Abstract:
An interface circuit that interconnects a terminal device at an extension station with the adjunct port circuit of a telephone of a business communications system (BCS), such as a digital PBX. The interface circuit enables a call diverted to a BCS telephone to be answered at the extension station. The interface circuit receives a ringing control signal from the adjunct port circuit when its BCS telephone is rung on an incoming call. This causes a ringing current source in the interface to apply ringing current to the extension station simultaneously with ringing of the BCS telephone.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a telephone interface circuit and in particular to an interface circuit that operationally couples a telephone of a business communication system (BCS), such as a PBX, with a terminal of an extension station. In particular, this invention relates to an interface circuit that couples the adjunct port of a business communication system with an extension station to enable the extension station to receive and serve calls directed to the associated telephone of the business communication system.  
       Problem  
       [0002]     Telephones of business communication systems often have an adjunct port which appears as a jack on the bottom of the business communication system. telephone. Terminals of the adjunct port may be connected by a plug to peripherals devices such as speaker phones to provide the user of the BCS telephone with additional services and facilities. It is known to connect the adjunct port to an interface circuit which, in turn, is connected to an extension station to enable the user of the BCS telephone to receive incoming calls at other locations. This is useful when the extension station is a cordless telephone which enables the user to wander throughout his work area while answering calls directed to his BCS telephone. This is also useful in call center applications where a high volume of calls are received and where it is important that each call be promptly answered rather than be dropped or routed to answering facilities. The provision of an interface circuit interconnecting the BCS telephone with a cordless telephone enables users of the BCS to receive calls directed to their BCS telephone without fear of the call being dropped or routed to answering facilities.  
         [0003]     A problem with the prior art interface circuits is that there is a substantial time delay between the initiation of ringing at the BCS telephone and the ringing of the extension station. The reason for this delay is due to the fact the ring signal for the BCS telephone is not applied to the extension station. Instead, the ringing signal applied to the BCS telephone causes a ring control signal to be generated and applied to the interface circuit which, in turn, generates the ring signal that is applied to the extension station. A delay interval within the interface circuit exists that may amount to a few seconds. At a result, ringing may not begin at the extension station until the initiation of the second or third ring cycle at the BCS telephone. As a result, calls can be lost or routed to answering facilities at the call center since the BCS system diverts calls to the answering facilities that are not answered on the first ring. This is undesirable and costly for the users of the call center since dropped calls represent lost revenue and calls directed to the answering facilities require the services of additional personnel who must retrieve the calls from the answering facilities and then attempt to contact the calling party that initiated each such call. All of this represents operational inefficiency and increased expense.  
       Solution  
       [0004]     The foregoing and other problems are solved in accordance with the present invention by the provision of an interface circuit which eliminates delayed ringing of the extension station and enables the extension station to be rung simultaneously with the initiation of ringing at its associated BCS telephone. This is effected by the provision of ring control circuitry within the interface circuit which receives a ring control signal from the adjunct port of the BCS telephone and immediately initiates the operation of ring circuitry internal to the interface circuit to cause the extension station, such as a cordless telephone, to ring. The elimination of a ring delay interval enables the extension station to ring simultaneously with the BCS telephone. This increases the efficiency of the users of the BCS systems since it enables them to receive calls on their extension cordless telephone without fear of the calls being dropped or diverted to answering machine facilities.  
         [0005]     Users of the BCS system served by facilities embodying the present invention may perform their duties with greater efficiency since they have the option of remaining at their desks while answering calls on their regular BCS telephone or, alternatively, by using their extension cordless telephones while performing useful services at nearby locations while being assured that calls incoming to their BCS telephone will be extended to their cordless telephone with immediate ringing.  
         [0006]     The interface circuit of the present invention is further advantageous in that it includes power generation circuitry that receives power via the adjunct port of the BCS telephone and converts this power to the voltage and current levels required by cordless telephones. This power is extended via a plug and jack arrangement to the cordless telephone. This enables the cordless telephone to be powered from the interface circuit and eliminates the necessity of the base of the cordless telephone to be connected to the conventional 110 volt service. This provides greater latitude in the location and placement of the base of the cordless telephone. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0007]     The above and other advantages and features of the invention may be better understood by the reading of a detailed description of one possible exemplary embodiment taken in conjunction with the drawings in which:  
         [0008]      FIG. 1  discloses apparatus embodying the present invention connected between an adjunct circuit and extension station;  
         [0009]      FIG. 2  discloses the power circuitry of the present invention including the power circuitry that supplies power to an extension station; and  
         [0010]      FIG. 3  discloses details of the tone detector and ring control circuit. 
     
    
     DETAILED DESCRIPTION  
       [0011]      FIG. 1  discloses the circuitry of an interface circuit  100  embodying the present invention together with a representation of an adjunct port  101  and a tone detector  110  connected by a path  111  to ring generator  112 . The TT and RR conductors  103  and  105  extending from the adjunct port  101  are comparable to conventional tip and ring circuitry and they extend to transformer T 1  and T 2  respectively. These conductors extend speech signal from the adjunct circuit  101  to the interface circuit  100  and they receive speech signals that originate in extension station  102 . COM  104  is a common path. The SO path  106  receives a ground when contacts  8  and  9  of relay K 2  operate when the called subscriber at extension station  102  goes off hook. This is subsequently described in detail. Integrated circuit IC 1 , element  122 , receives speech signals from the secondary winding of transformer T 1  via mate contacts  8  and  9  of relay K 3 , capacitor C 6  and conductor  126  extending to the + input of IC 1 . The output of IC 1  extends speech signals over path  122 , through capacitor C 7  and path  117  to the ring conductor of extension station  102 . Integrated circuit  121  receives speech signals generated by extension station  102  over the tip path, make contacts of relay  5  and  4  of relay K 2 , capacitor C 8  and the + input of integrated circuit  121 . The output of integrated circuit  121  is extended through resistor R 10  capacitor C 4 , path  125  to secondary winding of transformer T 2  which extends the signals to the adjunct port  101  over path  105 .  
         [0012]     Relay K 1  is an opto isolator and operates when a party at extension station  102  goes off hook. The operation of relay K 1  operates relays K 2  and K 3  over the path beginning at −48V, make contacts  4  and  5  of relay K 1 , to extend −48V to the terminal  1  side of relay K 2 . The path continues to the coil of relay K 2  to terminal  12  and over path  127  to terminal  1  of relay K 3 , through the coil of relay K 3 , to terminal  12  in ground.  
         [0013]     In accordance with the present invention, ringing current is applied by ring generator  112  to extension station  102  concurrently with ringing at the associated BCS telephone. The receipt of a call by the BCS telephone immediately rings the telephone of the BCS. The internal circuitry of the BCS telephone including its adjunct port  101  causes a dtmf (dual tone multiple frequency) signal, assigned with ringing, to be applied from the RR lead to the left winding of transformer T 1 . This signal appears at the secondary winding of transformer T 1  and is extended, over path  118 , break contacts  3  and  4  or relay K 3  which is unoperated at this time, path  114  to one side of the tone detector  110 . The other side of the tone detector is connected via path  113 , break contacts  9  and  10  of relay K 3  to path  126  on the other side of the secondary winding of transformer T 1 .  
         [0014]     Thus, the dtmf signal is applied via paths  113  and  114  to tone detector  110  concurrently with the application of the dtmf signal to path RR of the adjunct port  101 . Since the adjunct port  101  applies the dtmf signal to this path concurrently with the application of ringing to the BCS telephone, tone detector  110  is activated to detect the dtmf signal as soon as the BCS telephone begins to ring. The tone detector  110  applies a signal over path  111  to ring generator  112  which immediately applies ringing current to path  115 . This ringing current is then extended to extension station  102  over path  115 , break contacts  3  and  4  of relay K 2 , and the tip of extension station  102 . The path is extended through the internal circuitry of extension station  102  and loops back to ring conductor  117 , through capacitor C 7 , through resistors R 8  and R 9  in series to ground. This path applies the ringing current to extension station  102  immediately upon the application of ringing current to the BCS telephone.  
         [0015]     Relay K 1  remains un-operated during the ringing. When the extension station  102  is answered, the internal impendence of the ringing path decreases. At this time, relay K 1  operates and in turn operates relays K 2  and K 3 . Relay K 1  operates to ground through resistor R 16  at this time and latches in an operated state-for the duration of the call until extension station  102  returns to an on hook state. The path to operate and latch relay K 1  includes the ring conductor, the internal circuitry of extension station  102 , the tip conductor, and make contacts of  4  and  5  of relay K 2 , which is now operated, to potential +5V through resistor R 12 . This path maintains relay K 1  in a latch state for the call duration and, in turn, maintains relay K 2  and K 3  operated.  
         [0016]     The operation of relays K 2  and K 3  disconnects ring generator  112  and tone detector  110  from the transmission path by the opening of break contacts  3  and  4  of relay K 2  and  3  and  4  of relay K 3 . The closure of make contacts  4  and  5  of relay K 2  extends the tip conductor of extension station  102  through capacitor C 8  to the + input of integrated circuit  121  whose output further extends the signals through resistor R 10  and capacitor C 4  and conductor  125  to transformer T 2  by means of which the signals are extended to the TT conductor  105  of the adjunct port  101 .  
         [0017]     The operation of relay K 2  operates its make contacts  8  and  9  which extend ground through resistor R 11  to the SO conductor  106  of the adjunct port  101 . This signal notifies the adjunct port that the call has been answered at extension station  102 . The adjunct port together with the internal circuitry of the BCS telephone then terminates ringing at the BCS telephone concurrently with the termination of ringing at the extension station  102  when station  102  goes off hook as the call is answered.  
         [0018]     The operation of make contacts  4  and  5  of relay K 3  extend capacitor C 10  to path  118  to apply the proper impendence and capacitance to path  118 . The operation of relay K 3  when the call is answered closes it make contacts  8  and  9  to extend capacitors C 6  to path  126  and transformer T 1 . This completes a speech path connecting the right side winding of transformer T 1  to make contacts  8  and  9  of relay K 3  and capacitor C 6  and path  123  to the + input of integrated circuit  122 . The output of integrated circuit  122  extends the received speech signals through capacitor C 7  and path  117  to the ring conductor of station  102 . Station  102  now receives speech signals from the BCS telephone via integrated circuit  122  on its ring conductor and can transmit speech signals over the tip conductor, make contacts  4  and  5  of relay K 2 , capacitor C 8 , to the + input of integrated circuit  121  whose output is connected signal-wise with path  125  and one side of transformer T 2 .  
         [0019]     Interface circuit  100  of  FIG. 1  remains in this state as long as the call remains off hook at station  102 . The user at station  102  to answer the call immediately when it is received at the BCS telephone since interface circuit  100  operates ring generator  112  so that ringing current is applied to extension station  102  concurrently with the ringing of the associated telephone in the BCS system. The called party at station  102  can converse with the calling party with the same ease and facility as if the call had been answered at the BCS telephone. The call remains in this state as long as the station  102  remains off hook. When station  102  goes on hook at the termination of the call, relay K 1  releases and in turn releases relays K 2  and K 3 . The release of these relays opens make contacts  8  and  9  of relay K 3 , contacts  4  and  5  of relay K 3 , make contacts  4  and  5  of relay K 2  to break the speech path between conductors RR  103  and TT  105  of the adjunct port  101  and the tip and ring conductors of extension station  102 . The release of these relays also closes break contacts  3  and  4  of relays K 2  and K 3  as well as break contacts  9  and  10  of relay K 3 . This reconnects the tone detector  110  and ring generator  112  to a condition in which they can receive a dtmf ring control signal.  
         [0020]     Calls can be initiated at extension station  102 . The off hook state of the station upon the initiation of the call operates relay K 1  and, in turn, relays K 2  and K 3 . This establishes a voice signaling path through the circuitry of  FIG. 1  to interconnect the tip and ring of extension station  102  signal-wise with the RR and TT conductors  103  and  105  in the adjunct port circuit  101 . At the same time, the operation of make contacts  8  and  9  of relay K 2  extends a ground to the SO conductor  106  of the adjunct port circuit  101  via resistor R 11 . This ground notifies the adjunct port circuit and its associated BCS telephone that a call is being placed by extension station  102 . The circuitry of the BCS telephone is then placed in a condition for it to receive tone signaling generated at extension station  102 . This tone signaling is extended via the adjunct port circuit and the BCS which responds and sets up the call specified by the digits represented by the tone signaling to the same extent as if the same call had been initiated at the BCS telephone associated with the adjunct port circuit  101 .  
         [0021]      FIG. 2  discloses the circuitry that receives power from adjunct port  101  converts it to appropriate potentials and extends these potentials as energizing power to extension station  102  to energize it in the event that it is of the cordless type that requires an external power source. The conductors involved in this process are conductors  205 (−),  206  (+5V), and  203  (−48V) of the adjunct port  101 . The receipt of power over these conductors from adjunct port  101  energizes the full wave rectifier bridge  216  to generate the  48 V potential that is applied to capacitor C 1  and conductor  214 . This −48V potential is applied to voltage regulators VR 1  and VR 2 . Voltage regulator VR 2  receives this −48V potential and converts it to a positive potential of +5 volts to supply the indicated plus power to the circuitry of  FIG. 1 . The reception of the −48V by the regulator VR 1  generates a +12 volt potential that is applied to the terminals of power jacks  210 . The terminals of power jack  210  supply the appropriate power required by cordless station  102 . This permits the user of cordless station  102  to dispense with the use of the typical 110 volt AC power. The circuitry of  FIG. 2  is particularly advantageous since it increases the functionality of a typical cordless station by freeing the control base of the cordless telephone from the necessity of a connection to 110 volts. Thus, the base of the cordless telephone can be placed at any convenient location irrespective of whether 110 volts is available. This also makes the cordless telephone useful in periods of emergencies such as power outages when 110 volts might not be available since at that time, in accordance with the present invention, the cordless telephone may be used as part of an emergency circuit or facility to maintain communication during periods of emergency when commercial 110 volt power is not available.  
         [0022]      FIG. 3  discloses the details of tone detector  110  and ring generator  112  of  FIG. 1 . Conductors  113  and  114  apply the dtmf ring control signal to tone detector  112  shown in the upper left hand portion of  FIG. 3 . Conductor  115  extends ringing current from ring generator  112  of  FIG. 1  to the tip conductor of station  102  of  FIG. 1 . Conductor  115  is shown on the lower right hand portion of  FIG. 3 . This circuitry of  FIG. 3  is effective to receive the dtmf ring control signal on conductors  113  and  114  and immediately apply ringing current to conductor  115  simultaneously with the application of ringing current to the associated BCS telephone. The following describes the operation of the circuitry of  FIG. 3  in detecting the receipt of the dtmf ringing control signal on path RR  103  and immediately applying a ringing signal to path  115 .  
         [0023]     The circuit of  FIG. 3  is in an idle state when a ringing control signal is not applied on paths  114  and  113 . At that time pin  8  of integrated circuit  302  is at a high potential. This high potential is extended through resistor  319  to the base of transistor  303 . This high potential holds transistor  303  on in a saturated state. The current through resistor  320  maintains the collector of transistor  303  low at a potential essentially equal to that of the emitter of transistor  303 . This low collector potential is extended over paths  111  and  328  to pin  4  of integrated circuit  305 . This low potential on path  328  is further extended through the RC circuit of resistor  326  and capacitor  330  whose junction is connected to pin  4  of integrated circuit  304 . This low potential maintains capacitor  330  in a discharged state and which maintains pin  4  of integrated circuit  304  at a low potential that holds integrated circuit  304 , which is a timer, in an off condition. The circuit of  FIG. 3  remains in this state until a ringing control signal is received on paths  113  and  114 .  
         [0024]     When a ringing control signal is received on paths  113  and  114 , it is amplified by op-amp  301  and extended through capacitor  315  to pin  3  of integrated circuit  302 . This amplified signal turns on integrated circuit  302 . The on state of integrated circuit  302  causes a current through resistor  316  that lowers the potential at pin  8  of integrated circuit  302 . This low signal on pin  8  is extended through resistor  319  to the base of transistor  303 . This low potential turns transistor  303  off, terminates the current flow through resistor  320  so that the collector of transistor  303  and path  111  switch to a high potential essentially equal to that of the +5 volt power source. This high potential on paths  111  and  328  is extended to pin  4  of timer  305  to turn it on. Integrated circuit  305  is a 20 hertz timer which, when it is on, applies a 20 hertz signal from its pin  3  over path  363  to amplifier  307  which amplifies the 20 Hz signal to a 90 volt ringing signal. This signal is then applied over path  115  to the tip conductor of the extension station  102  via break contacts  3  and  4  on  FIG. 1  of relay K 2 . Paths  111  and  328  remain high and hold timer  305  in an on state for a brief initial interval such as for example 2 seconds. This maintains the ringing signal on path  115  for 2 seconds.  
         [0025]     In the mean time, capacitor  330  is initially at a ground potential but begins to charge slowly towards a positive potential through resistor  326  whose top side is connected to the plus potential on paths  328  and  111 . Integrated circuit  304  is normally in an off state, but switches to on state when capacitor  330  charges sufficiently. This occurs approximately 2 seconds after the application of the positive signal to paths  328  and  111 . The turn on of integrated circuit  304  after a delay of approximately 2 seconds extends a low from pin  3  of integrated circuit  304  to pin  1  of timer  305 . The ground on pin  1  of timer  305  turns it off after the 2 second delay controlled by the charging of capacitor  330 . The turn off of timer  305  terminates the ringing on path  115  for the duration of time that timer  305  remains off.  
         [0026]     Integrated circuit  304  is a timer programmed to have a 2 second on and 4 second off cycle. Timer  304  remains on for approximately 4 seconds, maintains the ground on pin  1  of timer  305  to hold it off and inhibit ringing for the duration of the 4 second interval. Timer  304  switches to off state for 2 seconds at the termination of its initial 4 second on interval. This causes ground to be removed from pin  1  of integrated circuit  305  so that it may turn on for 2 seconds and cause ringing to be applied via amplifier  307  to path  115 .  
         [0027]     Timers  304  and  305  continue to operate in this manner so that timer  305  is on for 2 seconds and off for 4 seconds. This causes interrupted ringing current to be applied to path  115  in a 2 second on and 4 second off pattern so long as the ringing control signal is applied to paths  113  and  114  in the upper left hand corner of  FIG. 3 .  
         [0028]     Timer  305  turns off whenever its pins  1  and  8  are at the same +5 volt potential and turns on when its pin  8  is at a +5 volt potential but pin  1  but is at a ground potential. An alternating signal appears on pin  3  of timer  304  for 4 seconds followed by a ground potential for 2 seconds. The application of this alternating signal is extended to pin  1  of timer  305  to hold it off for 4 seconds followed by an on for 2 seconds, etc. as long as the ring control signal is applied to conductors  113  and  114  to hold paths  328  and  111  of  FIG. 3  high.  
         [0029]     The function of diode  300  is to discharge capacitor  330  to ground on the collector of transistor  303  immediately upon the termination of the receipt of the ringing control signal on paths  113  and  114 . Diode  300  assures that capacitor  330  is discharged immediately so that  FIG. 3  conserves the receipt of a new call immediately upon the termination of ringing for a failed called.  
         [0030]     Extension station  102  may be of any type of terminal device or telephone equipped with a trip and ring interface. This would include cordless telephones and conventional telephones. It would also include personal computers and PDAs.  
         [0031]     The above description provides one possible exemplary embodiment of this invention. It is expected that those skilled in the art can and will design alternative embodiments that infringe on this invention as set forth in the claims below literally or through the Doctrine of Equivalents.