DEVICE FOR SHAPING AND GENERATING ELECTRIC PULSES AND USE OF SAID DEVICE AS A PROTECTIVE CIRCUIT FOR ELECTRONIC COMPONENTS

Abstract: A device for passive shaping and generation of electric pulses from an electric signal incoming to the device, comprising a first coaxial conductor, which is connected along its extension to one or several pairs of coaxial conductors, of which one or several at their end located remotest from the first coaxial conductor are either short-circuited or open. According to the invention, said pair of coaxial conductors consist of only one coaxial conductor, viz. a second coaxial conductor (5). Said first coaxial conductor (2) is provided with a recess (6) extending from its shell surface (7) to its central conductor (8) and along an axial distance substantially corresponding to the outer diameter of said second coaxial conductor (5). Each of said second coaxial conductors (5) is provided with a recess (9) corresponding to said recess (6). The recesses (6, 9) of the two coaxial conductors (2, 5) so co-operate, that the central conductors (8) of the two coaxial conductors (2, 5) abut each other, and so that the shells (7, 10) of the two coaxial conductors (2, 5) are in electric connection with each other, where a connecting member (17, 18) is provided for retaining the two coaxial conductors (2, 5) in said electric connection with each other.

Description: "Device for shaping and generating electric pulses and use of said device as a protective circuit for electronic components". This invention relates to a. device for shaping and gener¬ ating electric pulses of short duration and to a use of said device. The development of high-speed electronics and electro-opt¬ ical components has rendered it possible to generate elec¬ tric transients of the magnitude picoseconds (ps) and even fractions of picoseconds. It is, howeve often desired to shape a generated signal by means of an independent device in order to produce a certain necessary shape of a pulse. It has previously been proposed for the shaping and gener¬ ation of pulses to utilize a coaxial conductor, which was connected along its extension to two coaxial conductors extending from the firstmentioned coaxial conductor, which two connected coaxial conductors either were short-circuit¬ ed at the ends or had so-called open ends, i.e. were not connected to any further element. As example thereof can be mentioned devices consisting of four coaxial conductors, which were so coupled together that two constitute a transient conductor and two constit¬ ute reflecting elements. Such devices, however, could not be used for the generati¬ on and shaping of pulses with a length of the magnitude picoseconds. Such known devices, furthermore, were complicated to change in respect of, for example, the length of the reflecting elements, because the components comprised are coupled by soldering. At many applications of a pulse shaper of the kind here referred to it is necessary to be able to change the length of the reflecting elements. This requirement is especially essential when the pulse shaper is used for the generation of pulses, which are utilized for studying other electronic components, such as different types of semiconductor elements. The present invention provides, a device for shaping and generating pulses which is a considerable improvement over known similar devices. The foremost advantages of the present device are that it is extremely simple in 5 its structure and that it is capable to operate with pulses having a rise time and/or duration in the range of picoseconds. The present Invention, thus, refers to a device forrpass- ive shaping and generation of electric pulses from an ' 10 electric signal entering the device, comprising a first coaxial conductor, which along its .extension is connected to one or several pairs of coaxial conductors, of which one or several at their ends located remotest from the first coaxial conductor either are short-circuited or '.1-5 open. The device is characterized in that said pair of coaxial conductors consist of only one coaxial conductor, viz. a second coaxial conductor, that aaid first coaxial conductor is provided with a recess extending from the outer surface of the conductor to its central conductor _20 and along an axial distance corresponding substantially to the outer diameter of said second coaxial conductor, that each of said second coaxial conductors are provided with a recess corresponding to said recess, and that the recesses of the two coaxial conductors co-operate so that 25 the central conductors of the two coaxial conductors abut each other , and so that the outer surfaces of the two coaxial conductors are electrically connected to each other, and that connecting means are provided for retain¬ ing the two coaxial conductors in said electric connect- 30 ion with each other. The invention further refers to a use of a device com¬ prising a first coaxial conductor, which along its ex¬ tension is connected to one or several pairs of coaxial conductors 3 of which one or several at their ends locat- 35 ed remotest from the first coaxial conductor are short- -circuited, where said pair of coaxial conductor con- sist of only one coaxial conductor, viz. a second coaxial conductor, and a recess is provided in the first coaxial conductor and, respectively, the second coaxial conductor or conductors, so that the recesses of the two coaxial conductors so co-operate, that the central conductors of the two coaxial conductors abut each other, and so that the outer surfaces of the two coaxial conductors are in electric contact with each other, which said useis charact¬ erized in that the device is coupled-in as a protective circuit for electronic components, which protective circ¬ uit filters out electric signals, which vary slowly in relation to the time required for transporting electric signals in the two branches of said second coaxial con¬ ductor. The invention is described in greater detail in the foll¬ owing, with reference to the accompanying drawings show¬ ing and illustrating exemplified embodiments of the in¬ vention. In said drawings Fig. 1 is an exploded -view of the device, Pig. 2 is a view of a detail of the lower co- axial cable in Pig. 1, Fig. 3 is a view from above of the coaxial cable in Fig. 2, Fi ^ 4 is a lateral view of the coaxial cable in Fig. 2, Fig. 5 shows an input signal to the present device. Figs . 6-11 show an output signal from different variants of the present device. In Fig. 1 a device 1 for passive shaping and generation of electric pulses is shown when an electric signal is supplied to it. The device 1 comprises a first coaxial conductor 2, which is provided with high-speed connections 3,4, such as so-called S A-connections. The coaxial conductor 2 can, for example, be a so-called 50 i -coaxial conductor with a length of 5 cm and an outer diameter of 3,6 mm. This coaxial conductor 2 is connected along its extension to one or several pairs of coaxial conductors. According to the invention, each such pair of coaxial conductors consist of only one coaxial conductor 5, which also is a so-called 50 -Λ -coaxial conductor. The coaxial conductors consist of a metallic central con¬ ductor and a metallic shelly between which an insulation of a plastic material is located. The firstmentioned coaxial conductor 2 is provided with a recess 6, see Fig. 2, extending from its shell surface 7 to its central conductor 8. As appears from Fig. 2, the recess has such a depth that the central conductor 8 has been ground off partially, or preferably to about its half. The recess is carried out along an axial distance corresponding substantially to the outer diameter of the second coaxial conductor 5. Each of said second coaxial conductors 5 also is provided with a recess 9 correspond¬ ing to the recess in the first coaxial conductor. The recesses 6,9 of the two coaxial conductors 2,5 are arr¬ anged to co-operate so that the central conductors of the two coaxial conductors abut each other and thereby are connected to each other, and so that the respective shell surfaces 7,10 of the two coaxial conductors are connected to each other. In Figs. 3 and 4 said recesses are shown in greater det¬ ail. Preferred measures concerning coaxial cables with an outer diameter of 3,6 mm are also shown. In order to prev¬ ent the central conductor 11 of the second coaxial conduct- or 5 to contact the shell 7 of the first coaxial conductor 2, the shell 7 is ground off along the straight edges of the recess 6,. so that the distance between the straight edges 12 and the upper surface 14 of the insulation 13 is about 0,2 mm, as best shown in Figs. 2 and 4. The second coaxial conductor 5 is provided with an identical recess as the first coaxial conductor 2. The coaxial -conductors preferably have a recess, the depth of which is slightly smaller than half its diameter, for example 1,6-1,7 mm.The shell surface of the first coaxial con- ductόr 2 as well as that of the second coaxial conductor 5 preferably are ground off on both sides of the recess, so that plane surfaces 15,l are formed, as shown in Fig. 2 in order to facilitate joining of the two coaxial conduct¬ ors as indicated in Fig. 1. The coaxial conductors 2,5 are combined to a cross by means of a connecting member, which retains the coaxial conductors in the aforesaid electric connection with each other. The connecting member comprises two portions 17,18 matching each other, which in assembled state together form two intersecting channels 19,20, which respective channels have a diameter corresponding to the outer diam¬ eter of the coaxial conductors 2,5, and intohwhich channels the respective coaxial conductor is intended to be placed. The portions are made of an electrically conductive mater¬ ial, for example brass. The portions 17,18 preferably are held together by means of a screw joint 21,22] 23,24; 25, 26. After the formation of the channel parts in the port¬ ions 17,18, the grooved surface of one portion is ground off slightly, for example 0,1 mm, so that the channels in the assembly direction of the portions have a diameter slightly smaller than the outer diameter of the coaxial conductors. The channel conductors hereby can be pressed against each other by tightening the screws 21,22. According to one embodiment, the recess in said second coaxial conductor 5 is located centrally along the length of the coaxial conductor 5, whereby two branches of exact¬ ly the same length are formed, where the entire length of the coaxial conductor 5 is 2L. Both free ends 27,28 of said second coaxial conductor 5 according to one embod¬ iment are short-circuited or open. In Fig. 1 the right- -hand end 27 is shown open. Short-circuiting of an end preferably is carried out, for example, by coating the end with an electrically conductive layer containing silv¬ er, whereby the central conductor 11 is electrically connected to the shell 10. J OJ N> ro _, n o Ul o l o Ul signal due to the number of second coaxial conductors 5, the branch length L thereof and whether their free ends are open or short-circuited. The present device, thus, is a passive element. For determining the output signal from the pulse shaper 1 for a given input signal in the form of a step pulse with the amplitude V , it is necessary to study expressions concerning the amplitude of the pulse V, transmitted through the first coaxial conductor and the pulse V re- fleeted by the second coaxial conductor in response to an incoming pulse V- . The following expressions concerning a transmission line including a discontinuity can be writt¬ en: and where Z. and Z, are the impedance for an incoming and, respectively, a transmitted pulse. For a short-circuited 50 . -coaxial conductor Z. = 50 Ω. and Z, - On . This yields V = -V.. For a coaxial conductor with open end Z. = 50 i and Z, = *--n . This yields V = +V-. For an arrangement according to above where an incoming pulse can choose one of three identical ways Z- = 50 and Z^ = 16.67-Ω . Thus, the pulse propagating in any one of them is V, = " . 12 . An incoming step pulse, thus, with the amplitude V gives rise to a positive step with the amplitude V 12 at the output. It is assumed that both ends of the second coaxial conductor 5 are short-circuited to earth. It follows from the aforesaid, that each branch of the second coaxial conduct- O * 5 gives rise to a signal with the amplitude -V /4 at the output. As a consequence thereof, thus, a positive step is followed by an identical step with inverse sign, where the later step follows after a time delay correspond¬ ing to the propagation time along a branch with the length . At an experiment each branch at the second coaxial con¬ ductor 5 had a length in the interval 2 to 150 mm, which corresponds to a delay of about 20 ps to 1,5 ns. Provided that the source of the incoming pulse and the load at the output both are adjusted to 50. , the present device thereby did not give rise to any undesirable re¬ flected additional pulses. With the present device, for example, a square pulse with a duration in response to the length of the second coaxial conductor can be created from an incoming step pulse. This is a very essential application of the present invention, especially as regards the aforesaid time range. In the attached Figures 5-10 examples of pulses are shown. These Figures are signal progresses described by means of oscilloscope. Fig. 5 shows the signal incoming to the input 29 of the device, and Figs. 6-10 show signals appearing at the output -30 of the device. In the Figures the following scales apply: Fig.No. Vertical scale Horizontal scale (voltage,mV) (time, ps) 5 50 50 6 20 20 7 20 50 8 .50 50 9 * 50 50 10 20 100 The Figures 6-9 are taken from a device with only one second coaxial conductor 5, both ends of which are short- -circuited. The Figures 6-9 show the output signal from the first coaxial conductor 2 for different branch lengths of the second coaxial conductor 5, which correspond to time delays according to below: Fig.No. Branch length (L) of Corresponding second coaxial conductor time delay (ps) (mm). . . . 6 3 28 7 5 47 8 10 93 9 15 140 As appears from the Figures 6 - 9, an output signal is obtained which in respect of pulse duration and amplitude (V /2 ) corresponds to what is said above. Furthermore, the fact that even the fastest signals have symmetric shape, proves that the short-circuiting at the ends of the second coaxi¬ al cable reflects the electromagnetic waves into the coax¬ ial cable without appreciable losses. This applies at least up to a frequency of about 15 Gc_/s. A comparison between the Figures 6,8 and 9 shows clearly how the branch length (L) of the second coaxial cable influences the app¬ earance of the output signal, where Pig. 9 almost can be regarded as a square wave. A great number of different pulses, thus, can be shaped by the present device in a simple way and during very short times. Another essential application field for the present device is as derivator. Provided that the entire length of the second coaxial conductor 5 is sufficiently short, the out¬ put signal namely is proportional to the derivata of the input signal. This is due to the fact that for an input signal f(t) an output signal is obtained which is equal to 1/2 ' f(t) - f(t - i t ) £Z 1/2 r<ff(t)j where eft is small. It was found extremely advantageous to use the present device as derivator at the measuring of laser pulses in the time range picoseconds. As an example can be mention- Seen in the wave propagation direction for the first co¬ axial conductor,the first one of the second coaxial con¬ ductors has short-circuited ends,:-.while the second one of the second coaxial conductors has open ends. The conductor with short-circuited ends determines the duration of the pulses while the conductor with open ends determines the distance, i.e. the separation between the pulses. By this embodiment of the invention both the duration of the puls¬ es and the separation between the pulses can be changed easily and rapidly. In Fig. 11 a series of output signals taken up by an oscill¬ oscope from such a device are shown, where between each take-up the zero-level was lowered. The input signal was a single step pulse of the type shown in Fig. 5 - The dur- ation of the pulses was determined to be 50 ps while the separation between the pulses was varied from about 100 ps, which is illustrated by the uppermost curve, to about 1,4 ns, which is illustrated by the lowermost curve. The utilization of the device for the generation of two separated pulses with very short duration is advantageous at measurements on electronic components, such as trans¬ istors, integrated circuits, semiconductors, lasers, opt¬ ical wave-guides etc., in respect of the capacity of the components to react on short pulses. It is, thus, apparent from the aforesaid that the present invention provides a pulse shaper, which owing to its structure can be utilized for the shaping and generation of pulses with very short duration and very short rise time. Its structural design renders it possible that the appearance and number of pulses easily can be varied by combining different coaxial cables of said first and, respectively, second type. As mentioned above, the present invention also comprises a special use of the present device. According to this use, the present device is utilized as a protective circuit for electronic components, which are sensitive to transients of a voltage high for the compon¬ ents. The use is based in the fact that the device acts as a superfast filter for direct voltage components, because the output signal always is electrica-lly earthed for sign¬ als, which vary slowly in relation to the time required for transporting the signal in the second coaxial conduct¬ or. At this use the ends of the second coaxial conductor are short-circuited. According to a preferred embodiment, at the use of the dev- vice as a protective circuit the said time delay is lower than 1 ns, preferably 50 ps, in each of the two branches of a second coaxial conductor. When, for example, the said time delay, due to the distance covered by the signal in the second wave-guide, is about 50 ps, voltage transients with a rise time of about 1 ns or longer are filtered out substantially entirely. More precisely, the output signal is -only 5% of the input signal. Second ' coaxial conductors longer than correspond- ing to 50 ps can be used. The attenuation, however, depends on the ratio between said time delay and the rise time of the input signal. As an example can be mentioned that at experiments a- ' .volt¬ age transient with the maximum voltage 50V and with a dur- ation of several nanoseconds was applied on the input of the present device, while its output was connected to an electronic component adapted for a maximum input voltage of 5V. The transient was filtered out, and the electronic component was not affected. The present device, thus, can be used with great advantage as protective circuit for electronic components, where it has the special advantage of filtering out very fast transients, which are detrimental for the electric compon¬ ent or components in question. The present invention can be modified in many ways obvious to the expert. The detail design, for example, of said recess can be varied, a.o. in response to the utilization of coaxial conductors of a different type. The present invention, thus, must not be regarded restrict¬ ed to the embodiments described above, but can be varied within the scope of the attached claims. In the above, coaxial conductors with a diameter of 3,6 mm were chosen as example. Other coaxial conductors, however, can be used. In certain cases the use of coaxial conduct¬ ors with a diameter of 1,8 mm is preferred, because such conductors imply that shortare branch lengths can be obt¬ ained.

Claims: Claims 1. A device for passive shaping and generation of electr¬ ic pulses ' from an electric signal incoming to the device, comprising a first coaxial conductor, which is connected 5 along its extension to one or several pairs of coaxial conductors, of which one or several at the end located remotest from the first coaxial conductor are either short-circuited or open, c h a r a c t e r i z e d i n that said pair of coaxial conductors consists of only one 0 coaxial conductor, viz. a second coaxial conductor (5), that said first coaxial conductor (2) is provided with a recess (6) extending from its shell surface (7) to its central conductor (8) and along an axial distance corres¬ ponding substantially to the outer diameter of said second co- 5 axial conductor 5, that each of said second coaxial conduct*•_.- . ors (5) is provided with a recess (9) corresponding to • said first recess (6), that the recesses (6,9) of the two coaxial conductors (2,5) so co-operate that the central conductors (8) of the two coaxial conductors (2,5) abut each 0 other and so that the shells (7,10) of the two coaxial conductors (2,5) are in electric connection with each other, and that a connecting member (17,18) is provided for retaining the two coaxial conductors (2,5) in said electric connection with each other. 5 2. A device as .defined in claim 1, c h a r a c t e r ¬ i z e d i n that the recess (9) in said second coaxi¬ al conductor (5) is located centrally on the coaxial cond¬ uctor (5) along its length. 3. A device as defined in claim l or 2, c h a r a c t - 0 e r i z e d i n that both free ends of the second coaxial conductor (5) are short-circuited or open. 4. A device as defined in claim 1 or 2, c h a r a c t - e r i z e d i n that one free end of the second coaxi¬ al conductor (5) is short-circuited and the other end is 5 open. 5. A device as defined in claim 1,2,3 or 4, c h a r ¬ a c t e r i z e d i n that several recesses (6) are located along the length of the first coaxial conductor (2), each of which recesses is arranged to co-operate 5 with a second coaxial conductor (5). 6. A device as defined in claim 1,2,3,4 or 5, c h a r - a c t e r i z e d i n that the second coaxial conduct¬ or (5) forms a right angle with the first coaxial conduct¬ or (2). 107. A device as defined in claims 1,2,3,4,5 or 6, c h a r a c t e r i z e d i n that said connecting member comprises two portions (17,18), which in assembled state form two intersecting channels (19,20), which res¬ pective channels have a diameter substantially correspond- 15 ing to the respective outer diameter of the coaxial cond¬ uctor ' s (2,5), into which channels (19,20) the respective coaxial conductor are intended to be placed. 8. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the length 20 of each of said coaxial conductors is shorter than 150 mm. 9. A use of a device according to claim 1 comprising a first coaxial conductor (2), which is connected along its extension to one or several pairs of coaxial conductors, one or several of which at their ends located remotest 25 from the first coaxial conductor are short-circuited, where said pair of coaxial conductors consist of only one coaxial conductor (5), viz. a second coaxial conduct¬ or, and where a recess (6;9) is located in the first (2) and, respectively, the second coaxial conductors (5), 30 so that the recesses of the two coaxial conductors so co-operate, that the central conductors (8) of the two coaxial conductors (2,5) abut each other, and so that the shells (7,10) of the two coaxial conductors (2,5) are in electric contact with each other, c h a r a c t - 35e r i z e d i n that said device is coupled in as a protective circuit for electronic components, which protective circuit filters out electric signals, which vary slowly in relation to the time required for trans¬ porting electric signals in the two branches of said second coaxial conductor (5). 10, A use as defined in claim 9, c h a r a c t e r ¬ i z e d i n that the device is designed so that said time is shorter than 1 ns, preferably 50 ps.

Inventors: MARGULIS WALTER, PERSSON RUNE, MARGULIS, WALTER, PERSSON, RUNE
Applicants: MARGULIS WALTER, PERSSON RUNE, MARGULIS, WALTER, PERSSON, RUNE
Application year: 1986
Main classification: H01P1
IPC codes: H01P1