Showing papers on "Noise (electronics) published in 1968"

Fluctuation phenomena in nerve membrane

Abstract: The fluctuations of the voltage across the resting membrane of myelinated nerve fibers have been analyzed. They show a 1/f spectrum and a Gaussian amplitude distribution and are related to the net flow of potassium through the membrane. When the average membrane voltage is made more negative by means of an external current, depolarizing deflections can be observed. They cause an asymmetry in the noise amplitude distribution and a marked increase in the subaudio spectral components of the noise. The depolarizing deflections can be attributed to batch-wise inflow of sodium ions. Possible mechanisms of both types of membrane voltage fluctuations are discussed.

Probabilities of Error for Adaptive Reception of M-Phase Signals

Abstract: Probabilities of error are derived for 2- and 4-phase signaling over an L -diversity branch, time-invariant, additive Gaussian noise channel and for M -phase signaling over an L diversity branch, Rayleigh fading, additive Gaussian noise channel. Both channels corrupt the signaling waveforms transmitted through them by introducing an additive Gaussian noise and an unknown or random multiplicative gain and phase shift in the transmitted signal. The receiver processing consists of cross correlating the signal plus noise received over each diversity branch by a noisy reference signal, which is derived either from the previously received informationbearing signals or from the transmission and reception of a pilot signal, and adding the outputs from all L -diversity branches to form the decision variable. The novel aspects of this paper are: 1) the result for the phase distribution of the decision variable for M -phase signaling over an L -diversity branch, Rayleigh fading channel, 2) the explicit expressions for the probabilities of error for M -phase signaling systems operating over an L -diversity branch, Rayleigh fading channel, and 3) the expression for the probability of error for 4-phase signaling over a time-invariant channel. Previously published error probabilities for 2- and 4-phase signaling over a Rayleigh fading channel are obtained as special cases.

The quantum fluctuations of the optical parametric oscillator. i.

Abstract: Our treatment is based on a microscopically correct Hamiltonian which contains the Bose-operators of the light modes and the Fermi-operators of the optically active electrons in the medium. The coupling between modes and atoms is taken from quantum-electrodynamics. Besides that, the light modes may interact with external “heat baths” like the mirrors, scattering centers etc., while the atoms interact with lattice vibrations, incoherent light fields etc. Using recently developed methods the effect of these heatbaths is taken into account in a quantum mechanically consistent fashion. In the present paper we apply quantum mechanical Langevin equations for the field and electron operators which contain dissipation and fluctuation terms. The elimination of the electron operators by an iteration procedure finally leaves us with a set of coupled nonlinear field equations which are shown to be quantum mechanically consistent. They are solved in the Heisenberg picture below threshold by linearization and well above threshold by quantum mechanical quasi-linearization. The solutions show that the line width of the signal mode below threshold is due to the vacuum fluctuations in the idler and vice versa, whereas the thermal noise of the resonator and the spontaneous emission noise of the medium may be neglected. Above threshold the linewidth is caused by the undamped diffusion of the phase difference between signal and idler, to which the vacuum fluctuations of both modes contribute in equal parts. The phase sum of both modes adiabatically follows the slow phase diffusion of the external pump light, produced by a laser, and therefore contributes to the linewidth too. Well above threshold the amplitudes are stable. Correlation and cross-correlation functions of their small residual fluctuations are calculated.

Analysis of thermal and shot noise in pumped resistive diodes

Abstract: This paper discusses certain important aspects of the noise behavior of a pumped resistive diode containing shot and thermal noise sources. The derivation of the following result has a central role in the discussion. It is shown that the noise behavior of a pumped diode which does not contain 1/f noise sources can be derived in a very simple way from Nyquist's theorem. This follows from the fact that the small-signal terminal behavior of such a diode can always be represented, in the frequency range of practical interest, by means of a connection of two linear and time-invariant networks of which one is noiseless and the other is dissipative, contains only thermal noise sources and is held at a uniform temperature.

The Measurement of Near-Carrier Noise in Microwave Amplifiers

Abstract: This paper discusses the measurement of additive noise in microwave power amplifiers, under CW and pulsed condition. The introduction of a pulsed carrier cancellation principle permits, for the first time, an investigation of the additive noise of pulsed amplifiers down to the thermal noise level. The measurement apparatus consists of three channels fed from a common source. One channel contains the amplifier under test. The other channel is pulsed by a "noise-free" modulator with the same pulse parameters as those of the test channel. The two signals are algebraically cancelled in a hybrid circuit and the difference signal, containing only the noise sideband of the amplifier, is coherently detected with the signal in the third channel. Measurements made on klystron amplifiers indicate that the level of the power spectral density of the FM noise approaches the thermal noise level, and that it has nearly the same value for CW and for pulsed operation.

Surface-State Related l/f Noise in p-n Junctions and MOS Transistors

Abstract: It is shown experimentally that l/f noise both in silicon p‐n junctions and in MOS transistors can be increased by the introduction of a particular type of surface state. The additional noise power is proportional to the density of these states. The surface states are introduced by the application of an electric field across the oxide at elevated temperatures (e.g., ∼300°C); they are relatively ineffective as surface recombination centers.

Lateralization Threshold of a Signal in Noise

Abstract: Experiments are described in which the accuracy of the perceived lateral position of a signal against a continuous background of masking noise is determined. Both signal and masker consisted of octave bands of thermal noise, with the same center frequency of 500 Hz. The signal‐to‐noise ratio and signal duration served as parameters. The results can be understood on a statistical basis, the random fluctuations of nerve impulses playing an important role. The fluctuations due to “internal” noise are found to have a standard deviation of about 80 μsec. It appeared that, as a result of the increase of the sound‐pressure level, the onset part of the signal contributes more to the lateral position perceived than the ongoing part does. The relation to the precedence effect is discussed. The statistical procedure underlying the accuracy of the lateral position perceived suggests an approach to the binaural masking level difference effect based on a masking pattern in the binaural‐hearing mechanism.

Microwave Thermal Noise Standards

Abstract: Calibrated microwave thermal noise standards usually consist of a matched resistive element thermally isolated by a transmission line. They are used for microwave radiometry, antenna temperature calibrations, loss measurements, low-noise amplifier performance evaluation, and low-level CW signal level calibrations. The formula used to account for the distributed loss and temperature along the transmission line is derived and simplifying approximations and limitations are noted. Exact (hf/kT<<1) and approximate (hf/kT<<1, /spl pound/<<1) solutions for various loss and temperature distributions are tabulated. A FORTRAN computer program is available for a general solution that uses the transmission-line temperature and loss distributions for input data. The single largest source of calibration error is usually the microwave insertion loss measurements. The construction, calibration, and errors are discussed for a field-operational liquid-nitrogen-cooled waveguide noise standard. This standard is precisely calibrated and has a nominal noise temperature of (78.09 /spl plusmn/ 0.12 peak)/spl deg/K.

Theory of a Josephson Oscillator

Abstract: A quantum mechanical theory of superconducting tunnel junctions including noise is developed. The theory is applied to the calculation of the frequency pulling, linewidth of the radiation, and voltage power spectrum in the ac Josephson effect.

The uncorrelated output components of a nonlinearity

Abstract: Using his characteristic-function approach, Rice (1945) obtained a double series for the autocorrelation function of a sinusoidal signal and Gaussian noise after passage through a memoryless nonlinearity. It is shown here that the output of the nonlinearity can be expressed as the sum of uncorrelated terms whose auto-correlation functions are the terms of Rice's double series. Such a decomposition of the output is shown to be generally possible if and only if the bivariate probability density functions of the input signal and the input noise can both be expressed in the diagonal form studied by Barrett and Lampard (1955), though not necessarily involving polynomials, as they can in the sinusoidal and Gaussian cases. In addition, a more direct and meaningful equation is found for the coefficients in Rice's double series.

The Effect of Mismatched Components on Microwave Noise-Temperature Calibrations

Abstract: A technique is presented for analyzing the effect of mismatched components on the absolute noise-temperature calibrations of principal noise sources in a microwave receiving system. Scattering parameters are used to describe the properties of the microwave network that is connected between noise source and receiver. The calibration method discussed is the Y-factor power-ratio measurement technique involving the use of two thermal noise reference standards. Calculations made for an operational low-noise antenna receiving system indicate that, even when components have reasonably low-voltage reflection coefficients (typically less than 0.05), peak errors due to mismatches could be as high as 70 percent and 11 percent on measured antenna and effective input noise-temperature values, respectively. For the special case where the reflected and direct wave receiver noise sources are fully correlated, the peak errors can be even larger.

Thermal Noise from a Passive Linear Multiport

Abstract: The thermal noise from passive multiports is discussed from fundamentals so that it can be understood, measured, or calculated by a microwave engineer The multiports are assumed to have a uniform temperature, but with no restriction on reciprocity or mismatch The noise temperature, T/sub N/, contributed by such a multiport is T/sub N/=A T where T is its physical temperature and A is its absorption coefficient An approximate method of measuring A, and a method of measuring an A as small as 0008 within 5 percent, are pointed out Also, exact and approximate expressions for A in terms of scattering matrix elements and termination reflection coefficients are derived Finally, the crosscorrelation of the noise from different ports is briefly considered

Noise in Hot‐Wire Anemometers

Abstract: An analysis is given of the electronic noise and the signal‐to‐noise ratio for constant‐temperature and constant‐current hot‐wire anemometers. The analysis shows that both anemometers are equivalent in their signal‐to‐noise ratio if the noise sources are equivalent and the hot‐wires are operated at the same conditions. A discussion of the theoretical results and a comparison of both anemometer types based on these results are given. In addition, some noise measurements on a constant‐temperature anemometer and the methods to obtain them are reported and compared with theoretical results. The agreement between measured and theoretical results is rather good.

Noise Loading Analysis of a Third-Order Nonlinear System with Memory

Abstract: This paper presents the noise loading analysis of a third-order nonlinear system characterized by Volterra kernels. The analysis is of practical interest since intermodulation distortion is often a limiting consideration in the design of solid-state long-haul broad-band frequency-division multiplexed transmission systems, and since speech on such systems is best represented by zero mean Gaussian noise. The analysis technique is amenable to digital computer calculation; as such, quantitive results are readily obtained. The analysis was applied to a single-stage transistor amplifier that was represented by a frequency-dependent nonlinear model. An excellent agreement between measured and calculated results was obtained. Portions of the program written for this example are readily applicable to the calculation of intermodulation distortion for any thirdorder nonlinear system (e.g., amplifier, repeater, or cascade of repeaters and cable sections) given the appropriate Volterra kernels.

The clipping loss in correlation detectors for arbitrary input signal-to-noise ratios

Abstract: The detection of stationary Gaussian signals in a background of stationary Gaussian noise by the analog multiplier correlator, the polarity coincidence correlator (PCC), and the sample polarity coincidence correlator (SPCC) is considered. It is assumed that signal and noise have identical normalized autocovariance functions, and they are not cross correlated with each other. The main contributions of this paper are the exact expressions for the output signal-to-noise ratio (SNR) for the correlators mentioned for all values of the input SNR. It is shown that there exists a critical value of the input SNR, such that, whenever this value is exceeded, the PCC output SNR exceeds that of the analog correlator. A sufficient condition for this gain in output SNR is obtained in terms of the input SNR. This result is illustrated for stationary Gauss-Markov processes.

Subcarrier Tracking Methods and Communication System Design

Abstract: It is advantageous from power considerations to allow suppressed-carrier coherently-detected communications. Two methods for generating a coherent reference for the demodulation of a suppressed-carrier signal, namely, the squaring loop and the mathematically equivalent Costas loop, are analyzed, including at some points the effects of VCO noise and initial frequency detuning. The steady-state phase error probability distribution is presented, as is the expected time to first loss of lock in the first-order loop. Probabilities of error in coded or uncoded telemetry systems which use a squaring loop to generate a coherent subcarrier reference are investigated, allowing appropriate values of system parameters to be chosen by system designers.

Extent of the 1/f Noise Spectrum

Abstract: SPECULATIONS are often made about the possible extent of the 1/f noise spectrum which is exhibited by many electronic devices at low frequencies. This has been found to extend to the lowest frequencies so far investigated (about 10−4 Hz), but the view is often expressed that it can only hold for a limited frequency range. The reason invoked is that the total noise power would tend to become infinite if the 1/f spectrum extended over a sufficient frequency range. This is either implied or explicitly stated in several papers1–6, and I examine the question in this communication.

Computation of FM distortion in linear networks for bandlimited periodic signals

Abstract: Computations of the distortion generated in passing large-index, frequency-modulated signals through symmetrical single-pole and three-pole bandpass filters are presented. The computation is for a bandlimited periodic modulation signal; noise modulation is simulated by the use of periodic noise samples in a Monte Carlo procedure. The convergence of the Monte Carlo procedure is illustrated for the case of the single-pole filter and the results are in good agreement with measurements. Computations of envelope distortion are also presented. These data give the amplitude-to-phase conversion in the receiver containing the filter to within a constant factor, the constant being the AM/PM conversion coefficient of the limiter.

Investigations of the Noise Spectra of Avalanche Oscillators

Abstract: Measured amplitude noise spectra of X-band microwave oscillators rising silicon avalanche diodes are presented and compared with theoretical calculations. It was found that for the investigated diodes, the up-converted low-frequency noise (modulation noise) is the main contribution to the spectrum. In a frequency range extending from 1 kHz to several hundred MHz, the spectral noise power distribution is a sensitive function of the bias network impedance. Improvements in the noise-to-carrier power ratio of 5 to 15 dB were obtained by optimizing the bias network impedance. The dc current dependence of the amplitude noise spectrum is a complicated function of diode and circuit parameters. In general, the noise-to-signal ratio improves with increasing current. At high current densities, a reversal of this behavior may occor due to excess noise generation in the breakdown region and saturation effects of the signal power output. The equivalent rms deviation of the frequency modulation noise spectrum is typically one order of magnitude below that of the RF phase noise contribution due to RF noise sources, The phase noise spectrum of the oscillator is, therefore, not affected by the bias network impedance. Measurements on recent diodes indicate that the noise characteristics can be improved by careful control of the semiconductor device processing.

Method of synthesizing low-frequency noise

Abstract: A method of synthesizing low-frequency noise wherein the lowfrequency noise has a controllable amplitude distribution, so as to be able to select a desired amplitude-level distribution, such as Gaussian, Poisson, or Uniform distribution. The desired amplitude distribution is derived from a digital-random-variable sequence, having a plurality of characteristics, by selecting the characteristic appropriate to the desired amplitude distribution and performing an appropriate digital operation on the selected characteristic.

Thermodynamics of Nonlinearity and Noise in Diodes

Abstract: The irreversible thermodynamics of a nonlinear diode are discussed by considering a circuit in which a biased diode exchanges noise power with a linear resistor at a different temperature. By applying the Onsager reciprocity relations to the two cross terms involving the rectification of thermal noise, and the generation of current noise by the diode, respectively, an equation is obtained relating the nonlinearity of the diode and a parameter which specifies its current‐noise behavior. The implications of this equation are discussed in relation to the existence of a maximum value of the nonlinearity. The analysis predicts that a reverse current will flow through the diode when the resistor is at a lower temperature, and an experiment to confirm this is reported briefly.

Intermodulation Distortion in Freqency-Division-Multiplex FM Systems--A Tutorial Summary

Abstract: In the design of FDM-FM communication systems, a great deal of importance is attached to an appreciation of those transmission irregularities that yield second- and third-order intermodulation spectra. Such spectra are readily generated by amplitude, phase, and AM/PM conversion anomalies within the FM transmission path. In this paper the results of the available journal literature have been reworked for presentation in a generalized form appropriate for use by equipment designers and system analysts. Intermodulation noise magnitudes and spectral distributions are expressed in terms of the transmission network and system modulation parameters with the AM/PM conversion characteristic extended to that of a second-order power series in radian frequency. To fully exploit the usefulness of the foregoing, the coherency between the intermodulation spectra of all distortion mechanisms is considered. The effects of this correlation is then exemplified for a tandemly interconnected set of distorters. It is found that all secondand third-order distortion mechanisms may be grouped under the classifications of: amplitude, delay, equivalent amplitude/delay, and quasi-equivalent amplitude/delay distortion. It is concluded that, as a result of the correlative structure of the distortion processes, an overall system measurement of intermodulation noise may exhibit an unexpected level of magnitude and/or have a spectral distribution significantly different from any of the inherent system distortions.

Optimum spatial processing in a noisy environment for arbitrary antenna arrays subject to random errors

Abstract: A procedure is presented for the maximization of the expected signal-to-noise ratio improvement factor for arbitrary antenna arrays whose excitation amplitudes and phases, as well as element positions, are subject to random errors. In its general form, the formulation imposes no restrictions on either the probability distribution or the variance of the random errors. Correlations are allowed to exist between the random variations in array parameters, and the effect of system internal noise is considered. Computed results for a linear endfire array in a typical noise environment are given, illustrating the dependence of the signal-to-noise ratio improvement factor on the system internal noise; the system bandwidth; the amplitude, phase, and position errors; and the error correlation intervals. Typical expected power pattern functions are also plotted.

Position-Sensitive Semiconductor Particle Detectors Fabricated by Ion Implantation

Abstract: The advantages and problems associated with the use of ion implantation for the fabrication of position-sensitive particle detectors are discussed. Analysis of the noise and pulse risetime properties of such devices shows the desirability of using a high sheet resistance in the distributing resistive layer for optimum position resolution while restricting the RC of the detector to values approximately equal to the clipping times used in the measuring circuits in order to obtain good position linearity. From both detector noise and pulse rise-time considerations it is found desirable to use equal pulse shaping in the energy and the position signal measuring systems. Detectors were made by implantation of 60 keV boron and phosphorus ions into 4000 ohm-cm n-type silicon. Representative results are shown for a 4×32 mm2 one dimensional detector which shows integral and differential position nonlinearity of less than one percent and position resolution of less than 0.2 mm. Extension to one dimensional detectors up to 50 mm and to 10×10mm two dimensional detectors is discussed.

Noise generation under large signal conditions in the Read microwave avalanche diode

Abstract: In this report the noise generation mechanism of the Read microwave avalanche diode is examined. Using a large signal approximation to the operation of the device as an oscillator, the current variation with time in the avalanche region is examined and an expression for the variance of this current, due to fluctuations in the ionization process, is obtained. The effect of this, current variance upon the output waveform of the device is then investigated It is found that as the bias current is increased the output waveform rapidly becomes very noisy. This is due to the build-up mechanism of the avalanche which tends to amplify the ionization fluctuations occurring while the current is small. Various means of reducing this effect are considered, the most promising of which seems to involve widening the avalanche region of the device. Finaly, expressions are derived for the F.M. and A.M. noise characteristics which would be obtained at the output of a microwave oscillator driven by a Head diode. The expected...

High noise immunity system for integrated circuits

Abstract: An input logic circuit for integrated circuits, particularly integrated circuits utilized in digital or pulse systems, prevents spurious signals (i.e., noise) from causing false triggering of the integrated circuit components.