Abstract:
Multiple digital audio transformer circuits are included in a module for mounting in a chassis. These digital audio transformer circuits are comprised of a front mounted twisted pair digital audio cable connector and a rear mounted coaxial cable connector, with circuitry including baluns electrically linking the front and rear connectors to reduce the impedance of the signal and attenuate the amplitude of the signal voltage. In one embodiment, the module may also include removable attenuation pads accessible through the front face of the module to allow variation of the level of voltage attenuation. The preferred embodiment of the module bi-directional transforms 110 Ohm digital audio signals and 75 Ohm coaxial signals. If transformation of other levels of impedance are desired, modules may also allow for removal and replacement of the baluns. A digital audio transformer system including multi-circuit modules and rack mount equipment chassis is also provided.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to telecommunications signal transmission equipment. More particularly, the present invention relates to conversion of signals from balanced twisted pair cables for transmission via unbalanced coaxial cable, and from unbalanced coaxial cables for transmission via balanced twisted pair cables.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the professional audio and video industry, digital audio signals are typically transmitted via balanced twisted pair cables. These twisted pair cables typically operate at a signal impedance of 110 ohms. However, transmitting digital audio signals over longer distances using the balanced twisted pair cable is somewhat problematic. The signal degrades as it passes through the twisted pair cable conductors. Amplification devices to magnify and retransmit the digital audio signals are often required if the digital audio signal transmission length is greater than 150 feet over twisted pair cables.  
           [0003]    To address this issue, users are known to pass digital audio signals through a digital audio impedance transformer and transmit the transformed signal via unbalanced coaxial cable at a signal impedance of 75 ohms. Using the unbalanced 75 ohm coaxial cable, the maximum cable distance for transmission without amplification devices can be extended.  
           [0004]    The nature of the signal conversion process is such that a single digital audio impedance transformer can handle both unbalanced and balanced signals and the higher and lower impedance conversions. Thus a single transformer can be used to handle bi-directional signal flow.  
           [0005]    One known device which handles this signal conversion process is an in-line digital audio transformer for transforming signals between a single twisted pair cable and a single coaxial cable. This in-line device is mounted in the digital audio signal transmission path between cable ends and is then left on the floor or ground subject to environmental exposure and other physical abuse. Often, if multiple circuits with these devices are in one area, organization and identification of the devices can be quite difficult.  
           [0006]    Sometimes in these digital audio circuits, voltage attenuation is required, due to an incoming signal with a voltage amplitude beyond the capabilities of a downstream device to handle. This voltage attenuation function can be incorporated into the digital audio transformer device in the form of an attenuation pad. An attenuation pad works by controlling the dB loss in the transformer circuit, thereby moderating the voltage to a more suitable range. The known single circuit in-line devices include attenuation pads of fixed voltage attenuation value within the device. Unfortunately, a fixed attenuation value does not permit alterations of the overall signal transmission environment, if changes are needed. If these transmission environment conditions do change enough to require the alteration of the attenuation value within the in-line digital audio impedance transformer, the entire transformer will need to be switched out to ensure the resulting output voltage is at a proper amplitude for the downstream device.  
           [0007]    The known in-line transformer devices typically have a coaxial connector on the coaxial cable side and an XLR connector on the twisted pair side. XLR connectors are relatively expensive compared to alternative connectors, but XLR connectors have traditionally been used in transmitting audio signals. The known in-line devices are also typically cylindrical or barrel-shaped and have machined housings. Manufacture and assembly of such devices is labor intensive and therefore more costly.  
           [0008]    Further improvements are desired for signal transformers, such as for digital audio signal transmission systems to address the above concerns or other concerns.  
         SUMMARY OF THE INVENTION  
         [0009]    In one aspect of the present invention, a transformer module includes one or more impedance transformer circuits in a chassis-mountable housing with connectors mounted on the front and rear of the module for attaching twisted pair wires and coaxial wires, and circuitry including baluns connecting pairs of front and rear connectors. The circuitry may include removable attenuation pads adjacent to one of the connectors of the circuit to which the attenuation pad is attached. The circuitry may include provisions for the baluns to be removably inserted, so that baluns of different impedance levels may be utilized. The module may also have a cable clip adjacent to the connectors to aid in cable management.  
           [0010]    A further aspect of the present invention includes providing a digital audio impedance system made up of a plurality of the digital impedance transformer modules of the present invention mounted in a chassis.  
           [0011]    Another aspect of the present invention is to provide a multi-circuit impedance transformer module for use with a chassis with linearly arrayed connectors mounted on opposite faces of the module with transformer circuits including baluns. Attenuation pads can be mounted adjacent to one of the sets of connectors.  
           [0012]    A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The accompanying drawings, which are incorporated in and constitute a part of the description, illustrate several aspects of the invention and together with the description, serve to explain the principles of the invention. A brief description of the drawings is as follows:  
         [0014]    [0014]FIG. 1 is a perspective view of a preferred embodiment of a system in accordance with the present invention showing a chassis partially loaded with a plurality of multi-circuit modules and another multi-circuit module in position for insertion.  
         [0015]    [0015]FIG. 2 is a front perspective view of a multi-circuit module with front QCP twisted pair connectors, rear BNC coaxial connectors and a front cable clip.  
         [0016]    [0016]FIG. 3 is a rear perspective view of the multi-circuit module of FIG. 2.  
         [0017]    FIGS.  4 A-D are front, side, top, and rear views, respectively, of the multi-circuit module of FIG. 2.  
         [0018]    [0018]FIG. 5 is a partially exploded front perspective view of the multi-circuit module of FIG. 2.  
         [0019]    [0019]FIG. 6 is an exploded front perspective view of the multi-circuit module of FIG. 2, with some items removed for drawing clarity.  
         [0020]    [0020]FIG. 7 is an exploded rear perspective view of the multi-circuit module of FIG. 2.  
         [0021]    [0021]FIG. 8 is a front perspective view of a second embodiment of a multi-circuit module with front 3-pin twisted pair connectors and rear BNC coaxial connectors.  
         [0022]    FIGS.  9 A-D are front, side, top, and rear views, respectively, of the multi-circuit module of FIG. 8.  
         [0023]    [0023]FIG. 10 is a partially exploded front perspective view of the multi-circuit module of FIG. 8.  
         [0024]    [0024]FIG. 11 is an exploded front perspective view of the multi-circuit module of FIG. 8.  
         [0025]    [0025]FIG. 12 is an exploded rear perspective view of the multi-circuit module of FIG. 8.  
         [0026]    FIGS.  13 A-D are front, side, top, and rear views, respectively, of the housing component for the multi-circuit modules of FIGS. 2 and 8.  
         [0027]    FIGS.  14 A-D are front, side, top, and rear views, respectively, of a circuit board subassembly for the multi-circuit modules of FIGS. 2 and 8.  
         [0028]    FIGS.  15 A-E are front, side, top, rear and perspective views, respectively, of a 3-pin twisted pair connector housing.  
         [0029]    [0029]FIG. 16 is a front view of the front face of the housing for the multi-circuit module of FIG. 2 adapted for front QCP twisted pair connectors and with an opening for removable attenuation pads.  
         [0030]    [0030]FIG. 17 is a front view of the front face of the housing for the multi-circuit module of FIG. 8 adapted for front 3-pin twisted pair connectors and with an opening for removable attenuation pads.  
         [0031]    [0031]FIG. 18 is a front perspective view of a further alternative embodiment of a multi-circuit module with front QCP connectors and without the front cable clip.  
     
    
     DETAILED DESCRIPTION  
       [0032]    Reference will now be made in detail to exemplary aspects of the present invention which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0033]    Referring now to FIG. 1, one embodiment of a transformer system  10  includes a chassis  12  and a plurality of multi-circuit modules  20 . Modules  20   a - d  are shown mounted to the chassis  12 , with module  20   e  shown in position to be slidably inserted into chassis  12 . Chassis  12  in the illustrated embodiment is capable of housing up to  16  of the multi-circuit modules  20 , as shown in FIG. 1. Chassis  12  can be made to conform to standard international format (approximately  19 ″ width), standard U.S. format (approximately  23 ″ width), or any other desired frame, rack or cabinet configuration. Chassis  12  includes a flange  14  on each end for securing the chassis to a support structure, such as an equipment cabinet for holding further chassis  12  and other equipment. Module bays  15  of chassis  12  are for slidably receiving multi-circuit modules  20 . Module flanges  16  are for securing multi-circuit modules  20  to chassis  12 , using threaded fasteners  48  inserted through module mounting openings  17  in flanges  19  of the modules  20  and threadably received by threaded mounting openings  18  on flanges  16 .  
         [0034]    Multi-circuit modules  20  can be mounted to any convenient frame, rack or cabinet support structure through flanges  19  or other structure. Multi-circuit modules  20  include multiple transformer circuits each for transforming a signal from a balanced twisted pair signal to an unbalanced coaxial signal. Alternatively, module  20  may, if desired, be constructed as a single circuit device. Module  20  includes connectors on one side (the front in the example embodiment) for connecting to balanced twisted pair cables. Module  20  includes further connectors on a further side, preferably the opposite side (rear in the example embodiment) for connecting to unbalanced coaxial cables.  
         [0035]    Modules  20  with chassis  12  can be used in a communications system where the cabinet holds not only chassis  12 , but other related equipment such as switching jacks of a patch panel.  
         [0036]    Now referring to FIGS. 2 through 7 and FIGS.  13 A-D, multi-circuit module  20  includes main housing components  30  and  30   a,  and a front face  28 . Housing components  30  and  30   a,  detailed in FIG. 13, are shaped such that the two housing components  30  and  30   a  are identical. When components  30  and  30   a  are appropriately oriented and fastened to each other, they form the sides, top and bottom of module  20 . As shown in FIGS. 5 through 7, when viewed from the front, the left housing component  30  will receive several stand-off circuit board mounts but is otherwise identical, except for orientation, to the right housing component  30   a.  A flange block  32  is sized to permit mounting to chassis  12 , as shown in FIG. 1. On the front face  28  is mounted a cable clip  24 , which holds twisted pair cables  26  to the side of each module  20  and direct the cables to reduce obstruction and visual clutter in front of the front connectors of module  20 . Mounted through the front face  28  are four twisted pair connectors  22 . Each front connector  22  in the embodiment shown is a QCP type of twisted pair cable connector, with three posts for attaching to the three wires of a twisted pair digital audio cable (tip, ring, ground). Other three pin or wire connector types, such as 3-pin plugs, insulation displacement connectors, XLR connectors or XLB connectors could also be used.  
         [0037]    Illustrated in FIG. 3 are stand-off circuit board mounts  36 , flange blocks  32  and rear coaxial connectors  34 . The rear connectors in the embodiment shown are BNC type. Other types of coaxial connectors, such as F-connector, 1.6-5.6, SMB, MCX, Twinax or 7-16 DIN could also be used for the rear connectors for connecting to the coaxial cable (center conductor and ground).  
         [0038]    In FIGS. 4A and 4C, four attenuation pads  50  are shown inserted through front face  28 . In FIGS. 4B, 4C and  4 D, four BNC connectors  34  are shown at the rear of module  20 .  
         [0039]    In FIGS. 5 through 7, stand-off circuit board mounts  36  are mounted to and project through left housing component  30  and hold circuit board  38  at a fixed position within module  20 . Board  38  is shown parallel to the sides of module  20 . Other orientations are possible, such as transverse. Other circuitry can be used such as flex-circuitry.  
         [0040]    Symmetrically designed housing components  30  and  30   a  can be seen cooperating to form the external sides, top and bottom of module  20 . Flange blocks  32  are mounted between housing components  30  and  30   a  to provide support to front face  28  and provide mounting flanges for mounting module  20  within a chassis  12 , as shown in FIG. 1. Fastener  48  inserts through module mounting opening  17  in front face  28  and flange block  32  to mount module  20  to chassis  12 . Cable clip  24  is insertably mounted to front face  28 . Rear connector face  40  is mounted between housing components  30  and  30   a  and to the rear of circuit board  38 . Attenuation pad sites  44  are mounted at the front of circuit board  38 . Baluns  42  are mounted to circuit board  38  in an intermediate position between rear connector face  40  and attenuation pad sites  44 . Attenuation contacts  45  are mounted to circuit board  38  and electrically connect attenuation pads  50  to circuit board  38 . QCP connectors  22  are shown with twisted pair cables  26  inserted. Screws  46  are used to assemble module  20 .  
         [0041]    [0041]FIG. 7 includes those components removed for clarity from FIGS. 5 and 6. In addition to the items shown in FIGS. 5 and 6, the components comprising QCP connectors  22  are shown. These components are the QCP housings  52 , QCP posts  54  and QCP contacts  56 . QCP contacts  56  electrically connect twisted pair cables  26  (cables shown in earlier FIGS.), which are electrically connected to QCP posts  54 , to circuit board  38 . Circuit board  38  includes conductor pathways which are not illustrated here, but which electrically connect, in order, QCP contacts  56  to baluns  42 , baluns  42  to attenuation contacts  45 , and attenuation contacts  45  to BNC connectors  34 . BNC connectors  34  are mounted on rear connector face  40 , and permit connection of coaxial cables to module  20 .  
         [0042]    Now referring to FIGS. 8 through 12, these FIGS. detail an alternative embodiment of a multi-circuit module, module  21 , wherein the front mounted digital audio connectors are 3-pin connectors  58 , and the front face  29  is configured to accept 3-pin connectors  58 . All other external aspects of module  21  are as described above in reference to module  20 .  
         [0043]    In FIGS. 11 and 12, 3-pin housings  60  are mounted to front face  29 . 3-pin posts  62  extend through 3-pin housings  60  (3-pin housing  60  is described below with regard to FIGS.  15 A-E) and are electrically connected with 3-pin contacts  64 . 3-pin contacts  64  electrically connect with the conductor pathways of circuit board  38 . Conductor pathways on circuit board  38  are electrically configured as described above in reference to module  20 . 3-pin housings  60  each receive a 3-pin connector plug mounted to the twisted pair cable.  
         [0044]    FIGS.  13  A-D illustrates housing components  30  and  30   a,  which are constructed and formed to be identical, such as from sheet metal. The design of these components is such that two identical housing components may be combined to full enclose the sides, top and bottom of a module  20 , as shown in multiple FIGS. above, avoiding the need for design and manufacture of multiple different housing elements.  
         [0045]    Referring now to FIGS.  14 A-D, the circuit board subassembly  90  includes circuit board  38 , with baluns  42  installed. BNC connectors  34  and rear connector face  40  are mounted to the rear of circuit board  38 , and attenuation pad sites  44  are mounted to the front of circuit board  38 .  
         [0046]    FIGS.  15 A-E illustrates the details of 3-pin housing  60 . 3-pin housing  60  is formed from an elastically deformable material, such as plastic. To retainably mount 3-pin housing  60  to front face  29 , 3-pin housing  60  is inserted through 3-pin connector opening  80  so that key flange  68  passes through index notch  81  (index notch  81  is shown in FIG. 17). Locking flanges  66  and key flange  68  are compressed as they pass through 3-pin connector opening  80  and then spring back to shape once they pass through the 3-pin connector opening  80 , serving to retain 3-pin housing  60  to front face  29 . Post openings  70  extend through the length of 3-pin housing  60 , allowing for insertion of 3-pin post  62  through 3-pin housing  60 . Plug openings  72  extending partially through 3-pin housing  60  and permit the insertion of a mating 3-pin plug to connect digital audio cables to module  21 . Index flats  82  cooperate with a mating 3-pin plug to ensure proper orientation for insertion and retention tabs  84  cooperate with a mating plug to help retain the mating plug to module  21  upon insertion into 3-pin housing  60 .  
         [0047]    [0047]FIG. 16 illustrates front face  28 , including QCP connector openings  76  for mounting QCP connectors  22 , and attenuation pad site access opening  74 . FIG. 17 illustrates front face  29 , including 3-pin connector openings  80  for mounting 3-pin connectors  58 . Index notch  81  cooperates with key flange  68  to ensure correct mounting orientation of 3-pin connectors  58 . Attenuation pad site access opening  74  is also shown. Aperture  78  receives cable clip  24 .  
         [0048]    An alternative embodiment module  120  is shown in FIG. 18. Module  120  is identical to module  20  described above, except for the omission of any cable clip mounted to the front face.  
         [0049]    Further modifications to modules  20 ,  21  and  120  include switching the locations of the front and rear connectors, or switching the location of the attenuators from the front to the rear. Alternatively, the front and rear connectors do not have to be on opposite sides of the modules. Further, the attenuators can be located on a further panel of the module, or under a removable panel portion or cover.  
         [0050]    Having described preferred aspects and embodiments of the present invention, modifications and equivalents of the disclosed concepts may readily occur to one skilled in the art. However, it is intended that such modifications and equivalents be included within the scope of the claims which follow.