsive noise process, with a receiver operating as a maximum likelihood detector in white Gaussian interference. Methods to bound the error probability for ASK, PSK, and FSK systems in the cases where the noise is impulsive and quasi-Gaussian are described and the results discussed.

Filtering for Systems Excited by Poisson White Noise

Abstract: The application of martingale theory to filtering problems for linear systems, excited by Poisson white noise but with Gaussian observation noise, is described. Stochastic differential equations for the conditional density function and moments are derived, and two approximate methods for solving these equations are developed. Numerical results are presented. Preliminary results are given for the smoothing problem, and for filtering problems for distributed parameter systems excited by Poisson white noise.

Some exact distributions in traffic noise theory

Abstract: The moment-generating function of the traffic noise from a stream of vehicles with identical noise emissions cannot be readily inverted. If the emissions are not equal, this generating function can be inverted to obtain the exact form of the distribution function in some particular cases. Noise intensity has a maximally skew stable distribution with exponent 1/2 for observers on the highway, whatever the distribution of emissions. The distribution at any distance from the highway is an exponentially modified stable law with exponent 1/2 for an improper exponential distribution of emissions, and an infinite series involving this stable law and iterated error functions when emissions have an exponential distribution. A doubly stochastic process for emissions produces distributions of traffic noise intensity in the domain of attraction of skew stable laws with exponent a, 1/2 < a < 2. The inverse Gaussian (exponentially modified skew stable law with exponent 1/2) is recommended as the best choice of a two-parameter family for fitting traffic noise intensity distributions.

Minimum-mean-square-error estimation of photon pulse delay (Corresp.)

Abstract: The minimum-mean-square-error (rose) estimation of the delay of a coherent pulse of photons by a direct-detection receiver is shown to depend on the shape of the pulse envelope. Whereas with smooth envelopes the minimum mse decreases only as the expected energy in the pulse, with sharp-edged envelopes it decreases as its square, provided the optimum estimator is used. Occurrence of photoelectrons due to additive noise increases the rose by an additional term, proportional to the expected intensity of the noise. It approximately equals the photon-limited term at a signal-to-noise power ratio of 17 dB in the case of rectangular envelopes.

Process and apparatus for filament or slit size monitoring

Abstract: Method and apparatus for determining the width of an elongated element, such as a filament or slit which comprise producing a moving interference fringe zone by converging two beams of coherent light of the same intensity but slightly different frequency; positioning the element within the fringe zone in such manner that the longitudinal axis of the element is substantially normal to the plane of the convergent beams, namely, parallel to the plane of the fringes; maintaining the element substantially spatially stationary relative to the zone, whereby the moving fringe pattern continuously sweeps across the element; and determining the ratio of the AC to DC signal components of the radiation scattered or transmitted by the element. The method and system include respectively the step and means therefor of adjusting or scanning the fringe period value around the element to determine the size capable of producing a minimum AC/DC ratio. In the case of a system substantially free from noise, including non-compensating optical noise factors introduced by the element being measured, a zero ratio indicates that the filament diameter or slit width equals the known fringe period, and a non-zero ratio indicates diameter or slit width deviation from the fringe period, the degree of which can be determined from the signal ratio with the use of known means by adjusting the fringe period until the AC component of the signal becomes zero. In the case of a system having a substantial amount of noise, the AC/DC minimum ratio obtained at a given fringe period may have a finite value and indicates an element width equal to the given fringe period times a constant, the constant being the ratio of the width of the given element and the given fringe period. The element, though spatially stationary in the fringe zone, can be continuously moving longitudinally. The process and system are particularly useful for monitoring the width of manufactured elements and, by automatic feedback, correcting deviations. In some applications where change in the magnitude of the DC signal component during the fringe period scan is sufficiently nominal with respect to permissible width-sensing error, the AC/DC ratio measurement can be dispensed with and determination of the AC signal component minimum alone can be employed.

Fourier analysis of random sequences

Abstract: Computer-generated random sequences were submitted to a Fourier analysis. The distribution of the phase angle was not uniform over the circle, but some “bald patches” remained. The Fourier analysis itself allows the construction of ideal random sequences. For an “ideal white noise” the amplitudes were chosen as one, whereas the phase angles were uniformly distributed. For an “ideal random noise” both phase angles and amplitudes were uniformly distributed. Thus, ideal noise patterns were obtained which were analysed statistically.