Patent Document

FIELD OF THE INVENTION  
       [0001]     The present invention pertains to analog amplifiers, specifically amplifiers for use with unshielded twisted pair wires.  
       BACKGROUND OF THE INVENTION  
       [0002]     Users of data communications continue to demand ever faster service. Acoustical modems are typically able to deliver a maximum of fifty six thousand bits per second (kbps). Higher speed broadband connections have encouraged content providers to provide services that are not practical at lesser speeds, typically requiring a minimum of 150 kbps. Digital Subscriber Lines (“DSL”) offer speeds up to several megabits per second (Mbps), depending upon distance from the telephone service provider&#39;s Central Office (“CO”) to the Customer Premises Equipment (“CPE”) and the user&#39;s willingness to pay a premium. At certain distances high speed DSL is not available at any reasonable price simply because the technology is not able to do so. Typically consumer speed DSL is not offered by the telecommunications companies at greater than about 2.5 miles from the CO. Thus the service area of providers is limited by the number of COs and their proximity to each other. This limit is the result of DSL vendors&#39; utilization of the existing unshielded twisted pair (“UTP”) copper wire network that has been the mainstay of the telephone infrastructure from the inception of commercial telephony. An advantage of UTP is that it is into virtually every home and business by virtue of its use for carrying ordinary telephone connections. A disadvantage of UTP is that it is not well suited for high frequency signals in that the high frequencies necessary for the data rates desired are strongly attenuated by the wire media itself. This is the result of the build up of impedance with wire length.  
         [0003]     A competing broadband service is offered by television cable companies, wherein optical fiber service is installed into a neighborhood. A limited number of subscribers may then share the total bandwidth available up to approximately 1.25 miles from the termination end of the fiber connection via coaxial wire. Cable broadband speeds are often over 1 Mbps. To compete with the cable providers for broadband coverage as well as speed, the DSL providers are forced to also install more fiber connections, farther away from the CO, from which the DSL UTP lines may spawn. The installation of fiber is very costly in terms of labor, materials, and in some cases access rights. Though in the United States broadband cable currently has more market share than DSL, total market penetration of broadband service is very small. Thus the competition for share is very open.  
         [0004]     There would be economic and time to market advantage to the DSL providers if they could economically extend their market coverage with the existing UTP infrastructure and do so at a data rate that is competitive with broadband cable. The prior art has been largely based upon repeaters which receive the DSL signal, decode it using the pertinent protocol for error detection and correction, then reformulate the data and retransmit it with a rejuvenated signal. Such approaches are very costly. Other products of the relevant art utilize the UTP infrastructure but require the telecommunications companies to install different equipment at the CO and CPE, which is expensive.  
         [0005]     The present invention provides for the extension of the DSL service range via existing UTP lines with no change of equipment or software at the CO or at the CPE, often with a higher data rate than currently available. It is an objective of the present invention to enable DSL service providers to economically extend their market coverage, compete with broadband cable providers in terms of speed, and to enable them to roll out coverage and service improvements more rapidly than broadband cable suppliers due to lower capital needs for infrastructure extension.  
         [0006]     DSL technology is based upon a bidirectional connection between a Digital Subscriber Line Access Multiplexer (“DSLAM”) board at the CO and a DSL modem at the customer&#39;s premises. There is a one for one relationship. That is, a single, dedicated set of twisted pair wires extends from a single port on the DSLAM to the customer&#39;s DSL modem. No other subscriber is served by that same set of wires. A splitter at or near the premises entry point divides the frequency spectrum assigned to the analog voice signal (if present) from the spectrum dedicated to DSL use. The lower 30 khz is reserved for the voice signals. The DSL signals are assigned one or more separate, non-overlapping frequency bands for the “uplink” (towards the CO) direction and one or more non-overlapping frequency bands for the “downlink” (towards the CPE) direction. The data flowing in these two directions are independent of each other and flowing simultaneously, just in different directions through the same media at the same time, separated by frequency, not by time. Thus any device that is inserted between the premises splitter and the CO DSLAM must accommodate signals ranging from near dc to 1100 khz or more, without regard to direction, where “direction” distinguishes at which end of the connection is the transmitter (at the CPE for the uplink, at the CO for the downlink) and at which end is the receiver (at the CPE for the downlink, at the CO for the uplink).  
         [0007]     The Asymmetrical DSL (“ADSL”, ADSL meaning the downlink data rate is not the same as the uplink data rate) and Symmetrical DSL (“SDSL”) standards for transmission are for the voice, uplink, and downlink signals to be present on the UTP simultaneously. This is in contrast to High Bit Rate DSL (“HDSL”) wherein the downlink data is applied to one UTP set, the uplink to another UTP set, and the voice data is not carried at all by the system. The industry standard (described in ANSI T1.417 and others) segregates various categories of data by frequency range.  
         [0008]     In the 1100 khz bandwidth of the G.992.1 (ADSL) standard there are two hundred and fifty six 4.3125 khz “buckets”. The signal present on an ADSL physical wire line is called a Digital Multi-Tone (DMT) because it is comprised of the energy of different frequency tones. The higher frequency buckets of the DMT signal suffer greater attenuation as UTP wire line length increases. Consequently, the higher frequency buckets are hampered in their ability to effectively carry data relative to those buckets of lower frequency.  
         [0009]     For ADSL, the portion of the bandwidth from approximately 0 Hz (bucket  0 ) to 30 khz (bucket  7 ) is reserved for the voice channel and other signaling. The portion of the bandwidth from approximately 34 khz (bucket  8 ) to 125 khz (bucket  29 ) is assigned to the ADSL upstream channel, thus comprising the next 22 buckets. As UTP wire line increases in length, fewer upstream buckets are able to carry data, resulting in a reduction in upstream data rate.  
         [0010]     The portion of the bandwidth from approximately 164 khz (bucket  38 ) to 1100 khz (bucket  255 ) is assigned to the downstream channel, thus comprising the upper 218 buckets. As UTP wire line increases in length, fewer downstream buckets are able to carry data, resulting in a reduction in downstream data rate. The data rate is negotiated between the CO and the CPE.  
         [0011]     Beyond approximately 18,000 feet of commonly used UTP phone wire, most of the corresponding bandwidth is so attenuated, with most downstream buckets rendered useless, that communication per the ADSL standard ceases altogether.  
         [0012]     In the general case, any number of non-overlapping frequency bands may be assigned for uplink and downlink data, presumably the two being interleaved. For example,  FIG. 1  illustrates a generalized assignment scheme for interleaved DSL.  FIG. 2  illustrates the frequency band assignment standard for ADSL, wherein only one band (34 khz to 125 khz) is assign to uplink data and only one band (164 khz to 1100 khz) is assigned to downlink data. The spectrum above 1100 khz is not utilized. Other standards are evolving that may assign somewhat different frequency blocks and/or utilize a higher maximum frequency. One skilled in the art will understand that the present invention is applicable to such different frequency assignments by selecting different component values for the various circuit blocks described herein such that they are tuned to filter out or pass or amplify in the appropriate frequency ranges.  
         [0013]     The present invention operates on ISO OSI model Layer 1. That is, it is a purely analog device with no software or comprehension of protocols or frames. It takes a weak, noisy signal, cleans it up and amplifies it. Thus it is useful regardless of what protocol the signals may represent. Those skilled in the pertinent art will understand its applicability in improving signal quality within any UTP transmission system.  
       SUMMARY OF THE INVENTION  
       [0014]     An electronic circuit is inserted between a telecommunications central office and the customer premises equipment of an unshielded twisted pair DSL connection. The signals, having been separated as to downlink or uplink by assigned frequency bands, are separated for separate signal conditioning. The downlink signals, typically of a higher frequency than the uplink signals, are separated, amplified, filtered, equalized, amplified, and driven onto the UTP connection to the CPE. The uplink signals are separated, amplified, filtered, amplified, and driven onto the UTP connection to the CO. In another embodiment the uplink signals are separated, amplified, filtered, equalized, amplified, and driven onto the UTP connection to the CO. Any voice signals are passed bi-directionally, unmodified, around the active circuitry by a low pass filter for connection with the uplink and downlink signals on the UTP. In another embodiment the uplink and downlink signals do not share a common set of UTP wires and are amplified without mixing or filtering.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows frequency band assignments for an interleaved system.  
         [0016]      FIG. 2  shows frequency band assignments for an ADSL system.  
         [0017]      FIG. 3  is a block diagram of the present invention in a generalized form.  
         [0018]      FIG. 4  is a block diagram of the present invention, showing its major functional blocks and the direction of signal flow for an ADSL implementation.  
         [0019]      FIG. 5  is a schematic of MIXER 1 .  
         [0020]      FIG. 6  is a schematic of a preamplifier.  
         [0021]      FIG. 7  is a schematic of high pass filter FILTER 1 .  
         [0022]      FIG. 8  is a schematic of equalization amplifier AMP 1 .  
         [0023]      FIG. 9  is a schematic of low pass filter FILTER 2 .  
         [0024]      FIG. 10  is a schematic of low pass filter FILTER 3 .  
         [0025]      FIG. 11  is a schematic of a plurality of peaking amplifiers and a driver.  
         [0026]      FIG. 12  is a schematic of amplifier AMP 2 .  
         [0027]      FIG. 13  is a set of SPICE simulations for AMP 1 .  
         [0028]      FIG. 14  is a table of values for certain components as a function of distance from the CO and CPE. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     In one embodiment of the present invention an analog circuit is inserted in a UTP line at an appropriate distance between the CO and the CPE. It is an apparatus which separates the three or more frequency bands (assigned to voice if present, uplink(s), and downlink(s)). The present invention passes any voice signals through unmodified, filters and amplifies the uplink and downlink signals, then recombines any voice signal with uplink or downlink data signals as appropriate. Thus the telephone at the user&#39;s premises will continue to operate unchanged if the inserted device should fail for a power failure or the like. This satisfies the industry requirement that connectivity with the emergency number 911 not be compromised.  
         [0030]      FIG. 3  illustrates one embodiment of the present invention, suitable for a frequency assignment scheme wherein a plurality of “m” downlink and a plurality of “n” uplink frequency bands are specified, one example of which is illustrated in  FIG. 1 . The UTP lines from the CO are connected with a mixer/splitter MIXER 1 . 1   316 . A preamplifier PREAMP 1 . 1   300  and one or more band pass filters (FILTER 1 . 1 - 1   304  through FILTER 1 . 1 - m    306 ) are provided for each of m downlink frequency bands, each filter tuned appropriately for a specific frequency band. The output of the filter(s) is connected with a matching number of amplifiers, AMP 1 . 1 - 1   308  through AMP 1 . 1 - m    310 . The amplifier outputs are provided to a DRIVER 1 . 1   324 , which drives signals through MIXER 2 . 1  onto UTP lines which go to the CPE splitter. The uplink signals from the CPE are treated in a similar manner. The uplink signals, as shown in  FIG. 1 , are assigned n bands. If present, voice signals are not processed but instead passed around the active circuitry via a low pass filter FILTER 3 . 1   330 .  
         [0031]      FIG. 4  illustrates an embodiment for an ADSL system. The example frequency band assignments for an ADSL signal are shown in  FIG. 7 . A preamplifier and a filter are needed for the uplink and for the downlink frequency bands plus a low pass filter for the voice band. An inserted device, termed a Bi-directional Differential Broadband Equalizing Amplifier  100  (“BDBEA”), is connected with the CO at one end via differential signals on lines  420  and  422  and the CPE at the other end via differential signals on UTP lines  452  and  454 . Looking first at the end connected with the CO, the first element is MIXER 1   400  which has three purposes: 1) block the voice signals on lines  420  and  422  from entering PREAMP 1   402 , 2) split out the uplink signals on lines  456  and  458  from the downlink signals on lines  420  and  422 , 3) mix in the uplink signals from AMP 2   416  on lines  456  and  458  with the voice signals on lines  464  and  466 . Thus MIXER 1   400  is a blocker, a splitter, or a mixer, depending upon frequency band and to which port of MIXER 1   400  each signal is applied. Six db of the downlink signal is lost through MIXER 1   400 .  
         [0032]     For the downlink direction the next stage is PREAMP 1   402 , connected with MIXER 1   400  by lines  424  and  426 . PREAMP 1   402  provides approximately 12 db of gain to the downlink signal and to the residual amplified (by AMP 2   416 ) uplink signal, since all of the uplink signal is not cancelled by MIXER 1   1 . At the output of PREAMP 1   402  the voltage level of the unwanted uplink signal is significantly higher than that of the downlink signal. The downlink signal would appear as ripple riding upon the uplink signal. Thus FILTER 1   404  is needed to filter out the uplink signal, leaving the desired downlink signal.  
         [0033]     The input of FILTER 1   404  is connected with the output of PREAMP 1   402  by lines  428  and  430 . The signals assigned the frequency band below the downlink band is the uplink band and there are no signals assigned a frequency band higher that that of the downlink band. Thus FILTER 1   404  is a high pass filter whose cutoff frequency is just below 165 khz. At the output of FILTER 1   404  the only signal remaining is the downlink signal, the uplink signal now being approximately 70 db below the downlink signal. The output of FILTER 1   404  is connected with the input to AMP 1   406  by lines  432  and  434 . Approximately 6 db of the downlink signal is lost through FILTER 1   404 .  
         [0034]     The remaining downlink signal is amplified strongly by a peaking equalization amplifier AMP 1   406 , providing approximately 28 db to 46 db of gain, depending upon frequency.  
         [0035]     Equalization is the increase or decrease of signal strength at a certain “set frequency” with less effect at other frequencies. A peak equalizer amplifies at the designed-for set frequency and a range of frequencies close to the set frequency. The Q of the design sets the width of the band of frequencies that will be amplified; it affects the range of frequencies around the set frequency that will have an approximately similar amount of amplification. Equalization affects the data carrying ability of the buckets because it changes the strength relationship of the fundamental and harmonic frequencies.  
         [0036]     Since the BDBEA  100  is placed between the CO and CPE, the peak equalizer&#39;s set frequency and Q for the downstream signals in one embodiment compensates for signal attenuation already caused by the effects of wire line length from the CO to the BDBEA  100 , and pre-compensates for the anticipated signal attenuation from the effects of wire line length from the BDBEA  100  to the CPE. This causes the downlink data signals to arrive at the CPE modem pre-equalized.  
         [0037]     The output of AMP 1   406  on line  407  is single ended and not strong enough to adequately drive UTP lines  452  and  454 . So line  407  is connected with DRIVER 1   408 , which increases signal strength and provides a differential signal to MIXER 2   410  on lines  436  and  438 .  
         [0038]     In one embodiment for an ADSL system, wherein the downlink signals are assigned to a much higher frequency range than the uplink signals, equalization and pre-compensation are utilized only on the downstream signals. In another embodiment equalization and pre-compensation are used on most or all uplink and downlink frequency bands.  
         [0039]     MIXER 2   410  connects with the CPE splitter and subsequently the CPE DSL modem on UTP lines  452  and  454 . Thus the incoming downlink signal has been cleaned up, amplified, and retransmitted via the UTP, along with the voice signals from lines  460  and  462 .  
         [0040]     In one embodiment for an ADSL application the uplink path through the BDBEA  100  is nearly identical to that of the downlink path. The differences are that AMP 2   416  is not an equalization amplifier and there is no driver stage between AMP 2   416  and MIXER 1   400 . An equalization amplifier is not necessary in an ADSL system for the uplink direction because the lower frequency spectrum assignment causes the uplink signals to not experience as much signal loss as do the downlink signals. Also, FILTER 2   414  is different from FILTER 1   404  in that FILTER 2   414  is a low pass filter, filtering out any downlink signal that is still present on lines  444  and  446 . The final stage in the uplink direction is AMP 2   416 , providing approximately 6 db to 26 db of gain before being mixed by MIXER 1   400  and subsequently transmitted to the CO on UTP lines  420  and  422 , along with the voice signals from lines  464  and  466 .  
         [0041]     MIXER 1   400  and MIXER 2   410  are identical circuits. MIXER 1   400  is explained in detail; one skilled in the art will recognize the corresponding details for MIXER 2   410 .  
         [0042]     Referring to  FIG. 5 , the positive and negative signals COp and COn on lines  420  and  422  come from the CO. The entire dc to 1100 khz signal is carried by these lines. A DSL transformer  500  isolates the CO signals from the BDBEA  100 , and also effectively blocks the dc to 30 Khz voice signals. At the same time signals Acpep and Acpen are presented by AMP 2   416  on lines  456  and  458  at a very high level, much higher than the downstream signal coming from the output of transformer  500 . The left side of transformer  500  (as viewed in  FIG. 5 ) represents the secondary side of a transformer as seen by the downlink signal. But it also represents the primary side of a transformer as seen by the (amplified) uplink signals Acpep and Acpen. This is the dual nature of MIXER 1   400  and MIXER 2   410 ; both input and output, the very definition of bi-directionality. It is important that the impedance of transformer  500  presented to the CO closely match that of the CO, namely 100 ohms, an industry standard. This is accomplished by 50 ohm resistors Rtcon  502  and Rtcop  504  in series with what the uplink signal considers the primary side of transformer  500 . A capacitor Ccoac  506  blocks any dc component from going through the primary side of transformer  500 .  
         [0043]     Transformer  500  outputs  508  and  510  are connected with an R/2R hybrid coupler  512 , comprised of resistors R 1 cop  514 , R 1 con  516 , R 2 con  518  and R 2 cop  520 . Hybrid coupler  512  causes an approximately 6 db reduction in signal strength of the unwanted uplink signal of the mixed signal presented to PREAMP 1   402  on lines  424  and  426 . The values of resistors  514 ,  516 ,  518 , and  520  are not critical, only their ratio of 2:1. Nominal values are suggested in  FIG. 5 .  
         [0044]     Refer now to  FIG. 6 , detailing broadband PREAMP 1   402 . PREAMP 1   402  and PREAMP 2   412  are architecturally identical but may have different gains. One skilled in the art will understand the use of PREAMP 2   412  from this description. The input to PREAMP 1   402  is the signals on lines  424  and  426 , the output of MIXER 1   400 . At this point the signal contains the downlink signal plus some remaining uplink signal. Filter stage FILTER 1   404  will remove the remaining uplink signal, but needs good signal strength to work with, thus the need for amplification by PREAMP 1   402 . PREAMP 1   402  is a differential amplifier. The phase relationship between the signals on lines  424  and  426  is preserved by connecting them to the non-inverting input of amplifiers  600  and  602  respectively. The gain of the amplifiers is controlled by feedback resistors Rcoip  604 , Rcoin  606 , and Rcog  608 . The manufacturer&#39;s specification for opamps  600  and  602  should be consulted for recommended values for Rcoip  604  and Rcoin  606 . The resulting gain through PREAMP 1   402  is approximately 12 db. Care should be taken with PREAMP 1   402  and PREAMP 2   412  to insure that clipping does not occur. The differential output lines  428  and  430  are connected with high pass filter FILTER 1   404 .  
         [0045]     FILTER 1   404  is shown in detail in  FIG. 7 . In one embodiment FILTER 1   404  is a ninth order elliptical filter. One skilled in the art would know of other suitable high pass filters. The implementation of FILTER 1   404  is not critical, only that one use a high pass filter providing strong attenuation of signals below 164 khz with little or no attenuation above 164 khz. Resistors Rbpp  700 , Rbpn  702 , Pbpsp  704 , and Pbpsn  706  are for impedance matching. FILTER 1   404  is connected with PREAMP 1   402  via lines  428  and  430 . The output of FILTER 1   404  is on lines  432  and  434 , connecting with AMP 1   406 .  
         [0046]     AMP 1   406  is a peaking equalization amplifier. Referring to  FIG. 8 , the input signals from FILTER 1   404  via lines  432  and  434  are connected with a video difference amplifier  800 . The gain of video difference amplifier  800  is controlled by the voltage on line  804 . Line  802  is connected with ground. The gain is determined per the relationship  
         Gain   800     =         Z   ⁡     (   Rdfc   )         Z   ⁡     (     Rdbb   ,   Cdbb     )         +   1.         
 
         [0047]     The peak gain frequency of the video difference amplifier  800  is strongly controlled by capacitor Cdbb  808 . The peak gain frequency goes down as the value of Cdbb  808  goes up. The DSLAM at the CO and the CPE negotiate the data rate between them. They will pack most of the data into the lower buckets, where there is less loss than in the upper buckets, which are assigned higher frequencies. Accordingly the peak gain frequency in one embodiment is set somewhat below the highest frequency of the downstream band.  
         [0048]      FIG. 13  presents SPICE simulations for various component values. All were done with an Rdfc  812  of 1K ohms. In  FIG. 13A  Cdbb=33 nF and Rdbb is 10 ohms. Peak gain is at 805 khz and the maximum gain is 43 db. By changing Cdbb  808  to 47 nF we see in  FIG. 13B  that the peak gain frequency is lowered to 671 khz with little change in maximum gain. Conversely, changing Rdbb  810  to 5 ohms (with Cdbb at 33 nF), we see in  FIG. 13C  that the frequency stays at 805 khz and the gain is increased to 48 db. The roll off of gain at the peak is sharper for Rdbb=5 ohms than for Rdbb=10 ohms.  
         [0049]     The output from AMP 1   406  is a single-ended signal on line  407 . This signal is presented to toroidal coil  807  of DRIVER 1   408  through a current limiting resistor Rdse  809 . The purpose of toroidal coil  807  is to once again have differential signals. The secondary of toroidal coil  807  presents differential signals to amplifiers  816  and  818  on lines  815  and  817 .  
         [0050]     Amplifiers  816  and  818  are the drivers for UTP lines  452  and  454 , with coupling provided by MIXER 2   410 .  
         [0051]     The optimum value for the overall gain of AMP 1   406  and DRIVER 1   408  depends upon both the distance from the CO and the distance from the CPE. Additionally, there is an interplay between the gain of AMP 1   406 , DRIVER 1   408 , the maximum power that industry standards will permit on UTP lines  452  and  454 , and how effectively the R2/R hybrid coupler in MIXER 2   410  can reduce the unwanted downlink signals such that FILTER 2   414  can provide AMP 2   416  with signals wherein the downlink signals have been adequately attenuated. In one embodiment AMP 1   406  and DRIVER 1   408  are configured with values for Rdfc  812  and Rdgg  814  per a chart, which chart may be used to configure the BDBEA  100  for the specific distances from the CO and the CPE. An example is shown in  FIG. 14 .  FIG. 14  is for an installation that is 13,500 feet from the CO to the BDBEA  100 . Column A lists various distances from the BDBEA  100  to the CPE, from 3,000 feet to 13,000 feet. For each distance one finds a corresponding value for Rdfc  812  in Column B and Rddg  814  in Column C. These values have been determined empirically, considering the trade off factors just described.  
         [0052]     MIXER 2   410  is connected with DRIVER 1   408  via lines  436  and  438 . MIXER 2   410  passes the downlink signals to UTP wires  452  and  454  which extend to the CPE premises splitter. In addition, voice signals on lines  460  and  462  are physically connected with the UTP lines  452  and  454  at this point (outside of MIXER 2   410 ), thus preserving the bidirectional connection of voice signals between the CO and the CPE. MIXER 2   410  is designed and functions identically to MIXER 1   2 , though obviously the downlink signal is now the unwanted signal and the uplink signal is the desired signal to present to PREAMP 2   412 . MIXER 2   410  is connected with PREAMP 2   412  via lines  440  and  442 .  
         [0053]     As stated, PREAMP 2   412  is architecturally identical to PREAMP 1   402 . The gain of the two preamplifiers may be different, each being set to provide as much gain as possible without clipping. PREAMP 2   412  is connected with FILTER 2   414  via lines  444  and  446 .  
         [0054]     FILTER 2   414  is not the same as FILTER 1   404 . FILTER 2   414  is a low pass filter, whose cutoff frequency is just above 125 khz. The result is the passing of the uplink signals while attenuating the downlink signals. The design shown in  FIG. 9  is a ninth order elliptical filter, though as with FILTER 1   404  there are many alternative designs of a low pass filter one skilled in the art might chose. Suggested component values for this design are shown. Resistors  900 ,  902 ,  904 , and  906  selected to provide impedance matching. FILTER 2   414  is connected with AMP 2   416  via signals on lines  448  and  450 . At the output of FILTER 2   414  the unwanted downlink signal is approximately 70 db below the uplink signal.  
         [0055]     AMP 2   416 , as shown in  FIG. 12 , is not an equalization amplifier for reasons previously explained. It provides 6 db to 26 db of gain between the input signals on lines  448  and  450  and output signals on lines  456  and  458 , which are connected with MIXER 1   400 . AMP 2   416  has enough gain such that a driver stage is not needed. For the same concerns detailed in setting the overall gain of AMP 1   404  and DRIVER 1   406 , AMP 2   416  gain is determined empirically. Again referring to  FIG. 14 , for each distance to the CPE listed in Column A there is a recommended value of Rudg  950  ( FIG. 12 ).  
         [0056]     In one embodiment, for systems such as ADLS 2  and VDSLs, wherein there is a plurality of uplink and/or downlink bands, a filter and an amplifier is provided for each band. Referring again to  FIG. 3 , for a system with two downlink bands(“m” = 2 ) one embodiment includes a FILTER 1 . 1 - 1  and a FILTER 1 . 1 - 2 , each a band pass filter for the assigned band. Each filter output is connected with an amplifier whose gain and peak gain frequency is tuned for the frequency band of interest.  FIG. 11  illustrates how each amplifier is configured. Opamp  1110  receives signals on lines  1100  and  1102  from FILTER 1 . 1 - 1   304 . As described for the ADSL embodiment of AMP 1   406 , Rdbb. 1   1120  and Cdbb. 1   1122  are determined for optimum frequency and gain for the assigned band. Opamp  1112  receives signals on lines  1104  and  1106  from FILTER 1 . 2 . Because opamp  1112  is presented with signals of a different frequency band than those of opamp  1110 , the optimum values for Rdbb. 2   1106  and Cdbb. 2   1108  are different than for the corresponding components for opamp  1110 . The resulting outputs (following current limiting resistors) of these two amplifiers are connected with line  407 , which is further connected with toroidal coil  807  in DRIVER 1   408 .  
         [0057]     One skilled in the art will understand this arrangement may be extended to an arbitrary number of uplink and/or downlink frequency bands. In one embodiment the uplink signals are assigned a frequency band for signals that is high enough to cause appreciable signal loss, thus one or more peaking equalizing amplifiers are used. In another embodiment these signals are given another gain stage (DRIVER 2   328 ,  FIG. 3 ) to compensate for the high frequency loss and/or the distance to the CO.  
         [0058]     In one embodiment voice signals are present on the UTP lines between the CO and the CPE. In this case a low pass filter FILTER 3   418  passes the signals around the active circuitry of the BDBEA  100 . An example of FILTER 3   418  is illustrated in  FIG. 10 , though one skilled in the art will know of several alternative low pass filter designs.  
         [0059]     In some DSL systems one set of UTP wires is dedicated to downlink signals and another set of UTP wires is dedicated to uplink signals. There is no provision for voice signals. Since the uplink and downlink signals are separated the amplifier need not provide a mixer or filters, simply an equalization amplifier in each UTP set, with DSL transformers for coupling if desired.

Technology Category: 5