Telecommunications chassis, module, and bridging repeater circuitry

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.

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 such as heat, flames, loose material, and interference that may be emanating from other circuits also housed by the chassis. Because circuits fail, the module must maintain its ability to be removed from the chassis and replaced while continuing to protect the circuitry is houses during normal operation. As with a 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'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.

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 1Billustrate an embodiment of the chassis of the present invention. The chassis100has a top cover102, a bottom cover104, and a rear cover137forming an outer housing105. Front trim piece120and rear trim piece122fit around the rear edges of the top cover102and bottom cover104, respectively. Front extensions114,116extend forward from the front trim piece120.

A door108is connected to the front extensions114,116through hinges112. The door108has a finger110that catches on the left front extension114to hold the door108closed. A rotatable handle106is connected to the chassis100through mount107. One or more covers118are mounted on the chassis100to isolate the interior of the chassis100when corresponding modules are not present.

The rear cover137has several rows of holes138for exhausting heat produced by the modules housed within the chassis100. The rear cover137also has a power socket130with electrical connections132for receiving AC power, such as 110V and/or 220V, from an external source. Typically, power socket130is internally fused and is switchable to receive either either voltage. Rails124,128are mounted to the rear trim piece122and have feet126attached to them. The bottom cover104has a several rows of holes136for passing ambient air into the interior of the chassis100. The bottom cover104also has several feet134.

FIGS. 2A and 2Bshow sidewalls140,148of the chassis100. The sidewalls140,148are held in position by attachment to the front and rear trim pieces120,122. Several holes150are located at the top and the bottom of the left sidewall148. Similarly, several holes142are located at the top and bottom of the right sidewall140.

Ridges152are provided in the left sidewall148, and ridges144are provided in the right sidewall140. An inwardly recessed region154in the left sidewall148and inwardly recessed region146in the right sidewall140is created between the sets of ridges152and144. The inwardly recessed portions154,146are exposed between the top cover102and the bottom cover104, and the ridges152,144facilitate attachment of the top cover102and bottom cover104to the sidewalls140,148as discussed below. Handle mount holes156are provided in the recessed portions154,146to allow attachment of the handle mount107.

FIGS. 3A and 3Billustrate the assembly of the interior structures of the chassis100. A top horizontal surface162and a bottom horizontal surface160mount to a faceplate158and a vertical backplane164. Both the top and bottom horizontal surfaces162,160have several rows of ventilation holes168that allow air to pass up from the bottom of the chassis100through the installed modules and into the top of the chassis100where it is channeled between the top cover102and the top horizontal surface162and exhausted out the rear of the chassis100through holes138.

As can be seen the top and bottom horizontal surfaces162,160have curled edges172,173,174, and175that abut the faceplate158and the vertical backplane164. Each of these surfaces except the vertical backplane164is made of metal, such as cold rolled steel with a zinc chromate plating, such that metal-to-metal contact is established between them. The backplane164is typically printed circuit board material. Likewise, the sidewalls140,148are also made of metal, such as aluminum, and establish electrical continuity with the top and bottom horizontal surface162,160through metal brackets discussed below. A Faraday box, or shielding chamber, results which provides shielding for the modules housed by the chassis100. The grounding of the shielding chamber is discussed below. Similarly, an outer Faraday box results from the metal top and bottom covers102,104and the metal rear cover137whose grounding is also discussed below.

The vertical backplane has connectors166that allow the modules to be inserted into the chassis100and slidably engage connectors166to establish electrical connection. The vertical backplane connectors166typically provide DC power to the modules from a chassis power supply discussed below. The top and bottom horizontal surfaces162,160have slots170that receives fins on the module to guide it as it is inserted and to prevent lateral movement once it is installed. As best seen inFIG. 3B, the faceplate158has notches176that align with the slots170.

FIG. 4Ashows the chassis100with the top cover102and the bottom cover104of the outer housing105removed. As shown the shielding chamber101is fully installed in the chassis100. The shielding chamber101is held in place by brackets178,180that mount to both the top horizontal surface162and the sidewalls140,148. As can be seen an airspace103is created by the placement of the shielding chamber101. The airspace103of this embodiment includes the area between the top horizontal surface162and the top cover102, the area between the rear cover137and the vertical backplane164, and the area between the bottom horizontal surface160and the bottom cover104.

The airspace103allows air to enter through the bottom cover104, rise through the shielding chamber103, return to the rear of the chassis100, and exit out the rear cover137. Air may also enter through the bottom cover104and rise directly between the vertical backplane164and the rear cover137and then exit from the chassis100. As shown inFIG. 4B, the chassis power supply186is mounted to the rear cover137, and the air rising up the vertical backplane164may assist in dissipating heat from the power supply186. Because the top cover102has no holes, any flames imposed on the interior of chassis100cannot escape from the top and are, therefore, adequately contained.

Also shown inFIG. 4B, the rear cover has an aperture184that is used to mount the power socket130. The power socket130has rear terminals182for electrical connection to the power supply186. Also, a portion of the holes138of the rear cover137lie directly behind the power supply186and allow it to radiate some heat directly out of the chassis100. Mounting the power supply186directly to the rear cover137also permits easy installation and maintenance of the power supply186because it can be accessed by simply removing the rear cover137and its electrical connections can be easily made while the rear cover137is removed.

FIGS. 5A,5B, and5C show the ground wire connections of the shielding chamber101, vertical backplane164, and outer housing105, and also shows the power connections of the power supply186. The power supply186typically receives AC power from the power socket130through wires208and210connected to jack216of the power supply186. The power supply186then typically outputs DC power through output jack218to the vertical backplane164through wires212and214where it is then distributed to each of the connectors166.

A ground tab220of the power supply186is electrically connected to the ground prong207of the power socket130through wire206. The ground tab220is electrically connected to a ground post190of the rear cover137through wire204. Ground wires are fixed to the ground post190and ground post188of the rear cover137through the fastening assembly192.

A ground conductor164′ of the vertical backplane164that electrically connects the vertical backplane164to shielding pins of connectors166is also electrically connected to the ground post190through wire196. The right sidewall140is connected to the ground post188through wire198. The left sidewall148is connected to the ground post188through wire202. The top cover102is connected to the ground post188through wire200, and the bottom cover104is connected to the ground post190through wire194.

The top cover102and bottom cover104of the outer housing105have conductor tabs102′ that extend from them for receiving connectors201of the ground wires200and194. The top cover102and bottom cover104may have a powder coat finish applied and the conductor tabs102′ remain bare metal to establish electrical continuity with the ground wires200,194.

FIG. 6shows the installation of the rear cover137and left and right rails124,128as well as the connections of the ground wires to the sidewalls140,148. Because the rear cover137is mounted to the rear trim piece122, the airspace103remains between the rear cover piece137and the vertical backplane164. The airspace103accommodates the power supply186.

The ground wire198extending from ground post188fastens to the right sidewall140through one of the holes142in the top of the sidewall140. Likewise, the ground wire202extending from ground post188fastens to the left sidewall148through one of the holes150in the top of the sidewall148. The ground wire196extending from ground post190fastens to a mounting hole197of the vertical backplane164that is also used to attach the vertical backplane164to the bottom horizontal surface160.

FIG. 7Ashows an exploded view of the chassis100. As can be seen, the power supply186is placed within the airspace103, which is maintained by the spacing between the top cover102and top horizontal surface162, between the vertical backplane164and the rear cover137, and between the bottom cover104and the bottom horizontal surface160. A covering109may be placed over the faceplate158for aesthetics. The door108has a handle108′ extending forwardly to facilitate opening and closing.

FIG. 7Bshows a fastener for holding the top cover102onto the sidewall140. The ridges144of the sidewall140have a notched end222that receives a nut holder224and nut226that fits within the nut holder224. As shown inFIG. 7C, a nut holder224and nut226has been positioned by sliding it within the ridges144from the notched end222to an alignment dimple230. A screw passes through a hole in the bottom cover104to hold it in place. As shown, the top cover102and bottom cover104are both attached by four of these fasteners.

FIG. 8Ashows the door108of the chassis100. The door108includes the handle108′ which has the finger110extending from it. The finger110passes through a hole in the door108so that it may engage the front extension114.FIG. 8Bshows a hinge guide232that mounts to the front extensions114,116. The hinge guide232has a hole232′ for receiving a hinge shaft112′ extending from hinge112that mounts the door108but allows it to open and close.

FIGS. 9A,9B,9C, and9D show an embodiment of the module of the present invention. The module234has a shell235that has a frontplate236, a top surface250, a bottom surface262, and a back surface256. The top surface250has several ventilation holes252, and the bottom surface262has ventilation holes264. The ventilation holes allow air to rise from the bottom of the chassis such as chassis100, up through the modules234installed in the chassis100, and into the top of the chassis100prior to being exhausted through the rear cover137. The shell235is typically made of metal, such as aluminum. The edge266of the top surface250is folded, as is the edge268of the bottom surface262. The edge257of the back surface256is also folded.

A metal backplate254that is typically made of aluminum mounts to the edges266,268,257of the shell235. The metal backplate254supports a printed circuit board276. Portions255of the metal backplate254extend beyond the perimeter of the printed circuit board276and provide a surface that can establish metal-to-metal contact with the folds of edges266,268, and257.

Connector jacks274pass signals between the circuitry on the printed circuit board276and external cable connectors (not shown). A metal jack holder270is mounted to the shell235and to a faceplate238. The metal jack holder270provides support for the connector jacks274with holes272that surround the cylindrical sleeve of the connector jacks274. The metal jack holder270also establishes metal-to-metal contact with the shell235and with the faceplate238. The faceplate238also establishes metal-to-metal contact with the backplate254and the front edges of the shell235.

The printed circuit board276is enclosed within the shell235, the backplate254, and the jack holder270which together form a Faraday box providing shielding for the circuitry on the printed circuit board276. A connector260is mounted to the printed circuit board276and is in electrical communication with the circuitry. Typically, the connector260provides DC power from the vertical backplane connector166to the circuitry. The back surface256of the shell235has an opening258that allows the connector260to 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 faceplate238has several holes for sending and receiving signals to and from coaxial cables. For a module234housing a repeater circuit, such as the bridging repeater circuit of the present invention, a monitor out port242, a signal out port244and a signal in port246are provided for each data channel. As shown, the module234houses two data channels. The faceplate may have a decal278attached to it to provide a visual indication of the purpose of each jack, light emitting diode (LED), switch, or other feature provided on the faceplate238.

The faceplate238generally has a fastener240for attachment to the chassis100. The metal backplate254has fins248located on the top and bottom edges. The fins248fit within the notch176of the chassis faceplate158and within the slot170of the top and bottom horizontal surfaces162,160shown in FIG.3B.

FIG. 9Eshows the chassis100with a module234being partially installed. The fins of the module234pass into the slots170of the top and bottom horizontal surfaces162,160and notch176of the chassis faceplate158. The module234slides into the opening in the chassis faceplate158and then continues to slide into the shielding chamber until the module connector260engages the vertical backplane connector166.

FIG. 10is a closer view of the faceplate238of the module234. The faceplate238has the ports for monitor output242, signal output244, and signal input246. In addition, the faceplate may have a loss of signal (LOS) LED282that lights to indicate the signal through signal input port246is not adequately present. An LOS LED280may also be provided to indicate that the signal through signal output port244is not adequately present. Ports and LEDs for both a channel A and a channel B are shown.

FIG. 11shows an exemplary network environment employing bridging repeater circuits of the present invention. A bridging repeater circuit294, which may be channel A or B of a module such as module234, is included as is a second bridging repeater circuit292which may be the other channel of the module. The bridging repeater circuits292,294are being used to bypass a faulty digital signal cross-connect circuit (DSX)290without disrupting the signal path between the healthy DSX288and the electrical to optical (E/O) multiplexer (mux)298. The bridging repeater circuits292,294may be housed in a module234for installation in portable chassis100, 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)284that pass electrical signals to the mux286where they are multiplexed into an output line285. The mux286also receives multiplexed signals from a healthy DSX288through input line287and demultiplexes them for transfer to the several DDFs284. The healthy DSX288has output line304that feeds into the input of the faulty DSX290. The faulty DSX290has an output line306that feeds into the input of the healthy DSX288.

The faulty DSX290passes signals to the E/O mux298through line289and receives signals from the E/O mux298through line291. When the faulty DSX290needs to be temporarily or permanently replaced, a new DSX296is installed with a line295receiving signals from the E/O mux298that are the same as those signals received by the faulty DSX290through line289. The new DSX296is also installed with a line297sending signals to the E/O mux298. As discussed below, this line297duplicates the signal being provided over line291from the faulty DSX290to the E/O mux298.

The bridging repeater circuit294receives at its input the monitor signal output by the new DSX296through line308. The bridging repeater circuit294retransmits the data and clock information of the signal received from the new DSX296to the healthy DSX288through line302that connects to a make-before-break input jack of the healthy DSX288used for temporary connections. Because of this completed circuit through the bridging repeater circuit294, the line306connecting the output of faulty DSX290to the permanent input of healthy DSX288can be disconnected from the faulty DSX290and then redirected to the permanent output of new DSX296without breaking service in the channel.

The bridging repeater circuit292receives at its input the monitor signal output by the healthy DSX288through line300. The bridging repeater circuit292retransmits the data and clock information of the signal received from the healthy DSX288to the new DSX296through line310that connects to a make-before-break input jack of the new DSX296used for temporary connections. Because of this completed circuit through the bridging repeater circuit292, the line304connecting the input of faulty DSX290to the permanent output of healthy DSX288can be disconnected from the faulty DSX290and then redirected to the permanent input of new DSX296without breaking service in the channel. Once the healthy DSX288and the new DSX296have established communication in both channels through permanent connections, bridging repeater circuits292and294can be disconnected from both the healthy DSX288and the new DSX296.

FIG. 12shows a block diagram of the circuitry312of the bridging repeater circuits292(channel A) and294(channel B). The bridging repeater circuit input is typically a 75 ohm SMB connector314,316for 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 transformers318,320for channels A and B, and the transformers have a turns ratio of 1:1. The isolation transformers318,320are electrically connected to the amplification portion of the input section that includes a current feed back operational amplifier322,324for each channel in series with a voltage limiting operational amplifier326,328for each channel.

The voltage limiting operational amplifier326,328of 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 transceiver330,332of each channel. The transceiver330,332recovers 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 transformer338,340that passes the output signal to the output jack350,352, 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 jack350,352but the output signal is typically around 2 V.

The transceiver output is also connected to another isolation transformer334,336that passes the output signal to an additional voltage divider342,344that is connected to a monitor jack346,348, which may also be a 75 ohm SMB connector. The additional voltage divider342,344decreases the output signal received by the monitor jack346,348by about 27 dB.

A reference clock354, which is typically a 19.44 MHz oscillator, feeds a reference clock signal to the transceivers330,332. Rather than using a single oscillator, a separate oscillator for each transceiver330,332may also be employed. A low-voltage detector356may also be included to detect an under-voltage power supply condition. The low-voltage detector356feeds a detection signal to a programmable logic device (PLD) control358.

The PLD358also communicates with the transceivers330,332to determine whether the signals being received or output by the transceiver are of an adequate level. If the PLD358receives a detection signal from detector356indicating an improper supply voltage, the PLD358will trigger a major or minor alarm circuit360which is in communication with the backplane364. If the PLD358receives a transmit or receive signal from the transceiver330,332, it triggers a user LED362for channel A or B corresponding to transmit or receive to provide an indication of the loss of signal.

FIG. 13shows 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 transceiver330. 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 amplifier322to provide a source for the voltage limiting amplifier326. 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 amplifier326, 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 amplifier326to provide a source for the transceiver330. The output of the voltage divider has a gain of about 8 dB over the signal received from the current limiting amplifier322. 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 amplifier326has the additional task of limiting the voltage received by the transceiver330. The transceiver330has an input sensitivity range, and the voltage limiting amplifier326provides 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 amplifier326to 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 transceiver330has an analog data input leading to a data/clock recovery circuit336. The transceiver also has a loss of signal input feeding a LOS circuit334. The LOS circuit334receives the input signal from the voltage limiting amplifier stage326after 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 PLD358is activated.

FIG. 14shows the input circuit in more detail. A decoupling capacitor382and power supply filtering capacitors382′ are included as is a ferrite bead380to reduce electromagnetic emissions from the power supply. The current feedback operational amplifier is configured with a 402 ohm feedback resistor384and a 178 ohm resistor318tied to ground and the inverting input to produce a gain of 3.26=(1+402/178). The voltage divider386of the current feedback stage includes a 22.1 ohm resistor388and a 75 ohm resistor390that cut the gain to 2.52=[3.26*75/(22.1+75)].

The voltage limiting operational amplifier326also has power supply filtering capacitors396and a ferrite bead398. The voltage limiting amplifier326is configured with a feedback resistor392of 604 ohms and a 150 ohm resistor394tied to ground and the inverting input to produce a gain of 5.03=(1+604/150). The voltage divider408of the limiting amplifier stage includes a 22.1 ohm resistor410and another 22.1 ohm resistor412to cut the gain to 2.52=[5.03*22.1/(22.1+22.1)]. The signal passes through another decoupling capacitor396′ prior to entering the analog data input of the transceiver330.

The low voltage limiting function of the voltage limiting operational amplifier326is configured by an 18.22 kilo-ohm resistor400tied to the −5 V power supply and a 1 kilo-ohm resistor402tied to ground. A low voltage reference input of the operational amplifier326is tied between the resistor400and resistor402to set the low voltage limit to −0.26 V=[−5V*1000/(1000+18,220)].

The high voltage limiting function of the voltage limiting operational amplifier326is configured by an 18.22 kilo-ohm resistor404tied to the +5 V power supply and a 1 kilo-ohm resistor406tied to ground. A high voltage reference input of the operational amplifier326is tied between the resistor404and resistor406to set the high voltage limit to +0.26 V=[+5V*1000/(1000+18,220)].

FIG. 15shows a block diagram of the power supply368of the bridging repeater circuit. −48V is received from a pin of the backplane connector364and it delivered through a 0.5 amp fuse370to a DC/DC converter372, 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 amplifiers322,326and transceiver330. This DC/DC converter372also provides +5 V to a second DC/DC converter374, 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 device376, such as model DS1810. The reset control376sends a reset signal to the transceiver330during power-up and during low voltage conditions. If the +5 V dips below a threshold, such as 4.75 V, then the reset control376holds 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 transceiver330.

The +5V and −5 V supplies are also connected to the under-voltage detector356that connects to the PLD358. 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 PLD358that the voltage is beyond the acceptable range.

FIG. 16shows a top layer414of the printed circuit board, such as printed circuit board279ofFIG. 9C, for supporting the bridging repeater circuitry312. The printed circuit board279has signal traces that lead from the input jack area416to the output jack area436of channel A. A signal trace418carries the signal from the input jack area436to the isolation transformer area420. A signal trace422carries the signal from the isolation transformer area420to the first amplifier area424. A signal trace426carries the signal from the first amplifier area424to the second amplifier area428. A signal trace430carries the signal from the second amplifier area428to the transceiver area431to complete the input circuit.

As shown, the signal trace422between the transformer area420and first amplifier area424and signal trace426between the first amplifier area424and the second amplifier area428are individually linear. Furthermore, both of these traces422, and428are linear with respect to one another.

A signal trace432carries the signal from the transceiver area431to the second isolation transformer area433. A signal trace434carries the signal from the second isolation transformer area433to the output jack area436to complete the output circuit.

As can be seen the signal traces from input area416to output area436all lie within the top layer and are therefore disposed within a single spatial plane. Furthermore, the signal traces leading from the input area416to output area436have 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 oscillator354located in oscillator area417should be positioned closely to the transceiver portion431to minimize the length of the oscillator trace419. For maximizing signal integrity, the length of the oscillator trace419should be maintained at 0.8 inches or less.

FIG. 17shows another layer of the printed circuit board supporting the bridging repeater circuit. This ground layer437includes a continuous copper sheet440and shielding pin connections from the pin connector layout438. The continuous copper sheet440is tied to the shielding pins which may be tied to chassis ground, such as through the connector166that is tied to the ground wire196through the ground conductor164′ in chassis100.

The pins that are for shielding purposes, including pins shown with connections to the ground plane440such as pin453, surround the pins that carry −48V power and the −48 V return including pins441,442,443,444,445,446,447, and448as well as pins carrying alarm relays such as pins449,450,451, and452. These shielding pins such as pin453in conjunction with the continuous copper sheet440establish a ground plane that may permeate any gaps between the opening258and connector260in the back surface256of module234. As shown, 12 out of 55 pins carry power or alarm relays leaving 78% of the pins as shields.

FIG. 18shows a cross-section of the printed circuit board460. The printed circuit board460has several layers including conduction layers and dielectric layers. A solder mask462is applied to the top-most layer464, and another solder mask488is applied to the bottom-most layer486. A first conductive layer is made of two individual layers, a first layer466of copper and a plating layer464made of tin.

Beneath the first layer of copper466lies a resin dielectric layer468. Then a second conductive layer470of copper is included. Beneath the conductive layer470lies a dielectric layer472. Beneath the dielectric layer472lies a third conductive layer474. Beneath the conductive layer474lies a dielectric layer476. Beneath the dielectric layer476lies a fourth conductive layer478. Beneath the fourth conductive layer478lies a dielectric layer480. Beneath the dielectric layer480lies a fifth conductive layer482. Beneath the conductive layer482lies a dielectric layer484. The sixth and bottom-most conductive layer lies beneath the dielectric layer484and includes two individual layers, a copper layer486and a plating layer488that includes the solder mask.

The dielectric layer476has the greatest thickness, such as 28 mils followed by the two outer-most dielectric layers468and484having a thickness such as 8 mils. The intermediate dielectric layers472and480have the least thickness, such as 5 mils. The dielectric constant for these layers is about 4.3. The outer-most copper layers466and486contain about 0.5 oz of copper. The other copper layers470,474,478, and482contain about 1 oz of copper.

The conductive and dielectric layers are arranged such that the signals are on the outer conductive layer464to eliminate vias that add capacitance. The power and chassis ground are layers474and478, respectively, and are separated by the thickest dielectric476to limit the chassis noise that is introduced into the power lines. Conductive layer470is copper ground plane establishing a logic ground. Conductive layer482is another logic ground layer, and layer486carries power supply bypass lines including lines to resistors, capacitors, etc.