Abstract:
A telecommunications chassis, module, and repeater circuit for use with signals having data rates including STM-1 (155.52 megabits per second) are disclosed. The chassis provides structures for establishing shielding and heat dissipation for the circuitry modules it contains including an outer and an inner Faraday box with an integrated ventilation pattern for circulating air. The module provides its own structures for establishing shielding and heat dissipation including a Faraday box and a ventilation pattern. The repeater circuit provides the ability to bridge a data signal between a monitor jack of one device and a higher signal level input jack of another device through multiple amplification stages and circuit board structures. The telecommunications chassis, module, and repeater circuit can be used in conjunction.

Description:
RELATED APPLICATION 
   The present application is a divisional of U.S. patent application Ser. No. 11/126,853, filed May 10, 2005, which is a divisional of U.S. patent application Ser. No. 09/812,226, filed Mar. 19, 2001 entitled “Telecommunications Chassis, Module, and Bridging Repeater Circuitry,” the entirety of which are hereby incorporated by reference. 

   TECHNICAL FIELD 
   The present invention is directed to chassis for holding telecommunications modules, the modules themselves, and the repeater circuitry that may be contained within the modules. More specifically, the present invention is directed to a chassis and module with shielding and heat dissipation structures and to repeater circuitry for bridging applications. 
   BACKGROUND 
   A telecommunications chassis provides a mounting structure for telecommunications modules housing various types of circuitry. The telecommunications chassis must provide protection from externalities while also facilitating heat dissipation from the circuitry it contains. The chassis must also attempt to shield its interior from electromagnetic interference while limiting the amount of electromagnetic interference being emitted from the interior. For certain applications, such as providing uninterrupted service during maintenance, circuitry housed by the chassis may need to be moved from place to place. Thus, portability of the chassis for this type of application becomes important as well. As the data rate being handled by the circuitry within the chassis increases, the ability to shield and protect from externalities while dissipating heat becomes more difficult. 
   Similarly, with the telecommunications modules that may be housed by the chassis, the circuitry within the module must be protected from externalities within the chassis, the ability of the module to shield and protect the circuitry while dissipating heat becomes more difficult as the data rate being handled by the circuitry within the module increases. 
   Bridging repeater circuits, which may be housed by the modules and chassis previously discussed, must take a low-level electrical monitor signal from one device, such as a digital signal cross-connect, and recreate the electrical signal with the data and clock information intact and at a high level suitable for reception by another device. Bridging repeater circuits are useful where a device has failed or must otherwise be replaced but a break in service is to be avoided. The bridging repeater circuit bridges around the faulty device from one healthy device to a replacement device to establish signal transfer prior to the faulty device being disconnected. The bridging repeater circuit is generally housed by a portable structure which needs to provide protection from heat and interference so that it may be transported to the locations of faulty devices and successfully create the output signal. As the data rate increases, the repeater circuit&#39;s ability to recover the data and clock information from the low-level monitor signal to recreate the output signal becomes more difficult. 
   Therefore, there is a need for a chassis to provide protection to modules from externalities and interference while facilitating heat dissipation, even at high data rates and while being portable if necessary. There is also a need for a module to provide protection to circuits from externalities and interference while facilitating heat dissipation, even at high data rates. Additionally, there is a need for a bridging repeater circuit that can recover the data and clock portions from a low-level monitor signal to recreate a high-level output signal repeating the data and clock information, even at high data rates. 
   SUMMARY 
   The present invention includes various embodiments that facilitate telecommunications functions for electrical signals, including those with high data rates such as the STM-1 rate of 155.52 megabits per second (Mbps). A chassis and a module of the present invention provide heat dissipation and shielding structures that may be used for circuits operating at these high data rates. A repeater circuit of the present invention recovers data and clock information from low-level monitor signals to create an output signal with the data and clock information intact, even at these high data rates. 
   The present invention may be viewed as a telecommunications chassis. The chassis includes a shielding chamber having a first and second horizontal surface and a first and second vertical surface. The first and second vertical surfaces are disposed between the first and second horizontal surfaces, and the first and second horizontal surfaces and the first and second vertical surfaces are made of metal and are conductively connected. A vertical backplane has connectors for interfacing with repeater modules and is disposed between the first and second horizontal surfaces and the first and second vertical surfaces. The vertical backplane establishes contact with the first and second horizontal surfaces and the first and second vertical surfaces and has a ground conductor that is electrically connected to the connectors. An outer housing encompasses the shielding chamber and the vertical backplane and has an open side for receiving telecommunications modules. The outer housing has a first cover surface that is substantially parallel to but within a different spatial plane from the first horizontal surface and has a second cover surface that is substantially parallel to but within a different spatial plane from the vertical backplane. Spacing between the first cover surface and the first horizontal surface and spacing between the second cover surface and the vertical backplane form an airspace. A chassis ground conductor is also included and is electrically connected to the shielding chamber and the ground conductor of the vertical backplane. 
   The present invention may also be viewed as a telecommunications circuit module. The module includes a printed circuit board including circuitry. A metal backplate is substantially parallel to but within a different spatial plane from the printed circuit board. A metal shell has a frontplate, a top surface perpendicular to and extending from the frontplate, a bottom surface substantially parallel to the top surface and extending from a side of the frontplate away from the top surface, and a back surface perpendicular to the front plate and the top and bottom surfaces. The top surface, bottom surface, and back surface each has a folded edge that abuts the metal backplate to establish metal to metal contact. A metal jack holder extends perpendicularly from the printed circuit board and abuts the front plate, top surface, and bottom surface to establish metal to metal contact along a side away from the back surface. At least a portion of the circuitry is disposed between the frontplate and the backplate and between the metal jack holder and the back surface. 
   The present invention may be viewed as a repeater circuit. The repeater circuit includes an amplification portion that receives a first signal with data and clock information and increases the amplitude of the first signal to generate an amplified first signal. The amplification portion includes a current feedback amplifier stage and a voltage limiting amplifier stage. A transceiver portion receives the amplified first signal with increased amplitude, recovers the data and clock information from the received amplified first signal, and transmits a second signal with the data and clock information recovered from the first signal. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are front and back perspective views of an embodiment of the chassis of the present invention. 
       FIGS. 2A and 2B  are perspective and right side views, respectively, of the sidewalls and front and rear trim pieces of the chassis. 
       FIGS. 3A and 3B  are an exploded perspective view of inner components of the chassis and a perspective view of the chassis without outer coverings with the inner components being installed. 
       FIGS. 4A and 4B  are a rear perspective view of the chassis without the outer coverings and an exploded perspective view of the rear cover piece and power supply, respectively. 
       FIGS. 5A ,  5 B, and  5 C are a plan view of the uninstalled rear cover piece, power supply, and vertical backplane, a perspective of the rear cover piece and power supply showing ground wire connections, and a perspective with the top cover removed to show its ground wire connection. 
       FIG. 6  is a rear perspective view of the chassis without outer coverings showing ground wire connections and the rear cover piece installation. 
       FIGS. 7A ,  7 B, and  7 C are an exploded perspective view of the chassis, an exploded detail view of the top outer covering fastener, and an exploded detail view of the bottom outer covering fastener, respectively. 
       FIGS. 8A and 8B  are perspective views of an uninstalled door and hinge guide, respectively. 
       FIGS. 9A ,  9 B,  9 C, and  9 D are a front perspective view, a rear perspective view, and exploded perspective views of an embodiment of the module of the present invention. 
       FIG. 9E  is a perspective view of the chassis with a module partially inserted. 
       FIG. 10  is a plan view of the faceplate of the module. 
       FIG. 11  is a high-level block diagram showing the application of the bridging repeater circuit embodiment of the present invention to a network environment. 
       FIG. 12  is a block diagram of the circuitry of the bridging repeater circuit. 
       FIG. 13  is a block diagram of the input section of the bridging repeater circuit. 
       FIG. 14  is a circuit schematic of the input section. 
       FIG. 15  is a block-diagram of the power supply of the bridging repeater circuit. 
       FIG. 16  is a top layer view of the printed circuit board showing input signal paths. 
       FIG. 17  is an internal layer view of the printed circuit board showing the ground plane configuration of connector pins. 
       FIG. 18  is a cross-sectional view of the printed circuit board illustrating the six individual conductive layers separated by dielectrics. 
   

   DETAILED DESCRIPTION 
   Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies through the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. 
   Embodiments of the present invention provide a chassis design that facilitates high-speed data rates of electrical signals through implementation of structures that provide heat dissipation and shielding. Embodiments also provide a module design that further facilitates high-speed data rates of electrical signals through implementation of additional structures that provide heat dissipation and shielding. Bridging repeater circuitry embodiments of the present invention also facilitate high-speed data rates of electrical signals by implementing structures that recover the data and clock portions of a low-level monitor signal through sufficient amplification and create a higher-level output signal repeating the data and clock portions. 
     FIGS. 1A and 1B  illustrate an embodiment of the chassis of the present invention. The chassis  100  has a top cover  102 , a bottom cover  104 , and a rear cover  137  forming an outer housing  105 . Front trim piece  120  and rear trim piece  122  fit around the rear edges of the top cover  102  and bottom cover  104 , respectively. Front extensions  114 ,  116  extend forward from the front trim piece  120 . 
   A door  108  is connected to the front extensions  114 ,  116  through hinges  112 . The door  108  has a finger  110  that catches on the left front extension  114  to hold the door  108  closed. A rotatable handle  106  is connected to the chassis  100  through mount  107 . One or more covers  118  are mounted on the chassis  100  to isolate the interior of the chassis  100  when corresponding modules are not present. 
   The rear cover  137  has several rows of holes  138  for exhausting heat produced by the modules housed within the chassis  100 . The rear cover  137  also has a power socket  130  with electrical connections  132  for receiving AC power, such as 110V and/or 220V, from an external source. Typically, power socket  130  is internally fused and is switchable to receive either voltage. Rails  124 ,  128  are mounted to the rear trim piece  122  and have feet  126  attached to them. The bottom cover  104  has a several rows of holes  136  for passing ambient air into the interior of the chassis  100 . The bottom cover  104  also has several feet  134 . 
     FIGS. 2A and 2B  show sidewalls  140 ,  148  of the chassis  100 . The sidewalls  140 ,  148  are held in position by attachment to the front and rear trim pieces  120 ,  122 . Several holes  150  are located at the top and the bottom of the left sidewall  148 . Similarly, several holes  142  are located at the top and bottom of the right sidewall  140 . 
   Ridges  152  are provided in the left sidewall  148 , and ridges  144  are provided in the right sidewall  140 . An inwardly recessed region  154  in the left sidewall  148  and inwardly recessed region  146  in the right sidewall  140  is created between the sets of ridges  152  and  144 . The inwardly recessed portions  154 ,  146  are exposed between the top cover  102  and the bottom cover  104 , and the ridges  152 ,  144  facilitate attachment of the top cover  102  and bottom cover  104  to the sidewalls  140 ,  148  as discussed below. Handle mount holes  156  are provided in the recessed portions  154 ,  146  to allow attachment of the handle mount  107 . 
     FIGS. 3A and 3B  illustrate the assembly of the interior structures of the chassis  100 . A top horizontal surface  162  and a bottom horizontal surface  160  mount to a faceplate  158  and a vertical backplane  164 . Both the top and bottom horizontal surfaces  162 ,  160  have several rows of ventilation holes  168  that allow air to pass up from the bottom of the chassis  100  through the installed modules and into the top of the chassis  100  where it is channeled between the top cover  102  and the top horizontal surface  162  and exhausted out the rear of the chassis  100  through holes  138 . 
   As can be seen the top and bottom horizontal surfaces  162 ,  160  have curled edges  172 ,  173 ,  174 , and  175  that abut the faceplate  158  and the vertical backplane  164 . Each of these surfaces except the vertical backplane  164  is made of metal, such as cold rolled steel with a zinc chromate plating, such that metal-to-metal contact is established between them. The backplane  164  is typically printed circuit board material. Likewise, the sidewalls  140 ,  148  are also made of metal, such as aluminum, and establish electrical continuity with the top and bottom horizontal surface  162 ,  160  through metal brackets discussed below. A Faraday box, or shielding chamber, results which provides shielding for the modules housed by the chassis  100 . The grounding of the shielding chamber is discussed below. Similarly, an outer Faraday box results from the metal top and bottom covers  102 ,  104  and the metal rear cover  137  whose grounding is also discussed below. 
   The vertical backplane has connectors  166  that allow the modules to be inserted into the chassis  100  and slidably engage connectors  166  to establish electrical connection. The vertical backplane connectors  166  typically provide DC power to the modules from a chassis power supply discussed below. The top and bottom horizontal surfaces  162 ,  160  have slots  170  that receives fins on the module to guide it as it is inserted and to prevent lateral movement once it is installed. As best seen in  FIG. 3B , the faceplate  158  has notches  176  that align with the slots  170 . 
     FIG. 4A  shows the chassis  100  with the top cover  102  and the bottom cover  104  of the outer housing  105  removed. As shown the shielding chamber  101  is fully installed in the chassis  100 . The shielding chamber  101  is held in place by brackets  178 ,  180  that mount to both the top horizontal surface  162  and the sidewalls  140 ,  148 . As can be seen an airspace  103  is created by the placement of the shielding chamber  101 . The airspace  103  of this embodiment includes the area between the top horizontal surface  162  and the top cover  102 , the area between the rear cover  137  and the vertical backplane  164 , and the area between the bottom horizontal surface  160  and the bottom cover  104 . 
   The airspace  103  allows air to enter through the bottom cover  104 , rise through the shielding chamber  103 , return to the rear of the chassis  100 , and exit out the rear cover  137 . Air may also enter through the bottom cover  104  and rise directly between the vertical backplane  164  and the rear cover  137  and then exit from the chassis  100 . As shown in  FIG. 4B , the chassis power supply  186  is mounted to the rear cover  137 , and the air rising up the vertical backplane  164  may assist in dissipating heat from the power supply  186 . Because the top cover  102  has no holes, any flames imposed on the interior of chassis  100  cannot escape from the top and are, therefore, adequately contained. 
   Also shown in  FIG. 4B , the rear cover has an aperture  184  that is used to mount the power socket  130 . The power socket  130  has rear terminals  182  for electrical connection to the power supply  186 . Also, a portion of the holes  138  of the rear cover  137  lie directly behind the power supply  186  and allow it to radiate some heat directly out of the chassis  100 . Mounting the power supply  186  directly to the rear cover  137  also permits easy installation and maintenance of the power supply  186  because it can be accessed by simply removing the rear cover  137  and its electrical connections can be easily made while the rear cover  137  is removed. 
     FIGS. 5A ,  5 B, and  5 C show the ground wire connections of the shielding chamber  101 , vertical backplane  164 , and outer housing  105 , and also shows the power connections of the power supply  186 . The power supply  186  typically receives AC power from the power socket  130  through wires  208  and  210  connected to jack  216  of the power supply  186 . The power supply  186  then typically outputs DC power through output jack  218  to the vertical backplane  164  through wires  212  and  214  where it is then distributed to each of the connectors  166 . 
   A ground tab  220  of the power supply  186  is electrically connected to the ground prong  207  of the power socket  130  through wire  206 . The ground tab  220  is electrically connected to a ground post  190  of the rear cover  137  through wire  204 . Ground wires are fixed to the ground post  190  and ground post  188  of the rear cover  137  through the fastening assembly  192 . 
   A ground conductor  164 ′ of the vertical backplane  164  that electrically connects the vertical backplane  164  to shielding pins of connectors  166  is also electrically connected to the ground post  190  through wire  196 . The right sidewall  140  is connected to the ground post  188  through wire  198 . The left sidewall  148  is connected to the ground post  188  through wire  202 . The top cover  102  is connected to the ground post  188  through wire  200 , and the bottom cover  104  is connected to the ground post  190  through wire  194 . 
   The top cover  102  and bottom cover  104  of the outer housing  105  have conductor tabs  102 ′ that extend from them for receiving connectors  201  of the ground wires  200  and  194 . The top cover  102  and bottom cover  104  may have a powder coat finish applied and the conductor tabs  102 ′ remain bare metal to establish electrical continuity with the ground wires  200 ,  194 . 
     FIG. 6  shows the installation of the rear cover  137  and left and right rails  124 ,  128  as well as the connections of the ground wires to the sidewalls  140 ,  148 . Because the rear cover  137  is mounted to the rear trim piece  122 , the airspace  103  remains between the rear cover piece  137  and the vertical backplane  164 . The airspace  103  accommodates the power supply  186 . 
   The ground wire  198  extending from ground post  188  fastens to the right sidewall  140  through one of the holes  142  in the top of the sidewall  140 . Likewise, the ground wire  202  extending from ground post  188  fastens to the left sidewall  148  through one of the holes  150  in the top of the sidewall  148 . The ground wire  196  extending from ground post  190  fastens to a mounting hole  197  of the vertical backplane  164  that is also used to attach the vertical backplane  164  to the bottom horizontal surface  160 . 
     FIG. 7A  shows an exploded view of the chassis  100 . As can be seen, the power supply  186  is placed within the airspace  103 , which is maintained by the spacing between the top cover  102  and top horizontal surface  162 , between the vertical backplane  164  and the rear cover  137 , and between the bottom cover  104  and the bottom horizontal surface  160 . A covering  109  may be placed over the faceplate  158  for aesthetics. The door  108  has a handle  108 ′ extending forwardly to facilitate opening and closing. 
     FIG. 7B  shows a fastener for holding the top cover  102  onto the sidewall  140 . The ridges  144  of the sidewall  140  have a notched end  222  that receives a nut holder  224  and nut  226  that fits within the nut holder  224 . As shown in  FIG. 7C , a nut holder  224  and nut  226  has been positioned by sliding it within the ridges  144  from the notched end  222  to an alignment dimple  230 . A screw passes through a hole in the bottom cover  104  to hold it in place. As shown, the top cover  102  and bottom cover  104  are both attached by four of these fasteners. 
     FIG. 8A  shows the door  108  of the chassis  100 . The door  108  includes the handle  108 ′ which has the finger  110  extending from it. The finger  110  passes through a hole in the door  108  so that it may engage the front extension  114 .  FIG. 8B  shows a hinge guide  232  that mounts to the front extensions  114 ,  116 . The hinge guide  232  has a hole  232 ′ for receiving a hinge shaft  112 ′ extending from hinge  112  that mounts the door  108  but allows it to open and close. 
     FIGS. 9A ,  9 B,  9 C, and  9 D show an embodiment of the module of the present invention. The module  234  has a shell  235  that has a frontplate  236 , a top surface  250 , a bottom surface  262 , and a back surface  256 . The top surface  250  has several ventilation holes  252 , and the bottom surface  262  has ventilation holes  264 . The ventilation holes allow air to rise from the bottom of the chassis such as chassis  100 , up through the modules  234  installed in the chassis  100 , and into the top of the chassis  100  prior to being exhausted through the rear cover  137 . The shell  235  is typically made of metal, such as aluminum. The edge  266  of the top surface  250  is folded, as is the edge  268  of the bottom surface  262 . The edge  257  of the back surface  256  is also folded. 
   A metal backplate  254  that is typically made of aluminum mounts to the edges  266 ,  268 ,  257  of the shell  235 . The metal backplate  254  supports a printed circuit board  276 . Portions  255  of the metal backplate  254  extend beyond the perimeter of the printed circuit board  276  and provide a surface that can establish metal-to-metal contact with the folds of edges  266 ,  268 , and  257 . 
   Connector jacks  274  pass signals between the circuitry on the printed circuit board  276  and external cable connectors (not shown). A metal jack holder  270  is mounted to the shell  235  and to a faceplate  238 . The metal jack holder  270  provides support for the connector jacks  274  with holes  272  that surround the cylindrical sleeve of the connector jacks  274 . The metal jack holder  270  also establishes metal-to-metal contact with the shell  235  and with the faceplate  238 . The faceplate  238  also establishes metal-to-metal contact with the backplate  254  and the front edges of the shell  235 . 
   The printed circuit board  276  is enclosed within the shell  235 , the backplate  254 , and the jack holder  270  which together form a Faraday box providing shielding for the circuitry on the printed circuit board  276 . A connector  260  is mounted to the printed circuit board  276  and is in electrical communication with the circuitry. Typically, the connector  260  provides DC power from the vertical backplane connector  166  to the circuitry. The back surface  256  of the shell  235  has an opening  258  that allows the connector  260  to pass through. Typically when maximizing shielding, the largest dimension of the opening is one-twentieth or less of the shortest wavelength of the signal to be handled by the circuitry. 
   The faceplate  238  has several holes for sending and receiving signals to and from coaxial cables. For a module  234  housing a repeater circuit, such as the bridging repeater circuit of the present invention, a monitor out port  242 , a signal out port  244  and a signal in port  246  are provided for each data channel. As shown, the module  234  houses two data channels. The faceplate may have a decal  278  attached to it to provide a visual indication of the purpose of each jack, light emitting diode (LED), switch, or other feature provided on the faceplate  238 . 
   The faceplate  238  generally has a fastener  240  for attachment to the chassis  100 . The metal backplate  254  has fins  248  located on the top and bottom edges. The fins  248  fit within the notch  176  of the chassis faceplate  158  and within the slot  170  of the top and bottom horizontal surfaces  162 ,  160  shown in  FIG. 3B . 
     FIG. 9E  shows the chassis  100  with a module  234  being partially installed. The fins of the module  234  pass into the slots  170  of the top and bottom horizontal surfaces  162 ,  160  and notch  176  of the chassis faceplate  158 . The module  234  slides into the opening in the chassis faceplate  158  and then continues to slide into the shielding chamber until the module connector  260  engages the vertical backplane connector  166 . 
     FIG. 10  is a closer view of the faceplate  238  of the module  234 . The faceplate  238  has the ports for monitor output  242 , signal output  244 , and signal input  246 . In addition, the faceplate may have a loss of signal (LOS) LED  282  that lights to indicate the signal through signal input port  246  is not adequately present. An LOS LED  280  may also be provided to indicate that the signal through signal output port  244  is not adequately present. Ports and LEDs for both a channel A and a channel B are shown. 
     FIG. 11  shows an exemplary network environment employing bridging repeater circuits of the present invention. A bridging repeater circuit  294 , which may be channel A or B of a module such as module  234 , is included as is a second bridging repeater circuit  292  which may be the other channel of the module. The bridging repeater circuits  292 ,  294  are being used to bypass a faulty digital signal cross-connect circuit (DSX)  290  without disrupting the signal path between the healthy DSX  288  and the electrical to optical (E/O) multiplexer (mux)  298 . The bridging repeater circuits  292 ,  294  may be housed in a module  234  for installation in portable chassis  100 , or they may be housed in a module suitable for installation in an existing chassis in the network environment such as a chassis with positions for the DSX devices. 
   Signal transmission through the portion of the network shown passes between several digital distribution frames (DDF)  284  that pass electrical signals to the mux  286  where they are multiplexed into an output line  285 . The mux  286  also receives multiplexed signals from a healthy DSX  288  through input line  287  and demultiplexes them for transfer to the several DDFs  284 . The healthy DSX  288  has output line  304  that feeds into the input of the faulty DSX  290 . The faulty DSX  290  has an output line  306  that feeds into the input of the healthy DSX  288 . 
   The faulty DSX  290  passes signals to the E/O mux  298  through line  289  and receives signals from the E/O mux  298  through line  291 . When the faulty DSX  290  needs to be temporarily or permanently replaced, a new DSX  296  is installed with a line  295  receiving signals from the E/O mux  298  that are the same as those signals received by the faulty DSX  290  through line  289 . The new DSX  296  is also installed with a line  297  sending signals to the E/O mux  298 . As discussed below, this line  297  duplicates the signal being provided over line  291  from the faulty DSX  290  to the E/O mux  298 . 
   The bridging repeater circuit  294  receives at its input the monitor signal output by the new DSX  296  through line  308 . The bridging repeater circuit  294  retransmits the data and clock information of the signal received from the new DSX  296  to the healthy DSX  288  through line  302  that connects to a make-before-break input jack of the healthy DSX  288  used for temporary connections. Because of this completed circuit through the bridging repeater circuit  294 , the line  306  connecting the output of faulty DSX  290  to the permanent input of healthy DSX  288  can be disconnected from the faulty DSX  290  and then redirected to the permanent output of new DSX  296  without breaking service in the channel. 
   The bridging repeater circuit  292  receives at its input the monitor signal output by the healthy DSX  288  through line  300 . The bridging repeater circuit  292  retransmits the data and clock information of the signal received from the healthy DSX  288  to the new DSX  296  through line  310  that connects to a make-before-break input jack of the new DSX  296  used for temporary connections. Because of this completed circuit through the bridging repeater circuit  292 , the line  304  connecting the input of faulty DSX  290  to the permanent output of healthy DSX  288  can be disconnected from the faulty DSX  290  and then redirected to the permanent input of new DSX  296  without breaking service in the channel. Once the healthy DSX  288  and the new DSX  296  have established communication in both channels through permanent connections, bridging repeater circuits  292  and  294  can be disconnected from both the healthy DSX  288  and the new DSX  296 . 
     FIG. 12  shows a block diagram of the circuitry  312  of the bridging repeater circuits  292  (channel A) and  294  (channel B). The bridging repeater circuit input is typically a 75 ohm SMB connector  314 ,  316  for both channel A and channel B that receives the monitor signal at approximately 0.1 Volts (V). The input connectors are electrically connected to isolation transformers  318 ,  320  for channels A and B, and the transformers have a turns ratio of 1:1. The isolation transformers  318 ,  320  are electrically connected to the amplification portion of the input section that includes a current feed back operational amplifier  322 ,  324  for each channel in series with a voltage limiting operational amplifier  326 ,  328  for each channel. 
   The voltage limiting operational amplifier  326 ,  328  of each channel feeds the amplified signal containing data and clock information, such as in a coded mark inversion (CMI) format, to an analog data input of the transceiver  330 ,  332  of each channel. The transceiver  330 ,  332  recovers the data and clock information from the signal and creates an output signal that repeats the data and clock information, also in CMI format. The transceiver output is connected to an additional isolation transformer  338 ,  340  that passes the output signal to the output jack  350 ,  352 , which may also be a 75 ohm SMB connector. The output signal may pass through a voltage divider network (not shown) prior to reaching the output jack  350 ,  352  but the output signal is typically around 2 V. 
   The transceiver output is also connected to another isolation transformer  334 ,  336  that passes the output signal to an additional voltage divider  342 ,  344  that is connected to a monitor jack  346 ,  348 , which may also be a 75 ohm SMB connector. The additional voltage divider  342 ,  344  decreases the output signal received by the monitor jack  346 ,  348  by about 27 dB. 
   A reference clock  354 , which is typically a 19.44 MHz oscillator, feeds a reference clock signal to the transceivers  330 ,  332 . Rather than using a single oscillator, a separate oscillator for each transceiver  330 ,  332  may also be employed. A low-voltage detector  356  may also be included to detect an under-voltage power supply condition. The low-voltage detector  356  feeds a detection signal to a programmable logic device (PLD) control  358 . 
   The PLD  358  also communicates with the transceivers  330 ,  332  to determine whether the signals being received or output by the transceiver are of an adequate level. If the PLD  358  receives a detection signal from detector  356  indicating an improper supply voltage, the PLD  358  will trigger a major or minor alarm circuit  360  which is in communication with the backplane  364 . If the PLD  358  receives a transmit or receive signal from the transceiver  330 ,  332 , it triggers a user LED  362  for channel A or B corresponding to transmit or receive to provide an indication of the loss of signal. 
     FIG. 13  shows the input channel and some of the transceiver components in more detail for channel A. Two amplification stages are utilized to provide a sufficient Gain-Bandwidth product to increase the 0.1 V monitor signal to 0.5 V peak-to-peak before it is delivered to the transceiver  330 . At relatively high data rates for electrical signals, such as 155.52 Mbps for STM-1 transmission, the bandwidth of the amplification portion must also be relatively large so as to include the highest frequency for that data rate. The current feedback operational amplifier, such as the Burr-Brown OPA658, is configured to produce a significant portion of the overall gain. 
   A voltage divider network is included with the current feedback amplifier  322  to provide a source for the voltage limiting amplifier  326 . The output of the voltage divider has a gain of about 8 dB over the monitor signal. The Burr-Brown OPA658 has a sufficient gain bandwidth product to provide the 8 dB of gain through the voltage divider while maintaining a frequency response suitable for a 155.52 MHz signal, as might be received for a 155.52 Mbps data rate. 
   The voltage limiting amplifier  326 , such as the Burr-Brown OPA689, also produces a significant portion of the overall gain. A voltage divider circuit is included with the voltage limiting amplifier  326  to provide a source for the transceiver  330 . The output of the voltage divider has a gain of about 8 dB over the signal received from the current limiting amplifier  322 . The Burr-Brown OPA689 has a sufficient gain bandwidth product to provide the 8 dB of gain through the voltage divider while maintaining a frequency response suitable for a 155.52 MHz signal. 
   The voltage limiting amplifier  326  has the additional task of limiting the voltage received by the transceiver  330 . The transceiver  330  has an input sensitivity range, and the voltage limiting amplifier  326  provides an output through the voltage divider that is guaranteed to be within a designated range, even if the monitor signal has an amplitude greater than anticipated. For the AMCC model S3031B STM-1 transceiver, which is a fully integrated CMI encoding transmitter and CMI decoding receiver, the input sensitivity is from 110 milli-volts (mV) to 1.3 V. Thus, it is desirable to constrain the output of the voltage divider of the voltage limiting operational amplifier  326  to fit within this range, and a 0.5 V peak-to-peak voltage is suitable. This limit is set-up using a voltage divider discussed in more detail below. 
   The transceiver  330  has an analog data input leading to a data/clock recovery circuit  336 . The transceiver also has a loss of signal input feeding a LOS circuit  334 . The LOS circuit  334  receives the input signal from the voltage limiting amplifier stage  326  after it has passed through an additional voltage divider network that reduces the signal to about 0.170 volts to set the floor for adequate signal strength. If the signal at the analog data input drops below the 0.170 V reference, the LOS out line passing to the PLD  358  is activated. 
     FIG. 14  shows the input circuit in more detail. A decoupling capacitor  382  and power supply filtering capacitors  382 ′ are included as is a ferrite bead  380  to reduce electromagnetic emissions from the power supply. The current feedback operational amplifier is configured with a 402 ohm feedback resistor  384  and a 178 ohm resistor  318  tied to ground and the inverting input to produce a gain of 3.26=(1+402/178). The voltage divider  386  of the current feedback stage includes a 22.1 ohm resistor  388  and a 75 ohm resistor  390  that cut the gain to 2.52=[3.26*75/(22.1+75)]. 
   The voltage limiting operational amplifier  326  also has power supply filtering capacitors  396  and a ferrite bead  398 . The voltage limiting amplifier  326  is configured with a feedback resistor  392  of 604 ohms and a 150 ohm resistor  394  tied to ground and the inverting input to produce a gain of 5.03=(1+604/150). The voltage divider  408  of the limiting amplifier stage includes a 22.1 ohm resistor  410  and another 22.1 ohm resistor  412  to cut the gain to 2.52=[5.03*22.1/(22.1+22.1)]. The signal passes through another decoupling capacitor  396 ′ prior to entering the analog data input of the transceiver  330 . 
   The low voltage limiting function of the voltage limiting operational amplifier  326  is configured by an 18.22 kilo-ohm resistor  400  tied to the −5 V power supply and a 1 kilo-ohm resistor  402  tied to ground. A low voltage reference input of the operational amplifier  326  is tied between the resistor  400  and resistor  402  to set the low voltage limit to −0.26 V=[−5V*1000/(1000+18,220)]. 
   The high voltage limiting function of the voltage limiting operational amplifier  326  is configured by an 18.22 kilo-ohm resistor  404  tied to the +5 V power supply and a 1 kilo-ohm resistor  406  tied to ground. A high voltage reference input of the operational amplifier  326  is tied between the resistor  404  and resistor  406  to set the high voltage limit to +0.26 V=[+5V*1000/(1000+18,220)]. 
     FIG. 15  shows a block diagram of the power supply  368  of the bridging repeater circuit. −48V is received from a pin of the backplane connector  364  and it delivered through a 0.5 amp fuse  370  to a DC/DC converter  372 , such as model LW005A. This DC/DC converter converts the −48 V to +5 V and supplies the +5 volt to the appropriate circuitry including the amplifiers  322 ,  326  and transceiver  330 . This DC/DC converter  372  also provides +5 V to a second DC/DC converter  374 , such as model HPR1000. This DC/DC converter converts the +5 V to −5 V and supplies the −5 V to the appropriate circuitry. 
   The +5 V supply is also connected to a reset control device  376 , such as model DS1810. The reset control  376  sends a reset signal to the transceiver  330  during power-up and during low voltage conditions. If the +5 V dips below a threshold, such as 4.75 V, then the reset control  376  holds the reset line low until the voltage rises above the threshold and for an additional 150 milliseconds thereafter to reset both the transmitter and receiver portions of transceiver  330 . 
   The +5V and −5 V supplies are also connected to the under-voltage detector  356  that connects to the PLD  358 . The under-voltage detector, such as model ICL7665S, triggers an output signal when the received voltage dips below 4.45 V to indicate to the PLD  358  that the voltage is beyond the acceptable range. 
     FIG. 16  shows a top layer  414  of the printed circuit board, such as printed circuit board  279  of  FIG. 9C , for supporting the bridging repeater circuitry  312 . The printed circuit board  279  has signal traces that lead from the input jack area  416  to the output jack area  436  of channel A. A signal trace  418  carries the signal from the input jack area  436  to the isolation transformer area  420 . A signal trace  422  carries the signal from the isolation transformer area  420  to the first amplifier area  424 . A signal trace  426  carries the signal from the first amplifier area  424  to the second amplifier area  428 . A signal trace  430  carries the signal from the second amplifier area  428  to the transceiver area  431  to complete the input circuit. 
   As shown, the signal trace  422  between the transformer area  420  and first amplifier area  424  and signal trace  426  between the first amplifier area  424  and the second amplifier area  428  are individually linear. Furthermore, both of these traces  422 , and  428  are linear with respect to one another. 
   A signal trace  432  carries the signal from the transceiver area  431  to the second isolation transformer area  433 . A signal trace  434  carries the signal from the second isolation transformer area  433  to the output jack area  436  to complete the output circuit. 
   As can be seen the signal traces from input area  416  to output area  436  all lie within the top layer and are therefore disposed within a single spatial plane. Furthermore, the signal traces leading from the input area  416  to output area  436  have a constant width. No test vias or other trace deformations are present to disrupt the constant signal trace width. Placing the signals within the single spatial plane and maintaining the trace width from input to output improves the noise rejection of the bridging repeater circuit. 
   For maximizing signal integrity, the length of each continuous piece of signal trace should be maintained at 0.25 inches or below, especially for high data rates such as STM-1. Furthermore, potential interference sources such as the crystal oscillator  354  located in oscillator area  417  should be positioned closely to the transceiver portion  431  to minimize the length of the oscillator trace  419 . For maximizing signal integrity, the length of the oscillator trace  419  should be maintained at 0.8 inches or less. 
     FIG. 17  shows another layer of the printed circuit board supporting the bridging repeater circuit. This ground layer  437  includes a continuous copper sheet  440  and shielding pin connections from the pin connector layout  438 . The continuous copper sheet  440  is tied to the shielding pins which may be tied to chassis ground, such as through the connector  166  that is tied to the ground wire  196  through the ground conductor  164 ′ in chassis  100 . 
   The pins that are for shielding purposes, including pins shown with connections to the ground plane  440  such as pin  453 , surround the pins that carry −48 V power and the −48 V return including pins  441 ,  442 ,  443 ,  444 ,  445 ,  446 ,  447 , and  448  as well as pins carrying alarm relays such as pins  449 ,  450 ,  451 , and  452 . These shielding pins such as pin  453  in conjunction with the continuous copper sheet  440  establish a ground plane that may permeate any gaps between the opening  258  and connector  260  in the back surface  256  of module  234 . As shown, 12 out of 55 pins carry power or alarm relays leaving 78% of the pins as shields. 
     FIG. 18  shows a cross-section of the printed circuit board  460 . The printed circuit board  460  has several layers including conduction layers and dielectric layers. A solder mask  462  is applied to the top-most layer  464 , and another solder mask  488  is applied to the bottom-most layer  486 . A first conductive layer is made of two individual layers, a first layer  466  of copper and a plating layer  464  made of tin. 
   Beneath the first layer of copper  466  lies a resin dielectric layer  468 . Then a second conductive layer  470  of copper is included. Beneath the conductive layer  470  lies a dielectric layer  472 . Beneath the dielectric layer  472  lies a third conductive layer  474 . Beneath the conductive layer  474  lies a dielectric layer  476 . Beneath the dielectric layer  476  lies a fourth conductive layer  478 . Beneath the fourth conductive layer  478  lies a dielectric layer  480 . Beneath the dielectric layer  480  lies a fifth conductive layer  482 . Beneath the conductive layer  482  lies a dielectric layer  484 . The sixth and bottom-most conductive layer lies beneath the dielectric layer  484  and includes two individual layers, a copper layer  486  and a plating layer  488  that includes the solder mask. 
   The dielectric layer  476  has the greatest thickness, such as 28 mils followed by the two outer-most dielectric layers  468  and  484  having a thickness such as 8 mils. The intermediate dielectric layers  472  and  480  have the least thickness, such as 5 mils. The dielectric constant for these layers is about 4.3. The outer-most copper layers  466  and  486  contain about 0.5 oz of copper. The other copper layers  470 ,  474 ,  478 , and  482  contain about 1 oz of copper. 
   The conductive and dielectric layers are arranged such that the signals are on the outer conductive layer  464  to eliminate vias that add capacitance. The power and chassis ground are layers  474  and  478 , respectively, and are separated by the thickest dielectric  476  to limit the chassis noise that is introduced into the power lines. Conductive layer  470  is copper ground plane establishing a logic ground. Conductive layer  482  is another logic ground layer, and layer  486  carries power supply bypass lines including lines to resistors, capacitors, etc. 
   While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.