US2964638A - Electronic anticoincidence device - Google Patents

Description

Dec. 13, 1960 J. M. N. HANLET 2,964,638

ELECTRONIC ANTICOINCIDENCE DEVICE Filed Jan. 2, 1959 2 Sheets-Sheet 1' Dec. 13, 1960 J. M. N. HANLET 2,954,633

ELECTRONIC ANTICOINCIDENCE DEVICE Filed Jan. 2, 1959 2 Sheets-Sheet 2 F'IG.3.

United States Patent ELECTRONIC ANTICOINCIDENCE DEVICE Jacques Marie Noel Hanlet, Santa Monica, Calif., as-

signor to Societe dElectronique et dAutomatisme, Courbevoie, Seine, France, a corporation of France Filed Jan. 2, 1959, Ser. No. 784,554

Claims priority, application France Jan. 4, 1958 4 Claims. (Cl. 250-213) The present invention has for its object a device depending upon the physics of solids, which constitute in themselves, and independently of applications which may be made of them, a detector of temporary anti-coincidences of signals, assuring further, in the event of anti-coincidence, the identification of the signal then present.

The invention is characterized essentially in that it is made up of the combination of a pair of identical electroluminescent cells and by a photoconductor having a lateral effect (as defined later) having an axis of symmetry, on each side of which are established electrodes for the taking off of current and respectively projecting the lights of electro-luminescent cells when activated by distinct signals.

A photoconductor having lateral effect can be defined as follows, and in a manner per se suificient for the purposes of the invention, referring for greater simplicity to the diagram of annexed Fig. 1, which shows the principle of the invention. Figs. 2 and 3 show two examples of the invention in practical form:

Let there be a solid body 1 of type N conductivity in the form of a parallelepiped rectangle having a length L and a width 21, and the median plane of symmetry with reference to the width being indicated by M. Upon or in the material of this body is introduced another mate rial 2 forming a thin band or strip lengthwise of the path of the median plane M on the lower face of this solid. This second material is of the type P conduction, a conductor by lack of electrons (or in other words, by excess of holes). There has thus been made an N-P junction in this solid, according to the present well-known technology of the solid elements of electronics, diodes and transistors.

The prolonged lateral faces of this solid body 1 are covered with thin film conductive electrodes 3 and 4, to which are connected outlet terminals T1 and T2 respectively. For the disclosure one may consider that a resistance of charge R is connected between these outlets, shunted by a current-indicating device I.

In a general way when the light falls on the upper face of such a solid (the face opposite to the face containing the junction strip 2), there is created in the solid 'pairs of electrons holes which, if the junction did not exist, would move to recombine 0n the face opposite to that which receives the light. On the contrary, when the junction is present, the holes go towards the region P, for the most part, and the electrons towards the region N, that is, towards the lateral electrodes 3 and 4. As the material 2 has a greater conductibility than material 1, one can assume from the fact that material 2 is not subjected to any polarization, that it is equipotential and that, consequently, the holes redistribute themselves uniformly in the structure. However this may be, and if the light falls, for example, on surface 5 at the left of the median plane M of the solid on the diagram, light L there appears in the material 1 a current running from 2 towards 3 and, when taken off, this current will traverse 2,964,638 Patented Dec. 13, 1960 the resistance R in the direction indicated by arrow i If on the other hand the activating light falls to the right of the median plane M, as indicated by L there appears in the material 1 a current going from 2 towards 4 and, when taken off, this current will traverse the resistance R in the direction indicated by the arrow i Such action takes place if the length l is less than the distance of recombination of electron-hole, and if the thickness of e is very small with relation to the life duration and mobility of the carriers of charge in the material 1.

If the two activating lights L and L coexist on the upper face of the solid body 1, the two currents i and 1', develop simultaneously and, naturally, if the conditions of symmetry (mechanical as well as electric) are satisfied, these two currents will have the same value and one will cancel the other in the circuit of resistance R.

These effects, as seen from the point of view of the difference of potential between the outlets T and T can be construed as follows:

In the absence of incident light, or with incident light symmetrically applied over the surface opposite to the junction, there exists no difference in the relative potential between the outlets;

In the presence of a light L on surface 6 there appears a difference of potential between the outlets, with T positive with respect to T In the presence of a light L on surface 5 there appears a difference in potential between the outlets, with T positive with respect to T These current conditions can be confirmed by having the indicator I in the form of a voltmeter having high impedance.

Naturally, the definition of the type N and of the type P conductivity as given above should be considered as relative and may be assured by the proper choice of the materials 1 and 2. If, for example, the material 1 is germanium or silicon, the material 2 can consist of indium.

One form of a device according to the invention is shown by way of example only in Fig. 2, conventional details being omitted. Also, in this diagram, the relative dimensions of the elements, especially their thicknesses with relation to other dimensions, are not correctly shown, the thicknesses being exaggerated in order to assure clarity of the drawing. It should be understood that layers of very small thicknesses are involved, the electrodes or armatures being of thin films or skins.

This device includes the operative association of two members A and B, supported on opposite faces of a transparent supporting plate 11, formed of glass, for example. The member A is a double electro-lurninescent cell. The member B is made according to Fig. 1, that is, 1 is a plate of germanium or siliciurn crystal, having its edge faces covered with conductive metal for the formation of the electrodes 3 (not shown in Fig. 2) and 4, and in which the electrode 2 has been formed by a diffusion of indium or by a recrystallization of a deposit of indium. The member A is a double electroluminescent cell comprising, for example, a translucent film electrode 12 deposited upon the upper face of glass plate 11, a monocrystalline plate 13 of electroluminescent material producing, when excited, a light which passes through 12 and 11 and excites the material 1 of the member B, and two film electrodes 14 and 15 applied to the upper face of plate 13, these electrodes being of the same surface areas and disposed symmetrically on opposite sides of the median plane of the structure. A connection Z can be provided for junction electrode 2, and connections X and Y are provided for the application of input signals to electrodes 14 and 15 respectively. The electro-luminescent material can, for example, consist of a monocrystalline complex of oxides of zinc and copper, in a relation of zinc to copper greater than 99%. The electrode 12 can consist of a film of oxide of titanium. The electrodes 14 and 15 can be'o-f'silver, aluminum or "even of platinum or rhodium. Otherknow'n materials can, moreover, be "sub- 'stituted for those indicated above, without'thereby going outside the scope of the invention defined by the combination of the members A and Bin the foregoing description. V

In 'order to explain the functioning of the device'of Fig. 2, it will be considered that the input signals are electric, being applied to the terminals X and Y at the time that the terminal Z is held 'at a constant potential, for example that of the earth. It is clear nevertheless that the input signals could be luminous, appropriate polarization potentials being then applied between the terminals X-Z and Y-Z and the activation taking place by luminous excitation for each cell, or even each of the connections X and Y might come from a photoconductor element excited by a luminous radiation form ing the input signal. For the usual materials of'electroluminescence each applied signal should be of alternating character, not necessarily sinusoidal in form, and can be reduced to an impulse of suitably brief duration.

In the absence of excitation, at either Xo'r Y, no appreciable difference in potential exists between the terminals T and T When, however,'a. signal appears 'at X alone, the electro-luminescent cell at the left (in the drawing) lights up and in the member B there appears a difference in potential between T and T the positive pole of which is at T and the negative pole at T This response signal continues until the disappearance of the signal at X or until a signal is applied to Y, for then in this latter case the second signal produces illumination of the other electro-luminesce'nt cell at'the same time that the first cell is illuminated by the signal at X; thereby creating a difference of potential e'qu'alto the value of the first potential between the terminals T and T but in the inverse direction,'that is, negative pole at T and positive pole at T in the member B, and the two differences in potential, being equal, will annul each other.

If now the signal ceases at X andthe signal at Y persists, the difference of potential at terminals T and T exists with T negative with respect to T The device thus functions as a circuitfor the'indic'ation of anti-coincidence of two input signals of thesame characteristics and, by the polarity of its output, it provides identification of that one of these two signals which exists alone at a given instant.

From the point of view of the logic of the circuits this can be explained by saying that the equality of numerical values represented by the entering signals, X= and Y=0, or X=l and Y'=1, the value of the number represented by the outgoing signal is 0 but that, on the contrary, for one of the conditions X 0 and Y:1 or X=1 and Y=0, the value of the number represented by the out-going signal'is 1. This is the logical operation called disjunction. Here, however, the device discriminates between the two natures of number -1 at the output, according as'one has one or the other of the conditions of anti-coincidence. By such a function of disjunction the device can thus advantageously be employed as half-adders and "especially as halfsubtractors of binary numbers, since in thislatter case, it-can furnish directly the numbers retained when the number to be subtracted fromthe other is 1 at the time that the second is O.

From the viewpoint of commutation circuits the device functions as a circuit of conditional transfer, a gate circuit, in that one of the signals is allowed to pass to the output only in the absence of the other. Each signal thus serves to inhibit the other but the'output discriminates between the information signal and the inhibition signal. This is evidently anewfunction in commutation.

Finally, by its double function of ant1-coincidence-and of discrimination the device-can also serve for the development of a signal of error in a servo-mechanism, the magnitudes of input and output of which are coded numerically in binary values.

Returning to the applications of such a device in logical systems, it can then be mentioned thatamong the usual logical operations there exists also the operation called of union; an out-going signal ought to exist whenever at least one of the input signals, or thetlwo, exists on the device. And so, according to the diagram of Fig. 3, a device of the invention can, indirect manner, perform this logical function of reunion also, while establishing simultaneously the above mentioned "signal of disjunction. p p

In effect, in the diagram of Fig. 2, the N-P junction was, in fact, left floating since no out-going connection was made to electrode 2. In establishing such a connection and on connecting it at a point of potential defined by means of a resistiveunidirectional connection, onecan derive from it a reunion signal to be taken off at the terminals of the pure'resistance in this connection. This is shown in Fig. 3, where diode D and resistance R are connected in series between terminal T of electrode 2 and ground.

Under this condition the photo-voltaic component of the member B comes into play for, as is well understood, this component is not at all inhibited by the lateral photo-conductive effect defined above. The photo-voltaic component will exist as soon as one of the signals appears at X or at Y and will continue when the two signals are present at X and at Y. This component will be of a constant polarity and the provision of the element D even though not required, will be advantageous, for it will avoid action of this photo-voltaic component on the amplitude of the output signals at T and T Thus, in fact, it will be advantageous to establish the connection beginning with the electrode 2 even if one does not utilize the signal 'at the terminals of R Further, when needed, one can render equal to each other the values of the three out-put components, that is to say, the differences in potential at the terminals of the three resistances R R and R It is sufiicient for this purpose that:

where p is the resistivity in ohms/cm. of the semi-conductor 1, L the width of the plate between the terminals T and T and E the thickness of the plate 1. I The parameter b designates the ratio of the mobilities ofthe charges in the semi-conductor 1.

I claim:

1. A device for detecting anti-coincidence of two signals comprising in combination, a pair of electro-luminescent cells arranged to be activated by distinct signals, a photo-conductive elementpositioned so that equal areas thereof on opposite sides of a median plane are controlled by said cells respectively, electrode means extending along the path of said median plane on the oppositefac'e of said photo-conductive element from said cells to 'provide an N-P junction on said photo-conductive element, side electrodes carried by the two side faces of said photoconductive element in symmetrical relation with said junction, indicator means connected between said side electrodes and being responsive to the voltage'difie'rence developed between said electrodes, and a resistance element connected from each side electrode'to a point of fixed potential, said resistance elements having equal re sistance values.

2. A device according'to claim 1 and including indicator means connected between said side electrodes and being responsive to the voltage difierence developed between said electrodes. I v I 3. A device according to claim 1, and including "a ponnection incorporating a resistance and an element 5 having unidirectional conductivity extending from said side electrodes, to the product of its thickness times the junction electrode to a point of fixed potential. ratio of the mobilities of the electrons and the holes in 4. A device according to claim 3, in which the values said semi-conductor.

of the resistances connected to the said side electrodes and terminating at points of fixed potential, and for the 5 References Cited in the file of this patent resistance connected to the junction electrode are chosen equal to each other and to the ratio of the product of the UNITED STATES PATENTS resistivity of the semi-conductor of the type N of the 2,641,712 Kircher June 9, 1953 photo-conductive element times its width between said 2,863,056 Pankove Dec. 2, 1958

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