Patent Publication Number: US-2006018072-A1

Title: Load coil with digital signal bypass technology

Description:
FIELD OF INVENTION  
      The present invention relates to capacitance compensation devices for transmission lines. More particularly, the present invention relates to load coils having digital subscriber line (DSL) bypass technology for twisted pair transmission lines used in telephone service.  
     BACKGROUND OF THE INVENTION  
      As the communications needs in a particular area or neighborhood change, the flexibility of the network for that area may also change. Although plain old telephone service (POTS) and DSL service are both delivered via twisted pair transmission lines, those two services have different specifications for performance. For example, distributed stray capacitance of twisted pair lines causes an insertion loss that hinders the performance of voice services. When a POTS line is over 18,000 feet in length, load coils that cancel out stray capacitance on a line must be added to the POTS line beginning at 3000 feet from the central office (CO) and repeating every 6000 feet to the customer&#39;s premises. The added load coils compensate for the distributed stray capacitance and thus, keep voice services clear across the transmission lines over long distances.  
      However, these added load coils also increase the insertion loss at frequencies above the voice services band. This loss is a problem for services such as asynchronous digital subscriber line (ADSL), which operates using high frequency signals. The problem is that DSL signals cannot be transmitted via transmission lines that have load coils installed because DSL signals cannot pass through a load coil. As customers move away and cancel their POTS service, the transmission line with load coils (loaded pair) becomes available. Should a new customer order DSL provisioned via the available loaded pair, a technician must cut the load coils from the loaded pair before it can be used for conveying DSL. This results in service delays and wasted labor and expenses.  
      It is with respect to these and other considerations that the present invention has been made.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention, the above and other problems are solved by embodiments of the present invention. Illustrative embodiments of the present invention are directed to load coils with DSL bypass technology. The present invention allows for the transmission of both digital, e.g., DSL, and analog, e.g., POTS, signals via a loaded pair. A load coil with digital signal bypass technology will block digital signals away from the load coil and pass analog signals through the load coil. The present invention addresses problems such as, but not limited to, those mentioned above by adding high and low pass filters to a base section of the standard load coil. Thus, the present invention reduces service delays, wasted labor, and expenses.  
      One illustrative embodiment of the present invention is an apparatus including a load coil to be placed in series with a transmission line to compensate for capacitance in the transmission line. The apparatus also includes low pass filters. One low pass filter is electrically connected in series at an inbound connection of the load coil and a second low pass filter is connected at an outbound connection of the load coil. The low pass filters are to be electrically connected in series with the transmission line to pass analog signals on the transmission line through the load coil and exclude ADSL signals on the transmission line from the load coil. Although the present and following discussion refer to ADSL signals, it should be understood that the present invention applies equally to synchronous digital subscriber lines and service as well as asynchronous digital subscriber lines and service.  
      The apparatus also includes a high pass filter electrically connected in parallel with a combination of the load coil in series with the low pass filters. The high pass filter is to be electrically connected in series with the transmission line to exclude the ADSL signals from the load coil.  
      Another illustrative embodiment of the present invention is a digital signal bypass filter in a load coil. The load coil is of the type to be spliced in series with a dual conductor transmission line to compensate for capacitance in the dual conductor transmission line for transmitting analog signals. The digital signal bypass filter includes a first capacitor electrically connected in parallel with the load coil. The first capacitor is to be electrically connected in series with a first conductor of the dual transmission line. The digital signal bypass filter also includes a second capacitor electrically connected in parallel with the load coil. The second capacitor is to be electrically connected in series with a second conductor of the dual transmission line. The first and second capacitors pass digital signals on the transmission line away from the load coil and block analog signals away from the digital signal bypass filter.  
      Still another illustrative embodiment of the present invention is a bypass filter connected to a load coil and an incoming and outgoing wire pair. The bypass filter includes a first inductor connected in series between a first lead of the incoming wire pair and the load coil and a second inductor connected in series between a second lead of the incoming wire pair and the load coil. The first inductor and second inductor pass an analog signal on the incoming wire pair to the load coil. The bypass filter further includes a first capacitor and a second capacitor. The first capacitor is connected in parallel with the load coil and in series between the first lead of the incoming wire pair and a first lead of the outgoing wire pair. The second capacitor is connected in parallel with the load coil and in series between the second lead of the incoming wire pair and a second lead of the outgoing wire pair.  
      These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings. It is intended that all such additional features and advantages be included within this description, be within the scope of the present invention and be protected by the accompanying claims.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be further understood from the following description with reference to the accompanying drawings, in which:  
       FIG. 1  is a block diagram of a telecommunications system with load coils in a transmission line;  
       FIG. 2  is a perspective view of a known prior art load coil;  
       FIG. 3  is a perspective view of a load coil device with a base section that includes digital signal bypass technology according to an illustrative embodiment of the present invention;  
       FIG. 4  is a circuit diagram of the load coil device shown in  FIG. 3  shown in circuit with an idealized telephone line; and  
       FIG. 5  is an open front view of the load coil device shown in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION  
      The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.  
      Referring to  FIG. 1 , a telecommunications system  100  including a CO  102 , load coils  107   a - 107   n , transmission line  103 , and customer premises  110  is shown. The transmission line is a twisted pair and has conductors  104  and  105  connected between the CO  102  and the customer premises  110 . The load coils  107   a - 107   n  are distributed along the transmission line  103  beginning at 3000 ft from the CO  102  and repeating every 6000 ft until reaching the customer premises  110 . It should be understood that n represents the number of load coils installed between the load coil  107   b  and the customer premises  110 . The load coils  107  compensate for the stray capacitance in the transmission line  103 , as is known in the art.  
       FIG. 2  is a perspective view of a known load coil  200  in the prior art. The load coil  200  is hard spliced into the circuit for POTS lines that exceed 18,000 ft in length to improve voice quality and reduce signal loss. The load coil is spliced into the circuit utilizing the incoming leads or in facilities  202  and outgoing leads or out facilities  204 . DSL signals will not pass through the load coil  200  due to the reactance of the inductor inside to the high frequency of DSL signals.  
      Turning now to  FIG. 3 , a perspective view of a load coil device  300  having a load coil  307  with a base section  303  that includes DSL bypass technology will be described. The load coil  307  will perform the same function as the standard load coil  200  of  FIG. 2 . However, the load coil device  300  will also allow DSL signals to pass through. The passing of DSL signals is possible due to low pass and high pass filters located in the base section  303  including a housing  301 . The low and high pass filters route the signals based on the frequency band of the signal. High frequencies bypass the load coil and pass directly from the incoming leads of in facilities  302  to the outgoing leads or out facilities  304  that carry the signal in the direction of the customer premises  110  shown in  FIG. 1 .  
      In contrast, low frequencies are passed through the load coil  307  and then toward the customer premises  110 . The load coil device  300  improves network flexibility because no technicians will have to dispatch to remove load coils from transmission lines conveying DSL signals. Nor will technicians dispatch to return load coils to POTS transmission lines where load coils were previously removed to carry DSL. It should be appreciated that the load coil device  300  may be a single set load coil, meaning that each load coil device is manufactured separately with its own filters. Additional details regarding the low pass and high pass filters will be described below with respect to  FIGS. 4-5 .  
       FIG. 4  is a circuit diagram of the load coil device of  FIG. 3  with DSL bypass technology in accordance with embodiments of the present invention. The load coil device circuit  400  includes the load coil  307  to be placed in series with a transmission line at the in facilities  302  to compensate for capacitance in the transmission line. The load coil device circuit  400  also includes low pass filters  402   a  and  402   b . The low pass filter  402   a  is electrically connected in series at an inbound connection of the load coil  307 . The low pass filter  402   b  is connected at an outbound connection of the load coil  307 . The low pass filters  402   a  and  402   b  are to be electrically connected in series with the transmission line to pass POTS signals on the transmission line through the load coil  307  and exclude DSL signals on the transmission line from the load coil  307  while permitting passage of the relatively lower frequency POTS signals.  
      A high pass filter  404  is electrically connected in parallel with the combination of the load coil  307  and the low pass filters  402   a  and  402   b . The high pass filter  404  is to be electrically connected in series with the transmission line extending between the in facilities  302  and the out facilities  304  to bypass the DSL signals around the load coil  307 .  
      The transmission line with which the apparatus is to be used includes a pair of conductors  414  and  415 . The low pass filters  402   a  and  402   b  each include an inductor  407   a  and  407   c  to be electrically connected in series with the conductor  415  of the pair, respectively at an inbound connection and an outbound connection of the load coil  307 . The low pass filters  402   a  and  402   b  also respectively include second inductors  407   b  and  407   d  to be electrically connected in series with the conductor  415  of the pair, respectively at an inbound connection and an outbound connection of the load coil  307 .  
      Additionally, the high pass filter  404  includes a first capacitor  405   a  electrically connected in parallel with the inductors  407   a  and  407   c  and the load coil  307 . The first capacitor  405   a  is electrically connected in series with the conductor  415  of the transmission line. The high pass filter  404  also includes a second capacitor  405   b  electrically connected in parallel with the inductors  407   b  and  407   d  and the load coil  307 . The second capacitor  405   b  is to be electrically connected in series with the conductor  414  of the transmission line.  
       FIG. 5  is an open front view of the load coil device  300  of  FIG. 3  with DSL bypass technology in accordance with embodiments of the present invention. In operation, the capacitors  405   a  and  405   b  of the load coil device  300  will allow DSL signals to pass through, thereby bypassing the load coil  307 , while blocking the low frequency POTS signals. Having the POTS signals blocked by the capacitors  405   a  and  405   b  forces the POTS signals through the load coil  307 . Conversely, the inductors  407   a - 407   d  pass POTS signals while blocking any DSL signals present. The capacitors  405  and inductors  407  are reactive to alternating current and act together to route both POTS and DSL signals in the proper manner with no interaction from a field technician or other personnel.  
      The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.