Showing papers on "Noise (electronics) published in 1971"

Data adaptive spectral analysis methods

Abstract: Two new methods (Maximum Likelihood Method or MLM, and Maximum Entropy Method or MEM) for power spectral density estimation have been experimentally investigated. Both methods, unlike conventional methods, adapt to the actual characteristics of the noise process under study. The new techniques are particularly valuable if the process contains one or more narrow peaks in frequency which are to be resolved. In this case, the output peaks from MEM are proportional to the square of the power in the narrow peaks but the area is equal to power. The peak values of the MLM reflect power directly. Both methods yield the true spectrum if the spectrum changes slowly enough with frequency. Neither of the new methods appears to be unduly sensitive to small statistical fluctuations of the estimated correlation function used to obtain spectral estimates.

Characterization of low 1/f noise in MOS transistors

Abstract: By careful processing MOS transistors have been fabricated with a low value of the interface states density (2 × 1010/cm2eV). Consequently the 1/f noise in these devices is low and in the same order of magnitude as for junction FETs. The experimental values of the equivalent noise voltage and the equivalent noise current are compared to an expression derived from straight physical arguments. From the comparison it is concluded that the noise equivalent voltage in saturated operation is proportional to the effective gate voltage, the interface state density, and inversely proportional to the gate input capacitance. Moreover, it is concluded that a proper heat treatment not only reduces the number of states but also removes the near bandedge peaks, which usually appear in the trap distribution function.

Effects of intermodulation, AM-PM conversion, and additive noise in multicarrier TWT systems

Abstract: The intermodulation due to the traveling-wave tube (TWT) is analyzed for the case where arbitrarily modulated carriers and Gaussian noise are amplified through the TWT. Both AM-PM conversion effects and nonlinear amplification in the TWT are considered. The possibility of reducing intermodulation for system improvement is also discussed.

Sensitivity Enhancement of Superconducting Quantum Interference Devices through the Use of Fractional‐Turn Loops

Abstract: A new ``fractional‐turn'' configuration for superconducting quantum interference devices provides enhanced sensitivity, with large loop area and low loop inductance. By operating the new configuration at optimum bias frequency (300 MHz or higher), inherent field sensitivities of 10−15 T (10−11 G) or better can reasonably be expected. The operational sensitivity of an instrument using such a device would probably be limited by externally generated noise in most applications. The configuration is readily adaptable to measurements of both diagonal and offdiagonal components of the field gradient.

Stochastic Control for Small Noise Intensities

Abstract: This paper is concerned with the approximate solution of stochastic optimal control problems which arise by perturbing the system equations in the deterministic Pontryagin control model, through an additive white noise term with small coefficient. The system states are assumed completely observable. Mathematically the problem becomes one of singular perturbation of the Hamilton–Jacobi equation by a small second order term. Our main results concern expansions of solutions of the perturbed equation in powers $\varepsilon ,\varepsilon ^2 ,\varepsilon ^3 , \cdots $ of the noise variance coefficients. The results obtained hold in regions where the corresponding solution of the Hamilton-Jacobi equation is sufficiently well-behaved.

The Single-Cavity Multiple-Device Oscillator

Abstract: The output power from 12 IMPATT diodes has been combined in a single-cavity multiple-device oscillator. The oscillator is free from the well-known moding problem of multiple-device oscillators. The objective of this paper is to present the oscillator-circuit theory, which clearly indicates why this particular circuit configuration can give a stable operation free from moding problems. To handle the formidable equations necessary for the analysis, the eigenfunction approach is extensively used. The condition for stable operation, the noise performance, and the locking behavior of the oscillator are all discussed. The noise performance is similar and the locking behavior identical to those of single-device oscillators.

Noise thermometry with the josephson effect.

Abstract: Thermal noise causes a random frequency modulation of the self‐oscillation of a Josephson junction, and the temperature of the noise source can be determined by analysis of the generated signal. We show that a thermometer based on this principle would be theoretically capable of measuring temperatures in the microkelvin range, and describe a prototype thermometer which has recorded noise temperatures down to 0.075 K.

Semiconductor impurity analysis from low-frequency noise spectra

Abstract: The usefulness of material for semiconductor devices can be degraded by the presence of deep impurity levels or traps which are often difficult to detect. The equations necessary for using the noise emitted by a uniform semiconductor when biased with a small dc current to find the energy, degeneracy factor, density, and time constants of such a deep level are derived. The theory was verified by an experimental study of a level in n-GaAs which was found to have an energy 0.175 eV below the conduction band and an acceptor-like degeneracy factor of 4. This technique appears to be useful for fundamental studies and as a means of monitoring material used for devices.

Noise in the Measurement of Light with Photomultipliers

Abstract: In order to be able to compare light intensity measurements derived from the anode current of a photomultiplier with measurements derived from photoelectron pulse counting, a systematic investigation of the properties of some photomultiplier tubes has been made. This has led to a correlation of the properties of a photomultiplier based on an over-all quantum efficiency ηF, the gain G, a photoelectron noise factor S, and an effective dark rate D. In terms of these quantities the signal-to-noise ratio of an experimental measurement can be calculated, given the light flux and measurement technique. It is shown that the noise power spectral density is constant for a photomultiplier, down to about 10−2 Hz, and that pulse counting and current measurement will give similar signal-to-noise ratios under most experimental conditions.

Flicker noise in metal semiconductor Schottky barrier diodes due to multistep tunneling processes

Abstract: In a practical metal semiconductor Schottky barrier diode there is a certain amount of current flow by indirect tunneling through the barrier. Although this component of current is negligibly small compared to the thermionic emission or thermionic field emission current, a large low-frequency 1/f noise is associated with this multistep tunneling process. The multistep tunneling current introduces a random fluctuation of charge density at the trap states, which trap current carriers during the indirect tunneling process, in the space-charge region of the diode. The field intensity at the metal semiconductor interface is therefore modulated, which in turn modulates the Schottky effect and produces a random fluctuation of the diode current. The spectral intensity of noise due to this mechanism is calculated. Large flicker noise is expected at low frequencies.

Timing recovery in PAM systems

Abstract: It is shown how various timing recovery schemes are reasonable approximations of the maximum likelihood strategy for estimating an unknown timing parameter in additive white gaussian noise. These schemes derive an appropriate error signal from the received data which is then used in a closed-loop system to change the timing phase of a voltage-controlled oscillator. The technique of stochastic approximation is utilized to cast the synchronization problem as a regression problem and to develop an estimation algorithm which rapidly converges to the desired sampling time. This estimate does not depend upon knowledge of the system impulse response, is independent of the noise distribution, is computed in real time, and can be synthesized as a feedback structure. As is characteristic of stochastic approximation algorithms, the current estimate is the sum of the previous estimate and a time-varying weighted approximation of the estimation error. The error is approximated by sampling the derivative of the received signal, and the mean-square error of the resulting estimate is minimized by optimizing the choice of the gain sequence. If the receiver is provided with an ideal reference (or if the data error rate is small) it is shown that both the bias and the jitter (mean-square error) of the estimator approach zero as the number of iterations becomes large. The rate of convergence of the algorithm is derived and examples are provided which indicate that reliable synchronization information can be quickly acquired.

H.F. data transmission using chirp signals

Abstract: Swept-frequency or chirp signals are currently under investigation for data-transmission applications. In particular, long-range air/ground communication in the h.f. band may benefit from the use of these wideband signals owing to the inherent protection chirp signals offer against fading in a time-varying multipath channel. The theory of pulse compression and data transmission using chirp signals is outlined, and an experimental communication system is described with measured error rates in noise and carrier interference.

An Analysis of the Phase Coherent--Incoherent Output of the Bandpass Limiter

Abstract: Many applications of the bandpass limiter (BPL) involve coherent demodulation following the limiter. It is shown that as a result of demodulation, the signal mean and the noise variance are direct functions of the phase angle between the signal component passed by the BPL and the coherent reference. As a result, the relationship between the output and input signal-to-noise ratio may be significantly different than that obtained by Davenport for incoherent limiters. A study is also made of the output noise spectral density, and an approximate expressison is derived as a function of the input signal-to-noise ratio, reference phase angle, and the characteristics of the input bandpass filter to the limiter. Also discussed is the first-order signal-plus-noise probability density following coherent demodulation.

Apparatus for detecting arcs

Abstract: Apparatus for detecting the occurrence of an arc during a spark erosion process is based upon the principle that the noise component of the voltage across the discharge gap disappears when an arc occurs. The noise voltage is detected and compared with a reference voltage in a discriminator circuit. A signal from a logic circuit is also applied to the discriminator which determines the presence of a current through, and of a voltage across, the spark discharge gap.

Experimental and theoretical comparison of photon-counting and current measurements of light intensity.

Abstract: The effect of gain variation on the integrated output-charge distribution of a photomultiplier tube is investigated experimentally and shown to be a predictable function of the multiplier single-electron response. Standardized or nonstandardized pulses recorded using either capacitive or digital storage are considered. Theoretical values for the moment-generating functions and variances (noise powers) of the charge distributions obtained in these four cases are given, and the role of these various distributions in determining the length of time required to achieve a given accuracy in a light-flux measurement is discussed. The experimental measurements adequately confirm the theoretical predictions. The work includes a critical discussion of the field of theoretical and experimental noise investigations in photomultiplier tubes with regard to their relevance in the present state of technology.

Detection of a Distributed Target

Abstract: The influence of increasing range resolution on the detectability of targets with dimensions greater than the resolution cell is studied. An N-cell target model is assumed, which contains k reflecting cells, each reflecting independently according to the same Rayleigh amplitude distribution. It will be referred to as the (N,k) target. Detection based on one transmitted pulse is performed against a background of white normal noise. Detection in stationary clutter is also considered. The optimum detector is obtained but, in view of its complexity, the performance of a simpler detector, the square-law envelope detector with linear integrator (SLEDLI), is analyzed, and a formula for the probability of detection is obtained. Graphs are presented which show the probability of detection as a function of signal-to-noise ratio (SNR) for various values of N k, and false alarm probability. For N/k not too large it is shown that the SLEDLI is near optimum.

Multiple Error Performance of PSK Systems with Cochannel Interference and Noise

Abstract: The multiple error performance of a phase-shift-keyed (PSK) communications system, when both cochannel interference (due possibly to other cochannel angle-modulated systems) and Gaussian noise additively perturb the transmitted signals, is considered. The results are fairly general: the main requirement is that the interference be circularly symmetric. All of our findings are also applicable to the case when only noise is present. The results indicate that one cannot approximate well the effect of interference on the performance of a PSK system by treating it as additional Gaussian noise. First, we derive the probability density function f A of the phase angle of a cosinusoid plus interference and Gaussian noise. We then obtain readily computable expressions (in terms of f A ) for the probability of any number of consecutive errors in an m -phase system when either coherent or differential detection is utilized. For numerical results, the interference is assumed to be due to other cochannel angle-modulated communications systems, and the double error probability and conditional probability of error are given for 2- and 4-phase systems.

SLIC-a simulator for linear integrated circuits

Abstract: A computer program for the simulation of linear integrated circuits (SLIC) is described. The program formulates and solves nonlinear equations for d.c. node voltages and transistor operating points; generates linearized small-signal circuit models; and solves for the poles, zeros, frequency response, and noise response of specified transfer functions. Temperature variations and operating point dependence can be effectively simulated.

Performance of coherent phase-shift-keyed systems with intersymbol interference

Abstract: In order to optimize the design of a coherent phase-shift-keyed (CPSK) system, it is necessary to estimate the amount of degradation produced by intersymbol interference. In this paper, an upper bound to the probability of error of m -ary CPSK systems is given when an ideal CPSK signal is passed through a linear time-invariant noisy filter. This bound can be used to estimate the maximum amount of deterioration produced by intersymbol interference, and hence to choose the filter and channel parameters appropriately. It is assumed that all m symbols have equal a priori probabilities and that the noise is Gaussian.

Complex Gaussian noise moments

Abstract: The problem of the computation of moments of nonzero mean circularly complex Gaussian noise is treated. The noise need not be symmetric about the carrier frequency. In particular, the second-order moments are computed, and expansions are given. The necessary univariate and bivariate complex Hermite polynomials are discussed. The means of some rational functions useful in FM theory are given. This paper extends work of Rice, Middleton, and Zadeh to complex Gaussian noise with nonzero mean and nonsymmetrical power spectrum.

Noise Characteristics of Photographic Emulsions Used for Holography

Abstract: Photographic emulsion model for signal to average noise irradiance ratio analysis in hologram reconstruction

Spontaneous Voltage Fluctuations in Glass Microelectrodes

Abstract: The spontaneous fluctuations of voltage across a glass microelectrode have been studied as a function of the average difference in voltage (V) across the electrode and the concentration of internal (n 2 ) and external (n 1 ) salt solutions. A stationary fluctuation was observed, with a mean square value many times greater than that calculated from the Nyquist formula for noise due to the thermal agitation of charge, for all states of the electrode except n 2 =n 1 , V=0. Here the fluctuations equal the Johnson level. The spectral density of the fluctuation and its dependence on (n 1 , n 2 , V) are given in the range 3-0.003 MKCl and V = ±200 mV. The dependence on the species of cation (potassium and sodium) was also determined. The work has practical implications for users of microelectrodes who wish to minimize noise. It also serves as a model for studying noise generated when ions move through a micropore.

Performance Analysis of DPSK Systems in Both Thermal Noise and Intersymbol Interference

Abstract: In this paper a useful and mathematically rigorous method is presented for exactly evaluating the error-probability performance of a binary differentially coherent phase-shift-keyed (DPSK) system in the presence of both thermal noise and intersymbol interference. The channel filter and the receiver input signal-to-noise ratio are assumed to be given. This method suggests, first, to calculate the probability of error induced by both the thermal noise and the large interfering samples whose normalized amplitudes with respect to noise standard deviation are greater than unity, and then, to add the correction terms due to the presence of the other intersymbol interference samples. If the normalized interference amplitudes with respect to the noise standard deviation are less than unity (although the total interference power may still be greater than total noise power), then this method simply becomes that which first evaluates the error probability induced by thermal noise alone and then adds the correction terms due to the presence of intersymbol interference. For numerical computations, various recurrence relations are developed so that the probability of error can be easily obtained on a digital computer. These relations have been utilized in an example to calculate the performance of certain practical PSK and DPSK systems.