Solid-state Letter Display Device

Abstract

A plurality of luminous diodes and a driving circuit therefor adapted to cause selected combinations of the luminous diodes to luminesce to display selected letters are formed on the same or different sides of a substrate and the assembly is encapsulated by a transparent molded protective coating. The driving circuit in the form of a diode matrix circuit is fabricated by the integrated circuit technique.

Description

BACKGROUND OF THE INVENTION

This invention relates to a novel solid-state letter display device.

Among conventional letter display devices may be mentioned a light spot-type display device employing discharge tube-type display tubes, fluorescent display tubes or groups of small lamps. These prior devices are not advantageous in that the physical dimensions of the devices are large when compared with those of the letter or characters to be displayed or the number of letters to be displayed because all of these devices utilize vacuum tubes, require relatively high voltage and relatively large power, have poor space factor and require independent driving circuits.

Recently developed electronic circuits require miniaturization of the display device itself, low operating voltage, small driving power and decreased thickness of the device because of the tendency of utilizing integrated circuits and large scale integrated.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a new and improved letter display device which can eliminate disadvantages of the above described types of conventional display devices and can satisfy the requirements of modern display devices.

One of the features of this invention lies in a solid-state letter display device wherein well-known luminous diodes are used as the display elements, the display driving circuit is formed by the technique of the integrated circuit so that these elements are formed on a substrate and are then molded into a unitary structure. Accordingly, the solid-state letter display device embodying this invention is characterized in that it does not utilize any vacuum tube and that it is of small size and thin.

Another feature of this invention lies in a solid-state letter display device wherein luminous diodes and a display driving circuit are formed on a single-semiconductor wafer as an integrated circuit and are then molded into a unitary structure.

Still further feature of this invention is to provide a solid-state letter display device capable of displaying a number of letters.

In accordance with this invention there is provided a solid-state letter display device characterized by comprising a substrate, a plurality of luminous diodes which are formed on the substrate and arranged such that when they are suitably combined they can display any desired letter, a driving circuit for selectively exciting the luminous diodes, said driving circuit being formed on the substrate by the integrated circuit technique and a protective coating encapsulating the substrate, the luminous diodes and the driving circuit. The substrate may be an electric insulator, a metal plate or a semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages together with organization and operation of this invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a perspective view of a solid-state letter display device or unit embodying the principle of this invention with a portion of the casing broken away;

FIG. 2 is a partial sectional view showing the relation between a substrate and luminous elements;

FIG. 3 shows a diagram of one example of a diode matrix driving circuit employed in this invention and

FIG. 4 is a perspective view of a solid-state display device for displaying a plurality of letters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1 illustrating a perspective view, partly broken away, of a novel display unit for displaying digits, reference numeral 10 indicates an insulating substrate of ceramic and the like on which are formed a group of display elements a through h for constituting digits 0 through 9 inclusive wherein elements g and g' are formed electrically integral. These elements are comprised by luminous diodes having PN-junctions. The luminous diode is a solid-state luminous element typically consisting of GaAs, and as is well known in the art luminesces by the injection of charge carriers through the PN-junction by the application of a voltage and the recombination of such charge carriers. According to this invention, a preformed group of luminous diodes a through h is bonded to the substrate 10. As shown in FIG. 1, a driving circuit 20 formed by the integrated circuit technique is also bonded to the substrate. As will be described later in more detail, the driving circuit is comprised by a diode matrix circuit adapted to select predetermined combinations of display elements and to cause them to luminesce to form desired digits. One example of such a diode matrix circuit is illustrated in FIG. 3.

The diode matrix circuit shown in FIG. 3 is a so-called erasing system selecting circuit wherein the number of diodes utilized is decreased. In FIG. 3 reference numeral 0 through 9 represent terminals corresponding to respective digits to be displayed and terminals a through h correspond to respective luminous diodes shown in FIG. 1. It is now assumed that after closing a switch S, a wiper W is connected to a terminal corresponding to a digit desired to be displayed, then the digit will be displayed by a selected combination of luminous diodes. Thus for example, digit 3 is assumed to be displayed. Upon connecting the wiper W to terminal 3, diode D.sub.1 will short circuit element f, diodes D.sub.2 and D.sub.3 element e and diodes D.sub.4 and D.sub.3 elements g and g'. As a result, voltage is applied to elements a, b, c, d and h alone so that as can be readily understood from FIG. 1 these elements cooperate to display digit 3.

According to this invention the diode matrix circuit is fabricated by a well-known integrated circuit technique which may be either multitip, monolithic or mixed integrated circuit. In this manner, the circuit substrate 20 comprising an integrated circuit is of extremely small size. According to this invention, the circuit substrate 20 is bonded to the substrate 10 either on the front surface thereof as shown in FIG. 1 or on the rear surface. In addition to terminals 0 through 9, the circuit substrate 20 requires two more terminals for the source and ground. Thus there are 12 terminals. In FIG. 1 these terminals are shown by terminals T.

As best shown in FIG. 3, it is necessary to connect circuit substrate 20 to respective luminous elements a through h. FIG. 2 is a cross-sectional view to illustrate the manner of deriving out lead wires to respective elements when the circuit substrate 20 is bonded to the rear surface of the substrate 10. More particularly, luminous elements are bonded to the front surface of the substrate and two perforations 11 and 12 are provided near the opposite ends of each luminous element. Grounding lead 30 connected to the lower electrode of the luminous element extends through the perforation 11 while an exciting lead connected to the upper electrode extends through the perforation 12 to a driving circuit.

A protective coating 40 of a resinous material, for example, is molded to encapsulate the assembly, as shown in FIG. 1. In order to make visible the luminous elements, at least the front portion of the protective coating 40 should be transparent. Thus, FIG. 1 shows a solid-state letter display device or unit embodying this invention.

As can be noted from the foregoing description, the novel letter display device is characterized by having no vacuum tube or filament. In addition, since the luminous elements and their driving circuit are composed of semiconductors and since they are molded into a unitary structure, the device is not only thin and small size but also can withstand against mechanical vibrations and shocks. Further, as a driving circuit and luminous diodes are fabricated by the integrated circuit technique it is possible to operate them with low voltage and low power. For this reason the novel display device can be operated directly from an integrated circuit system. If the portion of the protective coating were constructed to act as an optical lens, more easy reading of the displayed letter would be possible. When suitably colored the coating acts as a filter. Inasmuch as the luminous elements utilized in this invention are comprised by luminous diodes, where indium and phosphorous are used in the semiconductor material, the luminous elements will emit red colored, while zinc and cerium provide blue colored. In this manner, letters of different colors can be displayed.

Although in the above embodiment, a plurality of independent luminous elements and an integrated driving circuit were bonded to a common insulating substrate of ceramic or the like, it will be obvious to those skilled in the art that such luminous elements and driving circuit may be formed on a single-semiconductor wafer by the integrated circuit technique. Where a metal plate is utilized as the substrate to act as one of the electrodes of the luminous diodes, not only the construction of the assembly can be simplified but also the efficiency of heat dissipation can be improved.

FIG. 4 shows a perspective view of a modified embodiment of this invention wherein a plurality of display units shown in FIG. 1 are arranged in side by side relationship to simultaneously display a number of letters or numerals of several orders of magnitude.

Although the invention has been shown and described in terms of preferred embodiments thereof numerous changes and modifications may occur to one skilled in the art within the scope of this invention as defined in the appended claim.

Claims

What is claimed is:

1. A self-contained solid-state character decoder display device comprising:

a thin support substrate having a rectangular area generally the size of a character space occupied in a display;

a plurality of luminous PN-junction diode display elements supported on said substrate in the form of a character raster with power and ground electrical leads respectively from each side of said PN-junction projecting through said substrate;

a set of plug connection terminals extending from one edge of said substrate, one terminal for each character to be selected and in addition power and ground terminals;

a unitary diode matrix decoder circuit supported on said substrate outside the area occupied by said character raster, said circuit having:

a first set of leads connected respectively to said power leads of said display elements and a second set of character selection leads with a diode connected selection circuit from each character selection lead of said second set to a predetermined combination of leads of said first set,

circuit connections from said ground terminal to said ground leads of all of said display elements, and

circuit connections from said power terminal through respective resistors to each lead of said first set; and an encapsulating shell for said substrate providing a transparent area over the area occupied by said display elements and having said terminals projecting therefrom.