Abstract:
A filtered connector is provided of the type that includes an inductor ( 40 ) and capacitors ( 51, 52 ) connected in a pi filter arrangement to each contact ( 20 ) of the connector to attenuate high frequency noise, is enhanced to better block very high frequency noise. Each of applicant&#39;s filters that are connected to a contact have at least two capacitors ( 51, 53  and  52, 54 ) on either side of the inductor, the two capacitors being connected to contact locations that are spaced apart.

Description:
BACKGROUND OF THE INVENTION 
   One type of filtered connector includes a plurality of pin-like contacts that project through holes in an insulator and though inductors in the form of ferrite beads. A pair of capacitors, which may be mounted on boards lying beyond opposite ends of the ferrite beads, are connected to corresponding contact locations. This arrangement, commonly referred to as a pi filter, is useful to block high frequency noise, such as noise of a frequency above one MHz. The attenuation of noise can be increased at lower frequencies by the use of a larger inductor and larger capacitors, but there are restrictions in the space available in filter connectors. For example, the filtered connector illustrated in the drawings has 128 contacts arranged in multiple rows, in a connector shell having a length of about 1.5 inch and an outer shell diameter of about 1.6 inch. The contacts in the shell are spaced apart (center-to-center) by 0.100 inch along each row. In a prior art connector of these dimensions, using a pi filter with two capacitors each of 5000 picofarads and a ferrite bead having a bead diameter of 0.065 inch and length of 0.125 inch, applicant achieved an attenuation of −42 dB at a frequency of 1 GHz. A significantly higher attenuation using filter elements that fit into the same connector shell, would be of value. 
   SUMMARY OF THE INVENTION 
   In accordance with one embodiment of the invention, a filtered connector is provided which includes filter components that fit into a small space and that provide increased attenuation of high frequency noise. The connector is of the type that includes a prior art pi filter for each connector contact, the pi filter including a ferrite bead inductor threaded onto the contact and first and second capacitors. In such pi filters, the capacitors are connected to the contact at first and second locations that lie beyond opposite ends of the bead. However, applicant greatly increases very high frequency noise attenuation by the use of third and fourth capacitors that lie beyond opposite ends of the ferrite bead. The third and fourth capacitors are connected to the contact at locations that are spaced from the first and second locations where the first and second capacitors are connected to the contact, to provide an extended pi filter. 
   The third and fourth locations along the contact where the third and fourth capacitors are connected to the contact, are spaced from the first and second locations by controlled distances. The spacing distances (center-to-center distances) are each a plurality of thousandths inch, preferably at least twenty thousandths inch. 
   The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an end view of a filtered connector of the present invention. 
       FIG. 2  is a partially section side elevation view of the connector of  FIG. 1 . 
       FIG. 3  is a view taken on line  3 — 3  of  FIG. 4 , showing a portion of one of the boards of the connector. 
       FIG. 4  is an enlarged sectional view of a portion of the connector of  FIG. 2 . 
       FIG. 5  is a schematic diagram showing the electrical characteristics of one of the contacts and associated filter elements of the connector of  FIG. 4 . 
       FIG. 6  is a graph showing change in noise attenuation with frequency, for a prior pi filter and for applicant&#39;s extended pi filter, that use the same total capacitance. 
       FIG. 7  is a graph showing change in noise attenuation with frequency, for a prior pi filter and for applicant&#39;s extended pi filter, where the prior pi filter uses a larger total capacitance than applicant&#39;s extended pi filter. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 , shows a connector  10  of the invention which includes a metal shell  12  having an axis  14 , an insulator  16  within the shell, and a plurality of elongated contacts  20  that extend through holes in the insulator. The particular connector includes 128 contacts arranged in multiple rows  22  and lying within a shell having an outside diameter of about 1.6 inches. The contacts are designed to carry low frequencies (DC to about one MHz), and the connector includes a filter for each contact that blocks high frequency noise, which is here generally defined as noise having a frequency above one MHz. 
     FIG. 2  shows that the connector has a construction similar to that described in U.S. patent application Ser. No. 10/430,933 filed May 6, 2003. U.S. Pat. No. 6,896,552 That is, the connector includes multiple elongated contacts  20  with opposite ends  26 ,  28  spaced in front F and rear R directions and that are accessible from opposite ends of the connector. As also shown in  FIG. 4 , a plurality of flexible circuit boards  31 ,  32 ,  33 , and  34  extend across a cavity  36  formed in the shell  12 , in planes that are normal to the connector axis  14 . A rigidizing board  38  lies below portions of each circuit board. An inductor in the form of a ferrite bead  40  with front and rear ends  42 ,  44 , is threaded around each contact. Two of the boards  31 ,  33  lie forward of the bead, while two of the boards  32 ,  34  lie rearward of the bead. The boards carry capacitors  51 ,  52 ,  53 , and  54  that are connected to the contact. The ferrite beads and capacitors provide filtering that blocks high frequency noise from passing along the contact. Many of the contacts of the connector are similarly filtered, with all of the contacts of the particular connector  10  being similarly filtered by providing a separate ferrite bead and set of capacitors for each contact. 
     FIG. 4  shows that each board has a hole  60  through which the contact  20  extends. Each capacitor such as  51 , has a pair of terminals, with one terminal  62  connected to a signal trace  64  on the circuit board that extends to, and preferably completely around the hole in the board. The signal trace is connected by a solder joint  66  to a location  71  on the contact. The other capacitor terminal  80  connects to a ground trace  82  that is electrically grounded.  FIG. 4  shows that the ground trace extends to a periphery  84  of the board where the board is bent and soldered by a solder joint  86  to the metal shell. 
   Previously, only the first and second capacitors  51 ,  52  were connected to the contact, at locations  71 ,  72 , with one location  71  lying forward of the ferrite bead  40  and the other  72  lying rearward of the bead, to create a pi filter. In accordance with the present invention, applicant provides third and fourth capacitors  53 ,  54  that connect to contact connect locations  73 ,  74 . One of the additional locations  73  where the third capacitor  53  connects to the contact, lies forward of the ferrite bead  40  and is spaced a distance A from the first location  71 . The other additional location  74 , where the fourth capacitor  54  connects to the contact, lies rearward of the ferrite bead and is spaced a distance B from the second location  72 . Applicant calls the combination of a pi filter and at least two additional capacitors  53 ,  54 , with an additional capacitor connected to a contact location lying beyond each end of the ferrite bead, an extended pi filter.  FIG. 5  is a schematic diagram of the contact  20  and of the ferrite bead and capacitors. 
     FIG. 6  is a graph that qualitatively shows the advantage of applicant&#39;s extended pi filter over a prior pi filter. Below a frequency of about 100 MHz, the filter characteristics are similar. However, considerably above 100 MHz, such as above 500 MHz, applicant&#39;s extended pi filter, whose performance is given by graph line  102 , is better at attenuating very high frequency noise. Tests conducted by applicant show that at 1 GHz, the prior pi filter (with two 5000 picofarad capacitors), whose performance is given by graph line  104 , produces an attenuation of −42 dB, while applicant&#39;s extended pi filter (with four 2500 picofarad capacitors) produces an attenuation of −67 dB. Also, applicant&#39;s extended pi filter has an attenuation that does not significantly decrease with increasing frequency near 1 GHZ. 
     FIG. 7  shows the effects of increasing the capacitance (to a plurality of times 5000 picofarads) of the two capacitors of a prior art pi filter, as compared to applicant&#39;s extended pi filter (with 4 capacitors of 2500 picofarads each and with an inductor having an inductance of 100 microneries). Graph line  112  shows the performance of applicant&#39;s extended pi filter, while graph line  114  shows the performance of a prior pi filter with increased capacitance (two capacitors, each with a capacitance of a plurality of times 5000 picofarads). It can be seen that the effect of the high capacitance in a prior pi filter is to obtain greater attenuation of noise at lower frequencies such as below about 500 MHz, while reducing attenuation of noise with increasing frequency more rapidly than in applicant&#39;s extended pi filter. 
     FIG. 4  shows that the contact pin portion  20 A that extends through the ferrite bead  40  has a diameter D of 0.020 inch (0.5 millimeter). The first and second locations  71 ,  72  where the first and second capacitors connect to the contact are spaced apart by a distance E of about 0.200 inch (5 mm). The distance A between the first contact connect location  71  and the third location  73 , is 0.060 inch (1.5 mm). Similarly, the distance B between the second and fourth contact connect locations is 0.060 inch (1.5 mm). Applicant tested the attenuation characteristics at both 0.040 inch and 0.060 inch separations and found that better attenuation was achieved at 0.060 inch separations. The separation should not exceed about 0.5 inch. 
   The connector of  FIG. 4  can be assembled by positioning, in a fixture, a pair of insulator plates  130 ,  132  of the insulator  16 , the four flexible circuit boards  31 – 34  with capacitors thereon, and the ferrite beads, all with their contact-receiving holes aligned. The contacts  20  are then inserted rearwardly though the holes, and the shell  12  is slid over the peripheries of the boards  31 – 34 . The assembly is soldered to form the solder joints, and other parts such as elastomeric seals  140 ,  142  are put in place. 
   The center-to-center spacings A and B between capacitors that both lie beyond the same end of the ferrite bead, should be a plurality of thousandths inch in any case, and preferably on the order of magnitude of 1.5 mm (0.060 inch). Applicant achieves an improvement in attenuation when the spacing A, B is at least equal to one half the diameter D of the contact portion that passes though the bead and capacitors, and especially when the spacing is at least equal to the contact diameter. Such spacing is preferably at least 1.5 millimeter (0.020 inch). As mentioned above, applicant has used spacings A, B of about 1.5 mm (1 to 2 millimeters) for best results while providing a filter arrangement that still fits into the connector of predetermined size. 
   Thus, the invention provides an extended pi filter for attenuating high frequency noise such as noise of at least one MHz, and especially noise above 100 or 500 MHz frequency, such as at 1 GHz, and that is especially useful in a connector of limited size where there is limited room available for filter components. The connector includes a pi filter connected to a contact, wherein the pi filter is modified by adding at least one capacitor beyond each end of the inductor. Two capacitors lying beyond each end of a ferrite bead inductor, are connected to a contact at connect locations that are spaced apart along the length of the contact. The center-to-center spacing of the contact connect locations are a plurality of thousandths inch, preferably at least 0.020 inch (0.5 mm) but no more than about 0.5 inch, and preferably on the order of magnitude of 1.5 mm (0.06 inch). 
   Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.