United States Patent
`
`1191
`
`[11] Patent Number:
`
`5,754,644
`
`Akhteruzzaman
`
`[45] Date of Patent:
`
`May 19, 1998
`
`USOOS754644A
`
`[54] METHOD FOR CUSTOMIZING OPERATION
`OF A BATTERY FEED CIRCUIT [N A
`TELECOMMUNICATIONS NETWORK
`
`[75]
`
`Inventor: Akhteruzzaman. Naperville. Ill.
`
`[73] Assignee: Lucent Technologies Inc" Murray Hill.
`NJ.
`
`[21] Appl. No.: 672,189
`
`[22] Filed:
`
`Jun. 27, 1996
`
`Int. Cl.6
`[51]
`........................... H04M 19/00
`
`[52] US. Cl. ..................
`. 379/413; 379/399; 379/324
`[58] Field of Search ..................................... 379/413. 399.
`379/377, 379. 382. 324, 340, 383. 387
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,490,530 12/1984 Nagashima .............................. 379/379
`4,511,763
`4/1985 Skidaneuko et a1.
`..
`379/413
`4,652,701
`3/1987 Cuhbison, Jr.
`.. 379/373
`..
`5,596,637
`1/1997 Pasetxi et a1.
`379/399
`5,636,273
`6/1997 Schopfer et a1.
`.. 379/377
`
`
`
`..
`
`5,640,451
`
`6/ 1997 Schopfer ................................. 3791413
`
`Primary Examiner—Krista Zele
`Assistant Examiner—Jacques M. Saint-8min
`Attorney, Agent, or Firm—Mony R. Ghose
`
`[57]
`
`ABSTRACT
`
`A method for controlling power losses associated with the
`operation of line interface circuits in telecommunications
`networks comprises detecting a loop current of at least one
`subscriber loop interconnected to at least one line interface
`circuit. The detected loop current is used to access a thresh-
`old voltage value from a line interface circuit database. A
`threshold voltage based on the threshold voltage value
`retrieved from the database is compared to a feedback
`voltage to control a duty cycle of a switching converter
`circuit in the line interface circuit. Controlling the duty cycle
`of the switching converter circuit enables control of battery
`voltages based on the comparison of the threshold voltage
`and the feedback voltage. In the preferred embodiment. the
`battery voltage is controlled to be a minimum voltage
`needed to provide a predetermined magnitude of the mini-
`mum loop current.
`
`7 Claims, 3 Drawing Sheets
`
`
`
`ADMINISTRATIVE
`MODULE
`
`
`
`
`
`COMMUNICATIONS
`MODULE
`
`
`
`
`LINE INTERFACE UNIT
`
`(lSLU/AIU)
`
`AVAYA INC. AV-1005
`
`AVAYA INC. AV-1005
`
`

`

`US. Patent
`
`May 19, 1998
`
`Sheet 1 of 3
`
`5,754,644
`
`I02
`
`ADMINISTRATIVE
`
`MODULE
`
`104
`
`COMMUNICATIONS
`
`MODULE
`
`
`
`
`
`CONTROLLER
`
`SWITCH MODULE
`
`LINE INTERFACE UNIT
`(lSLU/AIU)
`
`
`
`
`1
`
`

`

`US. Patent
`
`S
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`2
`
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`US. Patent
`
`May 19, 1993
`
`Sheet 3 of 3
`
`5,754,644
`
`FIG. 3
`
`300
`
`
`
`RECEIVE LOOP
`CURRENT (Imp)
`
`
`
`302
`
`
`
`ACCESS DATA BASE T0
`
`
`VOLTAGE VALUE
`
`
`
`RETRIEVE THRESHOLD
`
`
`
`305
`
`USE DEFAULT VTH VALUE
`
`
`WAS
`THRESHOLD
`
`VOLTAGE VALUE
`
`
`FOUND?
`
`308
`
`
` APPLY THRESHOLD
`VOLTAGE TO
`‘
`
`COMPARATOR CIRCUIT
`
`
`
`
`ADJUST SWITCHING
`
`
`
`
`CONVERTER CIRCUIT
`TO PROVIDE OPTIMUM
`VBAT To BATTERY
`FEED CIRCUIT
`
`
`
`
`

`

`5.754.644
`
`1
`METHOD FOR CUSTOMIZING OPERATION
`OF A BATTERY FEED CIRCUIT IN A
`TELECOMMUNICATIONS NETWORK
`
`CROSS—REFERENCE TO RELATED
`APPLICATION
`
`This application is related to the applications of Akhter—
`uzzaman entitled “Method For Controlling Power Losses
`Associated With Line Interface Circuits In Telecommunica-
`
`tions Networks” and “Method For Customizing Operation
`Of A Line Interface Circuit In A Telecommunications
`Network”. which applications are assigned to the assignee of
`the present application. and are being filed concurrently
`herewith.
`
`TECHNICAL FIELD
`
`This invention relates to line interface circuits and. more
`particularly. to supplying power to battery feed circuits in
`such line interface circuits deployed in telecommunications
`networks.
`
`BACKGROUND OF THE INVENTION
`
`Line interface circuits (LIC) interconnect customer pre-
`mises equipment to central otfice switches by subscriber
`lines (commonly referred to as “subscriber loops”). For
`administrative purposes. a plurality of LICs are grouped in
`an integrated line services unit (ISLU). A LIC includes
`means for delivering current to a subscriber loop. and an
`external power source. In modern LICs.
`the means for
`delivering current to the subscriber loop is a battery feed
`circuit comprising a complex set of integrated circuits.
`Voltage generated by the external power source. is processed
`by a LIC switching converter circuit before delivery to the
`battery feed circuit. The power delivered to the subscriber
`loop by the battery feed circuit enables a serving central
`switch to detect
`the presence. and status. of customer
`premises equipment served by the loop. The battery feed
`circuit also couples audio signals transmitted by the central
`office switch to the customer premises equipment. and vice
`versa. Power supplied to the switching converter circuit is
`processed by a transformer which produces a predetermined
`battery voltage (Vm“). The predetermined voltage is estab—
`lished to provide adequate current to interconnect customer
`premises equipment
`to a central office switch when
`appropriate. and to provide high quality voice transmission
`to the subscriber loop.
`It is well known that normal LIC operation results in the
`dissipation of power due to losses associated with internal
`LIC components. Particularly. a substantial amount of power
`is lost at the battery feed circuit. Although losses associated
`with individual LICs might be tolerable. the accumulation of
`LIC losses (due to the large number of LICs deployed in a
`single ISLU) significantly impacts the overall efficiency of
`a central office switch. For this reason. controlling LIC
`power losses is of critical importance to telecommunications
`service providers. Although cooling devices are frequently
`employed to control power losses. these devices are expen-
`sive to operate. and require a non-trivial amount of space.
`Therefore. there is a need in the art for controlling power
`losses associated with the operation of LICs in telecommu-
`nications networks.
`
`SUMMARY OF THE INVENTION
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`voltage supplied to a battery feed circuit in a LIC according
`to subscriber loop length.
`The electrical resistance of a subscriber loop is directly
`proportional to the geographical distance of its associated
`customer premises equipment from a serving central office
`switch. Customer premises equipment located relatively
`near the serving central office switch has a shorter subscriber
`loop (and hence. lower resistance) than customer premises
`equipment located a great distance (higher resistance) from
`the switch. Due to a smaller total resistance. short subscriber
`
`loops do not require as much voltage to generate the needed
`amount of current as do longer subscriber loops to intercon-
`nect customer premises equipment to the serving central
`oflice switch.
`
`In accordance with the preferred embodiment of the
`present invention. each LIC detects a loop current (Loop) of
`its associated subscriber loop. and uses the detected loop
`current to determine a threshold voltage (V,,). The threshold
`voltage affects the value of the customized battery feed
`voltage (me) supplied to the battery feed circuit of the LIC.
`More particularly. the loop current is detected by a current
`detector in the battery feed circuit. and is detected by a
`digital signal processor (DSP). The DSP uses the loop
`current as an index to access a threshold voltage database.
`The threshold voltage afl’ects a duty cycle of the LIC
`switching converter circuit to produce an optimum battery
`feed voltage to be supplied to the battery feed circuit. The
`optimum battery feed voltage is just sufficient to produce the
`correct amount of current necessary to interconnect the
`customer premises equipment to the central office switch.
`and provide telecommunications service. By providing the
`optimum battery feed voltage. the dissipation of power is
`minimized for short subscriber loops. and the overall effi-
`ciency of the serving central oflice switch is enhanced.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a central office switch in
`which the present invention may be practiced;
`FIG. 2 is a block diagram of a LIC in accordance with a
`preferred embodiment of the present invention; and
`FIG. 3 is a flow diagram of the steps performed in a LIC
`in accordance with the preferred embodiment of the method
`of the present invention.
`
`DETAILED DESCRIPTION
`
`FIG. 1 shows a simplified block diagram of a central ofice
`telecommunications switch 100 (hereinafter. switch 100). In
`the preferred embodiment. switch 100 is the SESS®
`manufactured. and sold. by Lucent Technologies. Although
`a central office switch is shown. any system in which power
`is supplied to subscriber loops may be utilized.
`Switch 100 includes three major components: adminis—
`trative module 102 for providing system-wide
`administration. maintenance. and resource allocation; com—
`munications module 104 for serving as a distribution hub in
`switching voice. control information. and synchronization
`signals; and a plurality of switching modules (SM) 108. 110
`and 112 for performing local switching and control func—
`tions. Communication among the elements of central office
`switch 100 is accomplished over network control and timing
`(NCT) links 113. As required by convention. dual NCI‘ links
`are shown for the interconnection of each SM to commu-
`nications module 104.
`
`This need is addressed and technological advance is
`achieved in the art by substantially controlling the battery
`
`SMs 108. 110 and 112 include controllers for coordinating
`switching functions. memory for retaining specific sub-
`
`

`

`5,754,644
`
`3
`scriber line data. and network elements for routing calls to.
`and from. individual subscriber lines. In the embodiment
`
`shown. switch module 108 comprises controller 120. data
`memory 122. and network element 124. Similarly. switch
`module 110 includes controller 130. data memory 132. and
`network element 134. Switch module 112 comprises con-
`troller 140. data memory 142. and network element 144.
`Each SM is equipped with an ISLU. also known as an
`access interface unit (AIU). for interconnecting each sub—
`scriber loop to the network element of the SM. Although an
`operational central ofice switch includes many ISLUs. a
`single ISLU is shown for clarity. Particularly. ISLU 138.
`comprised of a plurality of LICs.
`is interconnected to
`network element 134 of switch module 110 via link 135.
`Each subscriber loop served by switch 100 is interconnected
`to a network element via a particular LIC and ISLU. In this
`example. telephone 170 is interconnected to 11C 171 Via
`subscriber line 173. and telephone 180 is interconnected to
`LIC 182 via subscriber line 183.
`
`FIG. 2 is a detailed diagram of a preferred embodiment of
`a LIC in which the present invention may be practiced. In
`this embodiment. LIC 200 interconnects telephone 202 to a
`switch module of a central office switch. such as switch 100.
`The interconnection of subscriber line 203 to the central
`oflice switch enables the detection. and transmission of
`audio signals from telephone 202 to the central office switch.
`In this example. telephone 202 is interconnected to LIC 200
`via subscriber loop 203 comprising “tip” line 203A. and
`“ring” line 203B. Both tip and ring lines have first ends
`terminating at telephone 202. and second ends connected to
`battery feed circuit 206.
`DSP 213 translates audio signals received from telephone
`202 via battery feed circuit 206 and link 207 into digital
`format before delivering these signals to main controller 210
`over link 209. Conversely. digital signals received from the
`switch module via link 219 are converted to analog format
`prior to delivery to battery feed circuit 206 over link 217.
`Signals between main controller 210 and the switching
`module of the serving central office switch are exchanged
`over signaling link 236.
`DSP 213 is powered by 5 volt power supply 214. and
`produces threshold voltage V,,,. More particularly. DSP 213
`receives the loop current (lbw) associated with subscriber
`loop 203 from battery feed circuit 206 over link 229. Loop
`current (1,00?) is equivalent to the current in tip line 203A.
`or ring line 203B. In the preferred embodiment. the loop
`current is detected by current detector 205 of battery feed
`circuit 206. As is well-known in the art. Imp is proportional
`to the electrical resistance of the subscriber loop. DSP 213
`also includes voltage database 227 for storing a table of
`threshold voltages (Va.) correlated by loop current values. In
`alternative embodiments. database 227 stores an algorithm
`for determining threshold voltage using loop current.
`Switching converter unit 210 receives power (—48 volts)
`from external power source 228 to supply voltage to battery
`feed circuit 206 via links 220 and 221. In the preferred
`embodiment. the switching converter circuit includes: trans—
`former circuit 224; filter 222; switching transistor Q1;
`application-specific integrated circuit (ASIC) controller 230;
`frequency selection circuit 231 and feedback/comparator
`circuit 234. In this embodiment. transformer circuit 224 is
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`designed to provide voltages ranging from —39.5 volts to
`-60 volts. Diode D1 rectifies the output of transformer
`circuit 224. as is known in the art. Filter 222. comprised of
`conductor L1 and capacitor C1. serves to smooth the output
`voltage of transformer circuit 224. and meet ripple require-
`
`65
`
`4
`
`ments. ASIC controller 230 produces output voltage Vop for
`operating switching transistor Q1. as described below.
`Feedback/comparator circuit 234 includes amplifier A1.
`capacitor C3. C4 and resistors R3. R4. R5 and R6.
`In accordance with the preferred embodiment of the
`present invention. the loop current of subscriber loop 203 is
`detected by current detector 205 of battery feed circuit 206.
`The detected loop current
`is received in digital signal
`processor 213 via link 229. and is used as an index to access
`a threshold voltage value from database 227. Upon deter-
`mination of the threshold voltage (V,,,) value. digital signal
`processor 213 uses internal processing to deliver an analog
`output V,,, to an input of amplifier A1 in comparator circuit
`234 via signaling link 223.
`Comparator circuit 234 compares threshold voltage V", at
`the first input of amplifier A1 to feedback voltage Vfze at a
`second input of amplifier A1. Feedback voltage Vf“ is the
`voltage is detected at lead 220 and is delivered to comparator
`circuit 234 via link 235. Resistors R3. R4. R6 and capacitor
`C4 act as a voltage divider to attenuate VM. As known in the
`art. comparator circuit 234 seeks to equalize threshold
`voltage V”. with feedback voltage Vf“. The output of
`amplifier Al
`is voltage V0 which is extended to ASIC
`controller 230 over link 237. ASIC controller 230 uses
`
`voltage V0 to produce operating voltage Vop. The frequency
`of operating voltage Vop is controlled by frequency selection
`circuit 231. which is composed of resistor R2 and capacitor
`C2. Operan'ng voltage Vop controls the switching frequency
`of transistor Q1. and therefore determines the value of
`battery feed voltage Vb“. In accordance with the preferred
`embodiment. Vm is chosen to alter the duty cycle of switch—
`ing converter circuit 218. Selectively altering the duty cycle
`of the switching converter circuit enables the control of
`battery feed voltages. In another preferred embodiment. the
`loop voltage of subscriber loop 203 is the threshold voltage
`which is applied to the first input of amplifier A1 of com—
`parator circuit 234. In other words. no database look~up is
`required.
`FIG. 3 illustrates steps performed in accordance with a
`preferred embodiment of the method of the present inven-
`tion. For purposes of example. assume the steps described
`below are implemented by LIC 200 for serving telephone
`202. The process begins in step 300 in which digital signal
`processor 213 receives a loop current value from battery
`feed circuit 206 over link 229.
`
`The process continues to step 302 in which digital signal
`processor 213 uses the received loop current value as an
`index to access a database to retrieve a threshold voltage
`associated with a received loop current. In this embodiment.
`digital signal processor 213 uses 1,00,, to access a table in
`previously initialized database 227 for determining thresh-
`old voltage V,,,. In alternative embodiments. an algorithm
`may be used to determine threshold voltage V“ll from the
`detected loop current. The threshold voltage V”, specified in
`database 227 is chosen to alter the duty cycle of switching
`converter circuit in order to obtain a battery feed voltage
`customized to subscriber loop length. In other words. a
`minimum battery feed voltage is provided so that it results
`in a just sufficient amount of current provided to the sub-
`scriber loop. In the preferred embodiment. the battery feed
`voltage ranges from —39.5 volts to —60 volts. The range of
`current provided to subscriber loops is 10 milliamps to 40
`milliamps. In decision step 304. the digital signal processor
`determines whether a threshold voltage V,,, was found in the
`database. In a rare circumstance. the loop current detected
`by the digital signal processor may not have a corresponding
`threshold voltage. If the outcome of decision step 304 is a
`
`

`

`5 ,754,644
`
`5
`
`“NO” determination. the process continues to step 305 in
`which the digital signal processor applies a default threshold
`voltage to comparator circuit 234. In this embodiment. the
`default
`threshold voltage results in switching converter
`circuit 218 providing a Vb,” of approximately —55 volts to
`battery feed circuit 206. The default battery feed voltage is
`enough to provide sufficient current to interconnect cus—
`tomer premises equipment of most subscriber loops to the
`serving central office switch. If the outcome of decision step
`304 is a “YES” determination. the process continues to step
`306 in which the digital signal processor applies a voltage
`which equals the retrieved threshold voltage V", to a com-
`parator circuit In this embodiment. digital signal processor
`213 applies threshold voltage V”, to comparator circuit 234
`over signaling link 223. In step 308. comparator circuit 234
`uses threshold voltage Va; to produce output voltage V0.
`Output voltage Vo determines the duty cycle of switching
`converter circuit 218. and has a direct impact on battery feed
`voltage Vb“. as described above.
`The battery feed voltage of each LIC is tailored for
`providing the minimum amount of voltage needed to send a
`predetermined magnitude of loop current to the subscriber
`loop. Advantageously. short subscriber loops are not pro—
`vided with the same amount of current as longer subscriber
`loops. and thereby. resulting in power savings for the central
`oflice switch. While the invention has been particularly
`illustrated and described with reference to the preferred
`embodiment. alternative embodiments may be devised by
`those skilled in the art without departing from the scope of
`the invention.
`I claim:
`
`1. A method for enhancing the efficiency of power usage
`of individual line interface circuits (LIC) connected to a
`plurality of subscriber loops comprises the steps of:
`detecting a loop current of at least one subscriber loop;
`using the loop current
`to access a threshold voltage
`database including a plurality of threshold voltage
`values. each threshold voltage value customized for a
`particular subscriber loop length;
`comparing a threshold voltage to a feedback voltage; and
`controlling a battery voltage based on the comparison of
`the threshold voltage and the feedback voltage to cause
`the battery voltage to be a minimum needed for a
`particular subscriber loop.
`2. The method of claim 1 wherein detecting a loop current
`of a subscriber loop comprises the step of:
`
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`6
`using a current detector to continuously monitor loop
`current.
`
`3. The method of claim 1 further comprising the step of:
`generating a threshold voltage based on the threshold
`voltage value obtained from the database.
`4. The method of claim 1 further comprising the step of:
`using an algorithm to derive a threshold voltage value
`from the loop current; and
`generating a threshold voltage based on the derivation.
`5. The method of claim 1 wherein the step of controlling
`a battery voltage based on the comparison of the threshold
`voltage and the feedback voltage comprises the step of:
`altering a duty cycle of a switching converter circuit to
`cause the battery voltage to be a minimum voltage
`needed to provide a predetermined magnitude of a
`minimum loop current.
`6. A telecommunications line interface circuit (LIC) oom-
`prises;
`a battery feed circuit for transmitting messages between
`customer premises equipment (CPE). and a main con-
`troller;
`
`a switching converter circuit coupled between a DC
`power source and the battery feed circuit. the switching
`converter circuit having an output voltage coupled to
`the battery feed circuit; and
`a voltage database for storing a table of threshold voltages
`correlated by loop currents for controlling the output of
`voltage of the switching converter circuit so as to
`minimize power losses.
`7. A method for decreasing power losses associated with
`individual line interface circuits (LIC) interconnected to a
`plurality of subscriber loops comprises the steps of:
`detecting a loop current of at least one subscriber loop;
`using the loop current to generate a threshold voltage
`based on a value obtained from a threshold voltage
`database including threshold voltage values customized
`by subscriber loop length; and
`applying the threshold voltage to a comparator circuit for
`controlling a battery voltage based on the comparison
`of the threshold voltage and a feedback voltage to cause
`the battery voltage to be a minimum voltage needed to
`provide a predetermined magnitude of the minimum
`loop current.
`
`