The present invention relates generally to electrostatic discharge protection devices. More particularly, the invention relates to electrostatic discharge protection devices for connector-receptor assemblies where the electrostatic discharge protection device connects ground and core conductors to inhibit electrostatic charge accumulation when

the connector-receptor are disconnected, and automatically disconnects this ground

connection upon operative combination of the connector-receptor. Electrostatic charge is a stationary electric charge which accumulates on various surfaces. An electrostatic discharge occurs when the electrostatic charge becomes substantial enough to overcome a dielectric material between the charge and another surface of a lower electrical potential. An example of such a discharge is naturally occurring lightning. Electrostatic discharge in the realm of electronics can be devastating to microelectronic devices. A sharp voltage spike caused by an electrostatic discharge

can cause permanent and costly damage to individual precision devices, such as random access memory (RAM) or other semiconductor devices, inter alia. Circuit designs which are specially susceptible to electrostatic discharge are those having external connections.

For example, a thicknet local area network (LAN) card in a personal computer is often designed with a BNC type connector extending to the exterior of the personal

computer. A coaxial cable having a complimentary BNC connector is attached to the

BNC connector on the card to provide access to a network. While the coaxial cable is

unattached, electrostatic discharge can occur destroying the devices or components on

the card without any physical manifestation leading to costly hardware diagnostics and

subsequent repairs.

One solution to this problem has been to place a fixed shunting device on the

connector until it is ready for use. The fixed shunting device would create a short

circuit between the conductors in the connector, one of which is generally grounded,

ensuring that electrostatic charge does not reach the internal electronics. A problem with this device is that it must be removed before the connector is mated with a

receptor, id est, a complementary connector. Upon withdrawing the connector, the

shunting device is often unavailable for re-insertion into the connector which again opens the electronic devices to possible damage.

A prior art electrical connector-receptor arrangement that provides for an automatic

shorting of conductors upon disconnection and opening upon connection which does

not require specifically configured receptacle surfaces is disclosed in U.S. Pat. No.

3,467,940 entitled "Electrical Connecting Spring Device", by W. H. Wallo, issued

September 16, 1969. This patent shows a coiled compression spring mounted in a

separable plug and jack connector assembly wherein the spring automatically expands

and grounds the plug in the absence of the jack. The spring is automatically

compressed upon insertion of the jack into the plug and compressed so as to

electrically disconnect from the plug. However, the coiled compression spring is

shown as operating on only a single pin or elongated electrical conductor and would be

difficult to adapt to a connector having multiple pins. Additionally, many connectors for high frequency cable contain an dielectric material cylinder that protrudes at least

the length of the pin. For such connectors, the coiled compression spring would not be

able to contact both the pin and the exterior conductor when uncompressed.

Another prior art electrical connector-receptacle arrangement is described in commonly assigned U.S. patent No. 4,971,568 entitled "Electrical Connector Attachment for Automatically Shorting Select Conductors Upon Disconnection of

Connector" by David V. Cronin issued November 20, 1990. This patent shows a shunt

attachment placed on pins of the connector arranged to provide a short circuit across

selected pins. Upon insertion into the receptor, the attachment is compressed causing the short circuit to be broken. While this arrangement is an improvement and is useful

for connectors having multiple pins, it is planar and, therefore, can not connect

conductors separated by an insulating layer of the type commonly employed in coaxial

cable connectors. Other commonly assigned patents relating to electrostatic discharge

protection include U.S. Pat. No. 5,163,850 entitled "Electrostatic Discharge Protection

Devices for Semiconductor Chip Packages," by David V. Cronin, issued November

17, 1992; U.S. Pat. No. 5,164,880 entitled "Electrostatic Discharge Protection Device

for a Printed Circuit Board," by David V. Cronin, issued November 17, 1992; and U.S.

Pat. No. 5,108,299 entitled "Electrostatic Discharge Devices for Semiconductor Chip

Packages," by David V. Cronin, issued April 28, 1992.

Summary

The aforementioned and other objects are achieved by the invention which provides,

in one aspect, an electrostatic discharge protection device. The electrostatic discharge protection device is useful with a connector having first and second complimentary members which are adapted to be joined electrically connecting corresponding parts of

multiple high frequency cables.

High frequency cables generally have a ground conductor formed in a tubular

arrangement to encompass one or more core conductors. The ground conductor is adapted to be electrically grounded and is spaced apart from the core conductors by a dielectric material medium for providing electrical insulation between the cone conductors and the ground conductor. Each of two complimentary members of the

connector have a ground shell which is electrically connected to the ground conductor and have at least one or more core connector where each core connector electrically connected to a corresponding one of one or more core conductors.

The electrostatic discharge protection device comprises grounding means which is disposed within the ground shell of the first complimentary member. When the first complimentary member is detached from the second complimentary member, the grounding means in the first complimentary member is in an operative position establishing a shunt between the ground shell and each of the one or more core connectors. This shunt places the ground shell and such core connectors of the first

complimentary member at a substantially equivalent electrical potential to prevent

electrostatic discharge therebetween. Upon joining the first and second complimentary

members, the grounding means automatically is displaced into an inoperative position

where the shunt is disconnected, allowing the ground shell and such one or more core

conductors of the first complimentary member to become substantially electrically

isolated.

The electrostatic discharge protection device can be used with a male-type or female- type connector and is reusable in that the first complimentary member and the second complimentary member can be joined and disconnected multiple times without

detriment to the operation of the grounding member.

In further aspects, the invention provides methods in accord with the apparatus described above. The aforementioned and other aspects of the invention are evident in the drawings and in the description that follows.

Brief Description of the Drawings

The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description, when read together with the accompanying drawings in which:

Figure 1 shows an exploded perspective view of a BNC-type electrical connector-

receptor and an electrostatic discharge protection device in accordance with the

invention;

Figure 2 shows perspective view of a BNC-type connector utilizing the electrostatic discharge protection device of Figure 1.

Figure 3 shows perspective view of a BNC-type connector utilizing the electrostatic discharge protection device of Figure 4 in full engagement with a receptor.

Figure 4 shows an exploded perspective view of a BNC-type electrical connector- receptor and an electrostatic discharge protection device in accordance with the invention;

Figure 5 shows perspective view of a BNC-type receptor utilizing the electrostatic discharge protection device of Figure 4.

Figure 6 shows cross-sectional view of a BNC-type connector in full engagement

with a receptor utilizing the electrostatic discharge protection device of Figure 4.

Figure 7 shows an exploded perspective view of a SMA-type electrical connector-

receptor and an electrostatic discharge protection device in accordance with the invention;

Figure 8 shows perspective view of a SMA-type receptor utilizing the electrostatic

discharge protection device of Figure 7.

Figure 9 shows perspective view of a SMA-type connector in full engagement with a receptor utilizing the electrostatic discharge protection device of Figure 7.

Figure 10 shows a perspective view of a BNC-type connector for a twinaxial cable with an electrostatic discharge protection device in accordance with the invention.

Detailed Description

The invention is used with connector-receptor pairs for high frequency cable. High

frequency cable is generally designed with one outside conductor surrounding one or more core conductors. The outside conductor is generally grounded such that it

remains electrically neutral. In this way, the enclosed core conductors are shielded

from electromagnetic signals and noise. Connecting two or more of these high

frequency cables requires connectors adapted for such a conductor arrangement.

Examples of such connectors are known in the art as a sub-miniature connector (hereinafter "SMA") and a bayonet navy connector (hereinafter "BNC") connector, both of which are illustrated herein.

While the present invention retains utility within a wide variety of electrical

connectors and may be embodied in several different forms, it is advantageously employed in connection with the above-mentioned connectors. Though these are the forms of the illustrated embodiments and will be described as such, these embodiments should be considered illustrative and not restrictive.

Referring now to Figures 1-3, there is shown generally the electrical connector and receptor assembly of the invention comprising a connector 20, a receptor 30 and a electrostatic discharge protection device 10. The connector 20 in one embodiment is a

BNC connector having a cylindrical housing 21 for securing the receptor 30 upon insertion. Enclosed within the cylindrical housing 21 is a cable terminator 23 which is

electrically connected to a high frequency cable. In the following discussion, the high frequency cable is a coaxial cable consisting of a conducting outer metal tube enclosing and insulated from a central conducting core. Though this is the exemplified

form, other high frequency shielded cables may be substituted without detriment to the invention and therefore the use of coaxial cable should be considered illustrative and not restrictive.

The cable terminator 23 is arranged for a coaxial cable as previously discussed. A ground conductor or shell 22 is in electrical communication with the outer metal tube 22a of the coaxial cable and is arranged in the connector 20 in a manner similar to that of the outer metal tube in a coaxial cable. The outer metal tube 22a of a coaxial cable is generally held electrically neutral, or ground, which provides a shield for inner conductors. Outside electromagnetic interference strikes the outside metal tube and is grounded thus stopping penetration into the cable. As such, the ground conductor 22, being in electrical communication with the outside metal tube, is also electrically neutral.

A dielectric material ring 24 is enclosed by the ground conductor. The dielectric material ring 24 is an electrical insulator ensuring that conduction between the ground conductor 22 and central conductor is inhibited.

An open bore 26 is enclosed by the dielectric material ring 24 for receiving the receptor as further described herein.

Extending axialiy through the center of the bore 26 is a core connector 28. The core connector 28 is a hollow pin which receives and is electrically connected to the central

conducting core of the coaxial cable which ultimately connects to other electrical components remotely stationed with respect to the connector 20 in a well known manner.

The connector 20 is adapted for ready insertion or withdrawal from the

complimentary receptor 30 which is also a termination point for a coaxial cable. The receptor 30 mates with the connector 20 in such a way as to allow electrical communication between the coaxial cables. In the BNC connector, this is accomplished by inserting two pegs 31 extending radially outward from the receptor

following a diameter of the cable into a slot 25 in the cylindrical housing 21. The receptor 30 is pushed down into the connector 20 such that the pegs 31 follow the slot 25 into a locked position. Withdrawal is accomplished following a similar process, but reversed.

When the receptor 30 is inserted into the connector 20, a ground shell 32 passes between the cylindrical housing 21 and the ground conductor 22. The ground shell 32 may or may not make mechanical contact with the ground conductor 22, but in either event, conduction is allowed through the cylindrical housing 21 which is in electrical communication with the ground conductor 22.

As with the connector 20, the receptor 30 uses a dielectric material to separate the conductors. In the case of the receptor 30, a dielectric material ring 34 is formed with an outside diameter slightly less than the diameter of the bore 26 of the connector such

that upon insertion the dielectric material ring 34 fits within the bore 26.

Enclosed by the dielectric material ring 34 is a ferrule or complimentary connector

38 which is in electrical communication with the central conducting core of the coaxial cable attached to the receptor 30. The ferule has an inside diameter which is which is substantially the same as the outside diameter of the core connector 28. As the core connector 28 is inserted into the ferrule 38, the ferrule expands due to radial pressure caused by the mechanical contact with the core conductor 28. This mechanical contact establishes electrical continuity within the coaxial cables thus electrically connecting same.

The electrostatic discharge protection device 10 of the invention is a conductive device in the form of a grounding member or means that operates with the above- described connector-receptor relationship to ground electrostatic charge from the central conducting core of the coaxial cable gathered while in an unconnected state. The electrostatic discharge protection device 10 accomplishes this by creating a shunt between the outer metal tube 22 and the central core connector 28 thus making the central conducting core electrically neutral and stopping propagation of electrostatic charge or noise to any attached electronic components.

This is accomplished in one embodiment by electrostatic discharge protection device

10. The electrostatic discharge protection device 10 is fabricated to be electrically conductive while having a high spring constant providing resiliency. In the preferred embodiment, a spring alloy of beryllium copper is used.

It should be noted that the addition of any conductive device into a connector for a

high frequency cable increases susceptance. This becomes a problem at extremely

high frequencies in the gigahertz range at which point losses due to conductance to

ground affect the connector. For the times when this becomes an issue, the electrostatic discharge protection device 10 may be fabricated of conductive plastic or other material having a higher impedance, or a contact on the electrostatic discharge protection device can be coated with a resistive material to increase overall impedance. Since a characteristic of electrostatic discharge is high voltage with low current, a higher impedance has minimal effect upon the protective capabilities of the electrostatic discharge protection device.

The electrostatic discharge protection device 10 for the connector 20 comprises three basic parts: a ground tab 12, a bridge 14, and a contact 16. In the preferred embodiment, the ground tab 12 is planar and has a width which was experimentally determined to be optimum at approximately 1/8 inch. The experimentation weighed

the fact that as the width increased susceptibility increased proportionally and as susceptance increases the usable frequency range for the connector decreases; but if the

width was too small then the force holding the electrostatic discharge protection device

in position would not be enough and the electrostatic discharge protection device would cock upon combination of the connector and receptor and fall out upon withdrawal. Therefore, the width of the ground tab 12 should be minimized while still retaining its ability to hold the electrostatic discharge protection device in position.

The ground tab 12 is placed between the ground conductor 22 and the dielectric material ring 24. Because the ground tab 12 is planar and is placed between two concentric annular bodies, the ground tab is forced to curve along the outer radius of the dielectric material ring 24. The ground tab 12 in attempting to retain its planar structure due to its resilient spring bias, extends outward against the inner radius of the ground conductor 22. This arrangement creates a strong frictional resistance against removing the electrostatic discharge protection device 10 from this position and ensures good electrical contact with the ground conductor 22.

Other embodiments are held in placed by placing a curve in the ground tab 12 that has a radius substantially less than the radius of the dielectric material ring 24 and the ground conductor 22. Upon insertion, the spring bias forces the ground tab 12 against the lateral surface of the ground conductor 22 holding the electrostatic discharge protection device in position. One skilled in the art knows that other alternatives, such as using a conductive adhesive or bending the corners of the ground tab 12, may also be used to retain the electrostatic discharge protection device 10 in connector 20.

The bridge 14 extends from the ground tab 12 radially inward toward the center of the connector 20. The length of the bridge 14 is substantially the same as that of the dielectric material ring 24 thus carrying the electrostatic discharge protection device

over the dielectric material into the bore 26.

The contact 16 extends from the bridge 14 downward at an angle with respect to the ground tab 12 pressing the contact 16 against the core conductor 28. The transition

between the bridge 14 and the contact 16 is curved such that repeated combinations of

the receptor-connector do not cause the bend to kink and break. A similar gradual bend is placed in the contact 16 making the bend tangent to a lateral surface of the dielectric material ring 24 and then proceeding along a circular radius, further avoiding the problem of kinking.

When fabricated, the contact 16 has an angle with respect to the ground tab 12 in excess of the angle maintained when the electrostatic discharge protection device 10 is inserted into the connector 20. In this way, the resilient spring bias of the electrostatic discharge protection device 10 urges the contact 16 against the core conductor 28 thus establishing electrical communication between the core conductor 28 and the ground conductor 22.

The contact 16 has a notch 18 at its distal end in the shape of a "N". The "N" ensures that the contact 16 will always engage the core conductor 28 in the desired

position: the center of the "V. At the same time, the "N" increases surface area

contact to ensure proper conduction.

Grounding the core conductor 28 is desirable when the connector-receptor are

detached, but when connected, grounding the core connector undermines the

usefulness of the cable. Therefore, the electrostatic discharge protection device 10 of

the invention automatically breaks the shunt between the core conductor 28 and the

ground conductor 22 upon combination with the receptor 30. Looking more

specifically at Figure 3, the invention accomplishes this by allowing the dielectric

material ring 24 to displace or push the contact 16 away from the core conductor 28

such that is immured between the dielectric material ring 24 of the connector 20 and

the dielectric material ring 34 of the receptor.

Upon withdrawal of the receptor 30, the spring bias of the contact 16 immediately forces the contact 16 back into electrical communication with the core conductor 28 again grounding the core conductor 28.

Referring now to Figures 4-6 where like numerals designate previously described

elements, there is shown an alternate embodiment of the invention. In contrast to the

previous embodiment, the electrostatic discharge protection device 40 is inserted into

the receptor 30 ^* . Having made this distinction, it should be noted that these

embodiments are not mutually exclusive for use in one connector-receptor assembly.

An electrostatic discharge protection device may be on both the receptor and on the

connector without detriment as long as there exists an angular separation distance of

approximately 45° to avoid an impedance drop between the two conductive devices.

In this embodiment, the electrostatic discharge protection device 40 or grounding

means is placed over the dielectric material ring 34' as before such that a bridge 44 spans the dielectric material ring 34'. Extending down from the bridge and radially

outward is a ground contact 42. As with the contact 16 of the connector 20

arrangement, the ground contact 42 is formed such that placement of the ground

contact 42 within the bore 36 ^* forces the ground contact inward from its fabricated position. This creates an outward spring bias causing the ground contact to engage the ground shell 32'.

The distal end of the ground contact 42 is slightly rounded such that upon

disengagement of the connector-receptor, the ground contact 42 will not bind the connector by biting into the dielectric material ring 24'.

Extending down from the bridge toward the center of the receptor 30' is a ferrule contact 46. Analogous to the ground tab 12 of the connector arrangement, the ferrule

contact 46 is planar and is forced in between two concentric annular rings: the ferrule

38' and the dielectric material ring 34'. The spring bias pushes the ferrule contact 46 toward a planar geometry creating a force that holds the electrostatic discharge protection device 40 in place as well as establishing an electrical contact against the

ferrule 38 ^* .

Upon insertion into the connector 20', the dielectric material ring 24' of the

connector pushes the ground contact 42 down away from the ground shell 32' breaking the short circuit previously established.

The electrostatic discharge protection device 40 remains in this disengaged position

until the receptor 30' is removed from the connector 20' at which time the spring bias of the ground contact 42 causes the short circuit to be reestablished.

The previous embodiments are well adapted for use with connectors having a central core contact which extends axialiy from within the connectors. For connectors that do not have such an arrangement, such as an SMA connector, a different configuration of the electrostatic discharge protection device must be used. The SMA connector is oriented similarly to the BNC connector with a primary difference being that the central conductor and dielectric material ring do not extend axialiy from the bottom of the connector.

Referring now to Figure 7-9, there is shown an alternate embodiment of the invention. In contrast to the previous embodiments, the electrostatic discharge protection device 40 is adapted for a ferrule which does not project from the base of the connector. The depicted receptor 110 of an SMA connector illustrates such an arrangement.

A ground shell 112 forms the outer housing of the receptor and is connected to the outer metal tube of the coaxial cable. In the case of an SMA connector, the ground

shell is threaded on its exterior surface to allow a locking connection with a connector

120.

Housed within the ground shell 112 is a dielectric material 114 surrounding a ferrule

116. The arrangement is similar to the previously described BNC connector except

that the dielectric material 114 extends radially out to the ground shell 112. The

ferrule 116 at a proximal point is flush with a surface 118 of the dielectric material.

In this embodiment, a electrostatic discharge protection device 100 is arranged to

contact only the top of the ferrule 116 and to conduct between the ground shell 112 and the ferrule 116 in this way.

The electrostatic discharge protection device 100 is formed to be substantially planar

such that a ground plate 102 can be placed flatly over the surface 118 of the dielectric

material 114. When placed in this way, extensions from the ground plate 102, called

darts 108, are bent slightly upward away from the surface 118 and in contact with the ground shell 112. The darts 108 hold the electrostatic discharge protection device 100 firmly in place by biting into the lateral surface of the ground shell 112 and at the same

time establish an electrical connection with the ground shell 112.

The ground plate 102 is a flat annular ring having two flanks 104 that extend toward

the enclosed region of the ring. The flanks 104 are formed having a semicircular bend

extending outward from the plane of the ground plate 102 away from the surface 118

of the dielectric material 114. The flanks 104 are formed of a resilient conductive

material, such as beryllium copper, such that the may be repeatedly compressed flat

and upon removal of the compression force, the flanks regain their former shape. The

two flanks 104 meet at a distal point near a geometric center of the ground plate 102 to

form an aperture 107 which is bounded by the flanks 104 and the ground plate 102.

Projecting into the aperture 107 from the flanks 104 is a barb 106. The barb 106 is bent at an angle axialiy with respect to the central axis of the electrostatic discharge

protection device but projects toward the surface 118 of the dielectric material. The

barb 106 is fabricated of the same or similar resilient conductive material as the flanks and provides a contact with the ferrule 116.

When the electrostatic discharge protection device 100 is pushed down into the

ground shell 112, the darts 108 bend slightly biting into the lateral surface of the ground shell to both hold the electrostatic discharge protection device 100 into place as well as create an electrical contact with the ground shell 112. The electrostatic discharge protection device 100 being in an uncompressed form, places the barb 106

slightly inside the ferrule 116 such that a surface of the barb 106 is resting against the

top of the ferrule 116. In this way, electrical communication is established between the

ferrule 116 and the ground shell 112 thus grounding any electrostatic discharge in the

ferrule.

The connector 120 is then used to mate with the receptor 110 to combine two or

more coaxial cables. The connector 120 has a housing 122 which has interior threads

and is in electrical communication with outer metal tube of the coaxial cable. The housing 122 is threaded in such a way as to be complimentary to the threads of the ground shell 112, thus allowing threaded combination of the connector 120 and the receptor 110.

The connector 120 has a core conductor 126 which projects out axialiy from the

center of the connector 120 and out beyond a dielectric material 124 which separates

the core conductor 126 and the housing.

When the connector 120 is inserted into the receptor 110 and the housing 122 is rotated such that the connector is fully inserted, see Figure 9, compression between the dielectric material 124 and the dielectric material 114 forces the flanks 104 and the

barb 106 to flatten. By flattening, the flanks 104 push the barb 106 away from the ferrule 116 and toward the ground shell 112 breaking electrical communication and opening the short circuit which had been established.

Upon removal of the connector 120 from the receptor 110 to disconnect the coaxial cable, the electrostatic discharge protection device 100 resumes its normal form thus reestablishing a short circuit across the ferrule 116 and the ground shell 112.

Referring to Figures 10 where like numerals designate previously described elements, there is shown an alternate embodiment of the invention. In contrast to the

previous embodiment, the electrostatic discharge protection device 130 is designed for

use with a twinaxial cable which a high frequency cable having two core conductors.

Though the invention may be used with cable arrangements having multiple core conductors in excess of the two described herein, one skilled in the art will realize that such an adaptation is simply an extension of this teaching. The connector is shown having two corresponding core connectors 28". Otherwise, the BNC connector is as previously described.

In this embodiment, the electrostatic discharge protection device 130 is placed over the dielectric ring 24" as before such that bridges 134 span the dielectric ring 34".

Extending down from the bridges 134 radially inward are contacts 136, each having a notch 138. From an outer point of the bridge 134 extends a ground tab 132 which is structured similarly to the ground tab of the first embodiment described herein. In this embodiment, there are two bridges extending from the ground tab 132. One skilled in the art will realize that other arrangements are possible, such as a single bridge and multiple contacts extending therefrom, without departing from the inventive aspects described herein. Adapting the receptor version of the electrostatic discharge protection device is accomplished in a similar manner and is considered a trivial exercise for one skilled in the art.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing

description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.