Patent Grant
RE45581
The present invention relates generally to electronic filter assemblies used in the cable television (CATV) industry, and more specifically to a filter assembly that prevents personal data network signals from passing outside a user's network.
A typical cable television (“CATV”) network includes a head end facility from which a plurality of feeder cable lines emanate. The feeder cable lines branch off at a tap having ports. A cable drop, which may be a single coaxial cable, extends from each port to a respective user. The cable television system is a two-way communication system. A downstream bandwidth carries signals from the head end to a user and an upstream bandwidth carries upstream signals from a user to the head end.
One example of such a system is a bidirectional CATV system with a head end controlled by a system operator and with a plurality of user's televisions equipped with set top boxes or cable modems. Downstream bandwidth of the CATV system may include broadcast television channels, video on demand services, internet data, home security services, and voice over internet (VOIP) services. Upstream bandwidth may include data related to video on demand, internet access, or other services provided by the system operator. In one possible configuration, the upstream and downstream bandwidths are transmitted between the head end and the tap via optical fiber, and between the tap and the user via coaxial cable. Upstream and downstream bandwidths are typically transmitted via oscillatory electrical signals propagated along the cable lines in a discrete frequency range, or channel. Downstream bandwidth frequencies typically range from 54-1002 megahertz (MHz), and upstream bandwidth frequencies typically range from 5-42 MHz.
A personal data network may be coupled to the cable television network via coaxial cable. Often, the personal data network is a home entertainment network providing multiple streams of high definition video and entertainment. In one example, the personal data network may employ technology standards developed by the Multimedia over Coax Alliance (MoCA). The MoCA standards promote networking of personal data utilizing the existing coaxial cable that is wired throughout the user premises. MoCA technology provides the backbone for personal data networks of multiple wired and wireless products including voice, data, security, home heating/cooling, and video technologies. In such an arrangement, the cable drop from the cable system operator connects to a MoCA-certified device such as a broadband router.
The underlying technology behind the MoCA standard is utilization of orthogonal frequency-division multiplexing (OFDM) modulation, which is a modulation method wherein a large number of closely-spaced orthogonal sub-carriers are used to carry data. The signals are generated with the exact minimum frequency spacing needed to make them orthogonal so that they do not interfere with each other. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase shift keying) at a low symbol rate. In this manner, OFDM may be likened to using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. One advantage of OFDM is that problems such as attenuation of high frequencies in a long copper wire are alleviated without complex equalization filters.
A MoCA-certified device such as the broadband router interconnects other MoCA-certified components located within the premises, for example additional set top boxes, routers and gateways, bridges, optical network terminals, personal computers, and gaming systems. The personal data network allows distribution and sharing of entertainment content among the MoCA-connected devices. For example, a high definition program recorded on a set top box in the living room may be played back by a second set top box located in a bedroom. And, a high definition movie recorded on a camcorder and stored on a user's personal computer may be accessed and displayed through any of the set top boxes within the premises. The personal data network may also allow high-definition gaming between rooms.
The personal data network may utilize an open spectrum bandwidth on the coaxial cable to transmit the personal data content, such as entertainment content. For example, a cable system operator may utilize a bandwidth of frequencies up to 1002 MHz, and a satellite system operator may utilize a bandwidth of frequencies from 1550-2450 MHz. The unused range of frequencies, or open spectrum bandwidth, is 1125-1525 MHz. In another example, the open spectrum bandwidth may higher than 2450 MHz. A personal data network utilizing the open spectrum bandwidth does not interfere with any of the bandwidth being utilized by the cable television services provider or a satellite services provider.
As may be appreciated, a personal data network utilizing coaxial cable must be able to pass signals backwards through a splitter in order to properly transmit the content room-to-room. Coaxial splitters are essentially directional couplers designed to isolate splitter outputs and prevent signals from flowing room-to-room or outlet-to-outlet. The isolation is needed to reduce interference from other devices and maximize the power transfer from the point of entry to the outlets, so as to achieve the best television reception.
The MoCA standard has been specifically designed to allow signals to travel backward through splitters, termed insertion, and pass from splitter output to output, termed isolation. All coaxial outlets in a house may be reached from each other by a single isolation jump and a number of insertion jumps.
One problem with this arrangement is that, unless preventive measures are taken, the content on the personal data bandwidth may also pass through the coaxial cable drop and potentially to other users or subscribers on the cable television network.
According to an embodiment of the invention, a filter circuit assembly includes a printed circuit board having first and second opposed major surfaces and first and second opposing sides. The opposed major surfaces are substantially parallel to a single plane and are bisected by a longitudinal axis. The first and second opposing sides are substantially parallel to the longitudinal axis. The filter circuit assembly includes an input terminal connected to the printed circuit board, the input terminal having an axis extending substantially parallel to the longitudinal axis. The filter circuit assembly further includes an output terminal connected to the printed circuit board, the output terminal having an axis extending substantially parallel to the longitudinal axis. A signal path disposed on the printed circuit board extends from the input terminal toward the output terminal. A plurality of resonator elements are fabricated upon at least one of the major surfaces. The resonator elements are arranged in series along the signal path and define a footprint being less than 540 square millimeters. The filter passes a first range of frequencies in a provider bandwidth and attenuates a second range of frequencies in a personal data network bandwidth.
The novel features that are characteristic of the preferred embodiment of the invention are set forth with particularity in the claims. The invention itself may be best understood, with respect to its organization and method of operation, with reference to the following description taken in connection with the accompanying drawings in which:
Referring to the simple schematic of
The cable drop 22 connects to a ground block 23, which is typically the first device encountered within the drop system 20. The ground block 23 is a device generally placed on the outside of a premises 24 between the cable drop 22 and the internal coaxial wiring of a home, and provides an electrical ground to the drop system 20 by bonding the outer shield of the coaxial cable to the electrical ground of the premises. The ground block 23 may be secured by solid copper to either a cold water pipe or to the ground of the electrical service drop.
In some cable television networks, the distribution line 14 and the cable drop 22 are fiber optic lines. In some drop systems 20, then, an optical network terminal 25 is connected in series to the ground block 23 to convert the fiber optic downstream bandwidth to electrical signals to be carried by coaxial cable.
In one example personal data network, the optical network terminal 25 includes integrated MoCA technology allowing the MoCA platform to govern the personal data network within the premises. In the illustrated example the optical network terminal 25 is located outside the premises (e.g., fixed to the outside of a house), but it may also be located within the premises.
A coaxial cable 30 connects the ground block 23 to a first splitter 26 located within the premises 24. In the disclosed embodiment, the first splitter 26 is a two-way splitter having an input 28a and two distribution ports 28b and 28c. Coaxial cable 31a connects port 28b to a first set top box 32. The first set top box 32 incorporates MoCA technology so as to be included in the personal data network. Port 28c is shown connected via coaxial cable 31b to a second splitter 34. The second signal splitter 34 is illustrated as a two-way splitter having two distribution ports 36a and 36b. Port 36a connects to a wireless broadband router 38. The router 38 is wired via Ethernet cable 39 to a personal computer 40 having gaming software installed thereupon.
Port 36b is connected via coaxial cable to a third splitter 42 having distribution ports 44a, 44b, and 44c. Port 44a connects to a second set top box 46 that also includes MoCA technology. Port 44b of the splitter 42 connects to a cable modem 52, which is in turn connected to a desktop personal computer 54 via Ethernet cable. Port 44c connects to a third set top box 58 that also includes MoCA technology. Also shown is a laptop computer 48 having a wireless link to the broadband router 38. The laptop computer 48 includes a MoCA-enabled broadband wireless adapter 50 that plugs into the laptop's USB port.
In the disclosed example, the router 38 includes a MoCA chipset to serve as the platform for the personal data network. The MoCA-enabled router permits the distribution of high quality multimedia content and high-speed data with throughput exceeding 100 megabits per second (Mbps). For example, in the illustrated MoCA-enabled personal data network of
As mentioned hereinabove, the MoCA standard has been specifically designed to allow signals to travel backward through splitters. One problem with this arrangement is that the content on the personal data bandwidth may also pass to other users or subscribers on the cable television network. For example, entertainment content being passed from the first set top box 32 backwards through first splitter 26 en route to the second set top box 58 may potentially also travel along coaxial cable 30, through tap port 18, and along the distribution line 14.
Another problem with the MoCA arrangement is that the coaxial cable will also carry personal data from other users on the CATV network. Those signals will pass from the distribution line 14 to the user drop system 20. For example, a neighbor may purchase MoCA-enabled products and set up a personal data network within their home. Unless precautions are taken, personal data carried within the MoCA bandwidth will pass back to the distribution line 14.
The inventor has determined that the problems associated with personal data content passing through the drop system 20 may be mitigated by including a low pass filter circuit 100 in the drop system 20. In the illustrated example, the low pass filter circuit 100 is placed before the input 28a of the first splitter 26, in front of any MoCA-enabled devices. In another example, the low pass filter circuit 100 is integrated within the circuitry of the optical network terminal 25. In yet another example, the low pass filter circuit 100 is integrated within the circuitry of the ground block 23.
The filter circuit 100 is designed to pass the cable television bandwidth, but reject or attenuate the personal data network bandwidth. In one example, the MoCA standard specifies passing a bandwidth having a range of frequencies from 5 to 1002 MHz, and rejecting, or attenuating, a bandwidth having a range of frequencies from 1125 to 1525 MHz. In this manner, personal data in the 1125 to 1525 MHz frequency range will be prevented from entering or leaving the user drop system 20.
Referring to
In another embodiment, the filter circuit 100 may be adapted to pass satellite service provider bandwidth and reject the personal data network bandwidth. In one example, personal data in the 1125 to 1525 MHz frequency range will be prevented from entering or leaving the user drop system 20, and satellite service provider bandwidth in the 1550 to 2450 MHz range will pass. The filter circuit 100 may also be adapted to operate as a band stop filter, in which both CATV bandwidth and satellite bandwidth are allowed to pass, but the personal data network bandwidth in between the two is attenuated. Other frequency ranges are possible depending upon the specific provider bandwidth (e.g., CATV and/or satellite).
An exemplary first step in the design of the low pass filter to meet the requirements of the MoCA specification is to obtain the number of orders for the filter and the topology. This step may be completed using theoretical calculations (e.g., by hand) or using design synthesis software. In one example, Genesys circuit simulation software available through Agilent Technologies (formerly Eagleware) is utilized to arrive at the low pass MoCA filter schematic shown in
Referring now to
The signal path 305 includes a conductor, such as the center conductor in a coaxial cable, to carry the upstream bandwidth, the downstream bandwidth, and the personal data network bandwidth. The signal path 305 further includes a ground, such as the outer sheath of the coaxial cable 30 that provides a path to ground with various cable connector devices.
The filter circuit 100 further includes a plurality of resonator elements 310a-310d which, in one embodiment, comprise parallel inductor/capacitor (LC) arrangements L1/C2, L2/C4, L3/C6, and L4/C8, respectively. Capacitive shunts 315a-315e are disposed along the signal path 305 and are in electrical communication with the ground. Capacitive shunts 315b, 315c, and 315d are disposed between the resonator elements 310a-310d, respectively. The arrangement of resonator elements 310 and shunt capacitor elements 315 collectively form a minimum inductance elliptic function filter that meets the signal response requirements from the MoCA specification, as depicted in
Once the topology and number of orders has been determined for the filter circuit 100, an exemplary second step in the filter design is to design the individual inductor elements (e.g., L1-L4) and obtain insertion loss and return loss response using the circuit simulation software. Once completed, an exemplary third step in the design process is to model the entire circuit board with inductors, capacitors and the like and conduct a simulated response of the circuit using three-dimensional electromagnetic simulation (3-D EM) software, such as CST Microwave Studio by Computer Simulation Technology, Ansoft HFSS, or Sonnet Suites by Sonnet Software, Inc. The 3-D EM software is more accurate than the circuit simulation software and allows the designer to fine-tune the circuit board elements to achieve the proper signal response.
One obstacle encountered in designing the filter circuit 100 of the present invention was that the “low pass” bandwidth was very broad (e.g., from DC up to approximately 1000 MHz), and the attenuation bandwidth was very high (e.g., between approximately 1125 MHz and 1500 MHz). Prior art low pass filters typically passed a range of frequencies much lower and narrower, for example from 5 MHz to 40 MHz, and attenuated frequencies above 54 MHz. As a result of the very broad bandwidth in the present application, conventional surface-mount inductor elements meeting the design criteria were physically large, and needed relatively large spacing to achieve proper resonant characteristics. In other words, in order to minimize coupling effects the surface-mount inductor elements needed to be spaced such that the finished circuit board was quite large: approximately three inches long and one inch wide. This sizing was much too large to practically fit in a coaxial cable connector.
One solution to this problem was to design the inductor elements L1 thru L4 as etched inductor elements, etched or metalized directly into the printed circuit board. However, etched inductor elements are open structures, generating magnetic and electrical fields, which travel through air and cross through conductive traces of adjacent inductor elements, thereby modifying their individual inductances. Modification of the individual inductance values alters the performance of the resonator elements 310. For example, referring to
One means of compensating for coupling effects is to use surface-mounted inductors (e.g., wire-wound) that may be tuned to achieve desired characteristics. As mentioned hereinabove, that option was not feasible in the present invention due to the resulting large-area circuit board.
Another means of compensating for coupling effects is to add one or more decoupling elements in proximity to the inductors. Referring to
Although inductors L1-L4 were designed to produce the inductance values required by the filter circuit 100 illustrated in
Despite arduous attempts by the inventor to reconfigure the location of the decoupling elements 61, a suitable frequency response was not attained. Although the reason for this failure is not understood with certainty, it is believed that the decoupling element 61 causes significant signal parasitic or fringe capacitance, which, in turn, causes significant deterioration of the filter's 100 ability to pass signals having a frequency of up to 1000 MHz while attenuating frequencies greater than 1125 MHz. Accordingly, parasitic or fringe capacitance that could be tolerated in low pass filters operating at frequencies below 54 MHz could no longer be tolerated in low pass filters operating up to the 1000 MHz threshold. With this insight, the inventor removed the decoupling element 61, counter to common practice.
Referring now to
The exemplary printed circuit board 60 is formed from 0.8 millimeter FR-4 (woven glass and epoxy) with 1 ounce copper, double sided, but depending upon the dielectric requirements of the circuit the substrate may be other materials such as FR-2 (phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-6 (matte glass and polyester), CEM-1 (cotton paper and epoxy), CEM-5 (woven glass and polyester), aluminum, or ceramic. The circuit board 60 is not limited to rigid substrate materials. In one embodiment, the circuit 100 is disposed on flexible circuit board material.
In the disclosed embodiment, the capacitor elements C1-C9 are the surface-mount variety; however, metalized or etched capacitors would function adequately and may even have benefits over the surface mount. The inventor has found the inductive properties of the etched capacitors to be beneficial in the resonance tuning of the circuit.
Turning now to
Typical etched inductors found in the prior art cannot be tuned because the inductor geometry is fixed. This inflexibility may be problematic in a mass-production environment because manufacturing tolerances and variables such as changes to the circuit board substrate may alter the resonating characteristics of the inductor arrangement. For this reason, etched inductors are disfavored in many filter circuit applications. The inventor has overcome this obstacle by adding one or more tuning elements 76 to the illustrated etched inductor element 72. The tuning elements 76 are adapted to alter the length of the inductor trace 74, thereby changing the inductance of the inductor element 72. In the disclosed embodiment, a plurality of tuning elements 76a-76c comprise additional conductive traces etched into the circuit board substrate, bridging intermediate portions of an inner loop 75 to the via 70. One or more of the tuning elements 76 may be removed, for example by mechanical scraping, if the inductance value of the inductor element 72 requires adjustment. Conversely, tuning elements 76 may be added after filter fabrication by way of conductive strips.
The inductor element 72 may be arranged in geometries other than spiral, as long as the inductor length is sufficient to provide the resonant characteristics. For example, referring to
Referring to
Referring now to
The arrangement of the inductor elements 72 defines the footprint 78 on the printed circuit board 60. The inventor has found that the removal of the decoupling elements allows close-coupling of the etched inductor elements 72 such that they may be arranged in a heretofore unknown smaller area. In the disclosed embodiment, the footprint 78 encompasses only the inductor elements 72 because the capacitor elements are arranged on the back side of the substrate. However, the inductor/capacitor resonator elements 310 may also be arranged on only a single surface of the substrate.
The inventor has also found that the individual quality factor (e.g., Q value) of each inductor 72 may not be of primary importance to the design of the filter circuit 100, contrary to the teachings of the prior art. The inventor has found that the close-coupling of the inductor elements 72 with the substrate material and capacitor elements 315 has a greater effect on the overall quality factor than the individual Q values. In other words, the close-coupling of the inductor elements 72 may compensate for less-than-ideal individual Q values. Filter designers may therefore spend less time trying to achieve high Q values for the individual inductors so long as the inductors are close-coupled.
The etched inductor elements 72 may be arranged within a footprint 78 small enough to be integrated with a variety of standard cable housings. In one embodiment, the housing is a standard cable connector body.
Referring to
The body 82 is shaped so as to provide a first cable connector 98 at an end thereof. In the exemplary embodiment, body 82 has a male cable connector, but one of ordinary skill in the art can readily construct a body having a female connector thereon.
The nut 84 fits on an end of the body 82 opposite the cable connector 98 of the body. The nut 84 provides a second cable connector 102 at an end thereof opposite the first cable connector 98. Preferably, the connector 102 is of the opposite type from connector 98. For example, connector 98 is male, and connector 102 is female. The nut 84 is connected to the body 82 by solder 104 along a periphery of the nut to form a water tight seal. The exemplary nut 84 is formed from C36000 brass, (ASTM B16, ½ hard), but other materials may be used. Although the exemplary nut 84 has a conical shape, a variety of nut shapes may be used. For example, the nut may be cylindrical, conical, or may have two or more sections, each having a different shape (e.g. a cylindrical section and a conical section). Other shapes are also contemplated.
The ground plane 68 of the printed circuit board 60 is connected to an inner wall of the body 82 by solder 106. Preferably, the solder 106 joining the nut 84 to the body 82 flows into, and is continuous with, the solder 104 connecting the ground plane 68 to the body 82.
The pair of terminals 88 and 90 are electrically connected at opposite ends of the printed circuit board 60. Each of the terminals 88 and 90 has a slot (108 and 110, respectively) sized to receive a respective end (112 and 114, respectively) of the printed circuit board 60. Preferably, the slot is used to form a friction fit between the printed circuit board and the terminals during assembly. The terminals are then soldered to the printed circuit board 60. The ends 112 and 114 of the printed circuit board 60 have electrical contact pads thereon, for forming electrical contact with the terminals 88 and 90. When assembled, the terminals 88 and 90 are in line with the printed circuit board 60. That is, the longitudinal axis of each terminal 88, 90 passes through a central longitudinal axis of the printed circuit board 60. The central longitudinal axis of the printed circuit board 60 is centrally located with respect to both the width and thickness of the printed circuit board.
One of the terminals 90 is a male terminal having a pin 116 extending away from the printed circuit board 60. The other terminal 88 is a female terminal capable of receiving a cylindrical pin. The pin may be, for example, of the size and shape of pin 116, and the pin may belong to either a cable connector or another filter having a connector end similar to connector 102. The terminals 88 and 90 may, for example be formed from C36000 brass, ASTM B16, ½ hard, with the contacts of terminal 88 formed from beryllium copper alloy.
The filter assembly 10 has an insulator 92, an elastomeric seal 96 at the end of the body 82 having the first connector 98. The insulator 92 may be formed of a polymer, such as natural TPX RT-18. The elastomeric seal 96 creates a water-tight seal between the body 82 and the terminal 88. The seal 96 may be formed of rubber, silicone, or other compressible insulating material. The exemplary seal 96 is formed from 30-40 durometer silicone rubber.
The insulator 94 that is provided at the end of the nut 84 having the second connector 102 creates a water-tight seal between the nut 84 and the terminal 90. Insulator 94 may be formed of a polymer, such as polypropylene.
The exemplary housing 82 may have several sizes, depending upon the particular needs of the application. In one example, the housing 82 is approximately 19 mm (0.75 inches) in diameter. With reference to
Although not shown in the drawings, the printed circuit board 60 may be a circular wafer shape, and fit within the hollow circumferential cavity defined by the interior of the connector body 82. This configuration results in a much shorter connector length. The footprint 78 in this example is approximately
or 250 mm2.
In another example, the housing 82 is approximately 7.2 mm (0.285 inches) in diameter. Accordingly, the footprint 78 may therefore include a width W of approximately 6.2 mm and a length L of approximately 30.5 mm, resulting in the footprint 78 having an area of 190 mm2.
Referring to
Turning now to
The filter assembly 210 adapted for use as the ground block 23 may comprise alternate configurations. Although not shown in the drawings, the filter assembly 210 including the filter circuit 100 may include surface-mounted capacitors and inductors on the printed circuit board 260.
The inventor has found that the ground block location is preferred for the low pass filter of the present invention. Signals travelling on the personal data bandwidth (e.g., 1125 MHz to 1525 MHz) travel unobstructed throughout the premises 24, but are attenuated at the ground block location before they may travel to the tap port 18.
In another embodiment, the standard cable housing to which the filter circuit 100 is integrated is a splitter housing, such as the splitter 26 illustrated in
In yet another embodiment, the standard cable housing to which the filter circuit 100 is integrated is a drop amplifier housing (not shown). Alternately, the filter circuit 100 may be integrated with the drop amplifier and the ground block into a single housing.
The close-coupled arrangement of inductor elements not only provides a small enough footprint to allow usage in housings that were previously too limiting, but also provides a superior signal response. Referring to
While the present invention has been described with reference to a particular preferred embodiment and the accompanying drawings, it will be understood by those skilled in the art that the invention is not limited to the preferred embodiment and that various modifications and the like could be made thereto without departing from the scope of the invention as defined in the following claims. For example, the disclosed filter circuit may be incorporated into other circuit form factors, either by applying the circuit to additional circuit board layers or combining the filter circuit with a more complex circuit on a single layer.
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| Number | Date | Country | |
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| Parent | 12501041 | Jul 2009 | US |
| Child | 13861256 | US |
