US 3710285 A
A plurality of ground planes establish a low impedance ground return circuit for a filter pin connector comprising a connector pin, a tubular filter, and a housing. The ground planes comprising thin metal sheets in electrical contact with the outer surface of the tubular filter are sandwiched between various insulators of the housing.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 I Schor et al.
[451- Jan. 9, 1973  FILTER PIN CONNECTOR HAVING LOW GROUND RETURN IMPEDANCE Calif.; William Baird Fritz, Hershey, Pa.
Assignee: AMP Incorporated, Harrisburg, Pa.
Filed: Jan. 25, 1971 Appl. No.: 109,423
US. Cl ..333/79, 339/147 Int. Cl. ..II03h 7/14, H03h 7/04 Field of Search ..333/79, 73, 73 C; 339/143,
References Cited UNITED STATES PATENTS Scott Peterson et al...
Schlicke Inventors: Ferdinand William Schor, Altadena,
Devot ..333/73 C 'Schlicke..............:::::::: .111333/79 3,185,944 5/1965 Tumage at al ,...333/73 c 3,568,109 3/1971 Neuens ..333/79 OTHER PUBLICATIONS Susskind, The Enchclopedia of Electronics Reinhold New York, 1962 TR 7804 S8; Title page & pp.
Primary Examiner-Herman Karl Saalbach AssistantExaminen-Marvin Nussbaum Attorney-William J. Keating, Ronald D. Grefe, Gerald K. Kits, Jay L. Setchik and John P. Vandenburg  ABSTRACT A plurality of ground planes establish a low impedance ground return circuit for a filter pin connector comprising a connector pin, a tubular filter, and a housing. The ground planes comprising thin metal sheets in electrical contact with the outer surface of the tubular filter are sandwiched between various insulators of the housing.
7"Claims, 7 Drawing Figures PATENTEDJAH 91973 3. 710,285
SHEET 1 BF 4 INVENTORS 71; FERDINAND WILLIAM HOR WILLIAM BAIRD FR JOHN VANDENBURG PAIENIEUJM' 9:915 3.710.285
SHEET 2 OF 4 PAIENTEUJAH 9 I975 SHEET UF 4 HIIN Om Ow ON 0m HP 880'! NOLLHEISNI FILTER PIN CONNECTOR HAIVNG LOW GROUND RETURN IMPEDANCE BACKGROUND OF THE INVENTION The present invention relates to electrical connectors wherein one or more contact terminals are carried by one connector member and complementary contact terminals are carried on a mating connector member to provide one or more electrical circuits upon mating of the connector members. More particularly, the invention relates to such a connector wherein R.F. filter assemblies comprising capacitive, inductive and/or lossy circuit elements are electrically connected to the contact terminals of one of the connector members so asto attenuate undesired R.F. signals.
Connector pins which form the contact terminals are inserted into the R.F. filter making electrical contact with the filter, usually at the inner surface, by soldering or through the use of a spring contact device. The filter is also connected to ground, usually at the outer surface and oftentimes through the metal shell of the connector housing. When the filter is installed in electrical equipment, this metal shell is conductively attached to the equipment ground. In this manner, a low resistance path to ground is provided for undesired RF. signals which may have frequencies above 1.0 GI-Iz (gigahertz) and extending up to GI-Iz or higher.
In large part, the effectiveness of a connector filter depends upon the filter internal shunt impedance and also upon the impedance of the ground return circuit associated with the filter. At higher frequencies, the equivalent shunt impedance of the filter becomes very small, usually less than a milliohm. On the other hand the impedance of the ground returncircuit, which includes a very small inductance in series with a i resistance, increases with increasing frequency. This is due to the increased reactance of ground return circuit .intrinsic inductance and also due to the skin effect of the conducting surface. Thus, at frequencies above 1.0
GHZ, the filtering effectiveness depends as much upon the ground return circuit as it does upon the filter itself.
In addition to the series inductance. and resistance contained in the ground plane, the outer surface or ground circuit of a filter also contains some residual impedance in the form of inductance and series resistance which add to those of the return circuitand become particularly manifest at frequencies above 3.0 GHZ.
From a performance standpoint, the ideal grounding method would involve a coaxial mount for a filter pin. However, the coaxial mount is impractical and expensive particularly in a multi-pin connector since the conductors are normally single conductor non-shielded wire.
As a consequence, the usual method of providing ground return has involved the use of a sheet metal ground plane at a right angle to the axis of the connector pins, or in the alternative, a ground plane comprising conductive rubber. Although such a grounding method provides acceptable performance for some applications, high frequency performance leaves much to be desired. In particular, the impedance of a ground return circuit utilizing a single conductive ground plane is too large at high frequencies to achieve the optimum in performance. In addition, the series inductance and resistance of the filter ground circuit itself, usually the outer surface of the filter, becomes troublesome at high may be minimized by utilizing a thickness at least equal to two skin depths at the lowest frequency of interest. Although some mechanical stability may be achieved by utilizing a ground plane of greater thickness, the impedance of the ground circuit is not reduced and there is therefore no improvement in electrical performance associated with this increase in thickness.
SUMMARY OF THE INVENTION One object of this invention is to provide a low impedance ground'return circuit for filters in a filter connector and thus improve the filter performance.
Another object of the invention is to minimize the effect of the residual impedance in the filter ground circuit'and thus improve filterperformance.
A further object of the invention is to provide redundancy in the ground return circuit and thus improve the filter reliability factor under adverse environmental conditions such asshock, vibrations, temperature extremes and corrosive atmospheres.
A still further object of the invention is to provide rigid mechanical support for filters which tends to maintain the correct filter position and reduces filter breakage which otherwise would occur if the protruding contact pins are accidentally bent out of alignment in handling the filter connector. 7
A still'further object of the invention is to reduce assembly costs for filter connectors by assuring easy assembly.
In accordance with these objects and other objects, the'filter connector assembly may comprise a connector pin, a substantially tubular filter-having an axial opening for receiving the connector pin, and a housing including an insulator means and ground returnmeans. The ground return means may comprise a plurality of conductive planes separated by the insulatormeans of the housing.
BRIEF; DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a prior art filter connector assembly;
FIG. 2 is a sectional view of a filter connector assembly embodying the invention;
FIG. 3 is an enlarged view of a portion of the connector assembly of FIG. 2;
FIG. 4 is an electrical schematic diagram of the connector assembly of FIG. 1;
FIG. 5 isa similar schematic diagram of the connector assembly of FIG. 2;
FIG. 6 is a diagram showing filter performance curves including the filter performance curves of the connector assemblies of FIGS. 1 and 2; and
FIG. 7 is a sectional view of another connector assembly embodying the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the prior art filter connector assembly shown in FIG. 1, the connector pins 10 and tubular filter elements 12 are retained within a housing 14 comprising a conductive shell 15 adapted to be connected to a grounded support thereby establishing ground for the assembly, a front insulator 16, a rear insulator 18, a
ground plane 20, and a grommet 22. The single ground plane 20 is sandwiched between the front insulator 16 and the rear insulator 18 with perforations in the ground plane 20 aligned with the openings through the front insulator 16, the rear insulator l8, and the grommet 22. By inserting the connector pins through the tubular filter elements 12 and providing suitable spring contact means therebetween, a filter circuit is established having input and output terminals formed by the ends of the connector pins 10 and a ground connection provided by the metal shell 15 and the ground plane 20. The ground plane includes integral tines 24 in contact with the metal shell 15 and similar tines 26 at the perforations in the ground plane 20 to establish contact with the outer or ground surfaces of the filter elements 12.
Referring now to FIG. 2 and a preferred embodiment of the invention, it will be seen that the insulator means of the housing 14 comprises an intermediate insulator 28 separating a mutually insulated pair of parallel ground planes 30 providing a pair of ground return paths. By utilizing the pair of ground planes 30, the impedances of the ground return circuits for the filter elements 12 can be reduced and the effect of the residual impedances of the filter ground circuits at the outer surfaces of the filter elements 12 is minimized. In addition, the reliability and mechanical strength of the filter assembly can be maximized as may be seen by reference to FIG. 3.
As shown there, the use of two ground planes 30 provides longitudinally spaced support along each filter element 12 at the tines 26. The two ground planes 30 assist in holding the filter rigidly in position thereby greatly reducing the radial stress on the filter 12 if the connector pin 10 is accidentally bent, as sometimes happens during handling or use of the device. As a result of this reduction of stress, filter breakage is minimized. In addition to the mechanical support provided at the tines 26, it will be seen that a certain redundancy in the ground connection is provided so as to increase the reliability factor of the filter assembly. Furthermore, it has been found that the assembly of the front insulator 16 and the rear insulator 18 is facilitated with the use of the two ground planes 30.
FIG. 3 also discloses the nature of each filter element 12 which comprises a tubular dielectric 32, an outer conductive layer 34 at the outer or ground surface of the dielectric 32, and a relatively conductive ferrite sleeve 40 having an axial opening receiving the connector pin 10 and establishing electrical contact between the pin 10 and the filter. The filter element 12 in its preferred form is disclosed more fully in patent application Ser. No. 883,501, filed Dec. 9, 1969, now abancloned, in the name of William B. Fritz, and assigned to the assignee of the present invention.
F IG. 4 is a schematic circuit diagram representing the single ground plane filter connector of FIG. 1. The circuit includes an input terminal 41, an output terminal 42, ground 44, a filter 46, and a ground return circuit 48. The inductive-resistive path between the input terminal 41 and the output terminal 42 comprises an inductor 50 and a resistor 52 which corresponds with and is established by the pin 12 and the ferrite sleeve 40. The capacitors 54 and 56 represent the capacitive paths between the terminals 41 and 42 and the outer conductive layer 34. Inductors 58 and 60 in series with resistors 62 and 64 represent the filter ground circuit or inductive-resistive path along the outer conductive layer 34 with the inductor 58 and the resistor 62 representing the inductive-resistive path on the one side of the single ground plane 20 and the inductor 60 and the resistor 64 representing the inductive-resistive path on the other side of the ground plane 20. Accordingly, the ground return circuit 48 comprising a series inductive-resistive path including an inductor 66 and a resistor 68 is shown as connected between the junction of the inductor-resistor combinations 58-62 and 60-64 and ground 44.
It is an object of this invention to minimize the impedance of the ground return circuit. It is also an object of this invention to minimize the effect of the residual impedance of the filter ground circuit. This may be accomplished by utilizing a plurality of ground planes as can be seen more clearly with reference to the schematic diagram of FIG. 5.
As shown in FIG. 5, the residual impedance of the outer layer 34 has been subdivided into three different series inductive-paths including inductors 70, 72, 74 and resistors 76, 78 and 80. Since the ground return circuit comprises two separate ground planes 30, the ground return circuit 82 comprises a first series inductive-resistive path comprising an inductor 84 and a resistor 86 and a second inductive-resistive path comprising an inductor 88 and a resistor 90. By providing a substantial separation between the ground planes 30 relative to the thickness of the thin ground planes, the impedance of the inductor 72 and the resistor 78 will be substantial and the impedances of the inductors and 74 and the resistors 76 and 80 will be correspondingly diminished so as to minimize the effect of the residual impedance of the filter ground circuit. Furthermore, by virtue of the fact that the ground return circuit 82 comprises two branches as shown by FIG. 5, its resultant impedance will be substantially reduced and the performance of the filter is enhanced accordingly. This is to be contrasted with the substantial effect of the residual impedance of the filter ground circuit 34 as represented by the inductors 58 and 60 and the resistors 62 and 64 of the prior art arrangement depicted in FIG. 4 and the large impedance of the ground return circuit 48 therein which has a single branch comprising the inductor 66 and the resistor 68.
It therefore may be seen that the use of two ground planes instead of one reduces the impedance of the ground return circuit by at least 50 percent. This in itself can account for an approximate 6dB improvement in filter performance if the filter shunt impedance is small compared to the ground plane impedance. Furthermore, the effect of the residual impedance due to the filter ground circuit in the form of the outer layer 34 may be substantially reduced since the voltage appearing across the inductor 84 and the resistor 86 must divide between the inductors 72 and 88 and the resistors 78 and 90.
It may now be seen that the spacing between the ground planes 30 and the connection to theouter conductive layer at different and mutually spaced regions is very important since it affects the magnitude of the impedance represented by the inductor 72 and the resistor 78. It has been found that increasing the distance between the ground planes by one-sixteenth of an inch may increase the insertion loss of the filter by 3dB in the very high frequency range. It has also been found that the use of two ground planes in mutual electrical contact provides a filter performance substantially identical to that provided by a filter assembly utilizing a single ground plane. It will be understood that further improvements in the performance of the filter may be effected by more than two ground planes as shown in FIG. 7.
In FIG. 6, a number of performance curves corresponding to various filter connectors are shown. The single metal ground plane curve represents the performance of the filter connector FIG. 1 when a 3 mil, 6 tine silver-plated beryllium copper ground plane is utilized. As shown, the insertion loss never reaches 70dB even at low frequencies. The curve characteristic of a filter connector wherein a one-sixteenth inch conductive rubber ground plane is utilized represents a somewhat improved performance. However the maximum insertion loss is only 80dB and this is achieved only at frequencies in the vicinity of 0.7 GI-Iz. In contrast, the performance of the filter connector of FIG. 2 wherein two 3 mil, 6 tine silver-plated beryllium copper ground planes are utilized, the two ground planes being spaced apart as shown, provides an approximate 85dB insertion loss over frequency ranges extending from 0.2 GHz to nearly 3.0 GHz. Even at the higher frequencies approaching 10.0 GHz, the performance of the double metal ground plane connector is vastly improved over either the conductive rubber ground plane connector or the single metal ground plane connector. As can be seen, performance is improved by a factor of approximately l0dB.
The last curve shown is a curve of a filter connector mounted in a coaxial fixture. This curve represents a near optimum in performance with an insertion loss greater than 85dB from 0.3 to 10.0 GHz. Of course, such a filter connector arrangement is impractical for the reasons outlined previously. Significantly, the double metal ground plane connector approaches near optimum performance over a substantial frequency range. Furthermore, the performance of the double metal ground plane may be improved by the use of further or additional ground planes beyond the two shown in FIG. 2. Of course, only the most critical high frequency application would require the use of additional ground planes since the insertion loss of a double metal ground plane is nearly 60dB at 10.0 GHz.
Although the invention has been described in terms of particular filter connectors, it will be understood the invention comprehends various modifications and equivalents of that connector which fall within the scope of the appended claims.
What is claimed:
1. A filter connector assembly comprising:
i a connector pin; v
a substantially tubular filter element having an axial opening receiving and electrically contacting said connector pin;
a housing comprising front, rear, and intermediate insulator means having aligned openings for receiving said connector pin within said tubular filter, and a pair of conductive ground planes, one
of said ground planes located between said front insulator means and said intermediate insulator means and the other of said ground planes located between said rear insulator means and said intermediate insulator means, said ground planes providing a low impedance ground return path for said filter.
2. The filter connector assembly of claim 1 wherein said ground planes comprise thin sheets of metal having perforations aligned with the openings of said insulator means.
3. The filter connector assembly of claim 2 wherein said sheets of metal comprise integral tines for establishing electrical contact with said filter at said perforations.
4. A connector comprising a tubular housing means for connection to ground,
at least one end portion of said housing means being filled with dielectric material,
a feed-through contact terminal means within said dielectric material extending in an axial direction relative to the housing and exposed at its ends for mating with complementary contact terminal means, 1
filter means comprising a dielectric element exhibiting increasing resistance with frequency mounted on the contact terminal means within the housing for attenuating high frequencies,
and means for grounding the filter means at highfrequencies through a low impedance coupling comprising:
a conductive member coextensive with and capacitively coupled to the dielectric element, and a plurality of axially spaced conductive elements intermediate the ends of the conductive member extending transversely of said axial direction and connecting the housing to said conductive member.
5. A connector according to claim 4 wherein the conductive elements comprise substantially planar discs. r
6. A connector according to claim 4 in which the contact terminal means includes a plurality of like substantially contacting devices exposed at their ends for mating with respective complementary contact devices,
each of the contacting devices. being provided with a said filter means and a said 'capacitively coupled conductive member,
said conductive elements connecting all of the conductive members to said housing.
7. A connector according to claim 6 wherein the conductive elements comprise substantially planar discs.