US 3668415 A
A supply device for delivering rectangular voltage pulses of very small width between two outputs comprise a storage capacitor, a transmission flat or coaxial line constituted by a plurality of two-conductor sections having the same characteristic impedance and placed in series. A rapid-closure switching means connects the terminals of the capacitor to a circuit in which the two conductors of the line are incorporated. The two outputs are connected to the same conductor of the line at each end of one of said sections.
Description (OCR text may contain errors)
United States Patent Marilleau 1 June 6, 1972  DEVICE FOR SUPPLY VOLTAGE  References Cited PULSES UNITED STATES PATENTS  Inventor: Jacques Marilleau, 7, rue Emile Zola-94, 3,225,223 12/1965 Martin ..307/108 Nogent sur Marne, France 3,402,370 9/1968 Ross ..333/20  'Flled: 1971 Primary Examiner-Herman J. Hohauser [21 Appl. No.: 1 16,006 Attorney-Cameron, Kerkam & Sutton  Foreign ApplicationPriority Data  ABS CT A supply device for delivering rectangular voltage pulses of Feb. 23, 1970 France ..7006238 very Small width between two outpms comprise a Storage capacitor, a transmission flat or coaxial line constituted by a  U.S.Cl ..307/106, 328/56, 332384722), pmramy of twoconductor Sections having the Same charac 51 1 Cl "03k 3/00 teristic impedance and placed in series. A rapid-closure 23 333/20 switching means connects the terminals of the capacitor to a circuit in which the two conductors of the line are incorporated. The two outputs are connected to the same conductor of the line at each end of one of said sections.
7 Claims, 5 Drawing Figures This invention relates to an high-speed supply device which is intended to deliver rectangular voltage pulses of very small width to a receiving element. Among the potential applications of a device of this type, there can be mentioned in particular the control of image converter tubes of the bi-planar diode type having a uniform electric field (and involving either proximity focusing or magnetic focusing) and the Kerr or Pockels cells. It is known that, in all these cases, it is-necessary to deliver to the receiving element a rectangular voltage pulse having a well-determined height V and time-width T. The profile of the pulse must be as rectangular as possible although the stringency of this requirement is largely dependent on the type of receiver. It is known in particular that the design conditions (such as the ratio of rise time to pulse width, etc.) are less critical in the case of image converter tubes of the proximity-focusing type in which the anode and the cathode are very closely spaced than in the case of magneticfocusing tubes which nevertheless have the advantage of a lower interelectrode capacitance.
Up to the present time, two types of supply devices have essentially been employed for delivering rectangular pulses of very small width. The first type makes use of a coaxially line which is closed on its characteristic impedance and on the receiving element and a second line which has the same characteristic impedance as the first, which can be loaded at double the voltage to be delivered to the receiving element and which can be closed on the first line by means of a highspeed switch (usually a triggered spark-gap). This device is subject to many disadvantages: the second line must be loaded at double the voltage to be delivered to the receiving element; the pulse delivered to the receiver remains rectangular only if the product of the capacitance of the receiver (which is assumed to be localized) and of the characteristic impedance is very distinctly lower than the time-width T.
The second type makes use of two transmission lines (usually coaxial lines) which have the same characteristic impedance but different propagation times and a storage capacitor which is first charged and then closed on both lines at the same time by means of a high-speed switch. The rectangular pulse is then collected between the ends of the two lines opposite to those on which the storage capacitor is closed.
As will become apparent hereinafter, this device has the disadvantage of requiring a capacitor having a very high capacitance in order that the decrease in voltage during the pulse time should remain acceptable. Moreover, after delivery of the pulse, the device gives rise to the appearance of a counter-voltage or undershoot which can be of appreciable amplitude if the capacitance of the capacitor is sufficient.
The aim of the invention is to provide a device which meets practical requirements more effectively than those which have been employed heretofore, especially insofar as the abovementioned disadvantages are largely removed.
With this objective, the invention proposes a supply device which is capable of delivering rectangular voltage pulses of very small width between two outputs and comprises a twoconductor transmission line, a storage capacitor and rapidclosure switching means for closing the capacitor on a circuit comprising the two conductors of the line, characterized in that said line is constituted by a plurality of sections having the same characteristic impedance and that the two outputs are connected to the same conductor of the line at each end of one of said sections and that said pulses are delivered between said two outputs.
The line can be coaxial; it can also be flat and have parallel flat conductors. The line can be closed on its characteristic impedance beyond the second output or be extended by a further section which may supply another element if so required.
A better understanding of the invention will be gained from the following description of a supply device constituting one mode of application of the invention which is given by way of non-limitative example and also from a comparison between said device and a device of the reference will be made to the which:
FIG. 1 shows very diagrammatically a supply device comprising a storage capacitor and two coaxial lines in accordance with the prior art;
FIGS. 24 and 2b show very diagrammatically the variation in time of the different voltages developed at the time of operation of the device shown in FIG. 1;
FIG. 3 shows very diagrammatically a device in accordance with the invention for supplying a receiving element which is connected in shunt, a coaxial line being employed in this prior art. In the description, accompanying drawings, in
. FIG. 4 shows very diagrammatically an alternative embodiment of the device of FIG. 3 in which the receiving element is connected in series.
The storage-capacitor device which is illustrated in FIG. 1 is intended to deliver rectangular voltage pulses to a receiving element 10 consisting, for example, of an image converter tube of the proximity-focusing type. This device comprises two coaxial lines 12 and 14 which are of unequal length in order to have transit times whose difference is equal to the duration or time-width T of the pulses to be delivered. Said two lines 12 and 14 have the same characteristic-impedance lo and are respectively closed on impedances l6 and 18 which are equal to their characteristic impedance. The load element 10 is placed between the outputs 20 and 22 on the input side of the impedances l6 and 18.
The two lines 12 and 14 are supplied in parallel from the same storage capacitor 24 via a distribution tee 26 and a highspeed switch 28 which preferably consists of a triggered sparkgap. Provision is evidently made for a circuit (not shown) for charging the capacitor 24 through a resistor 30 having a high value. I
Assuming that ideal conditions are achieved (namely a capacitor 24 which has infinite capacitance, which is geometrically localized and has no stray inductance as well as negligible dimensions of the assembly constituted by thestorage capacitor 24, the high-speed switch 28 and the supply tee 26), the two transmission lines 12 and 14 carry rectangular voltage pulses having a height V which is equal to the charging voltage E of the storage capacitor 24. There is in fact obtained in this case a rectangular pulse having a width T and a constant height V. However, the capacitance of the storage capacitor 24 is finite in practice and the voltages developed between the output 20 and ground (full-line curve in FIG. 2a) and between the output 22 and ground (dashed-line curve in FIG. 2a) are exponential quantities having a negative coefficient in which the time constant is C.Zc/2, wherein C is the capacitance of the storage capacitor 24. In this case, the voltage pulse which appears between the outputs 20 and 22 assumes the shape which is shown in FIG. 2b. The voltage decreases by a value dV during the time interval T and there appears after the rectangular pulse a negative counter-voltage whose amplitude at the origin is equal to dV.
The device in accordance with the invention as illustrated in FIG. 3 makes use of a single coaxial transmission line. For the sake of greater simplicity, the components of the device which correspond to those already shown in FIG. 1 are designated in FIG. 3 by the same reference numerals followed by the index a. There is again shown in this figure a storage capacitor 240 which can be charged through a resistor 30a. Said capacitor can be closed on the coaxial line-by means of a high-speed switch 28a which can consist of a triggered spark-gap, for example. The coaxial line comprises a first connecting section 32 followed by a section 34 having a transit time which is equal to the width T of the pulses to be produced. Provision is made in FIG. 3 for a third section 36 having the characteristics of a line of infinite length which can in any case be replaced by a loop impedance whose value is equal to that of the characteristic impedance Zc of each section 32 and 34. In the case of ideal characteristics of the capacitor 24a and of the assembly 24a-28bq, there appears at the time of discharge of the capaci- 7 of the section 34.
The device of FIG. 3 offers advantages over that of FIG. 1 in that only one connecting line is required between the storage capacitor, the switch and the load element. The impedance through which the storage capacitor discharges is multiplied by two if the lines employed have identical characteristics since said impedance increases from Zc/2 to Zc. The discharge current is therefore one-half the value within the spark-gap 28, with the result that the service life of this latter is extended accordingly; the pulse has a faster rise time (the ratio of the stray inductance of the discharge circuit to the discharge impedance being twice as small as in the previous case) and it is only necessary to have a value of one-half the capacitance of the storage capacitor in respect of a given voltage drop dV (the discharge time constant being C.Zc instead of C.Zc/2). This reduction gives rise to a correlative decrease in the stray inductance of the storage capacitor.
In the embodiment which is illustrated in FIG. 3, the receiving element is connected in shunt on the coaxial line. This solution is preferable in the case of some types of load element. In other types (such as some Kerr cells and certain types of bi-planar diode tubes, for example), it is preferable to adopt the series arrangement which is illustrated diagrammatically in FIG. 4. In the case of this figure in which the elements corresponding to those of FIG. 3 are designated by the same reference numerals followed by the index b, it is apparent that the arrangement of the section 34b with respect to the electrodes 38 and 40 of the receiving element is such that the width of the rectangular pulse is constant over the entire surface area of the electrodes. The section 36b can be employed for supplying an additional receiving element or can altematively be replaced by a loop impedance having a value which is equal to the characteristic impedance of the line. The impedance of the receiving element must in all cases be matched with that of the coaxial line, if necessary by inserting said impedance in a suitable four-input mounting in order to minimize reflection phenomena.
The transmission lines which are illustrated in FIGS. 1 and 3 are of the coaxial type. When the load element has a flat geometry, it is often preferable to employ flat propagation lines or at least to associate flat propagation lines with coaxial lines by means of suitable transition couplers.
What we claim is:
1. A supply device for delivering rectangular voltage pulses of very small width comprising two outputs, a storage capacitor, a transmission line constituted by a plurality of two-conductor sections having the same characteristic impedance and placed in series, and rapid-closure switching means for connecting the terminals of the capacitor to a circuit in which the two conductors of the line are incorporated, one of said two outputs being connected at each end of one of said sections of the same conductor of the line.
2. A device according to claim 1, wherein the line is coaxial and the two outputs are connected to the central conductor.
3. A device according to claim 1, wherein the line is flat and has parallel conductors.
4. A device according to claim 1, wherein the line is closed on its characteristic impedance beyond the second output.
5. A device according to claim 1, wherein the line has a section which can be assimilated to an infinite line beyond the second output.
6. A device according to claim 2, wherein a load element connected to said outputs is connected in shunt on the line.
7. A device according to claim 2, wherein a load element is connected in series in the line and has an impedance which is matched with the characteristic impedance of the line.