US2922924A

US2922924A - Signal generator

Info

Publication number: US2922924A
Application number: US730666A
Authority: US
Inventors: Robert F Bundy
Original assignee: Allen B du Mont Laboratories Inc
Current assignee: Allen B du Mont Laboratories Inc
Priority date: 1958-04-24
Filing date: 1958-04-24
Publication date: 1960-01-26
Anticipated expiration: 1977-01-26

Description

Jan. 26, 1960 Filed April 24. 1958 R. F. BUNDY SIGNAL GENERATOR 2 Sheets-Sheet 1 1 FIXED FREQUENCY MOVEMENT PRODUCING DEVICE SIGNAL SOURCE VARIABLE FREQUENCY SIGNAL SOURCE MODIFYING CIRCUITRY SIGNAL UTILIZATION Fig.

2o DEVICE UTILIZATION DEVICE PULSE GENERATOR UTILIZATION DEVICE INVENTOR. ROBERT F. BUNDY ATTORNEYS Jan. 26, 1960 2 SheetsSheet 2 Filed April 24. 1958 INVENTOR. ROBERT F. BUNDY ATTORNEYS SIGNAL GENERATOR Robert F. Bundy, Philadelphia, Pa., assignor to Allen B.

Du Mont Laboratories, Inc., Clifton, N.J., a corporation of Delaware Application April 24, 1958, Serial No. 730,666

2 Claims. (Cl. 315-169) This invention relates to the production of recurrent signals, and more particularly to the production of sequential signals which may be used for triggering, commutating, or gating of apapratus requiring this type of signals.

There are innumerable trigger signal utilizing apparatuses which may advantageously use the benefits of my invention. These would include Oscilloscopes, ignition systems, signs, etc. For the purpose of more fully explaining the operation and advantages of, my invention, I shall consider its use with a fiat display device, since this device has many inherent problems which are not present in other simpler utilization apparatus.

The so-called flat display device is one which extends the display abilities of prior art cathode ray tubes. Many forms of flat display devices have been proposed, most of them envisioning a flat sandwich type structure which has a set of planar vertical conductors and another set of planar horizontal conductors. The separate sets of conductors are separated by a light producing medium which is energized when signals are applied to selected conductors of each set.

In order for a flat display device to be compatible with established television standards, the device must be capable of producing approximately 480 horizontal lines, which are to be sequentially energized, and approximately 580 vertical lines which are also, but separately, sequentially excited. One of the most perplexing problems in the development of a satisfactory flat display device is the obtaining of a commutator which can sequentially trigger the necessary lines at the required rate. Another problem associated with the flat display device is that of actually applying the triggering pulses to the respective lines which are to be energized. The third problem, related to the second, concerns the distance between the trigger pulse source and the utilization device. If this distance is great the length of the connecting Wires introduces a bulky arrangement; and the proximity of the multitudinous connecting wires introduces distributed capacitance which establishes severely limited frequency response and thus restricts the detail of the final presentation.

It is therefore the principal object of my invention to provide an improved source of triggering impulses.

It is another object of my invention to provide a triggering impulse source which is compact enough to be included within the framework of a fiat display device.

The attainment of these objects and others Will be realized from the following specification, taken in conjunction with the 'drawings, in which,

Fig. 1 illustrates the basic concept of my invention;

Fig. 2 depicts another embodiment thereof;

Fig. 3 shows a further embodiment; and

Fig. 4 shows how my invention can be incorporated into the structure of a flat display device.

Basically, my invention contemplates a transmission line within which is produced an exciting wave pattern, and the positioning of a plurality of pickup elements United States Patent at selected points of said transmission line. A particular element is energized by the wave pattern to produce a triggering signal, whereupon I cause the wave pattern to vary thus sequentially energizing selected pickup elements which may be loops, buttons, probes or other suitable arrangements.

The fundamental inventive concept is best explained with reference to Fig. 1, which illustrates apparatus for producing triggering pulses in accordance with my invention. Basically, it comprises a transmission line 10, which may take the form of a coaxial conductor, a waveguide, or a similar arrangement. A signal source 12, such as an oscillator, is connected to one end of transmission line 10, and applies thereto exciting signals of a fixed frequency to produce an exciting wave pattern. In accordance with well known principles, these signals set up a pattern of standing waves as illustrated by dotted line 14.

The theory behind standing wave patterns, their prodaction, and variation is extremely involved, and therefore no explanation will be presented here beyond the statement that the desired patterns may be readily produced. The literature abounds in discussions of this subject, particularly simple explanations being offered in Radio Engineering by Terman, third edition, pages 79-86, and Communication Engineering by Everitt, second edition, pages 139-153.

Standing wave pattern 14 of Fig. 1 has positive and negative peaks, at each of which the voltage of the standing wave is a maximum. For simplicity, the following explanation will consider the use of the negative peaks, although the positive peaks, or both the positive and negative peaks, may be readily utilized.

According to my invention, a first pickup element such as a probe 18 is positioned at a point where a peak occurs, As previously pointed out, the value of the voltage at that point is a maximum, and a signal is picked up by probe 18 and transmitted through suitable circuitry 19 to a utilization device 20.

Transmission line 10 also has positioned along its length other probes such as 22 and 24. For the standing wave pattern described above, only probe 18 is positioned to be energized by the peak of the standing wave, and therefore the only signal applied to utilization device 29 is received from probe 18.

-A.second triggering signal may be obtained from the second pickup probe 22. As shown in Fig. 1, a movable piston 26 is positioned at the far end of transmission line it). Piston 26 is made of conductive material, so it elfectively short-circuits transmission line 10 at whatever point it happens to be. A movement producing device 27 now causes piston 26 to move to the right. As it moves, the zero potential point of the standing wave pattern (caused by the short circuit) moves along with it, thus causing the entire standing wave pattern to move to the right. In this Way, the peaks are slightly displaced toward the right. As the subject peak moves in that direction, it eventually leaves the position of probe 18, and falls upon pickup probe 22, thus producing a signal which is applied to utilization device 20 in the manner previously described. It will be realized that as the peak moves from the position of probe 18 to that of probe 22, the signal at probe 18 will gradually diminish while that at probe 22 progressively increases. If the rate of change is too slow, or if a more abrupt change is desired, suitable circuitry incorporating amplitude limit devices, pulse shaping apparatus, etc., may be employed.

In a similar manner, additional pickup probes positioned along transmission line 10 pick up signals as piston 26 is moved.

The simplified drawing of Fig. 1 is obviously only for the purpose of explanation. A device incorporating the principles of my invention would have many more suitably positioned pickup probes. Under some conditions it may be desirable to position the pickup elements closer together than is physically feasible. This problem can be solved by arranging the pickup elements helically about the transmission line. The helical arrangement permits each element to have the necessary longitudinal separation from its neighbors, and yet have sufficient physical spacing to satisfy mechanical considerations.

Piston 26, which was described as being made of conductive material to form a short circuited end for the transmission line, may alternatively be plastic coated. This structure would form a capacitive arrangement which would also be a short circuit at the desired frequency, and would also produce a better sliding surface. The movement device 27 may take any suitable form in order to provide the piston movement which produces the desired movement of the standing wave pattern. Mechanical devices would be suitable for slow excursions, whereas magnetostriction or other arrangements might be preferred for more rapid response.

It is obvious that mechanical movement of a piston will introduce problems, and that the return movement of the piston will energize the pickup probes in the opposite sequence, a procedure which might be undesirable under certain conditions. In order to overcome the above problems, the embodiment of Fig. 2 may be used. This embodiment does not utilize a piston, but uses a signal source 112 which provides an exciting signal of varying frequency. In accordance with well known principles, a signal of a first given frequency will produce a particular exciting wave pattern and a first probe 30 is positioned to pick up the signal at a point where a peak occurs. When source 112 produces a second given frequency, the original wave pattern is modified to produce a slightly different standing wave pattern, the signal producing peaks occurring at slightly different positions along transmission line 10. A second pickup probe 32 is positioned to be energized by a peak of the second pattern. When a signal of a third frequency is used, a third standing wave pattern occurs and a third probe 34 is positioned to be energized thereby. Thus as source 112 produces signals covering a given frequency spectrum, additional probes will be sequentially energized, and will be enabled to transmit their respective signals to the utilization device. This embodiment obviates the mechanical problems of Fig. l, and further permits signal source 112 to be designed so that the generated frequency abruptly returns to its starting value, thus eliminating the reverse sequence of excitations. Again, in this embodiment, the distal end of transmission line 110 is preferably short circuited to fix one end of the standing wave pattern.

Each embodiment so far described uses a source which generates a continuous exciting signal. An embodiment utilizing a slightly different principle is shown in Fig. 3,

wherein a source 212 produces an exciting signal which consists of a single pulse of one cycle of a given frequency. As the pulse travels toward the distant end of transmission line 210, the overall wave pattern changes, and the peak sequentially energizes the various probes. For the embodiment of Fig. 3, transmission line 210 preferably takes the form of a delay line, which may be straight or coiled. The amount of delay and the positioning of the pickup probes determines the interval between sequential excitations of the utilization device.

In the embodiment of Fig. 3, a standing wave pattern is not desired, and an absorbing material 31 is therefore positioned at the far end of the transmission line 210.

Present day fiat display devices are generally designed to be energized by positive going triggering pulses. In order that only the positive maximum portion of the standing wave pattern is transmitted to the fiat display device, circuitry may be connected between the pickup probes and the fiat display device to insure only the passage of the desired signals. This circuitry may include phase detectors, rectifying means which pass only the correct polarity of signal, bias means which assure that only signals between predetermined amplitude limits will be transmitted, signal shapiilg circuits, and any other circuitry to achieve the desired results.

As previously pointed out, it is advantageous to incorporate the pulse producing apparatus within the structure of the flat display device. My invention as described above may be so utilized since it is small, compact, mechanically stable, and will operate in a vacuum.

Fig. 4 illustrates in fragmentary form, a structure in which this is done. As previously explained, the fiat display device comprises two

wall portions

32 and 34, each having strips of conductive material positioned on or adjacent the inner surface. These strips may be conductive material deposited directly on the wall surface, or may be suitably positioned wires. Fig. 4 shows a set of vertical strips 36 on the inner surface of wall 32. There would also be a similar, but horizontal, set of strips on the inner surface of wall 34, but these have been omitted for the purpose of clarity. As previously explained the space between the two walls is filled with the light producing medium, but again for the purposes of clarity this material has been omitted.

The flat display device ordinarily has a top piece 38, which adds to the structural strength and provides a vacuum tight seal. According to my invention, a transmission line is produced by incorporating a shelf 40 between and perpendicular to the walls, and parallel to the top piece 38. The transmission line thus formed corresponds to those shown in Figs. 1 through 3. Other arrangements would of course be possible. The vertical conductors are shown as extending into the transmission line, and thus correspond to the pickup probes shown in previous drawings. Standing wave patterns are produced as previously explained in connection with Figs. 2 and 3. Sequential probes are energized as previously explained, and since the probes and strips consist of the same unitary structure, the triggering pulses produced by the transmission line are applied directly to the strips of the flat display device.

It is obvious that horizontal strips on the inner surface of wall 34 may be energized by a similarly procluced transmission line which is vertical.

It will be realized that the unitary structure of Fig. 4 is only one of many possible arrangements. Another structure would be one wherein a separate transmission line is physically included in the structure of the fiat display device.

Incorporating my device into the envelope of a flat display device solves the problems previously mentioned. First of all, the triggering pulses for each set of conductors may be individually produced at the desired rate, polarity, amplitude, etc., that may be required. Seeondly, since my device may be incorporated within the envelope of fiat display devices, the connecting leads are short, which minimizes attenuation; and are spread out, which minimizes distributed capacitance. The pickup elements are connected internally of the envelope to the proper strips of the display device, and the only external connection is that to the signal source.

Under some conditions, particularly where low frequency excitation is used, the peaks produced in the transmission line are rounded rather than pointed. If in addition, closely spaced trigger pulses are required, the pickup probes must be placed very close to each other. Under these conditions, it may happen that two or more adjacent probes will be energized simultaneously, and to almost the same extent. In order to overcome this situation, harmonic frequencies may be supplied to the transmission line in addition to the fundamental frequencies. Each of the frequencies would establish a standing wave pattern of its own. The resultant effect would be to cancel each other in some areas, and to reinforce each other in other areas, thereby producing a standing wave pattern having sharp, narrow high-amplitude peaks. Since the operation of the invention depends upon the excitation produced by the peaks, the cancellation would have no effect at all, while the emphasized peaks would produce extremely narrow pulses of high amplitude. An improved output may therefore be produced by proper selection of the frequencies and amplitudes of the added harmonics.

As a result of my having described the principles and several embodiments of my invention, those skilled in related arts may envision variations which are within the scope thereof. I desire therefore that my invention be limited not by the foregoing illustrations and explanations, but rather by the following claims.

What is claimed is:

l. A parallelpiped comprising: a front wall, a back wall, and a top; means producing a transmission line within said device, said means comprising a shelf positioned between said walls and substantially parallel to said top, whereby said transmission line is formed between said top, walls, and shelf, the axis of said transmission line being parallel to said top; means propagating a wave along said transmission line; and pickup elements positioned along the line of propagation of said wave, said elements comprising strips of conductive material positioned adjacent one of said walls and perpendicular to said axis whereby said pickup elements are sequentially energized by said moving Wave pattern.

2. A unitary structure including triggering apparatus and a flat display device, comprising: an envelope having a front wall, a back wall, sides, a top, and a bottom; means producing a transmission line within said device, said means comprising a shelf positioned between said walls and substantially parallel to said top whereby the axis of said transmission line is parallel to said top, and perpendicular to said sides; means causing a wave pattern to advance along said transmission line; and a plurality of pickup elements positioned along the line of advance of said wave pattern, said elements comprising parallel strips of conductive material positioned on one of said walls and perpendicular to said axis, one end of said elements being in said transmission line while the rest of said elements are in the flat display portion of said structure.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,131 Webber June 28, 1949 2,414,541 Madsen Jan. 21, 1947 2,442,606 Korman June 1, 1948 2,524,283 Blitz Oct. 3, 1950 2,605,323 Samuel July 29, 1952 2,625,460 Cloud et a1. Jan. 13, 1953 2,670,402 Marks Feb. 23, 1954 2,818,531 Peek Dec. 31, 1957 2,851,634 Kazan Sept. 9, 1958