US3764941A

US3764941A - Stripline directional coupling device

Info

Publication number: US3764941A
Application number: US00313298A
Authority: US
Inventors: H Nick
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1972-12-08
Filing date: 1972-12-08
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09

Abstract

A directional coupling device is provided having a first and second conductor of a first pair of conductors extending parallel to and closely spaced from one another. A second pair of conductors having a first and second conductor extending parallel to and closely spaced from one another are spaced laterally from the first and second conductors of the first pair of conductors, respectively. A first end of the first conductor of the first pair of conductors is electrically connected to the first end of the second conductor of the second pair of conductors. Also, the first end of the first conductor of the second pair of conductors is electrically connected to a first end of the second conductor of the first pair of conductors. The first and the second conductors of the first pair of conductors at the second end thereof respectively include an input and an output means. The second end of each of the first and second conductors of the second pair of conductors includes a terminating means so that electrical pulses arriving thereat will be terminated.

Description

United States Patent [191 Nick [1;] 3,764,941 [451 Oct; 9,1973

[ STRIPLINE DIRECTIONAL COUPLING DEVICE [75] Inventor: Howard H. Nick, Poughkeepsie,

[73] Assignee: International Business Machines Corporation, Arrnonk, N.Y.

22 Filed: Dec. 8, 1972 [21] Appl. No.: 313,298

[52] U.S. Cl..- 333/10, 333/1, 333/84 M [51-] Int. Cl. H01p 5/14, HOlp 3/08 [S8] Field of Search 333/10, 9, 1,84 M

[56] References Cited UNITED STATES PATENTS 3,460,069 8/1969 Uberbacher et a1. 333/10 Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Attorney-W. N. Barrett, Jr. et al.

[57] ABSTRACT A directional coupling device is provided having a first and second conductor of a first pair of conductors extending parallel to and closely spaced from one another. A second pair of conductors having a first and second conductor extending parallel to and closely spaced from one another are spaced laterally from the first and second conductors of the first pair of conductors, respectively. A first end of the first conductor of the first pair of conductors is electrically connected to the first end of the second conductor of the second pair of conductors. Also, the first end of the first conductor of the second pair of conductors is electrically connected to a first end of the second conductor of the first pair of conductors. The first and the second conductors of the first pair of conductors at the second end thereof respectively include an input and an output means. The second end of each of the first and second conductors of the second pair of conductors includes a terminating means so that electrical pulses arriving thereat will be terminated.

8 Claims, 5 Drawing Figures STRIPLINE DIRECTIONAL COUPLING DEVICE This invention relatesv to directional couplers and more particularly, to an improved stripline directional coupling device which can be used to fulfill high density connector requirements.

With the increase in operating speed of devices, such as computers, into the nanosecond range, it has been foundthat directional couplers can be utilized to couple high speed pulses to and from the transmission lines with respective sub-lines leading to and from various peripheral devices. In U. S. No., No, 3,516,065 filed Jan. 13, 1967, a system for transmitting digital data between a plurality-of data processing devices using striplinedirectional couplers is disclosed. The use ofthe directional coupler in the system eliminates the stub length limitations and allows any stub or stublines connecting individual devices to the transmission line'tobe limited in length only by the degradation of a signal passed along the line.

As is known, a stripline directional coupleris a device wherein two parallel adjacent printed circuit striplines, sandwiched between twoground planes,-are inductively and capacitively coupled so that'theedges of a first pulse of fast rise and fall time characteristics, propagating along one line, produce a positive pulse It is an object of'the present invention-to provide a directional coupler in which unwanted cross coupling signals are practically eliminated.

It is another object of the present invention to'provide a stripline directional coupler in which shorter lengths of conductive coupling elements are used. It is a futher object of the present invention toprovide a striplingdirectional coupler which'can be packand'a negative pulse in the other line. The lines are coupled such that the thus produced pulses propagate along the, second line in a'direction opposite to the direction in which the first pulse propagates along the first line. The energy transferred be'tweenthe conducting segments of the two-element directional coupler is effected by the various physical characteristics of the directional couplersuch as the length, width and distance between the couplingsegments.Accordingly, the long coupling element lengths needed to obtain a good energytransfer between thesegments of the coupler introduces obvious disadvantages inpackaging the twoelement directional coupler, especially where a large numberfof such devices are to be combined in the same package. I

The directional coupler conductors have two general configurations when used as a connecting device. For example, the coplanar directional coupler consists of parallel lengths of stripline conductor located in the same plane and spaced adjacent to each other. The other known arrangement is the broadside directional coupler in which the conductors are located broadside to one another in adjacent parallel planes so that the coupling is between the facing surfaces of the coupling segments rather than coupling from edge to edge as is the case in the coplanar directional coupler. Packaging a plurality of the broadside directional couplers introduces the problem of unwanted edge coupling between the coplanar adjacent conductive segments. This cross coupling seriously impacts the packaging density of the broadside directional coupler.

There are a number of inherent advantages to using the directional coupler as a connector rather than the direct line connection that is normally used. The socalled loose coupling provides isolation between islands of logical functions electrically and, thus, overcomes some of the present day power problems. Actually, the loose coupling device provides the necessary isolation and matched impedance to allow for welldefined, almost noiseless, less power consumption signal transmission.

aged in a much smaller space and at a much greater density.

Briefly, a directional coupling device is provided for transmitting signals into and out of circuit modules of the type havingahigh density connector requirement. The coupler-contains a first and second conductor of a first pair of conductorswhich extend :parallel to and closely spaced from one another. The coupler also contains a first and second conductor of a second pair of conductors which extend parallel to and closely spaced from another and later-allyspaced from thefirst and second conductors of the first pair of conductors, re-

spectively. A first'end'of the first conductor of the first pair of conductors is connected to a'first end ofthe second conductor of the second pair'of conductors by a first electrical connectionuAlso, the first endof the first conductor of the second pair of conductors is connected to the first end of the secondconductor of the firstpair of conductors by a second electrical connection. The second ends of the first and second conductors of the'first pair of conductors includes an input and BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of the prior art twoelement broadside directional coupler showing the input and output wave forms thereof;

FIG. 2 is across-sectional diagram taken along the line 2--2 of FIG. 1 identifying the various dimensions;

FIG. 3 is a schematicdiagram of the four element directional coupler of the invention showing the input and output wave forms thereof;

FIG. 4 is a cross-sectional diagram taken along the lines 44 of FIG. 3 indicating the various dimensions of the elements in the invention;

FIG. 5 is a schematic diagram showing a pair of the four element directional couplers and indicating the interaction with one another.

Referring to FIG. 1, there is shown a schematic diagram of the prior art two-element stripline directional coupler which consists of two stripline conductive segments l0 and 12 extending parallel to and closely spaced from one another from an end A to an end B. These conductors or

conductive segments

10 and 12 are located broadside to one another and closely spaced. Usually, the conductors are mounted in a substrate 14 made of a dielectric material such as epoxy glass and are arranged between two ground plates 16 and 18 which usually consist of sheets of copper arranged on either side of the pair of conductors. Each conductive element and 12 has a

terminal

20,22 at the end B of the coupler serving as an input or output terminal. Each

conductor

10, 12 has a

terminating resistance

24, 26 connected at the A end of the coupler which matches the coupler to the characteristic impedance of the line to which it is connected. The coupling takes place along the length of the

segments

10, 12. The coupler operation as defined depends upon the steepness of the incident pulse rise time. The width or duration of the pulse produced by the coupling is determined by the length of the two

segments

10, 12. The performance of the coupler is described by the impedances offered to signals on the transmission line and the coupling ratio, which are determined by the widths of the lines in the coupled region, the thickness of the lines, the distance between ground planes, the distance between conductive elements and the relative dielectric constant of the material. It has been determined that coupling segments of electrical length L will produce a pulse having a time duration equal to 2L. For example, a one volt amplitude ideal step function input signal applied to the input terminal of segment 10, when the-coupler has a coupling ration of one to four and an electrical length L of two nanoseconds, will produce an output pulse having a time duration of four nanoseconds and a pulse amplitude of A of a volt. The input pulse can begenerated by a driver connected to the input to one of the conductive elements. As is shown in FIG. 1 by arrows, the coupled pulse travels in an opposite direction in the conductive segment 12 to the direction of travel in the coupling segment 10. It will be appreciated, that either of the

conductive segments

10 and 12 can serve as the input and likewise the other would serve as the output. A stripline coupler is operated by the edge of the wave passing along one of the lines and this wave edge should have a rise or fall time that is twice as fast as thetime duration of the pulse induced by coupling in order that the relationship of the height of th induced pulse be related to the height of the driving pulse in the manner defined by the coupling ratio. The various critical dimensions of the directional coupler for proper operation are indicated in the cross-sectional diagram of the prior art directional coupler shown in FIG. 2.

Packaging of these prior art directional couplers presents a problem in that cross coupling takes place between the couplers when the devices are packaged within coupling distance of one another. Considering the case where a broadside directional coupler, shown in FIG. I, is located directly adjacent a similar device, the one volt ramp input pulse will not only couple to the stripline located broadside thereto but will also couple to an adjacent stripline that is within lateral coupling distance. The one volt pulse would produce a V4 volt pulse travelling in the opposite direction along any adjacent laterally spaced stripline. This A volt pulse for example would be seen at the input of the adjacent directional coupler and would produce essentially a signal to noise ratio of l to 4. The V4 volt pulse travelling in the opposite direction towards the output of the second conductor of the first directional coupler will also produce a l/l6 V pulse in the second conductor of the adjacent device which travels in the opposite direction, thus travelling towards the terminating resistance where it is terminated. It should also be appreciated that the second directional coupling device input pulse likewise causes a coupling signal travelling towards the input of the adjacent coupler. This unwanted coupling considered to be cross-talk or noise effectively limits any high density packaging of directional couplers.

The four element directional coupler, forming the present invention, is shown schematically in FIG. 3. The arrangement consists of a first pair of stripline

conductive elements

30, 32 spaced parallel to one another and extending from an end A to an end B. These first and second conductive elements, 30, 32 are closely spaced from one another with the bottom surface of the first conductor 30 facing the top surface of the second conductor 32 of the device. Similarly, a second pair of

conductive stripline elements

34, 36 are located laterally adjacent the first and

second elements

30, 32 of the first pair. The first conductive element 34 of the second pair of conductors is located adjacent to and laterally displaced from the first conductor 30 in the first pair of conductors. This distance is within electrical coupling distance. As a matter of fact, the lateral distance is made as small as possible so that a large number of directional coupler devices can be packaged in a small space. The second conductor 36 of the second pair of conductors is located adjacent the second conductor 32 of the first pair of conductors so that the first and second pairs of conductors lay parallel to one another side by side. The second pair of

conductors

34, 36 are spaced parallel to one another and have the broadside surfaces facing within coupling distance of one another. The first conductive element 30 of the first pair of conductors has an electrical connection 38 extending from one end thereof designated as the B end in FIG. 3 to a similar end of the second conductor 36 of the second pair of conductors. Similarly, the first conductor 34 of the second pair of conductors has an electrical connection 40 extending from one end thereof, the B end, to the adjacent end of the second conductor 32 of the first pair of conductors. The other end of the first conductor 30 of the first pair of conductors has an input terminal 42 for receiving input pulses. This end is designated as the A end in FIG. 3. Likewise, the second conductor 32 of the first pair of conductors has an output terminal 44 at the A end of the directional coupler device. Each of the

conductors

34, 36 of the second pair of conductors has a terminating

resistor

46, 48 at the ends thereof adjacent to the input and output terminals 42, 44 of the first pair of conductors at the A end of the device. It will be appreciated that the directional coupler device is embedded in a dielectric material 50 (see FIG. 4) for operation in this invention. It has been found that ceramic having a dielectric constant of 9.5 provides the best operation. The ceramic material 50 containing the conductive elements of the directional coupler are sandwiched between an upper and lower

ground plane conductor

52, 54. These ground planes 52, 54 can consist of thin sheets of copper. The characteristic impedance of the coupled lines Z is determined by the various dimensions and values of the directional coupler. For example, the characteristic impedance Z isv dependent on the width W of the coupled lines, the space S between coupled lines, the spacing D between ground planes, the thickness t of striplines, the relative dielectric constant E of the medium filling the region between the lines and the region between the lines and the ground planes. In a typical situation where W 3 mils, S 4.295 mils, D

596.9551 mils, 1 mil, E; 9.5 then Z, 79.1809 ohms. It should be noted that the length of the conductive element shown in FIG. 4 is less than the length of the conductive element shown in the prior art directional coupler of FIGS. 1 and 2. Although the overall length dimension is reduced, it will be appreciated that the directional coupler of FIG. 3 has an additional pair of

striplines

34, 36 added which, by the electrical connections 38, 40 from the B ends, essentially compensate for the loss of length.

In describing the operation of the invention, as is shown in FIG. 3, we will consider the coupling ratio as being one to four so that a one volt ramp input will couple to the adjacent lines a 41 volt pulse. Thus, applying the one volt ramp to the input terminal 42 of the first conductive element 30 of the first pair of conductors, as shown in FIG. 3, produces a /i volt pulse proceeding in the opposite direction towards the output terminal 44 of the second conductor 32 of the first pair of conductors. The one volt input signal also continues through the connection 38 from the B end of the first conductor 30 of the first pairof conductors to the B end of the second conductor 36 of the second pair of conductors where the one volt ramp travels along the conductor into the terminating resistance 48 at the A end of the second conductive element 36 of the second pair. This one volt ramp proceeding along the second conductor 36 of the second pair causes a 54 volt pulse to be coupled into the first conductive element 34 of the second pair travelling in the opposite direction. This volt pulse will travel through the connection 40 from the first conductive element 34 of the second pair to the second conductive element 32 of the first pair where it travels towards the output terminal 44 forming the output pulse. It should be noted that the A volt pulse in travelling along any conductive element causes a coupling tothe adjacent elements of a positive and negative pulse of.1/l6 of a volt.

Accordingly, the ,4 volt pulse coupled into the sec ond conductive element 32 of the first pair of conductors will cause coupling of H1 6 volt pulses to the coplanar adjacent conductive element which is the second conductive element 36 of the second pair wherein the H16 volt pulses travel toward the B end of the directional coupler through the interconnecting wire 38 and towards the A end of the coupler along the first conductor 30 of the first pair of conductors. These l/ 16 of a volt pulses can be easily handled by the driver, and accordingly, the signal-to-noise ratio can be considered to be 1 to 16 which appears to be favorable in comparison to the l to 4 signal-to-noise ratio of the prior art directional coupler. Similarly, the volt pulse causes a 54 V pulse to be coupled laterally from the first conductor 30 of the first pair of conductors to the first conductor 34 of the second pair. The /4 V pulse causes a 1/16 of a volt pulse to be coupled into the second conductor 36 of the second pair travelling towards the B end so that it passes through the electrical connection 38 at the B end to the first conductor 30 of the first pair where it travels towards the driver and is dissipated therein.

The most important advantage of the arrangement can be realized when a number of such devices are packaged in a small space. In FIG. 5, there are shown two directional coupler devices each of which is exactly the same as the directional coupler device described in connection with FIG. 3. Considering the coupling interaction caused by the first or left hand coupler, the one volt pulse travelling towards the terminating resistor 48a in thesecond conductive element 36a of the second pair of conductive elements 340, 36a will cause a 4 volt pulse coupling into a laterally adjacent element which is the second conductive element-32b of the first

pair'of conducting elements

30b, 32b of the second directional coupler or right hand directional coupler in FIG. 5. As this A wave pulse will be travelling towards the B endof the conductive element 32b and will, therefore, pass through the electrical connection 40b to the first conductive element 34b of thesecond pair of conductors where it travels towards the A end and is thus terminated in the terminating resistor 46b. Again the 56. volt pulse travelling towards the B end in the second conductor 32b-of the first pair will give rise by coupling to a 1/16 volt pulse travelling towards the A end in the first conductive element 30b of the first pair of conductors. As previously mentioned, this 1/ 16 volt pulse will be dissipated in the driver circuits. The V4 volt pulse travelling towards the A end of the first conductor 34b of the second pair of conductors gives riseto l /16volt pulses in the second conductor 36b of the second pair which is travelling towards the B end, and which passes through the electrical connection 38b and travels towards the A end or input end of the first conductor 30b of the first pair of conductors where, similarly, it is dissipated. Thus, the signal applied to the first directional coupler in the pair of directional couplers shown in FIG. 5 causes lateral coupling with a closely spaced second directional coupler, however, the-laterally coupled pulses areterminated.

The coupling interaction with the first directional coupler caused by the application of a signal input to the second directional coupler of the pair of directional couplers, shown in FIG. 5, will now be investigated. The one volt ramp input at the input terminal 42b of the first conductive element 30b of the first pair of conductors through lateral coupling causes a V4 volt pulse in the first conductor 34a of the second pair of conductors of the first coupler but travelling towards the A end where it is terminated in the-terminating resistor 460. This coupled A volt pulse in the first conductive ele ment 34a of the second pair of conductors gives rise to 1/ 16 of a volt pulses travelling the opposite direction, that is, towards the B end of the second conductor 36a of the second pair of conductors of the first directional coupler which, via the electrical connection 38a, is connected to the first conductor 30a of the first pair of conductors travelling towards the input 420 end where, as previously mentioned, it is dissipated in the driver. In FIG. 5, thre is included only those voltages which are due to the crosstalk or interaction of the two directional couplers shown. The important thing to note is that the interaction between the two directional couplers causes a A of a volt pulse which, in both directional couplers, is terminated by a terminating resistor. The l/l6 volt pulses caused by the V4 volt pulses by either broadside coupling or lateral coupling create no particular problemsince they are either terminated by terminating resistances or dissipated in the input circuitry. Thus, a directional coupler arranged as described in connection with FIG. 3 can be closely packaged with other similar directional couplers as shown in FIG. 5 without creating any spacing limitations because of coupling interactions such as crosstalk.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit nd scope of the invention.

What is claimed is:

l. A directional coupling device for connecting signals into and out of circuit modules having a high density connector requirement comprising:

a first and second conductor of a first pair of conductors extending parallel to and closely spaced from one another;

a first and second conductor of a second pair of conductors extending parallel to and closely spaced from one another and laterally spaced from said first and second conductors, respectively;

a first electrical connection extending from a first end of said first conductor of said first pair of conductors to a first end of said second conductor of said second pair of conductors;

a second electrical connection extending from the first end of said first conductor of said second pair of conductors to a first end of said second conductor of said first pair of conductors;

input means connected to the second ends of said first conductor of said first pair of conductors;

output means connected to the second end of said second conductor of said first pair of conductors and terminating means connected at the second ends of said first and second conductors of said second pair of conductors for terminating electrical pulses arriving thereat so that pulses applied at said input are coupled to said output and laterally coupled pulses are attenuated and terminated in said terminating means.

2. A directional coupling device according to claim 1, wherein said first and second conductor of said first pair of conductors and said first and second conductor of said second pair of conductors are sandwiched between first and second ground conductor planes.

3. A directional coupling device according to claim 1, wherein said first and second pairs of conductors are embedded in a dielectric material.

4. A directional coupling device according to claim 3, wherein said dielectric material is ceramic.

5. A directional coupling device according to claim 1, wherein said first and second conductors of said first and second pairs of conductors are printed line conductors of the same length, width and thickness.

6. A directional coupling device according to claim 5, wherein said first and second conductors of said first pair of conductors are spaced broadside to one another within pulse coupling distance and said first and second conductors of said second pair of conductors are spaced broadside to one another within pulse coupling distance and spaced coplanar within coupling distance to said first and second conductors, of said first pair, respectively.

7. A directional coupling device according to claim 1, wherein said terminating means connected to the second end of said first and second conductors of said second pair of conductors is a resistor having a value equal to the characteristic impedance of the line to which the directional coupler is to be connected.

8. A directional coupling device according to claim 1, wherein a plurality of directional coupling devices are placed side by side so that the first and second conductors of said first pair or conductors of each directional coupling device are spaced within pulse coupling distance from the first and second conductors of said second pair of conductors of the adjacent directional coupling device so that pulses coupled between directional coupling devices are attenuated and terminated.

Claims

1. A directional coupling device for connecting signals into and out of circuit modules having a high density connector requirement comprising: a first and second conductor of a first pair of conductors extending parallel to and closely spaced from one another; a first and second conductor of a second pair of conductors extending parallel to and closely spaced from one another and laterally spaced from said first and second conductors, respectively; a first electrical connection extending from a first end of said first conductor of said first pair of conductors to a first end of said second conductor of said second pair of conductors; a second electrical connection extending from the first end of said first conductor of said second pair of conductors to a first end of said second conductor of said first pair of conductors; input means connected to the second end of said first conductor of said first pair of conductors; output means connected to the second end of said second conductor of said first pair of conductors and terminating means connected at the second ends of said first and second conductors of said second pair of conductors for terminating electrical pulses arriving thereat so that pulses applied at said input are coupled to said output and laterally coupled pulses are attenuated and terminated in said terminating means.