Showing papers on "Noise (electronics) published in 1974"

Optimization of Two-Dimensional Signal Constellations in the Presence of Gaussian Noise

Abstract: A considerable amount of literature exists on the problem of selecting an efficient set of N digital signals with in-phase and quadrature components for use in a suppressed carrier data transmission system. However, the signal constellation which minimizes the probability of error in Gaussian noise, under an average power constraint, has not been determined when the number of signals is greater than two. In this paper an asymptotic (large signal-to-noise ratio) expression, of the minimum distance type, is derived for the error rate. Using this expression, a gradient-search procedure, which is initiated from several randomly chosen N -point arrays, converges in each case to a locally optimum constellation. The algorithm incorporates a radial contraction technique to meet the average signal power constraint. The best solutions are described for several values of N and compared with well-known signal formats. As an example, the best locally optimum 16-point constellation shows an advantage of about 0.5 dB in signal-signal-to-noise ratio over quadrature amplitude modulation. The locally optimum constellations are the vertices of a trellis of (almost) equilateral triangles. As N \rightarrow \infty , it is rigorously proved in the Appendix that the optimum constellations tend toward an equilateral structure, and become uniformly distributed in a circle.

Characterization of surface channel CCD image arrays at low light levels

Abstract: The characterization of surface channel charge-coupled device line imagers with front-surface imaging, interline transfer, and 2-phase stepped oxide, silicon-gate CCD registers is presented. The analysis, design, and evaluation of 1/spl times/64 CCD line arrays are described in terms of their performance at low light levels. The authors describe the responsivity, resolution, spectral, and noise measurements on silicon-gate CCD sensors and CCD interline shift-registers. The influence of transfer inefficiency and electrical fat-zero insertion on resolution and noise is described at low light levels.

An upper bound on the error probability in decision-feedback equalization

Abstract: An upper bound on the error probability of a decision-feedback equalizer which takes into account the effect of error propagation is derived. The bound, which assumes independent data symbols and noise samples, is readily evaluated numerically for arbitrary tap gains and is valid for multilevel and nonequally likely data. One specific result for equally likely binary symbols is that if the worst case intersymbol interference when the first J feedback taps are Set to zero is less than the original signal voltage, then the error probability is multiplied by at most a factor of 2^J relative to the error probability in the absence of decision errors at high S/N ratios. Numerical results are given for the special case of exponentially decreasing tap gains. These results demonstrate that the decision-feedback equalizer has a lower error probability than the linear zero-forcing equalizer when there is both a high S/N ratio and a fast roll-off of the feedback tap gains.

Determination of the single-scattering probability distribution from plural-scattering data

Abstract: A technique is presented which enables the recovery of the probability distribution for single scattering from plural-scattering electron energy loss data. Neither the scattering parameter t/? nor details of the component processes need be known. The computational method uses Fourier series in order to overcome a number of practical problems in the application of convolution series methods, to include instrumental effects and to permit the processing of data with large values of the scattering parameter. The effects of noise, specimen oxidation and the accuracy of the technique are considered.

II-3 the effects of bulk traps on the performance of bulk channel charge-coupled devices

Abstract: The effects of bulk traps on the transfer effciency and transfer noise in bulk channel charge-coupled devices (BCCD's) are calculated for different charge packet sizes and operating frequencies. These predictions are compared with experimental results and the distribution and density of bulk states in actual devices are thereby measured. The measured low transfer inefficiency of 10-4per transfer with no intentionally introduced background charge and low transfer noise are shown to be due to a low bulk state density of 2 × 1011/cm3. A detailed comparison of estimated noise in both surface and bulk channel versions of an image sensor and an analog delay line show that BCCD's are very attractive for low-light level imaging but not as attractive for analog signal processing.

A new method of Johnson noise thermometry

Abstract: A new method of Johnson noise thermometry was developed and experimentally evaluated. The absolute temperature Ts was determined by measuring the available thermal noise power, i.e., the product of the open‐circuit thermal noise voltage and the short‐circuit thermal noise current generated by a sensing resistor at temperature Ts. The measured thermal noise power from the thermometer is a linear function of absolute temperature. This new method is independent of the sensing‐resistor composition, the mass and nature of the charge carriers, and, in principle, the ohmic value of the resistor. Consequently, the method has a wide range of application, including use in the realization of an absolute thermodynamic temperature scale and especially in the measurement of high temperatures, particularly in nuclear reactors where the properties of sensor materials not only change due to the aging effects induced by the high temperatures but also change drastically because of radiation damage and transmutation. An eval...

Microcycle spectral estimates of 1/f noise in semiconductors

Abstract: Many physical occurrences are characterized by extremely low spectral variations, the measurement and estimation of which has been invariably difficult. An estimate of the density of the power spectrum of very‐low‐frequency semiconductor 1/f noise is experimentally obtained from 10−6.3 to 1.0 cps with a greater accuracy than that achieved in previous similar attempts; it is concluded that the spectrum is 1/fα with α approximately 1.3 over most of the frequency range, but appearing to have a value of about 1.0 in the lowest decade. A peculiar form of stationarity seems to distinguish 1/f noise from other noise in semiconductors. Ten independent noise sources were time multiplexed and their spectral estimates were subsequently averaged. If the sources have similar spectra, this reduces the necessary data‐taking time by a factor of 10 for a given accuracy. An estimator is derived for optimal spectral estimation based on a number of statistically independent noise sources. Other related topics considered are ...

Input amplifiers for optical PCM receivers

Abstract: This paper describes the noise performance of input amplifiers for optical pulse-code-modulation repeaters. The noise is treated in terms of an effective noise generator in parallel with the photocurrent induced in the detector and the effective noise, in turn, is related to error performance. The analysis applies to both conventional and integrating front ends. Both field effect and bipolar transistor amplifiers are treated. For the latter, an optimum bias current that minimizes the effect of thermal noise is derived. Finally, predicted and measured performance are compared for silicon field-effect transistor input amplifiers at 6.3 Mb/s and 50 Mb/s, and for bipolar transistor and GaAs field-effect transistor input amplifiers at 274 Mb/s.

An acoustically resonant system for detection of low‐level infrared absorption in atmospheric pollutants

Abstract: The use of acoustic detection for the measurement of infrared absorption in gases has been shown to be of value in measuring atmospheric pollutant gases. Further improvements in detection sensitivity may be achieved by the use of an acoustically resonant system and multipass optics wherein the incident laser radiation is reflected many times through the absorption sample. We have demonstrated acoustic Q's exceeding 750 and sensitivity increases of at least 10 using multipass optics. A microphone amplifier pair is described whose noise limitation approaches the thermal noise on the microphone diaphragm.

Measurements of amplitude probability distributions and power of automobile ignition noise at HF

Abstract: Measurements of the amplitude probability distribution (APD) of the envelope and measurements of other parameters of automobile ignition noise were made at frequencies between 24 and 30 MHz. The measurements were conducted at a quiet site where several single stationary vehicles were operated at engine speeds corresponding to idle and cruise. Measurements were also made at two distances near a freeway, for light traffic (approximately 20 vehicles per min) and for heavy traffic (approximately 45 vehicles per min). The principal instrumentation consisted of several phase-stable receivers with coherent quadrature detectors whose outputs were digitized at a rate of 200 samples per quadrature component per second and recorded on magnetic tape for computer processing. About 10 min of data (about 120 000 samples) were obtained during each measurement. The computer plotted the APD on a Rayleigh scale in dB relative to thermal noise and calculated the mean noise power available at the antenna terminals (related by a constant to the noise factor F a ) and V d --the ratio in dB of rms to average voltage. The average power of the ignition noise increases with engine r/min and V d usually decreases. Near a freeway, most of the noise is contributed by a small number of very noisy vehicles. The APD's for various situations are strikingly similar; all show that most of the noise envelope samples in a measurement are Rayleigh distributed. A small percentage of the noise samples do not follow the Rayleigh distribution, but are of higher amplitude. This percentage is higher for an engine at cruise speed than at idle speed, and higher for heavy traffic than for light traffic.

Voltage noise, current noise and impedance in space clamped squid giant axon.

Abstract: The relationship between voltage noise at constant current and current noise at constant voltage across a linear electrical system is emphasized. In systems like the nerve membrane near its resting state, which show a complicated dependence of impedance on frequency in the range 1–1000 hertz, current noise and voltage noise are completely different. Two different preparations of the axon at rest are used, resulting in small area (∼ 0.04 cm2) and large area (∼ 0.4 cm2) membranes, and in different intracellular compositions. These are shown to give the same results when membrane impedance is accounted for. A distinct hump exists in the voltage spectrum, which is absent in the current spectrum. This structure depends on temperature and voltage, and may be understood when membrane impedance is taken into account. This result is in contrast with previously published work of voltage noise from squid axon. It is argued here that voltageclamp/current-noise data is most likely to give significant kinetic information about conductance changes in membranes.

Measurements and interpretation of low-frequency noise in FET's

Abstract: Equivalent gate-noise voltage magnitudes of MOSFET's and JFET's have been measured by a direct method for the frequency range of 20 Hz-9 kHz. Results of a number of theoretical analyses of MOSFET flicker noise have been combined to yield a generalized expression for the drain-noise current. Experimental results showing the bias, temperature, and frequency dependence of the noise have been presented and carefully examined in cognizance with the divergent nature of various theories and relevant published experimental data.

Optical data storage potential of six materials.

Abstract: Measurements of writing sensitivity and theoretical projections of readout signal-to-noise ratio achievable for several magnetooptical materials and an amorphous semiconductor material are used to assess their storage density and data rate potential in a discrete bit recording system. Dynamic read/write experiments utilizing infrared GaAs lasers presently indicate a density limit of 107 bits/cm2 on MnAlGe and MnGaGe due to grain noise and on GdCo due to domain stability. Wavelength limited resolution appears obtainable on MnBi and TeGeAs although reversibility limitations exist. PtCo seems capable of exceeding 108 bits/cm2 at data rates of 50 M bits/sec.

On sensitivity and roundoff noise in wave digital filters

Abstract: In a wave digital (WD) filter, attenuation, and thus attenuation sensitivity, can be defined in two different ways. The first type of sensitivity is of importance from the point of view of attenuation distortion and can easily be kept small. The second, which differs from the first at most by an additive constant, is important from the point of view of roundoff noise. Structures are discussed for which both definitions coincide, thus ensuring the possibility of keeping both sensitivities simultaneously low.

Noise measurements on the floating diffusion input for charge‐coupled devices

Abstract: A technique is presented for electrically introducing charge into a charge‐coupled device (CCD) in a stable uniform low‐noise manner. The technique utilizes a floating diffusion whose capacitance (Cfd) can be tailored for particular applications or monitored directly for noise measurements. Experimental results are presented which demonstrate that charge can be introduced into a CCD with a variance of kTCfd. This technique is particularly germaine to the introduction of a ``fat zero'' into a low‐light‐level surface channel CCD imager.

A three-level metallization three-phase CCD

Abstract: A new electrode structure for CCD's is described. This structure is three-phase with three levels of metal and considerably relaxes the demands on the photolithography. It is predicted and shown that this structure leads to devices with a high performance, a high packing density, and a high yield over very large areas. Devices with 256 and 64 elements, primarily intended for analog delay applications, have been fabricated and measured. Transfer inefficiencies of 5 × 10-5with only 5-percent background charge and a transfer noise corresponding to an interface state density in the low 109cm-2eV-1have been measured in a surface channel device. The devices may be satisfactorily operated at pulse voltages of a few volts. In bulk channel devices, transfer ineffciencies of 2.5 × 10-5have been observed, and bulk state densities of 2 × 1011cm-3have been derived.

Noise in Josephson point contacts with and without rf bias

Abstract: Point contact Josephson junctions operated as microwave mixers at 36 GHz show conversion gain and lower noise than cooled Schottky barrier diodes in the same application. The noise in such junctions with and without rf bias is explored both experimentally and theoretically. The noise power is found to be about a factor 2 above the thermal noise in the resistively shunted junction model. In contrast to previous reports, the inclusion of a shot noise term in the theory for no rf bias overestimates the observed noise substantially.

Theory of noise in charge-transfer devices

Abstract: The noise introduced into charge packets transferred through and stored in charge-transfer devices is calculated in a manner that includes all important relaxation, suppression, and correlation effects. First, the noise induced into each packet during each transfer phase from thermal, trapping, emission-current, and leakage-current fluctuations, whose statistics are nonstationary, and from clock-voltage fluctuations, whose statistics are stationary, is determined. Relaxation of the transferring charge to these fluctuations is found to suppress their size. Second, the accumulation (collecting) of the noise as each packet is transferred through the device is calculated neglecting the role of incomplete charge transfer. Attention is drawn to the significant differences between the collecting of storage-process noise, which is unsuppressed, transfer-process noise, whose spectral density is nearly totally suppressed at low frequencies, and modulation noise, which is nearly totally suppressed for digital and analog signals. Third, the role of incomplete charge transfer in suppressing the collecting of the noise is shown for digital signals and indicated for analog signals. We conclude with a numerical calculation of the maximum possible signal-to-noise ratio that can be expected from charge-transfer devices. The presentation is sufficiently general and detailed that, with a minimum of background in formal noise theory, one can use the approach to evaluate noise in many novel, solid-state devices.

A Practical Gamma-Ray Camera System Using High-Purity Germanium

Abstract: A prototype gamma camera system has been constructed which is based on a high purity germanium detector fabricated with orthogonal strip electrodes. In this device, position sensitivity is obtained by connecting each contact strip on the detector to a charge-dividing resistor network. Excellent energy and spatial resolution have been achieved by cooling the resistor network to 77°K and by proper selection of noise filtering parameters in the pulse shaping amplifier circuitry. The significant advantage of employing this charge-splitting detector in a semiconductor gamma camera system is its electronic-readout simplicity, requiring only three amplifier channels to measure the energy and two-dimensional location of gamma ray events. A complete discussion of our investigation of the charge-splitting detector concept is presented with special reference to its potential use in the construction of a high resolution gamma imaging system having sufficient field of view and sensitivity for clinical utilization. Several orthogonal strip-electrode germanium detectors have been fabricated and evaluated experimentally in our laboratory. The most recent of these measures 2 cm × 2 cm × 5 mm thick and incorporates 10 contact strips on each surface which are spaced on 2 mm centers. The measured FWHM energy and spatial resolutions were 5.5 keV and 1.66 mm, respectively. Theoretical calculation of the magnitude of noise in the energy channel and comparison of these values to measured data shows that correlated noise cancellation significantly enhances the energy resolution in this type of charge splitting device.

Simdified 12-GHz Low-Noise Converter with Mounted Planar Circuit in Waveguide (Short Papers)

Abstract: A 12-GHz low-noise converter consisting of a planar circuit mounted in waveguide is described. This circuit consists of a metal sheet with proper patterns that is inserted in the middle of a waveguide parallel to the E plane. All circuit elements required for the converter are pressed or etched. This circuit is very useful for low-cost mass production and good performance. A measured noise figure of 4.5 dB was obtained with a 12-GHz signal frequency and a 420-MHz intermediate frequency.

Prediction differential pulse code modulation system with adaptive compounding

Abstract: The adaptive differential PCM transmission system uses a first-order prediction and a simple quantizing step-wise adaptation to improve signal-to-quantizing noise ratio.

Treatment of microscopic fluctuations in noise theory

Abstract: A new method is introduced and used to calculate the statistics of the microscopic fluctuations of charge carriers in devices. By expressing the fluctuations of the carriers in terms of elementary transfer fluctuations, we are able to separate the induced fluctuations from the spontaneous fluctuations experienced by such carriers. This enables us to treat correlation effects in the dynamical portion of the problem and reserve for the statistical portion only well-defined, uncorrelated random forces whose statistics are readily calculated. The method includes all important correlation effects as well as multiple-decay-time relaxation effects and, thus, it fills a gap in the Langevin method as well as in the impedance-field method of calculating noise in devices. The method is suitable for treating nonstationary as well as stationary noise, and in some cases can be used directly on macroscopic problems. We also present a derivation of a recently introduced expression for diffusion noise of carriers whose mobility is a nonlinear function of applied electric field. This microscopic approach may further illustrate the origin, nature, and treatment of fluctuations in devices.

Voltage contrast linearization with a hemispherical retarding analyser

Abstract: A system for the linearization of voltage contrast in the scanning electron microscope for potentials between +or-10V is described. The linearization is achieved by using two concentric hemispherical grids which form a retarding field analyser with the specimen at the centre of the grids. Collection is by either a solid hemispherical cup, or alternatively the conventional scintillator cage. Results are presented for both cases. A discussion of the minimum detectable potential in terms of the beam current and equivalent noise current is also included.

A marginal oscillator detector for ion cyclotron resonance spectrometers

Abstract: Design, construction, and performance of a solid state marginal oscillator for detection of ions in ion cyclotron resonance experiments are described. Special design features include noise matching a high Q tank to an FET preamplifier which sacrifices voltage level for improved S/N ratio, amplitude limiting to remove noise from the feedback signal, and impedance matching the feedback resistor to the tank to minimize phase shift, parasitic capacitive coupling, and tank loading. A simple electrical circuit which simulates power absorption by ions for performance testing and comparison among marginal oscillators for icr applications is also described.

Effect of source lead inductance on the noise figure of a GaAs FET

Abstract: The noise performance of a GaAs FET (series Gat. 1, Plessey, England), operating in the pinchoff mode and in the common-source configuration, is examined neglecting thermal effects due to the velocity saturation. The complete equivalent circuit of the transistor including all extrinsic and package elements is used to obtain the noise figure of the transistor in the frequency region between 0.5 and 4 GHz. All computations of the noise figure are made using the noise model of van der Ziel.