WO1995021498A1 - Interfaces pour lignes de systeme telephonique ordinaire de centraux prives - Google Patents

Interfaces pour lignes de systeme telephonique ordinaire de centraux prives Download PDF

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Publication number
WO1995021498A1
WO1995021498A1 PCT/US1995/001333 US9501333W WO9521498A1 WO 1995021498 A1 WO1995021498 A1 WO 1995021498A1 US 9501333 W US9501333 W US 9501333W WO 9521498 A1 WO9521498 A1 WO 9521498A1
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WO
WIPO (PCT)
Prior art keywords
analog
coupled
interface
ring
port
Prior art date
Application number
PCT/US1995/001333
Other languages
English (en)
Inventor
Earl R. Ii Goodrich
Thomas R. Bayerl
Original Assignee
Adak Communications Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Adak Communications Corporation filed Critical Adak Communications Corporation
Priority to AU17396/95A priority Critical patent/AU1739695A/en
Publication of WO1995021498A1 publication Critical patent/WO1995021498A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M3/00—Automatic or semi-automatic exchanges
    • H04M3/005—Interface circuits for subscriber lines

Definitions

  • the present invention pertains to private exchanges, and more particularly, to analog interfaces effecting analog POTS device operation from a subscriber premises private exchange connected to a digital network.
  • ISDN integrated services digital network
  • POTS plain old telephone service
  • the analog interface represents a significant consideration in the implementation of a private exchange which meets the cost and function requirements necessary to remove the perceived cost barrier impeding widespread acceptance of digital networks.
  • Analog interfaces effecting analog POTS subscriber station functions in existing exchange equipment use dedicated hardware to effect signalling operation for the analog lines.
  • this hardware is shared by all the lines such that its cost does not represent a significant factor when the cost of the private exchange is calculated on a per line basis.
  • the cost of dedicated hardware makes it virtually impossible to provide a private exchange capable of servicing a very limited number of analog lines in a cost efficient manner. This, accordingly, represents a significant impediment to providing a cost effective private exchange which services all types of existing subscriber premises analog devices from a limited number of lines.
  • the present invention overcomes many of the difficulties of existing analog interfaces by providing a low cost, fully functional, analog interface which operates in combination with a general purpose microprocessor to service the private exchange thereby effecting service to all known POTS subscriber equipment.
  • a private exchange analog line interface includes an input connected to a ringing signal supply having a DC offset.
  • the input is selectively connected to the ring lead of an analog port.
  • a switch is coupled to the input and to the ring lead for selectively connecting the ringing signal to the ring lead.
  • a tip lead is also coupled to the port.
  • a small impedance component is coupled to the tip lead.
  • a sensor is coupled across the impedance, the sensor detecting no DC signal during ringing signal generation when a POTS subscriber terminal device is On-Hook. However, the sensor detects a DC signal across the impedance when the subscriber terminal device is Off-Hook. In this manner, the sensor detects ring trip.
  • the sensor is coupled to a switch to disconnect the input from the ring lead when ring trip is detected.
  • an analog interface for a private exchange includes an analog port and a tip lead connected to the analog port.
  • a ring lead is also connected to the analog port.
  • a forced Off-Hook circuit is coupled to the ring and tip leads, the forced Off-Hook circuit introduces a current through a resistor connected between the tip and ring leads forcing tip and ring current sources to inject current across the tip and ring leads.
  • an analog interface for a plurality of analog lines includes a first analog port and a second analog port for connecting with subscriber devices.
  • a first digital interface converts between analog line signals and digital network signals for the first analog port.
  • a second digital interface converts between analog line signals and digital network signals for the second analog port.
  • a first analog circuit is coupled to the first digital interface by a first internal line.
  • a second analog circuit is coupled to the second digital interface through a second internal line.
  • a conferencing circuit is coupled between the first and second internal lines for effecting local calls and/or conferencing between the first and second analog ports.
  • the present invention provides an analog interface which effectively supplies the signalling requirements for all types of analog subscriber equipment.
  • the system is highly functional and interfaces with the private exchange general purpose microprocessor to effect the interface operation.
  • the analog interface provides ring signal injection, ring trip detection, forced Off-Hook operation and two analog line conferencing.
  • An important element of the present invention is the means by which the cost of providing all the services of a private exchange is minimized, which facilitates the manufacture of a low cost, fully functional digital network private exchange to thereby eliminate the perceived cost and compatibility barriers which are currently an impediment to the widespread adoption of digital network services, such as the ISDN basic rate interface implementation.
  • Fig. 1 is a circuit schematic in block diagram form of an analog interface for a private exchange according to the invention.
  • Fig. 2 is a detailed circuit diagram of the analog interface according to Fig. 1.
  • a POTS line interface 20 for a private exchange is shown in Fig. 1.
  • the POTS line interface includes digital interface circuits 22, 24 and 26 connected to the private exchange controller 28 through a local PCM bus 30.
  • the digital interface circuits each include a CODEC which convert between PCM signals on the PCM bus and analog signals in the POTS interface.
  • the analog side of the digital interfaces 22, 24 and 26 are connected to conference circuit 32.
  • Digital interface 22 is connected to Telephone Analog Interface Circuit (TAIC) 34 through analog line 36.
  • Digital interface 24 is connected to TAIC 38 through analog line 40.
  • Digital interface 26 is connected to DTMF detector 42.
  • TAIC Telephone Analog Interface Circuit
  • DTMF detector 42 detects DTMF signals on the PCM bus 30 after they are converted to analog signals by the CODEC in digital interface 26.
  • TAIC 34 is connected to Subscriber Loop Interface Circuit (SLIC) 46 and DTMF detector 48.
  • TAIC 38 is connected to SLIC 50 and DTMF detector 52.
  • DTMF detectors 42, 48 and 52 are connected to private exchange controller 28 through a local data bus 31.
  • SLIC 46 is connected to an analog subscriber device 54 through interface 56 and port 58.
  • SLIC 50 is connected to analog subscriber device 60 through interface 62 and port 64.
  • TAIC 34, SLIC 46, interface 56 and DTMF detector 48 provide analog line functions for analog POTS devices 54 connected to port 58.
  • TAIC 38, SLIC 50, interface 62 and DTMF detector 52 provide analog line functions for analog subscriber devices 60 connected to port 64.
  • a POTS line interface circuit 20 according to the invention is illustrated in greater detail in Figure 2.
  • the functions needed to support an ordinary phone line are known in the industry as the BORSCHT functions, and the acronym us defined as follows:
  • R Ringing About 70 VRMS AC at 20Hz to ring, plus off-hook detection during ringing, known as ring-trip.
  • S Supervisory Off-hook and line-fault detection through current sensing.
  • the fully functional analog interface must provide all the BORSCHT functions to service all types of analog devices.
  • the analog interface circuit 20 contains circuit 70 shared by both lines.
  • Circuit 70 includes integrated circuit (IC) U312A connected to local PCM bus 30.
  • IC U312A is a frequency divider which divides the 2.048MHz clock signal from the private exchange controller 28 of the private exchange.
  • IC U312A also divides the 256 KHz signal to generate a 128 KHz clock signal for filters in integrated circuits U303 and U304 which are TAICs 34 and 38.
  • Circuit 70 also includes IC U310, a 4x4 crosspoint switch which channels the digitized TXD and RXD signals on the local PCM bus 30 to and from the CODEC ICs U301 and U302 in digital interfaces 22 and 24.
  • the possible connections through crosspoint switch U310 are as follows: Rx/Tx Swap Switch
  • a digital interface for line 1 contains the COder/DECoder, or CODEC U301, which performs the conversion between the analog voice signals processed through analog port 58 and the pulse code modulated (PCM) data stream for the local PCM bus 30.
  • the PCM data stream is a series of 8-bit samples of the analog signal taken at a sampling rate of 8,000 samples per second.
  • the CODEC conversion is according to a mu-law data compression scheme which improves intelligibility for the given bandwith.
  • PCM bus 30 has four time slots Bl, B2, B3 and B4, which are identified by sync, signals.
  • the PCM bursts from CODEC U301 are put into the appropriate time slot (Bl, B2, B3 or B4) by the timing of the synchronizing signal POTSIFS on input pin 12 of IC U301 for line 1 (similarly the CODEC U302 time slot is selected by the synchronization signal POTS2FS for line 2).
  • Digital interface 22 includes an IC U311A which disables the receive data path to perform a mute function for line 1.
  • the mute function disables the receive line which has signals output to POTS device 54, although the transmit line continues to be active.
  • Conference circuit 32 performs conferencing between the two POTS line ports 58 and 64 with or without connection to the digital local exchange. From the conferencing circuit, access can be made to the digital local exchange.
  • Conference circuit 32 includes ICs U314 and U315, which are triple two-channel analog multiplexers. These multiplexers interconnect the analog signals for the transmit and receive directions on the two POTS lines.
  • the third switch in ICs U314 and U315 is used to inject analog signals from local PCM bus 30 through IC U300 into both analog lines 1 and 2 for tone insertion, voice monitoring or message retrieval functions to the conferenced analog lines.
  • Resistors R360, R339 and R340 perform current summing into the inverting input of IC U317A, an operational amplifier.
  • Resistor R359 sets the circuit gain and maintains the inverting input at 0 volts.
  • Resistors R338 and R301 perform current summing into the inverting input of IC U301.
  • Resistor R304 sets the gain and maintains the inverting input at 0 volts.
  • TAIC section 34 contains IC U303, a Telephone Analog Interface Circuit (TAIC).
  • This IC has a digitally controlled variable gain amplifier, which allows adjustment of the gain of a signal supplied to the POTS line 1 through port 58. Adjustment of the gain is in 3dB increments, from -15dB to +6dB. The gain set is accomplished through the serial port as selected by signal SPP1 (pin 4).
  • IC U303 also contains a digital filter to provide a steep high frequency roll-off of the analog signal from POTS line 1 which is input through port 58. This roll-off minimizes distortion in the analog-to-digital conversion by filtering out frequency components above the Nyquist frequency of 4 KHz.
  • the analog output from the auxiliary amplifier in TAIC IC U303 is coupled to the input amplifier of DTMF IC U307 through capacitor C324 and resistor R332.
  • the gain of the internal input amplifier in IC U307 is set by the ratio of resistor R337 to resistor R332.
  • IC U307 decodes DTMF signals originated by the POTS device(s) 54 connected to port 58.
  • a tone present signal (DTMFITP) is output by the DTMF detector 48 to request an interrupt from the private exchange controller 28 (Fig. 1).
  • the TOE1 signal at pin 10 of IC U307 (Fig. 2) is asserted and the DTMF decoder outputs a resulting digital signal in a 4 bit code onto the
  • IOBITS bus associated with local bus 31.
  • the TAIC IC U303 and DTMF IC U307 have an idle mode activated by a signal
  • POTS1PWDN generated by private exchange controller 28.
  • An inverter U313F inverts the POTSIWDN signal to assert a low signal to IC U303 when power down is desired. This powerdown is selectively activated to conserve power when the main power supply for the private exchange is interrupted.
  • SLIC IC U306 supplies the BOSH functions for basic support of the two-wire analog phone wire pair connected to port 58.
  • Transistors Q301 and Q302 and resistors R330, R322, R321, R331 and D305 combine with current sources within IC U306 to supply "battery voltage" and current injection to power POTS phone ring PHON1RNG and tip PHON1TIP connection. These outputs also drive audio signals to the analog port 58.
  • Capacitors C323 and C322 and diodes D302 and D303 provide protection against large transient noises.
  • SLIC 46 includes resistors R305 and R306 which are input resistors connected to internal current mirrors of SLIC IC U306. The internal current mirrors are part of an amplifier circuit which combines with resistors R357, R604, R318, R311 and R316 and capacitors C340, C305 and C318 to form a hybrid circuit which converts the two-wire circuit at the PHON1TIP and PHON1RNG leads to a four- wire circuit input to TAIC IC U303 and provides isolation of the transmit and receive signals. Resistor R365 and diode
  • D312 set a bias point for the RXI pin 14 of IC U306, which is coupled through resistor
  • Capacitor C315 provides a bias filter.
  • SLIC 46 also includes capacitor C308 and capacitor C343 which provide a hold time for ST2 pin 17 of IC U306, which is derived internally from the signal at input pin 18 (STl).
  • Pin 18 is POTSIHKI signal which indicates that the POTS phone is Off-Hook.
  • POTS1HK2 is an Off-Hook signal which is held by capacitor C308 and C343 to provide a reference compared with POTSIHKI, which comparison is used for detecting repertory dial pulses.
  • IC U313A provides hysteresis for, and inversion of, the ST2 output.
  • SLIC section 46 also includes circuit 80 which applies a load to the ring and tip lines (PHON1TIP and PHONE 1RNG) to force IC U306 into operation even though a
  • POTS phone connected to port 58 is not On-Hook.
  • Circuit 80 is responsive to the forced Off-Hook signal FRCOH1, which is asserted low and applies drive to the base of transistor Q310 through resistor R381.
  • Resistor R375 provides turn-off bias.
  • transistor Q301 When transistor Q301 is driven on, the collector drives the base of transistor Q306 through resistor R376. This turns transistor Q306 on, which connects resistor R373 across the ring and tip leads, which are isolated by the ring and tip drive resistors. This provides the load which SLIC U306 detects and responsive to which current is injected.
  • Circuit 80 allows transmission of caller ID information which can be used by a caller ID readout device connected to line 1 (Fig. 1).
  • the forced Off-Hook circuit 80 also provides for analog loop-back testing and software control of the SLIC power-up functions. Another use for this feature is to smooth the power-up of some electronic POTS phones. Some phones initially draw a current surge when they go Off-Hook, but when their internal power supplies stabilize, their current draw drops below the threshold necessary for the SLIC to detect On-Hook. Applying the auxiliary load briefly after each Off-Hook detection keeps the analog line from chattering when such a phone is connected to port 58.
  • a ringing signal injector 82 selective disconnects the POTS line 1 port 58 from the
  • SLIC 46 outputs and connects port 58 to the ring generator.
  • IC U311B goes high and drives the base of transistor Q304 through resistor R369.
  • the collector of transistor Q304 pulls low, applying drive current to the coil of relay X300.
  • the relay switch is therefore pulled in and makes the transfer to connect the ringing signal to port 58.
  • Diode D306 absorbs flyback energy when the relay coil is released.
  • a ring-trip detector 84 is also connected to the tip lead by relay X300.
  • the ringing signal is a 65 VRMS, 20 Hz ring voltage superimposed on a -28V battery voltage. Since the ringer circuit in the POTS phone is a series LC circuit, the DC bias does not appear on the ring and tip lines until the POTS phone goes Off-Hook, thereby placing a DC load across the line.
  • the amplifier U316A in ring-trip detector 84 detects this DC bias and terminates the ringing signal by driving transistor Q307 to pull POTSIHKI low, which in turn causes relay X300 in ringing signal injector 82 to drop, and transfer the phone from the ring generator to the output of SLIC IC U306.
  • Resistor R356 is a low value resistor (1 watt, approximately 100 Ohms) which is connected in series with the ring circuit on the ground return side (PHON1TIP). While ringing voltage is applied to the PHON1RING lead, and the analog device 54 is On-Hook, the ringing current causes a small AC voltage drop across resistor R356. This small AC voltage is filtered out by resistor R349 and capacitor C334 so that the voltage across capacitor C334 is near zero. When the analog device 54 goes Off-Hook, a DC component is generated across resistor R356. This DC voltage results in a DC voltage across capacitor C334 equal to the divider ratio of resistors R349 and R350 times the DC voltage across resistor R356.
  • This voltage is applied to the inverting input of comparator IC U316A, and compared to the negative voltage on the non-inverting input of IC U316A, which is set by the voltage divider of resistors R347 and R351 from ground to the -5V supply.
  • Resistor R348 pulls the reference slightly lower than the divider ratio would provide, and then raises it when the comparator output switches, to provide hysteresis around the switch point.
  • Resistors R371 and R352 provide pull-up for the open-collector output of comparator IC U316A. When the output of comparator IC U316A goes high due to detection of the DC voltage, resistor R371 can now supply current from the +5V supply into the base of transistor Q307.
  • Transistor Q307 therefore turns on, pulling POTSIHKI low and causing relay X300 to transfer the POTS circuit to the SLIC.
  • the SLIC then senses the load of the Off-Hook phone, turns on, and holds POTSIHKI low.
  • the state change causes an interrupt request in exchange controller 28, which subsequently turns off the ringing signal generator and deactivates the PHON1RING signal.
  • Diode circuit D315 is a SID AC connected to port 58 to provide protection in severe environments.
  • the phone line port 58 is an RJ14C.
  • Port 58 is connected to port 64 by conductors 90-93 such that both analog phone lines are available to a two-line subscriber device connected at either port 58 or port 64.
  • the analog lines are available on each of ports 58 and 64 in opposite order.
  • Section 94 contains voltage regulators for quiet analog +/- 5V power supplies from +6.5 and -8V switchmode supply voltages.
  • Capacitors C345 and C346 provide filtering of the input voltages.
  • IC U318 provides regulation of the +5 V analog supply.
  • Capacitor C342 provides additional filtering of the output.
  • Diodes D317 and D316 provide power transient protection by preventing the analog and digital +5V supplies from being more than a Schottky diode drop apart. This prevents activation of parasitic SCR structures in the CMOS devices that have power supply and signals in the different analog and digital environments.
  • IC U319 provides regulation for the -5 V analog supply.
  • DTMF circuit 42 includes a third detector IC U309, which provides an auxiliary decoding function to allow external devices connected through a digital port to have access for inputting DTMF signals.
  • IC U309 is provided by an IC No. 8870C commercially available from Motorola Corporation, or any other commercially available DTMF detector. The access of the IC U309 is used for voice mail access, changing call forwarding, or any other command functions.
  • Interface IC U300 which is a CODEC, is used only in the digital/analog decode mode. Its input can be either PCM data stream IL1TXD or PCM data stream IL1RXD on local PCM bus 30, as controlled by the 4 NANDgates in U320.
  • the selected output of NANDgate U300C is input to IC U309, which performs exactly the same as the DTMF decoders U307 and U308 in sections 22 and 24, for analog lines 1 and 2.
  • the output of IC U300 can also be connected to the POTS line by the analog switches in conference circuit 32 for injecting call waiting tones and other audible signals into the analog lines associated with ports 58 and 64.
  • IC U312 is a frequency divider configured to divide by four. It generates the 3.579545 MHz DTMF detector clock from the 14.31818 MHz used by the telephone answering machine.
  • an analog interface for a private exchange is disclosed which is compatible with all known types of analog POTS devices.
  • the analog interface provides forced Off-Hook operation, novel ring-trip detection, and two-line conferencing. Additionally, the analog interface operates with the general purpose microprocessor of the private exchange to effect the analog interface functions.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Telephonic Communication Services (AREA)
  • Interface Circuits In Exchanges (AREA)

Abstract

Une interface analogique (20) permettant le fonctionnement de dispositifs de systèmes téléphoniques ordinaires à partir d'un central privé (28) situé chez l'abonné, relié à un réseau numérique, comprend une entrée connectée à une alimentation en signaux d'appel présentant un décalage en continu, l'entrée étant reliée sélectivement aux fils d'appel d'un point d'accès analogique (58, 64). Un commutateur est couplé à l'entrée et aux fils d'appel afin de relier sélectivement le signal d'appel aux fils d'appel. Un capteur est couplé à l'impédance, le capteur ne détectant aucun signal de courant continu pendant qu'un appel est effectué lorsqu'une unité de terminaison d'abonné de système téléphonique ordinaire est raccrochée. Toutefois, le capteur détecte un signal de courant continu dans l'impédance lorsque le dispositif de terminaison d'abonné est décroché. Ainsi, le capteur détecte un arrêt de sonnerie et est couplé à un commutateur afin de déconnecter l'entrée du fil d'entrée dans lequel l'arrêt de sonnerie est détecté.
PCT/US1995/001333 1994-02-04 1995-02-02 Interfaces pour lignes de systeme telephonique ordinaire de centraux prives WO1995021498A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU17396/95A AU1739695A (en) 1994-02-04 1995-02-02 Private exchange pots line interfaces

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US19213194A 1994-02-04 1994-02-04
US08/192,131 1994-02-04

Publications (1)

Publication Number Publication Date
WO1995021498A1 true WO1995021498A1 (fr) 1995-08-10

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PCT/US1995/001333 WO1995021498A1 (fr) 1994-02-04 1995-02-02 Interfaces pour lignes de systeme telephonique ordinaire de centraux prives

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6034953A (en) * 1997-03-12 2000-03-07 Nortel Networks Corporation System for local voice distribution by an ISDN communications controller
US6125127A (en) * 1996-03-12 2000-09-26 Nortel Networks Corporation Method of convenient call acceptance for an ISDN communications controller
US6215796B1 (en) 1996-03-12 2001-04-10 Nortel Networks Limited Process for subchannel bandwidth allocation and extraction by an ISDN communications controller
US6243390B1 (en) 1996-03-12 2001-06-05 Nortel Networks Limited ISDN communications controller

Citations (8)

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US4551581A (en) * 1983-07-12 1985-11-05 At&T Bell Laboratories Method and apparatus for sending a data message to a selected station during a silent interval between ringing
US4709388A (en) * 1985-02-15 1987-11-24 Thomson-Csf Subscriber telephone line interface circuit with reduced power stand-by mode
US4797877A (en) * 1986-12-18 1989-01-10 American Telephone And Telegraph Company Communication system dynamic conferencer circuit
US4847896A (en) * 1986-11-13 1989-07-11 Sgs Microelettronica S.P.A. Monolithically integratable telephone circuit for supplying ringing signals to a subscriber's telephone line and for detecting an off the hook condition during ringing
US5067125A (en) * 1988-08-25 1991-11-19 Canon Kabushiki Kaisha Telephone system for isdn and public telephone networks
US5228081A (en) * 1990-10-18 1993-07-13 Ag Communication Systems Corporation Ringing signal control circuit for an enhanced subscriber line interface
US5289537A (en) * 1991-11-07 1994-02-22 Fujitsu Limited On-hook transmission circuit in cable line
US5293420A (en) * 1992-03-19 1994-03-08 Fujitsu Limited Ring trip circuit

Patent Citations (9)

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Publication number Priority date Publication date Assignee Title
US4551581A (en) * 1983-07-12 1985-11-05 At&T Bell Laboratories Method and apparatus for sending a data message to a selected station during a silent interval between ringing
US4551581B1 (en) * 1983-07-12 1995-06-20 Bell Telephone Labor Inc Method and apparatus for sending a data message to a selected station during a silent interval between ringing
US4709388A (en) * 1985-02-15 1987-11-24 Thomson-Csf Subscriber telephone line interface circuit with reduced power stand-by mode
US4847896A (en) * 1986-11-13 1989-07-11 Sgs Microelettronica S.P.A. Monolithically integratable telephone circuit for supplying ringing signals to a subscriber's telephone line and for detecting an off the hook condition during ringing
US4797877A (en) * 1986-12-18 1989-01-10 American Telephone And Telegraph Company Communication system dynamic conferencer circuit
US5067125A (en) * 1988-08-25 1991-11-19 Canon Kabushiki Kaisha Telephone system for isdn and public telephone networks
US5228081A (en) * 1990-10-18 1993-07-13 Ag Communication Systems Corporation Ringing signal control circuit for an enhanced subscriber line interface
US5289537A (en) * 1991-11-07 1994-02-22 Fujitsu Limited On-hook transmission circuit in cable line
US5293420A (en) * 1992-03-19 1994-03-08 Fujitsu Limited Ring trip circuit

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6125127A (en) * 1996-03-12 2000-09-26 Nortel Networks Corporation Method of convenient call acceptance for an ISDN communications controller
US6215796B1 (en) 1996-03-12 2001-04-10 Nortel Networks Limited Process for subchannel bandwidth allocation and extraction by an ISDN communications controller
US6243390B1 (en) 1996-03-12 2001-06-05 Nortel Networks Limited ISDN communications controller
US6034953A (en) * 1997-03-12 2000-03-07 Nortel Networks Corporation System for local voice distribution by an ISDN communications controller

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