Patent Abstract:
A filter assembly, comprising first and second terminal caps in opposing relation to each other. The caps are physically and electrically coupled to each other. First and second circuit boards are physically coupled to the first cap. The first circuit board includes—(i) front and rear surfaces, (ii) a first circuit located on either or both of the front and rear surfaces, (iii) a ground lead connected to the first circuit, and (iv) a first electrical terminal coupled to the first circuit. The second circuit board includes—(i) front and rear surfaces, (ii) a second circuit located on either or both of the front and rear surfaces, (iii) a ground lead connected to the second circuit, and (iv) a second electrical terminal coupled to the second circuit. The first and second circuits are electrically coupled to each other, and each are electrically coupled to the first terminal cap.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. Application Serial No. 10/056,899, filed Jan. 24, 2002, which is a continuation of U.S. application Ser. No. 09/898,543, filed Jun. 29, 2001, which in turn is a continuation of U.S. application Ser. No. 09/382,064, filed Aug. 24, 1999, now U.S. Pat. No. 6,323,743, the entireties of which are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention relates generally to electronic filters used in the cable television industry, and relates more particularly to the construction and assembly of such filters.  
           [0004]    2. Background Art  
           [0005]    Typical electronic filter constructions in the cable television (CATV) industry involve a considerable number of parts, such as, for example, one or more circuit boards, connecting wires or leads, filter circuit components, isolation plates, blocks or chambers, input and output terminals, moisture barrier seals or plugs, connector housings, sub-housings or caps, o-rings, outer housing sleeves, and potting material. This elaborate array of parts constrains efforts to: minimize the size and weight of the filters; reduce material and labor costs associated with assembly of the filters; and simplify and automate the assembly process. Examples of such filter constructions are shown and described in: U.S. Pat. No. 5,278,525 to Palinkas; U.S. Pat. No. 4,901,043 to Palinkas; U.S. Pat. No. 4,701,726 to Holdsworth; U.S. Pat. No. 4,451,803 to Holdsworth et al; U.S. Pat. No. 3,579,156 to Parfitt; and U.S. Pat. No. 3,065,434 to Calderhead.  
           [0006]    For such CATV filters as highpass and lowpass filters, diplex filters, windowed highpass filters, and step attenuator (or return path) filters, tunable filter circuits and shielding between filter components and circuits are not normally required. Thus, for these types of filters, an opportunity is presented to simplify filter components, construction and assembly. U.S. Pat. No.  5 , 745 , 838  to Tresness and Zelenz (Zelenz is a named inventor of the present invention) discloses (FIGS.  8 - 10 ) a filter construction for a return path filter called a “step attenuator.” This construction is also shown in FIG. 2 herein, as representing the prior art construction for this type of filter. While simplification was achieved in U.S. Pat. No. 5,745,838, the construction still required two major o-rings around the male and female terminal caps and an outer housing sleeve (See FIG. 2 herein); and, manual assembly of these parts was still required.  
           [0007]    Many diplex, windowed highpass, and return path filters (See, e.g., embodiments shown in FIGS.  1 - 5  of U.S. Pat. No. 5,745,838), have dual (or “parallel”) circuit paths. For example, FIG. 1, herein, shows a simplified step attenuator circuit  10  containing a forward (or highpass) path  12  and a return (or lowpass) path  14 . Cascaded or elongated circuit board arrangements such as shown in U.S. Pat. No. 5,770,983 to Zennamo, Jr. et al., U.S. Pat. No. 4,901,043 to Palinkas, U.S. Pat. No. 4,701,726 to Holdsworth, U.S. Pat. No. 4,451,803 to Holdsworth et al., U.S. Pat. No. 3,579,156 to Parfitt, and U.S. Pat. No. 3,065,434 to Calderhead, are not optimum platforms for such dual path filters. A more optimum platform would be to have two circuit boards disposed in a parallel arrangement.  
           [0008]    U.S. Pat. No. 5,278,525 to Palinkas discloses parallel circuit boards for a CATV notch filter (or “trap”), rather than for a dual path filter. The construction includes a considerable number of extra parts, such as an isolation shield, circuit board housings, tuning screw housings, o-rings, and an outer housing sleeve.  
           [0009]    In most CATV applications, the filters are installed in an outdoor environment. Thus, it is important that the filter construction be moisture resistant. Efforts to make filters moisture resistant have included enclosing the filter in an outer housing sleeve and employing o-rings between the filter and the outer housing sleeve. See, e.g., U.S. Pat. No. 5,745,838 to Tresness et al., U.S. Pat. No. 5,278,525 to Palinkas, U.S. Pat. No. 4,701,726 to Holdsworth, and U.S. Pat. No. 4,451,803 to Holdsworth et al. Such an approach requires the additional parts and expense of o-rings and outer housing sleeves, and may require manual assembly of such parts.  
           [0010]    A prime path for moisture penetration into the filter is through the terminal fittings or connectors. While efforts to prevent moisture penetration through filter connectors (such as disclosed in U.S. Pat. No. 5,278,525 to Palinkas) have been satisfactory, there remains a need to improve moisture resistance through these connector paths.  
           [0011]    Another consideration in CATV filter construction is to establish a good and reliable electrical ground between the filter circuit or circuits and the filter housing. Electrical ground has been established by soldering or fitting isolation shields or blocks between the circuit boards and the filter housing, or by soldering wires or leads between the circuit board and housing. See, for example, U.S. Pat. No. 4,701,726 to Holdsworth. However, such methods usually require additional components or manual assembly steps.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0012]    It is therefore an object of the present invention to provide an electronic filter construction that avoids the limits and problems associated with the prior art.  
           [0013]    It is another object of the present invention to provide an electronic filter construction that is more suitable for automated assembly than previous filter constructions.  
           [0014]    It is a further object of the present invention to provide an electronic filter construction that requires less parts than previous filter constructions.  
           [0015]    It is still another object of the present invention to reduce material and labor costs associated with the assembly of an electronic filter;  
           [0016]    It is still a further object of the present invention to reduce the size and weight of an electronic filter;  
           [0017]    It is yet another object of the present invention to provide an electronic filter construction that is optimum for dual (or parallel) path filter circuits;  
           [0018]    It is yet a further object of the present invention to provide an electronic filter construction that establishes an effective and reliable ground connection between the filter&#39;s circuitry and the filter housing; and  
           [0019]    It is still yet another object of the present invention to provide an electronic filter construction that has improved moisture resistance.  
           [0020]    These and other objects are attained in accordance with the present invention wherein there is provided a filter assembly, comprising (1) a first terminal cap, (2) a second terminal cap, (3) a first circuit board, and (4) a second circuit board. The first and second terminal caps are disposed along a longitudinal axis in opposing relation to each other. The terminal caps are physically and electrically coupled to each other.  
           [0021]    Both circuit boards are physically coupled to the first terminal cap. The first circuit board includes—(i) front and rear surfaces, (ii) a first filter circuit located on either or both of the front and the rear surfaces, (iii) a ground contact electrically coupled to the first filter circuit and to said first terminal cap, and (iv) a first filter terminal coupled to the first circuit. The second circuit board includes—(i) front and rear surfaces, (ii) a second filter circuit located on either or both of the front and the rear surfaces, (iii) a ground contact electrically connected to the second filter circuit and to said first terminal cap, and (iv) a second filter terminal coupled to the second circuit. The first and second circuits are electrically coupled to each other, and each circuit is electrically coupled to the first terminal cap via the ground contacts such that the circuits have a common ground through the first terminal cap.  
           [0022]    The first and second circuit boards are positioned substantially parallel to each other and to the longitudinal axis, between the terminal caps. The front surface of the first circuit board substantially faces the front surface of the second circuit board. The first and second terminals extend into and are operatively supported inside the first and second terminal caps, respectively.  
           [0023]    In a modified embodiment, the filter assembly of the present invention may include only a single circuit board physically coupled to the first terminal cap. In such an embodiment, the single circuit board would include—(i) front and rear surfaces, (2) a filter circuit located on either or both of the front and rear surfaces, (iii) a ground contact electrically coupled to the filter circuit and to the first terminal cap, and (iv) first and second filter terminals electrically coupled to the filter circuit. The filter circuit is electrically coupled to the first terminal cap via the ground lead, such that the circuit is grounded through the first terminal cap. The single circuit board is positioned substantially parallel to the longitudinal axis, between the terminal caps. The first and second terminals extend into and are operatively supported inside the first and second terminal caps, respectively.  
           [0024]    In an alternative embodiment, a filter assembly is provided, which comprises—(1) first and second terminal caps, (2) a filter circuit, (3) first and second filter terminals, (4) first and second sealing members, and (5) an o-ring. The first and second terminal caps are arranged in opposing relation to each other. The first cap is directly connected to the second cap to form a filter housing which defines an interior volume. The first cap contains an external groove, and the connection between the first and second caps is substantially sealed by solder received in the groove. The caps contain first and second terminal passages, respectively, between the interior volume and the exterior of the filter assembly.  
           [0025]    A filter circuit is mounted inside the filter housing. The filter terminals are electrically coupled to the filter circuit. The first and second terminals extend through and are operatively supported inside the first and second terminal passages, respectively. The first sealing member is secured in and substantially closes the first terminal passage. The first sealing member contains a hole through which the first terminal tightly fits. The second sealing member is secured in and substantially closes the second terminal passage. The second sealing member contains a hole through which the second terminal tightly fits. The o-ring is seated inside the second terminal passage, between the second sealing member and the second terminal cap. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0026]    Further objects of the present invention will become apparent from the following description of the preferred embodiment with reference to the accompanying drawing, in which:  
         [0027]    [0027]FIG. 1 is a schematic diagram of a dual-path filter circuit;  
         [0028]    [0028]FIG. 2 is a longitudinal cross-sectional view of a filter constructed in accordance with the teachings of the prior art;  
         [0029]    [0029]FIG. 3A is a longitudinal cross-sectional view of a filter constructed in accordance with the present invention;  
         [0030]    [0030]FIG. 3B is an enlarged cross-sectional view of the circled area in FIG. 3A;  
         [0031]    [0031]FIG. 4 is an exploded view of the filter shown in FIG. 3A;  
         [0032]    [0032]FIG. 5 is an exploded view showing a modification to the filter of FIG. 4; and  
         [0033]    [0033]FIG. 6 is an exploded view showing another modification to the filter of FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    The filter assembly of the present invention is especially suited for dual (or parallel) path filter circuits. As understood in the art, dual path circuits include at least two separate circuit paths. Examples of dual path filters are diplex, windowed highpass, and some step attenuator filters. Referring now to FIG. 1, there is shown a schematic of a dual path filter circuit  10 , having a highpass circuit path  12  and a lowpass circuit path  14 . Circuit  10  is a simplified version of a step attenuator circuit described in U.S. Pat. No. 5,745,838 to Tresness et al., incorporated herein by reference. The present invention is not limited to filter assemblies for any particular filter circuit. Circuit  10  is presented only as an example of a dual path circuit. An understanding of circuit  10  is not necessary for an understanding of the present invention.  
         [0035]    [0035]FIG. 2 shows a sectional view of a conventional filter construction. The construction includes a female terminal cap  16 , a male terminal cap  18 , an elongated circuit board  20 , a female terminal  22 , a male terminal  24 , o-rings  26  and  28 , and an outer housing sleeve  30 . Terminal caps  16  and  18  are soldered together by way of a solder ring  32 . Female terminal  22  is connected to a female connector assembly  34  which includes a sealing member  36 . Male terminal  24  extends through an internally threaded fitting  38  contained in cap  18 . Terminal  24  is tightly fitted through a sealing wafer  40  secured inside cap  18 . The filter shown in FIG. 2 is of the type that does not require shielding or tunable filter components. As a result, low profile, surface mounted filter components  44  are used. It is apparent from FIG. 2 that this conventional construction produces an enormous amount of wasted internal space, and the elongated shape of circuit board  20  constrains efforts to reduce the length of the filter.  
         [0036]    The conventional filter construction of FIG. 2 is contrasted markedly by the filter construction of the present invention, shown in FIG. 3A. FIG. 3A depicts the preferred embodiment of the present invention. It does not include the outer housing sleeve and accompanying o-rings. The elimination of these parts simplifies the assembly and allows the filter manufacturer to adopt a more automated assembly process.  
         [0037]    The preferred construction will now be described in detail with reference to FIGS. 3A, 3B and  4 . A filter  50  includes a female terminal cap  52  and a male terminal cap  54 . Caps  52  and  54  are disposed along a longitudinal axis L, in opposing relation to each other. Caps  52  and  54  are made of any suitable conductive metal typically used in the filter industry. Cap  52  includes a cylindrical portion  56  having an extension or crimping sleeve  58 . Cylindrical portion  56  extends to cap  54 , and sleeve  58  is crimped around cap  54 , to form a filter housing with an interior volume  60  (FIG. 3A). Cap  54  contains an external circumferential groove  62  (FIGS. 3A and 4). Caps  52  and  54  are sealed together using a solder ring  64  received in groove  62 . A circumferential solder joint is established with ring  64 , by way of induction soldering. The solder joint also establishes a good electrical ground connection between caps  52  and  54 . Induction soldering is preferred because it can be implemented as an automated assembly step. As a result of the above-described crimping and soldering, a secure physical and electrical connection is established between caps  52  and  54 .  
         [0038]    Female terminal cap  52  includes a fitting portion  66  containing external threads  67  and a terminal passage  68 . Male terminal cap  54  includes a fitting portion  70  containing internal threads  71  and a terminal passage  72 . Passages  68  and  72  each establish a passageway between interior volume  60  and the exterior of filter  50 .  
         [0039]    As shown in FIG. 3A, a pair of filter circuit boards  74 ,  76  are enclosed in interior volume  60 . Circuit boards  74 ,  76  are arranged substantially parallel to each other and to longitudinal axis L. In this disclosure and in the claims, the term “parallel” is not intended to mean precisely parallel. The term includes orientations that may produce acute angles between the circuit boards.  
         [0040]    As best shown in FIG. 4, circuit board  74  includes—(i) front and rear surfaces  78 ,  79 , (ii) a filter circuit  80  located on front surface  78 , (iii) a pair of ground contacts  82 ,  83  electrically connected to circuit  80 , and (iv) a terminal  84  electrically coupled to circuit  80 . Circuit board  76  includes—(i) front and rear surfaces  86 ,  87 , (ii) a filter circuit  88  located on front surface  86 , (iii) a pair of ground contacts  90 ,  91  electrically connected to circuit  88 , and (iv) a terminal  92  electrically coupled to circuit  88 . It is preferred that another, corresponding pair of ground contacts be located on the rear surfaces of boards  74 ,  76 , respectively (see corresponding contacts  82   a ,  83   a  and  90   a ,  91   a  in FIG. 4). These corresponding pairs of contacts are likewise electrically connected to their respective filter circuits ( 80 ,  88 ). Circuit  80  is connected to circuit  88  by way of jumper wires  93   a ,  93   b  (FIG. 4), to form a complete filter circuit (such as shown in FIG. 1). Circuits  80 ,  88  are preferably implemented with all surface mounted filter components, including fixed-tuned chip (ceramic medium) inductors and/or ferrite core inductors.  
         [0041]    Dual filter circuit  10  (FIG. 1) can be neatly arranged on circuit boards  74 ,  76 , as indicated by the broken lines in FIG. 1. As represented in FIG. 1, circuit board  74  contains circuit path  14  which is embodied in circuit  80 , and circuit board  76  contains circuit path  12  which is embodied in circuit  88 . These paths are joined together by jumper wires  93   a ,  93   b  (FIG. 1). It is to be noted that the present invention is not limited to dual path circuits or to the separation of dual circuit paths on respective circuit boards. Any operable arrangement may be employed. When we refer to a “filter circuit” or “circuit” on a circuit board, in this disclosure and in the claims, it is intended to mean any arrangement of a circuit component or circuit components, whether or not constituting a complete or identifiable filter circuit. The example presented in this disclosure is merely to illustrate the suitability of the parallel circuit board arrangement (of the present invention) to a dual path circuit.  
         [0042]    Circuit boards  74 ,  76  are mounted directly to male terminal cap  54 . As best shown in FIG. 4, circuit boards  74 ,  76  have mating ends  75 ,  77 , respectively, and the ground contacts are located at the mating ends. Terminal cap  54  contains two pairs of opposed notches  94   a ,  94   b  and  94   c ,  94   d . For the purpose of this disclosure and the claims, the term “groove” shall include its normally intended meanings and, in addition, it shall include notch pairs, such as notch pairs  94   a ,  94   b  and  94   c ,  94   d . Thus, e.g., notch pair  94   a ,  94   b  may be properly referred to herein as groove  94   a ,  94   b . Grooves  94   a ,  94   b  and  94   c ,  94   d  are configured to receive, in a tight press fit, the mating ends of circuit boards  74 ,  76 , respectively. This tight press fit secures the circuit boards in position.  
         [0043]    Circuits  80 ,  88  are electrically coupled to terminal cap  54  via the ground contacts, and thus establish a common electrical ground for circuits  80 ,  88 . Ground contacts  82 ,  82   a  and  83 ,  83   a  are in registration and direct contact with notches  94   a  and  94   b , respectively, and ground contacts  90 ,  90   a  and  91 ,  91   a  are in registration and direct contact with notches  94   c  and  94   d , respectively. Each of the ground contacts is coated with solder when circuit boards  74 ,  76  are produced. The solder coating ensures a tight fit between the contacts and the notches. In fact, during assembly, the some of the solder is sheared off during insertion of boards  74 ,  76  into notches process  94   a ,  94   b  and  94   c ,  94   d . The ground contacts are soldered to the notches by induction soldering (another automated assembly step). This arrangement establishes a good ground connection between the circuit boards and cap  54 .  
         [0044]    Terminal  92  is a male connector terminal which extends through and is operatively supported inside terminal passage  72 . A potting wafer  95 , made of low density polyethylene, is inserted into and substantially closes off terminal passage  72 . Wafer  95  contains an open bore through which terminal  92  tightly fits. Once installed, wafer  95  seals passage  72 , substantially preventing moisture from entering filter  50  through passage  72 .  
         [0045]    Terminal  84  includes a female terminal assembly  96  which extends through and is operatively supported inside terminal passage  68 . Terminal assembly  96  includes a female connector element or collet terminal  96   a , an polypropylene insulator  96   b  containing an external o-ring groove  96   c  (FIG. 4), and an o-ring  96   d  seated in groove  96   c . Assembly  96  is inserted into and substantially closes off terminal passage  68 . Insulator  96   b  and o-ring  96   d , together, seal passage  68 , substantially preventing moisture from entering the filter between passage  68  and insulator  96   b . Insulator  96   b  contains an open bore through which collet terminal  96   a  tightly fits.  
         [0046]    As shown in FIG. 3B, collet terminal  96   a  has a pair circumferential (360.degree.), protruding barbs or ribs  98 . Collet  96   a  is press fitted through the bore of insulator  96   b , causing barbs  98  to penetrate and anchor into insulator  96   b  (FIG. 3B). “Penetration” of barbs  98  may or may not include breaking into the insulator material—typically, the barbs will penetrate the insulator by deforming the insulator material. The barbs, and their penetration into the insulator, help prevent moisture from entering filter  50 , between the bore of insulator  96   b  and collet  96   a.    
         [0047]    As shown in FIGS. 3B and 4, insulator  96   b  has a cone-shaped nose  99 , which allows o-ring  96   d  to be easily slipped over the insulator and seated in groove  96   c . This cone-shape allows o-ring  96   d  to be installed on the insulator by an automated assembly step. In some filter constructions, it may be preferable to have collet  96   a  extend through the insulator to the point where it is flush with an insulator face  96   e  (See FIG. 3B). The construction, as above-described, may eliminate the need for potting material inside the filter, in most applications.  
         [0048]    Referring now to FIG. 5, there is shown a modification to the embodiment of FIG. 4. Like parts are indicated by like reference numbers, increased by  100 . The modification concerns the placement of printed circuit inductors on the rear surface of each circuit board. As shown in FIG. 5, circuits  180 ,  188  each include a pair of printed inductors  180   a ,  180   b  and  188   a ,  188   b , respectively, etched on respective rear surfaces  179  and  187 . Inductors  180   a ,  180   b  and  188   a ,  188   b  may serve, for example, as inductors L 3 , L 4  and L 1 , L 2 , respectively, in the circuit shown in FIG. 1. In this embodiment, the capacitors of circuits  180 ,  188  would remain on the front surfaces of circuit boards  174 ,  176 . The embodiment of FIG. 5 is otherwise the same as the embodiment of FIGS. 3A, 3B and  4 .  
         [0049]    Referring now to FIG. 6, there is shown another modification of the embodiment of FIG. 4. Like parts are indicated by like reference numbers, increased by  200 . In some applications, it may be desirable to have a certain degree of electromagnetic shielding between circuit boards. This can be achieved by locating the filter circuits on the rear surfaces of the circuit boards and locating ground planes on the front surfaces of the boards. As shown in FIG. 6, circuits  280 ,  288  are located on rear surfaces  279 ,  287 , respectively, and ground planes  281 ,  289  are located on the front surfaces of boards  274 ,  276 , respectively. The ground planes provide shielding between circuits  280 ,  288 . Ground planes  281 ,  289  are grounded by their direct physical contact with notches  294   a ,  294   b  and  294   c ,  294   d , respectively, when boards  274 ,  276  are seated in the notches. Thus, separate ground contacts are not necessary on the front surfaces of the boards. As shown in FIG. 6, ground contacts  282   a,    283   a  and  290   a ,  291   a  are located on the rear surfaces of boards  274  and  276 , respectively.  
         [0050]    A circular opening  281   a  is contained in ground plane  281  to allow terminal  284  to be connected to board  274  without shorting to ground. A similar opening is provided in ground plane  289  for terminal  292 . Openings are also contained in the ground planes to accommodate jumper wires  293   a ,  293   b . The embodiment of FIG. 6 is otherwise the same as the embodiment of FIGS. 3A, 3B and  4 .  
         [0051]    While the preferred embodiment of the invention has been particularly described in the specification and illustrated in the drawing, it should be understood that the invention is not so limited. Many modifications, equivalents, and adaptations of the invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention.

Technology Classification (CPC): 7