Connector With ESD Protection

The current invention applies to the field of electrical connectors, particularly those connectors used in equipment which is sensitive to electro-static discharge (ESD).

Electrical connectors are used for the completion of electrical circuits between different pieces of electrical equipment. Often, the equipment receiving such an electrical connection is susceptible to static discharge, known as electro-static discharge, or ESD. ESD is a serious problem in modern electrical equipment. The current developed between two conductive surfaces having different charges is: ##EQU1##

As can be seen from this equation, the maximum developed current is related to the difference in charge between the two surfaces. In the case of two conductors of different charge coming into contact, the equation would indicate unlimited current flow. In practice, there are actually two limiting factors of interest. The first limiting factor is the resistance between the two conductors. In this case, where the charge developed is applied across the input of a sensitive electron device, the device itself may be the source of this resistance, and the analysis of this dissipation is complicated by the highly non-linear characteristics of most modern electron device. The second limiting factor is the absolute energy available for destructive device breakdown. The energy U in a charge Q present in a capacitor having capacitance C is ##EQU2##

With modern small device geometries, this device breakdown energy is low, and will become lower as more sensitive devices and higher frequency devices utilizing these smaller device geometries become available.

Prior art patents have disclosed different classes of protection. These will be described in terms of the scope of protection. The first class of protection represents additions to integrated circuits to make them more ESD resistant. Examples are U.S. Pat. Nos. 5,532,901 and 5,654,860 for protective devices to be incorporated into an integrated circuit. U.S. Pat. No. 4,677,520 is for a protective device which operates external to an IC, but within the package of the IC. Another class described offers protection to the printed circuit boards which ordinarily interconnect many of the previously described integrated circuits. U.S. Pat. Nos. 5,563,450, 4,223,368, and 5,164,880, and 5,537,294 describe grounding clips to be used to protect the circuit boards from the application of ESD to these exposed connectors. These techniques are useful for increasing the immunity of semiconductor devices to ESD. Another class of disclosure represents packaging intended to prevent the application of ESD to the printed circuit board during handling, such as U.S. Pat. No. 5,405,000. Another class of protection is for electronics enclosed in a removable cartridge. U.S. Pat. No. 5,031,076 discloses the inclusion of a conductive material surrounding the enclosed electronics, and U.S. Pat. No. 5,357,402 discloses a grounding spring for the discharge of static charge. Another class of prior art is directed to connectors which operate to minimize the transfer of static charge into the sensitive signal pins. This is accomplished through the introduction of an conductive shield around the connector, wherein the signal pins are concealed within this shield to encourage charge to travel through the exposed conductive shield rather than sensitive signal pins. Examples of such art include U.S. Pat. Nos. 5,161,991, 5,167,516, 5,224,878, 5,256,074, 5,256,085, and 5,342,220. These devices do not address the removal of charge present on signal lines, but instead provide some type of discharge mechanism between the signal pins and conductive shield. Examples of this include U.S. Pat. Nos. 5,147,223, 5,567,168. A final class of ESD protection is disclosed in U.S. Pat. No. 5,268,592 for which a staggered length set of connector pins are used to activate FET switches to enable signals at different times, selected in accordance to when the risk of ESD transfer is minimized.

A first object of the invention is to provide a connector with high tolerance to ESD. A second object of the invention is to cause static charge to be removed from signal lines before completion of an electrical circuit, thereby protecting the signal lines from transferring ESD to the devices which use these pins as signal inputs or outputs. A third object is to provide a connector which can be used in a variety of different situations, including but not limited to a plug and jack, and a printed circuit board and an edge connector.

The present invention is directed to a class of connector which removes static charge from signal lines prior to making the electrical connection with these signal lines. The removal of static charge prior to electrical connection to signal lines protects signal circuits associated with these signal lines. This is achieved through a primary set of grounded discharge conductors which remove stray charge prior to mating with a secondary set of conductors, which are then utilized in the typical manner. The connector comprises a plug and jack combination, wherein the plug has exposed connector contacts, and the jack has internal non-exposed contacts. The connector plug is typical of and compatible with other plugs commonly used for this application. The jack contains two sets of internal contacts. The outermost jack connector contacts make individual contact with the contacts of the plug. This first set of jack contacts may contain dissipation resistors, a non-linear resistance material, or any other means for dissipation of this static charge energy. When the plug is first inserted into this jack, the plug contacts make a connection with the first set of jack contacts, thereby discharging harmlessly the charge available on the cable. As the plug is further inserted into the jack, connectivity is lost with the first set of contacts, and the signal conductors are now in charge equilibrium with the second set of jack contacts, such that when contact is established with this second set of jack contacts, there is no further transfer of energy, and the sensitive circuitry is protected from exposure to any transfer of static charge.

FIG. 1 is a schematic diagram showing generically a connector, a charge source, and devices needing protection.

FIGS. 2a and 2b are a prior art connector.

FIG. 3a is a side view of a connector jack.

FIG. 3b is a front view of a connector jack.

FIG. 3c is a side view of a connector plug.

FIG. 3d is a front view of a connector plug.

FIG. 4a is a side view of the present invention in first position of engagement.

FIG. 4b is a side view of the present invention in final position of engagement.

FIG. 5 is a side view of an alternate embodiment for use with printed circuit boards.

FIG. 1 is a schematic view of the connector ESD problem, showing the connector plug contacts 3a, 4a, and 5a and connector jack contacts 3b, 4b, and 5b. In the figure, connector contacts 3a and 3b comprise a signal line, connector contacts 4a and 4b comprise a signal return line, and connector contacts 5a and 5b comprise an earth line, which is also the charge 2 return line between the local earth 7 and the charge source 2 earth 6. Signal source 8 represents the signal which is intended to be applied across signal pins 3a and 3b, and signal return pins 4a and 4b. Semiconductor signal processing elements are normally present at these signal input connectors, as seen in Insulated Gate Metal Oxide Semiconductor Field Effect Transistor (IGMOS FET) 9a, bipolar transistor 9b, junction FET 9b, and signal diode 9d. As is well known to one skilled in the art, the semiconductor devices described are sensitive to applied voltages, and may begin to breakdown with voltages as low as 3 volts in the case of reverse base-emitter voltage on a bipolar transistor such as 9b. Devices 9a through 9d are shown as examples, and could be any electronic device with ESD breakdown characteristics. Static voltages as represented in charge source 2 may be as high as 10,000 volts. Clearly, a mechanism is needed to dissipate this potential prior to connection to the previously described sensitive electronic devices 9a through 9d. One such mechanism is to guarantee through mechanical arrangement of connector components that connector pins 5a and 5b make an electrical connection first, followed by connector pins 4a and 4b. This assures that charge 2 is dissipated prior to the engagement of signal pins 3a and 3b, although such discharge current is seen to pass through signal source 8, which is undesirable.

FIGS. 2a and 2b shows the prior art connector of U.S. Pat. No. 4,477,134, which grounds signal pins when they are not in use. In FIG. 2a, ESD sensitive circuit 302 is connected to connector contacts 312, which are all in contact with conductive housing 332, and therefore at equal potential and immune from ESD transfer. When board 324 is inserted, as shown in FIG. 2b, each connector contact 312 makes connection with each contact surface present on 324.

FIGS. 3a,b,c and d show a typical data communications jack and plug, commonly known as an RJ-45 connector, such as model #555153-1 manufactured by AMP Inc. FIG. 3a is the side view of the jack, which comprises a housing 12, a plug receiving area 14, and a set of contact pins 10a. FIG. 3b shows the front view of the jack. This view shows the previously described housing 12 and receiving area 14, and additionally shows contact pins 10a,b,c,d,e,f,g,h, which is typical for the eight signal contact RJ-45 connector. These contact pins are often made from a material with a high spring constant, such as beryllium copper, or phosphor bronze alloy. FIG. 3c is the corresponding side view of the mating plug, which comprises a plug housing 16, a set of crimp contacts 18a through 18h, a signal cable 20, and a spring loaded retaining clip 24, which engages with matching surface 15 in the jack, thereby securing the plug in the fully engaged position. When mated, each of crimp contacts 18a through 18h is in contact with each of jack contact pins 10a through 10h. FIG. 3d shows the front view of the mating plug, where each crimp connection 18a,b,c,d,e,f,g,h makes contact with each of the previously described contact pins 10a,b,c,d,e,f,g,h. Cable 20 is now seen to further comprise individual corresponding conductors 22a,b,c,d,e,f,g, and h, each of which is respectively connected to crimp connectors 18a through 18h.

The present invention is shown in FIG. 4a. Connector plug 16 is of identical design as previously described in FIGS. 3c and 3d, and comprises housing 16 with retaining clip 24, a plurality of conductors 22a through 22h within a cable 20, and a plurality of contacts 18a through 18h, each contact 18a through 18h having an electrical connection to each conductor 22a through 22h in cable 20. Referring again to FIG. 4a, there is a connector jack comprising a housing 46, a cavity 44 for receiving connector plug 16, a recess 56 in cavity 44 for receiving retaining clip 24, and two sets of connector contacts 42a through 42h and 40a through 40h. The first set of connector contacts 42a-h is positioned near the front of the connector housing 46. The second set of connector contacts 40a through 40h is positioned near the rear of the connector housing 46, in such a manner as to provide exclusive contact between pins 18a through 18h to either contacts 42a through 42h, or to contacts 40a through 40h, but not simultaneously to both. When the plug 16 is first inserted into the jack, as shown in FIG. 4a, the connector contacts of plug 16 come in contact with the first set of jack contacts 42a through 42h, which discharge accumulated ESD through dissipation elements 50a thorough 50h, as shown in FIG. 4b, or alternatively, jack contacts 42a through 42h could be all tied together and discharge to a single dissipation element 50 as shown in FIG. 4a. The plug 16 position during which this contact between plug contacts 18a through 18h and first contacts 42a through 42h is referred to as first position engagement, as shown in FIG. 4a. Dissipation element 50 is connected between the first set of connector contacts 42a through 42f, and conductive chassis 48. If connector housing 46 also includes a shield, this may be tied to conductive chassis 48 via a spring clip formed into the shield, or other means known to those skilled in this art. After the initial transfer of charge through jack contacts 42a through 42f, as the plug is further inserted into cavity 44, plug contacts 18a though 18h move past and break contact with front connector contacts 42a through 42h, and thereafter make contact with the rear set of contacts 40a through 40h, which are the signal contacts. Thereafter, the locking clip 24 engages with matching recess 56, thereby locking the plug into place, and the plug contacts 18a through 18h maintain connectivity with jack contacts 40a through 40h. This position is referred to as final position of engagement. Input circuits 52a through 52h which are connected to jack contacts 40a through 40h are thereby protected from the ESD energy which was earlier dissipated in dissipation elements 50a through 50h during first position of engagement.

FIG. 5 shows an alternate embodiment of the present invention. This connector is optimized for operation as an edge connector for a printed circuit board, which is the type of use shown in prior art FIG. 2. Printed circuit board 70 is of typical design, and includes a plurality of connector contacts directly etched on its substrate material, which is usually copper. Connector housing 72 includes a recess 74 for receiving PCB 70, as well as connector contacts 76, 78, 80, and 82. Contacts 76 and 82 make contact first, and are connected to dissipation means 86 and 84 respectively. Signal contacts 78 and 80 make contact last, and deliver low level signals without ESD to signal processing circuit 88.