Showing papers in "Bell System Technical Journal in 1960"

Capacity of a burst-noise channel

Abstract: A model of a burst-noise binary channel uses a Markov chain with two states G and B. In state G, transmission is error-free. In state B, the channel has only probability h of transmitting a digit correctly. For suitably small values of the probabilities, p, P of the B $rA G and G $rA B transitions, the model simulates burst-noise channels. Probability formulas relate the parameters p, P, h to easily measured statistics and provide run distributions for comparison with experimental measurements. The capacity C of the model channel exceeds the capacity C(sym. bin.) of a memoryless symmetric binary channel with the same error probability. However, the difference is slight for some values of h, p, P; then, time-division encoding schemes may be fairly efficient.

Solid solubilities of impurity elements in germanium and silicon

Abstract: The available data on solid solubilities of impurity elements in germanium and silicon are summarized in the form of solidus or solvus curves. New solubility data are presented for the lead-germanium, zinc-germanium, indium-germanium, antimony-silicon, gallium-silicon and aluminum-silicon systems. The correlation of the solid solubilities with the heats of sublimation and the atom sizes of the impurity elements is considered.

The theory and design of chirp radars

Abstract: A new radar technique has been developed that provides a solution for the conflicting requirements of simultaneous long-range and high-resolution performance in radar systems. This technique, called Chirp at Bell Telephone Laboratories, recognizes that resolution depends on the transmitted pulse bandwidth. A long high-duty-factor transmitted pulse, with suitable modulation (linear frequency modulation in the case of Chirp), which covers a frequency interval many times the inherent bandwidth of the envelope, is employed. The receiver is designed to make optimum use of the additional signal bandwidth. This paper contains many of the important analytical methods required for the design of a Chirp radar system. The details of two signal generation methods are considered and the resulting signal waveforms and power spectra are calculated. The required receiver characteristics are derived and the receiver output waveforms are presented. The time-bandwidth product is introduced and related to the effective increase in the performance of Chirp systems. The concept of a matched filler is presented and used as a reference standard in receiver design. The effect of amplitude and phase distortion is analyzed by the method of paired echoes. One consequence of the signal design is the presence of time side lobes on the receiver output pulse analogous to the spatial side lobes in antenna theory. A method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes. The weighting process is described, and calculated pulse envelopes, weighting network characteristics and dele-???

Binocular depth perception of computer-generated patterns

Abstract: The perception of depth involves monocular and binocular depth cues. The latter seem simpler and more suitable for investigation. Particularly important is the problem of finding binocular parallax, which involves matching patterns of the left and right visual fields. Stereo pictures of familiar objects or line drawings preclude the separation of interacting cues, and thus this pattern-matching process is difficult to investigate. More insight into the process can be gained by using unfamiliar picture material devoid of all cues except binocular parallax. To this end, artificial stereo picture pairs were generated on a digital computer. When viewed monocularly, they appear completely random, but if viewed binocularly, certain correlated point domains are seen in depth. By introducing distortions in this material and testing for perception of depth, it is possible to show that pattern-matching of corresponding points of the left and right visual fields can be achieved by first combining the two fields and then searching for patterns in the fused field. By this technique, some interesting properties of this fused binocular field are revealed, and a simple analog model is derived. The interaction between the monocular and binocular fields is also describea. A number of stereo images that demonstrate these and other findings are presented.

An alternative approach to the realization of network transfer functions: The N-path filter

Abstract: A particular time-varying network consisting of several parallel transmission paths, each containing input and output modulators, is described and analyzed. It is shown that, under certain conditions, the network may be characterized by a transfer function. A particular form of this transfer function yields periodic filtering characteristics over a limited frequency band without employing distributed elements. Techniques are also presented for realizing highly selective band-pass filters without the use of magnetic elements. Some practical applications are discussed in detail and experimental verification is presented.

Germanium and silicon liquidus curves

Abstract: New measurements are reported on the solubility of germanium in liquid gallium, thallium, tin, arsenic, bismuth, cadmium and zinc, and the solubility of silicon in liquid indium, tin, lead, antimony, bismuth and zinc. The measurements of other workers are renewed, including those of the solubility of germanium and silicon in liquid copper, silver, gold and aluminum; of germanium in liquid indium, lead and antimony; and of silicon in liquid arsenic and nickel. All but two of the liquidus curves can be described within experimental error by a two-constant equation. The form of this equation suggests that the liquid solutions exhibit certain simple thermodynamic properties, and some evidence is cited indicating that the constants of this equation can be used to estimate the excess free energy of the solutions. Figures for the complete liquidus curves of these binary systems (T-x and log x−1/T) have not been included in this paper, but sets of these figures can be supplied upon request.

Passage effects in paramagnetic resonance experiments

Abstract: An attempt is made to classify theoretically paramagnetic resonance signals of inhomogeneously broadened lines occurring under various experimental conditions. The theoretical predictions are checked experimentally. Special emphasis is given to cases in which T 1 is long, and to cases in which the adiabatic condition γH$$ $rQ dH/di is violated.

The charge and potential distributions at the zinc oxide electrode

Abstract: Capacitance measurements made on single crystal zinc oxide electrodes in contact with aqueous electrolytes are reported. Over a wide range of bias and bulk donor density, the results are in almost quantitative accord with predictions of the simple Poisson-Boltzmann (Poisson-Fermi in the degenerate case) equation. This is shown to imply the complete absence of surface-state effects in this system. A very sharp discontinuity in the flat-band potential is observed at bulk electron densities in the range from 0.6 × 1018 to 2 × 1018 cm−3. This and other effects, arising under varying surface treatments, are discussed in some detail. The use of the semiconductor/electrolyte interface in studying the properties of low-lying donors is illustrated for the case of boron, which is shown to lie about 0.3 ev below the conduction band.

Amplitude distribution of shot noise

Abstract: A shot noise, I(t), is a superposition of impulses occurring at random Poisson distributed times …, t −1 , t 0 , t 1 , t 2 , …. In the simplest case, if the impulses all have the same shape F(t), then $I(t)=\sum{\limits_{i}}F(t-t_i)$ . We study, in this and more general cases, the distribution function $Q(I)=Pr\[I(t)\ \leqq\ I\]$ . One of our results is an integral equation for Q(I). This yields explicit expressions for Q(I) in a number of cases, including F(t) = e−t; it also permits a computational technique which is applied to F(t) = e−t sin ωt for >> 1.

Some further theory of group codes

Abstract: The notion of equivalence for group codes is explored in some detail. A dual for a code, and the sum and product of two or more codes, are defined. Properties of these constructs are investigated. Indecomposable codes are defined and are shown to be optimal in two different senses. Various classes of codes are enumerated.

Capabilities of the telephone network for data transmission

Abstract: This paper presents the results of a nationwide data transmission field testing program on the telephone switched message network. Error performance using the FM digital subset is described and basic transmission characteristics such as net loss, bandwidth, envelope delay and noise are given.

Design and performance of ultraprecise 2.5-mc quartz crystal units

Abstract: A 2.5-mc crystal unit has been developed for use in a new, extremely stable frequency standard oscillator. A well-balanced design was achieved by using a 30-mm-diameter, plano-convex, polished quartz plate, coated with gold and operated on its fifth overtone. The quartz plate is mounted on its quiescent edge in an evacuated bulb, and achieves a Q of five to six million, representative of the Q of the quartz itself. The temperature coefficient, current coefficient, frequency adjustment tolerance and frequency aging of the crystal unit are all consistent with a frequency stability in the order of one part in 1010. It was necessary to develop polishing methods that would not disturb the crystal structure of the quartz plate and new methods of orienting the crystollographic axes to achieve better temperature coefficient control. New methods of mounting the quartz plate were found that avoid strain and reduce the effects of shock and vibration. The new crystal unit makes possible oscillators characterized by excellent frequency stability, small and uniform aging and straightforward design. For periods up to one month, the frequency stability of such standards compares favorably with that of atomic frequency standards.

Diffused junction depletion layer calculations

Abstract: Depletion layer properties have been calculated for diffused junctions in silicon and germanium as a function of reverse voltage and of diffusion parameters for the gaussian and the complementary error function distributions. These results bridge the gap between the linearly graded behavior generally exhibited by suck junctions at low voltage and the step behavior exhibited at high voltage. For total depletion layer thickness and capacitance, the transition from graded to step junction behavior extends over about one decade of voltage. For depletion layer thickness on a single side of the junction, it extends over several decades. Depletion layer thickness and peak electric field are presented graphically as a function of voltage for a variety of junction depths and impurity concentration functions. The ranges for which the. step and graded junction approximations are valid are apparent from these charts. The results were obtained by an analytical integration of Poisson's equation, and a subsequent use of the IBM 704 for a numerical evaluation of the transcendental equations obtained.

High-frequency negative-resistance circuit principles for Esaki diode applications

Abstract: Certain fundamental principles are presented for analyzing and designing high-frequency amplifiers and oscillators utilizing simple negative resistance elements such as the Esaki or tunnel diodes. The first part of the paper covers the conditions necessary for oscillation and amplification with a single negative-resistance diode, including stability criteria, gain and bandwidth. It is shown that the highest-frequency circuits require diodes with very small dimensions, so that a single-spot diode will have a very low power capacity. In order to obtain higher power at high frequencies, distributed circuits must be used, either with narrow-strip diodes or a multiplicity of small spot diodes. Such circuits present special stabilization problems in suppressing unwanted modes of oscillation. Methods of avoiding such difficulties are presented for one-port oscillator circuits and for traveling-wave amplifier circuits. In the latter case, nonreciprocal attenuation of the gyromagnetic type is recommended.

The design of radar signals having both high range resolution and high velocity resolution

Abstract: Radar systems that yield simultaneous information regarding the range and velocity of a target would be useful in certain applications. A discussion is presented of some fundamental limitations on simultaneous range-velocity determination in terms of ambiguity diagrams, with the aid of a quantum mechanical analog to the Wigner distribution function. A sequence of signals is found in which the signals yield both range and velocity information with increasing accuracy. However, this desired property is not accompanied by a waveform suitable for maximum operating efficiency.

Human factors engineering studies of the design and use of pushbutton telephone sets

Abstract: From the user's point of view, what are the desirable characteristics of pushbuttons for use in 500-type telephone sets? The studies reported bear on this question and also on questions of how people process information when keying telephone numbers. Four categories of design features were studied: key arrangement, force-displacement characteristics, button-top design and central office factors. The results indicate that considerable latitude exists for key set design in terms of user performance; however, the preference judgments are more selective. The studies also showed that the manner in which the person acquired and keyed the telephone number influenced performance appreciably. Technological progress in recent years has brought pushbutton signaling from the telephone set within sight of economic feasibility. What, from the user's viewpoint, are the desirable operating characteristics of the key set which should guide development and manufacture? And how do people process information when they key a telephone number?

Potential distribution and capacitance of a graded p-n junction

Abstract: For a graded p-n junction under sufficient forward bias, the usual space-charge approximation to the potential breaks down, and a numerical solution of the differential equation satisfied by the potential is required. A procedure is described which avoids the difficulties associated with direct numerical integration of the stiff differential equation, and which yields a pair of very close upper and lower bounds to the potential at all points. For a linearly graded junction, tables of bounds are given which nowhere differ by as much as 1 per cent, and which effectively bridge the gap between the space-charge case and the neutral case. The computer solutions are used to calculate the voltage dependence of the stored charge (low-frequency ac capacitance) of a graded junction numerically, as a function of the bias voltage across the junction. The expression for the capacitance is split into two parts, one of which dominates in the neutral case and the other in the space-charge case. With properly normalized variables, it is possible to give a universal plot of small-signal ac capacitance against applied voltage. The results differ from the usual approximate formulas by amounts ranging up to nearly 10 per cent.

Impurity redistribution and junction formation in silicon by thermal oxidation

Abstract: In the process of growing an oxide on doped silicon, electrically active impurities near the silicon/silicon dioxide interface are redistributed according to the diffusion coefficients and the distribution coefficient of the impurity between the oxide and the semiconductor. An analysis of the phenomenon predicts that single-junction or two-junction material can be obtained by oxidation of the surface of a compensated silicon crystal. For parabolic growth of the oxide, the surface concentration is independent of time, and the junction depth, gradient and sheet resistivity vary with t1/2. This has been demonstrated experimentally by oxidation of a compensated p-type silicon crystal doped with gallium and antimony.

Models for approximating basilar membrane displacement

Abstract: Three analytical models are developed for estimating the displacement of the basilar membrane in the human ear when the sound pressure at the eardrum is known. Frequency-domain data, derived experimentally by Bekesy, are Fourier-transformed to examine the impulse response of the membrane. Time-domain and frequency-domain responses of the models are compared with the experimental data. Excitation of the models by periodic impulses is considered. Calculations of membrane displacement are made for excitation by positive pulses, and by alternately positive and negative pulses. Applicability of the results to the perception of pitch is indicated.

The square of a tree

Abstract: The adjacency matrix of a graph of n points is the square matrix of order n, in which the i, j element is one if and only if the ith point and the jth point are adjacent, or i = j; and is zero otherwise. Let A be the adjacency matrix of graph G considered as a boolean matrix so that 1 + 1 = 1. Then G2, the square of G, is the graph whose adjacency matrix is A2. We obtain a necessary and sufficient condition for a graph to be the square of a tree by providing an algorithm for determining a tree that is the square root of any graph known to be the square of some tree. This algorithm cannot be carried through when a graph is not the square of a tree. It is shown that, if a graph is the square of a tree, then it has a unique tree square root. The method utilizes a previous result for determining all the cliques in a given graph, where a clique is a maximal complete subgraph. This result was obtained while attempting the more general problem of characterizing boolean matrices having a square root, or, in general, an nth root.

Pushbutton calling with a two-group voice-frequency code

Abstract: A customer voice-frequency pushbutton signaling scheme involving a new two-group signal code, termed “four-by-four”, is described. It is shown that the use of this code, with judiciously chosen frequencies, permits the detection of bona fide signals after transmission over any ordinary voice connection and facilitates discrimination against false signals resulting from speech. Apparatus for generating the tones is described, and the principles of reception are discussed.

On the recovery of a band-limited signal, after instantaneous companding and subsequent band limiting

Abstract: If f(t) is a band-limited function, with band limit −Ω to Ω, the result of instantaneously companding f(t) is in general no longer band-limited. Nevertheless, it has been proved that knowledge of merely those frequencies of the compandor output which lie in the band from — Ω to Ω is sufficient to recover the original signal f(t). An iteration formula has been proposed that, in theory, performs the desired recovery. In this paper we study in detail some of the practical questions raised by that formula. We show that the successive approximations converge to the solution f(t) at a geometric rate, uniformly for all t, and that the iteration procedure is stable. We then describe a method of performing the recovery in real time and a successful simulation, of it on a general-purpose analog computer. The circuit used in the simulation serves as a first approximation to a practical realization of the recovery scheme.

Electrical properties of gold-doped diffused silicon computer diodes

Abstract: Planar diffused silicon junctions with storage times of one millimicrosecond or less are readily obtained by gold doping. The introduction of uniform gold concentrations (in the range from 1.2 × 1015 cm−3 to 8 × 1016 cm−3) is conveniently done using solid state diffusion techniques. The gold diffusion technique allows relatively precise control of recombination center density, and, although applicable to almost any diffused silicon device, is particularly useful in control of storage time in small-area diffused silicon computer diodes. In this application, reverse recovery time of about one millimicrosecond may be obtained without substantial degradation of other electrical parameters. The process of gold doping by diffusion and its effect on electrical characteristics of diffused silicon computer diodes are discussed. Included are comparisons of first-order calculations and experimental results for variations of reverse recovery time, reverse current and forward current with gold atom density.

Synthesis of driving-point impedances with active RC networks

Abstract: A general method is presented for synthesizing driving-point impedances using RC networks and active elements. The procedure realizes any real rational driving-point function and leads to rather simple structures. Only one active device, a negative-impedance converter, is required. The synthesis of biquadratic impedance functions is considered in detail.

Semiconductor strain transducers

Abstract: The relatively recent discovery of the high piezoresistive sensitivity of semiconductors such as germanium and silicon has made miniature strain transducers available that compare with piezoelectric devices in dynamic applications but are also capable of producing dc signals After a historical survey of research in piezoresistivity, a brief phenomenological description of the physical effect is given and the pertinent solid slate theory is summarised. Various applications of semiconductor elements as strain transducers are then discussed in detail, special emphasis being given to surface strain gages. The problems of maximizing the bond rigidity for such gages and compensating far temperature effects are dealt with, and future efforts in these directions are outlined.

Automata and finite automata

Abstract: Since it is not clear, in general, how an automaton should best be characterized, one of the purposes of this paper is to find ways to go from one characterization to another. In doing so, we hare not been completely impartial — the programming approach has been emphasized more than the others. There are perhaps two reasons for this emphasis: First and the more obvious one is the closeness between theoretical programming discussed here and programming of digital computers. Secondly, the programming approach has provided a way of looking at automata that seems to make certain ideas less obscure — the construction of a universal program in Section. III of this paper is one such example. In the theory of finite automata, Theorem 3 is an attempt to unify the ideas of complete and partial automata, which have generally been treated separately in the past.

Evaluation of message circuit noise

Abstract: The reduction and control of message circuit noise requires that its effects be quantitatively characterized. This is achieved by measuring some physical attribute of the electrical noise such that two noises that are judged to be equally interfering are assigned approximately equal numerical magnitudes. To give meaning to such magnitudes, the scale of measurement is related by way of subjective assessment into terms useful to telephone engineering. Pertinent to message circuit noise measurement is the characterization of the relative interfering effect of single-frequency noise components and the way the ear combines these components to indicate the total effect. The correlation between a noise measurement and its associated over-all end-effect may be made by finding the transmission-loss equivalent of the noise being measured or by the direct application of telephone-user opinions expressing degree of transmission satisfaction. In addition to these topics, this paper discusses certain engineering aspects of noise evaluation.

Signaling systems for control of telephone switching

Abstract: Telephone signaling is basically a matter of transferring information between machines, and between humans and machines. The techniques developed to accomplish this have evolved over the years in step with advances in the total telephone art. The history of this evolution is traced, starting from the early simple manual switchboard days to the present Direct Distance Dialing era. The effect of the increasing sophistication in automatic switching and transmission systems and their influence on signaling principles are discussed. Emphasis is given to the signaling systems used between central offices of the nationwide telephone network and the influence on such systems of the characteristics of switching systems and their information requirements, the transmission media and the compatibility problem. A review is made of the forms and characteristics of some of the interoffice signaling systems presently in use. In addition, the problem of signaling between Bell System and overseas telephone systems is reviewed with reference to differing information requirements, signaling techniques and new transmission media. Finally, some speculation is made on the future trends of telephone signaling systems.

The construction of missile guidance codes resistant to random interference

Abstract: Many types of missiles are guided by a finite set of distinct commands radioed from the ground in the form of a time-sequence of RF pulses. The command information is contained in the n − 1 time spacings between successive pulses in a group of size n, and is encoded and decoded by means of multitapped delay lines combined with AND gates. This paper discusses the problem of encoding command information (i.e., selecting the time spacings between pulses) so that m false pulses (m $$ n − 2) cannot combine with the n true pulses in any way to form a false command. Although it is very easy to state the restrictions that must be imposed on the time spacings between the pulses in the different commands, no general methods exist for finding, among codes satisfying these restrictions, those codes in which the longest command is as short as possible. This paper presents certain lower bounds, together with a few empirically derived codes approaching these lower bounds. The relationship between these codes and the well-known error-correcting binary codes of information theory is discussed in an appendix.

Theory of current-carrier transport and photoconductivity in semiconductors with trapping

Abstract: Fundamental differential equations are derived under the unrestricted approximation of electrical neutrality that admits trapping. Extension is made for applied magnetic field. The transport equations derived hold without explicit reference to detailed trapping and recombination statistics. Modified ambipolar diffusivity, drift velocity and lifetime function apply in the steady state. The same diffusion length is shown to hold for both carriers, and a general “diffusion-length lifetime” is defined. Atass-action statistics are considered for cases of (one or) two energy levels. Certain “effective” — rather than physically proper — electron and hole capture and release frequencies or times that apply to concentration increments are defined. Criteria are given for minority-carrier trapping, recombination and majority-carrier trapping, and for “shallow” and “deep” traps. Applications of the formulation include: the diffusion-length lifetime for the Shock-ley-Read electron and hole lifetimes; linear and nonlinear steady-state and transient photoconductivity; negative photoconductivity; the photoconductive decay observed by Hornbeck and Haynes in p-type silicon; the photomagnctoelcctric effect; and drift of an injected pulse. Photomagnetoeleclric current is found to be decreased by minority-carrier trapping, through an increase in diffusion length. A simple general criterion is given for the local direction of drift of a concentration disturbance. With trapping, there may be “reverse drift,” whose direction is normally that for the opposite conductivity type, and also local regions of carrier depletion that may extend in practice over appreciable distances.