Showing papers on "Noise (electronics) published in 1972"

Detectors for discrete-time signals in non-Gaussian noise

Abstract: The structure and performance of a class of nonlinear detectors for discrete-time signals in additive white noise are investigated. The detectors considered consist of a zero-memory nonlinearity (ZNL) followed by a linear filter whose output is compared with a threshold. That this class of detectors is a reasonable one to study is apparent from the fact that both the Neyman-Pearson optimum and the locally optimum (i.e., weak-signal optimum) detectors for statistically independent noise samples can be put into this form. The measure of detector performance used is the asymptotic relative efficiency (ARE) of the nonlinear detector under study with respect to a linear detector appropriate for the same detection problem. A general expression for this ARE is given along with the result that the non-linearity maximizing this expression is any linear function of the nonlinearity in the appropriate constant-signal locally optimum detector. To illustrate the structure and performance of these nonlinear detectors for a wide range of non-Gaussian noise distributions, three general classes of symmetric, unimodal, univariate probability density functions are introduced that are generalizations of the Gaussian, Cauchy, and beta distributions.

Principles and methods of low-frequency electric and magnetic measurements using an rf-biased point-contact superconducting device

Abstract: A comprehensive study has been made of some low-frequency electric and magnetic measurements which can be made using an rf-biased point-contact superconducting device of the symmetric two-hole type introduced by Zimmerman. Section 1 begins with a qualitative description of the phenomena which are observed and utilized in making the measurements. In Section 2 a semiquantitative and semiempirical analysis is made of the weakly superconducting system as it interacts with the rf field. Reasonable agreement between the analysis and experiment is obtained, thereby establishing a basis for optimization of conditions for measurement. Empirical data are also given as needed on coupling-coil characteristics. In Section 3 noise in the measuring system is discussed and the characteristics of the flux-locked loop used in the measurements introduced. It is shown that the total observed noise may be divided into at least three parts: one intrinsic to the sensor, one which reflects voltage noise in the amplifier, and one coupled into the instrument by the measuring circuit. The noise power spectra of the first two are shown to be comparable in an actual system. Below 100 Hz the spectrum, relative to the square of the flux quantum, is white and estimated by 10−8 Hz−1. In Section 4 the characteristics are discussed of a dc voltmeter using a flux-locked loop and having a relatively high input impedance and good noise figure. An experimental study of noise is presented. A particular case with subpicovolt sensitivity limited by Johnson noise is discussed. In Section 5 low-frequency ac measurements of resistance, self-inductance, and mutual inductance are discussed using a novel bridge circuit and the superconducting sensor in a flux-locked loop as null detector. The noise characteristics are described and studied experimentally. Extreme sensitivity is achieved, both in resistance and inductance. A 1 µω resistor may be measured with a precision of 1 part in 105 with subpicowatt power dissipation. Measurements of the mutual inductance due to a 1.6-mg crystal of CMN are described in which the crystal temperature was reduced to the millidegree region. In Section 6 measurements of static magnetization are discussed and the ideas applied to measurement of temperature using milligram quantities of CMN. Measurements using a pair of thermometers, one inside and the other outside the mixing chamber of a dilution refrigerator, are presented. In Section 7 the concept of a device-noise temperature is introduced and shown to be in the microdegree region. A very simple Johnson noise thermometer is then described. Measurements with this thermometer in the mixing chamber of a dilution refrigerator were carried out to 12 mK, the effective device temperature being measured to be +0.8±1.3mK. A qualitative experimental estimate places the actual device temperature well below 1 mdeg. In appendices a technical discussion of the flux-locked loop and of noise is given.

Statistics of atomic frequency standards

Abstract: A theoretical development is presented which results in a relationship between the expectation value of the standard deviation of the frequency fluctuations for any finite number of data samples and the infinite time average value of the standard deviation, which provides an invariant measure of an important quality factor of a frequency standard. A practical and straightforward method of determining the power spectral density of the frequency fluctuations from the variance of the frequency fluctuations, the sampling time, the number of samples taken, and the dependence on system bandwidth is also developed. Additional insight is also given into some of the problems that arise from the presence of "flicker noise" (spectrum proportional to |ω|-1) modulation of the frequency of an oscillator. The theory is applied in classifying the types of noise on the signals of frequency standards made available at NBS, Boulder Laboratories, such as: masers (both H and N15H 3 ), the cesium beam frequency standard employed as the U. S. Frequency Standard, and rubidium gas cells. "Flicker noise" frequency modulation was not observed on the signals of masers for sampling times ranging from 0.1 second to 4 hours. In a comparison between the NBS hydrogen maser and the NBS III cesium beam, uncorrelated random noise was observed on the frequency fluctuations for sampling times extending to 4 hours; the fractional standard deviations of the frequency fluctuations were as low as 5 parts in 1014.

Thermal effects in JFET and MOSFET devices at cryogenic temperatures

Abstract: Various JFET and MOSFET devices have been studied at LN and LHe temperatures. Transient and steady-state heating of the devices at 4.2 K is investigated and it is found that the active part of the device typically heats to a steady-state temperature of 40-60 K. A transient and steady-state heating model of the device is constructed and the results are found to be in good agreement with the measured temperatures and heating transients. Studies of the noise at the various ambient temperatures show that different physical phenomena are responsible for the noise. Low-frequency noise in JFET's seems to be of generation-recombination type. Thermal noise is prevalent in the frequency region between 100 kHz and 1 MHz. The noise in some of the MOSFET devices increases with decreased temperature and seems to be surface state or "flicker" noise, The noise in MOSFET devices is by factor 5-100 times larger than the noise in investigated JFET devices.

General transport theory of noise in pn junction-like devices—I. Three-dimensional Green's function formulation

Abstract: A general collective treatment of noise in three-dimensional junction devices of arbitrary geometry is presented, using Green's functions as in recent transport noise theories. The low-injection theory is extended to open-circuited devices. The density spectra are given in a form in which the volume part is linear in the Green's function and the covariance function, while the surface part is quadratic in the Green's function. The density covariance function for the short-circuited junction is Poissonian for low injection, except for a surface singularity. The noise input e.m.f and output current generator, as well as their cross correlation, are found directly for the hybrid transistor model and are expressed in the h ′ parameters, without the usual network transformation. The exact results indicate distributed effects; in particular, the current gain in the noise expressions (α noise ) is not equal to the small signal current gain α. The one-dimensional standard results are recovered in a lumped model approximation. For high injection, only the case of quasi band-band recombination (the Shockley-Read levels have equal capture probabilities for electrons and holes) is considered in this paper. The covariance function is then as for low injection but of half strength. The terminal noise depends, besides on the admittance or impedance and the current, on the emitter efficiency γ, the mobility ratio b , and the ratio of the junction admittance and the bulk admittance resulting from modulation effects. As a byproduct of this study, all pertinent network parameters are expressed in Green's functions.

Coherent sampled readout circuit and signal processor for a charge coupled device array

Abstract: A coherent sampled CMOS readout circuit and signal processor coupled to a CCD shift register operated by a two-phase minority carrier transfer clock system. The invention comprises a multiplex MIS switch, a reverse biased collection diode, an N channel MOSFET reset switch, a P channel MOSFET electrometer amplifier, and a sample and hold circuit, the configuration having four distinct operational timing sub-intervals within a clock period wherein the charge is shifted from one shift register bit to another and finally to the output bit. This removes the Nyquist noise associated with the reset switch, suppresses switching transients and 1/f surface noise to thereby improve the signal to noise ratio, i.e., dynamic range, for a CCD array and readout system.

Noise in IMPATT diodes: Intrinsic properties

Abstract: The design of low-noise IMPATT diodes has been aided by theories describing the noise generation under small-signal conditions. A major deficiency in this procedure has existed in that there is no apparent connection between the small-signal behavior and the great increases in the noise observed in large-signal operation. As a remedy a theory has been developed for the noise generation at arbitrary signal levels by using a Read diode model. The theory is based on a linearization technique for calculating the spectrum of homogeneous noise with linear damping resulting in a separation of the large-signal and noise problems. The open-circuit noise voltage increases strongly at high signal levels due to nonlinear parametric interactions and gives rise to a rapid increase in the noise measure as a function of the generated microwave power. Operating parameters are derived that optimize the power-noise ratio. A long intrinsic response time is found to be beneficial in achieving high power as well as low noise. Other factors affecting the design and choice of material for IMPATT diodes are discussed. An important feature of the presented theory is that a complete design optimization with respect to the power-noise characteristics can be carried out provided reliable information exists about the ionization rates and the drift velocities. A simpler alternative is to obtain the physical quantities governing the power-noise behavior from small-signal admittance and noise measurements. Good agreement has been obtained with experimental power-noise measurements by this method. As an application of this procedure a state of the art comparison is given for GaAs, Ge, and Si diodes at 6 GHz.

Submillimeter Wave Generation by Difference‐Frequency Mixing in GaAs

Abstract: Non‐phase‐matched generation of 29.9 cm−1 is obtained by difference mixing of pulsed CO2 laser radiation in room‐temperature GaAs, with a detection signal‐to‐noise ratio of 103. Calculations show that comparable results could be obtained from 10 to 200 cm−1.

Nonparametric detection using spectral data

Abstract: A detection system is considered that analyzes the spectrum of the time-series output from a sensing element. The spectral data consist of a matrix of estimates of the energy in many small time-frequency cells. A decision procedure is formulated that is based on the multiple use of a two-sample statistic operating on the columns of the matrix. If the input noise is Gaussian with unknown power, the asymptotically optimum statistic t is a ratio of two sample means. Since in certain applications the Gaussian input assumption may be unreliable, nonparametrie techniques based on the Mann-Whitney U and Savage T statistics are studied. Asymptotic relative efficiency (ARE) is computed for general positive spectral noise data and a scale alternative. This alternative is appropriate since it includes, for SNR \rightarrow 0 , a Gaussian input with either a sinusoidal or Gaussian target. For a Gaussian input ARE_{U/t} \geq \frac{3}{4} and ARE_{T/t} \geq 0.816. Non-Gaussian examples indicate that U and T can be much better than t . It is shown that, subject to a reasonable restriction on the noise cumulative distribution function (cdf), ARE_{U/t} \geq \frac{27}{64} . The results obtained here for noncoherent detection, though not quite as strong, are analogous to the known bounds on ARE for linear coherent detection (a translation alternative).

FET noise sources and their effects on amplifier performance at low frequencies

Abstract: In this brief review paper analytical results concerning the low-frequency (LF) amplifier noise performance of FET's are presented. The effects of interaction between the device basic noise sources, the small-signal model parameters, and the signal source admittance parameters are clearly indicated. The noise performance is found to be essentially determined by the effective surface-state density and the gate insulator thickness product ( N_{ss}t_{ox} ) in the case of MOSFET's, whereas in the case of JFET's, this is determined by the bulk density of impurity and/or defect generation-recombination (g-r) centers within the depletion region and the half-channel height squared product ( N_{TT}a^{2} ). Although an increase in the gate electrode area can reduce the equivalent gate noise resistance, this does not improve the noise performance of the device. Quantitative results based on typical device parameters are graphically presented with proper indications as to the upper limit of the LF range, the excess minimum noise figure, and the frequency range within which the noise figure remains below 3 dB level for specified source resistance values. The effects of gate leakage current on the noise performance of JFET's are included in these results.

The avalanche photodiode as an electronic mixer in an optical receiver

Abstract: A new optical receiving system is described, which can improve the SNR when a very wide range of high-frequency signals is to be detected. It uses an avalanche photodiode both as an optical detector and as an electronic mixer. A theory is presented whereby mixer conversion losses and noise performance can be calculated. The results of a number of calculations for typical diodes are presented. Measurements of conversion losses and SNR have been made at 70 MHz. The results are in broad agreement with theory. The advantages of the system are shown to lie in that frequency down conversion in the diode permits more advantageous matching to the following stage, and that the optimum value of current gain required is much reduced. A simple numerical example is quoted that illustrates that an SNR improvement of 13 dB is obtainable in a particular case.

Nonlinearities of Photopolymer Holographic Recording Materials

Abstract: An analysis is presented of the nonlinear effects of holographically recording discrete image points on a phase recording material. The analysis is restricted to thin, two- and three-beam holographic gratings recorded on a material that exhibits a linear phase shift vs exposure. Harmonics, intermodulation noise, and small signal effects are considered. Experimental measurements were carried out for three-beam holographic gratings and diffuse object holograms recorded on photopolymer recording materials. Intermodulation noise is found to be a serious limitation for discrete image point holograms, because this noise cannot be spatially separated from the desired image points. Intermodulation noise can be reduced by increasing the reference-to-object beam irradiance ratio and by reducing the diffraction efficiency. Photopolymer gratings with 50-dB signal-to-intermodulation noise ratio were obtained with diffraction efficiency greater than 1/10% at beam irradiance ratios of 400:1. The image contrast of photopolymer holograms of diffuse objects is compared with the image contrast reported for bleached silver halide emulsions.

A physical process for 1/f noise in thin metallic films

Abstract: The concept of power spectra for nonstationary stochastic processes is examined and a definition of ``expected power spectrum'' is employed. This allows a derivation of the spectrum for a simple process where the current arises in a conductor consisting of a collection of sites by virtue of carrier jumps. If the noise may be described by a series of noise generators associated with each volume element of the conductor we are led to a spectrum essentially in accord with the experimental observations of noise in thin films subject to a certain condition. It is shown that this condition can be satisfied if a stochastic model is chosen in which the conduction takes place by a tunnelling mechanism between small islands of conductivity.

A.f.c. disabling circuitry

Abstract: A superheterodyne f.m. receiver having a manually tunable and voltage tunable local oscillator and a ratio detector for providing audio output signal and a.f.c. voltage in response to a received carrier and an a.f.c. channel for conveying the a.f.c. voltage to the local oscillator to maintain precise tuning of the latter, wherein is provided a switch for opening the a.f.c. channel and logic circuitry responsive to the a.f.c. voltage for controlling the switch to open the channel only when (1) the a.f.c. voltage exceeds predetermined levels, and (2) in response to interchannel noise, the a.f.c. channel including a voltage limiter for limiting a.f.c. voltage.

Agc for radiation counter

Abstract: Apparatus for detecting nuclear radiation from a source not absorbed by target material, in order to measure density or thickness of the material, employs a process for detecting radiation particles which converts the energy level of the particles to pulse height, through a photomultipler tube, one pulse for each separate particle detected, and develops an AGC signal for stabilizing the gain of the conversion system, through the high voltage power supply of the photomultiplier tube, by effectively comparing the pulse rate of a low level threshold detector, used to reject noise pulses in the conversion system, with come multiple R of a higher level threshold detector, where R is the anticipated ratio of low energy level particles to high energy level particles predetermined from an energy level spectrum or histogram of the source. The multiple R is introduced by dividing the lower-level rate by the product RN while the upper level rate is divided by N, where N is an arbitrary integer.

Noise and distortion considerations in charge-coupled devices

Abstract: Noise and distortion considerations for charge-coupled devices used in imaging applications are presented. Distortion occurs because of transfer inefficiency and leakage current. Noise contributions due to thermal noise during the formation of the potential wells, shot noise in the leakage current and interface-state noise are discussed.

Biological system transfer-function extraction using swept-frequency and correlation techniques

Abstract: The paper describes the application of a swept-frequency-system identification technique to biological systems. By linearly sweeping the frequency of the sinusoidal input signal over the range of frequencies of interest, the frequency-response profile of the biological system can be rapidly determined. System transfer characteristics are extracted from the input-power spectral density and output-input crosspower spectral-density computations. Noise, harmonic distortion and sweeptime considerations are given. Logarithmic frequencysweeping is suggested as a means of avoiding harmonic distortion.

Spacing Limitations of Geostationary Satellites Using Multilevel Coherent PSK Signals

Abstract: The relationship between intersatellite spacing, error probability, and carrier-to-thermal noise ratio is studied for the case where the satellites transmit multilevel coherent phase-shift-keyed signals. Numerical results based on computer evaluation of exact expressions are presented for 2-, 4-, 8-, and 16-phase systems.

Theory and Analysis of a Parametrically Excited Passive Power Converter

Abstract: A static power converter operating on the principle of parametric excitation is analyzed. The energy transfer from the input to the output takes place via the magnetic field without mutually coupling the windings. The transfer is accomplished by affecting the reluctance of the secondary winding. Thus output becomes available which is essentially independent of the waveform of the excitation; transients and noise are filtered. The characteristics of the converter are derived in a qualitative manner, and the outstanding characteristics of the device such as voltage regulations, under-and over- voltage protection, load dependence. and inherent protection against overload are explained.

Variance Noise Spectra of 1/f Noise

Abstract: Experimental measurements of 1/f noise variance fluctuations show the spectrum to depend on frequency to the −0.75 power over the frequency interval 10−5–1 Hz. The variance noise at 1 Hz is 10−14 V4/Hz in the case of current noise in a semiconductor diode, and 10−18 V4/Hz for current noise in a carbon resistor. The probability amplitude distributions of the variance for two different 1/f noise sources have the same magnitude and skewed shape as those previously reported. That is, the variance exhibits fluctuations as large as 200% and the most probable value is much less than the mean value. For band‐limited 1/f noise, the variance noise decreases with increasing averaging time.

Sensitivity of Josephson junctions in video detection of microwave and millimeter‐wave radiation

Abstract: The responsivity and the noise equivalent power (NEP) of Josephson junctions in video detection of microwave and millimeter‐wave radiation have been calculated. The sensitivity to radiation is assumed to be limited by the rounding of the voltage‐current curve due to thermal noise of both the source resistance and the junction resistance. The calculated NEP is at least several tens of times better than any experimentally established.

Error Formulae for Optimal Linear Filtering, Prediction and Interpolation of Stationary Time Series

Abstract: Several explicit expressions are presented for the minimum mean square error in linear causal filtering, prediction and interpolation of weakly stationary discrete-time processes corrupted by additive noise. A general procedure for deriving error expressions of this kind is established.

A general analysis of noise in Gunn oscillators

Abstract: Starting with Kurokawa's oscillator equations, it is shown that the two components of a Gunn oscillator's noise spectrum may be derived by considering flicker noise as equivalent bias fluctuations and thermal noise as a microwave frequency current source. The results are in agreement with expressions previously deduced from experiment.

Noise measurements of model jet-augmented lift systems

Abstract: Noise measurements were obtained on models of jet-augmented lift systems which are currently being considered for use on proposed short takeoff and landing vehicles These configurations included a conventional internally blown flap, an augmenter wing, an externally blown flap, and modifications of these basic concepts The tests were conducted in the Langley anechoic noise facility at zero forward speed with cold air jets The conventional internally blown flap exhibited lower noise levels than the augmenter wing and the externally blown flap at the same pressure ratios, being of the order of 8 dB or more at the lowest pressure ratio and of the order of 20 dB at the highest pressure ratio of the tests The data also indicated that for the conventional internally blown flap, there may be an optimum gap size (other than zero) between the turning lip and the flap leading edge from the standpoint of minimum noise generation or admittance Increasing the trailing-edge thickness of the plain internally blown flap produced no appreciable change in the overall sound pressure level or frequency spectral content in the range of the tests The data indicated that at a position on the ground directly under the jet exit, the externally blown flap and the augmeter-wing overall noise levels are comparable to each other throughout the pressure range of the tests

Methods of Measuring Small Phase Difference Changes in Interference Devices

Abstract: A review is presented of the present status of the technology of interference measurements of small changes of certain physical quantities. The capability limits of measurements with the aid of interference, imposed by diffraction and by noise in the radiation source and receiver, are analyzed. The most effective visual and photometric methods of measuring phase differences of interfering beams are described. The modulation method, in which a phase difference change of (10?5?10?6)?2? can be detected, and the phase method used in automatic interferometers are considered in greater detail.