Abstract:
Disclosed is a telephone subscriber call signal control device for calling a telephone set connected to a subscriber circuit by means of a ringing signal when an incoming call is outputted from a subscriber circuit terminating device.  
     The subscriber circuit terminating device comprises:  
     a zero crossing point detection circuit for generating a zero crossing point synchronization signal synchronous with a zero potential of said ringing signal, and an order output timing adjustment circuit for adjusting output timing of a ringing control order for controlling a ringing relay of the subscriber circuit synchronously with the zero crossing point synchronization signal, and the telephone set is called by the ringing signal through the subscriber circuit synchronously with the zero crossing point synchronization signal in accordance with reception of an order to output a command to turn on the ringing relay from an order output device connected to the subscriber terminating device.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a telephone subscriber call signal control device for ringing a ringing signal when an incoming call reaches a telephone set and a subscriber circuit terminating device including the telephone subscriber call signal control device.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventionally, if each telephone set is called by an incoming call tone from a subscriber circuit terminating device, a DC voltage ringing signal is supplied to the telephone set and a ringing tone is generated to thereby urge a telephone subscriber to hang up the receiver. A sinusoidal current signal of 16 Hz and 79 Vrms with respect to a DC voltage of -48 V is employed as the ringing signal for ringing the subscriber&#39;s telephone set with a call tone, which example is shown in FIG. 1 and will be described with reference to FIG. 1.  
           [0003]    In FIG. 1, an exchange or a repeater station connected by many telephone sets consists of an order transmission device  400  transmitting an order to output a ringing to, for example, a predetermined telephone number, a subscriber circuit terminating device  100  connected to the order output device  400  and having an order development circuit switching connection in accordance with an incoming call order, subscriber circuits # 0 , . . . #N usually provided in the exchange for respective subscribers, connected to the subscriber circuit terminating device and having relay control circuit  210  and switch relays RL 1  and RL 2 , a subscriber&#39;s telephone set  600  usually provided in the exchange and connected to each of the subscriber circuits # 0 , . . . #N by a ring line and a chip line, and a ringing signal transmission device  500  generating a ringing signal for notifying the telephone set  600  of an incoming call and provided in the exchange. Switching for connecting to the desired telephone set which is a main function of the exchange is conducted outside of the subscriber circuit terminating device  100  and it is connected to the order development circuit  120  as a voice signal.  
           [0004]    As shown in FIG. 1, at the time of outputting a call signal, the telephone exchange has an overvoltage suppression circuit (spark killer) for each subscriber circuit so as to suppress overvoltage generated on subscriber lines, ring lines and chip lines. The overvoltage suppression circuit constitutes a spark killer circuit out of a serial circuit consisting of a resistor R 11  and a capacitor C 11  connected to the both ends of each of the switch relays RL 1  and RL 2  within the subscriber circuits # 0  and #N. The switch relays RL 1  and RL 2  select a ringing signal for one second and the output of a relay control circuit  210  for two seconds, whereby a call tone is generated from the telephone set  600 .  
           [0005]    In this case, if the switch relays can be successfully switched with the ringing signal having a voltage close to 0V, excessive voltage change does not occur and no problem arises even without the spark killer. If the ringing signal is high and the switch relays RL 1  and RL 2  are switched, the ringing signal is sometimes superimposed in addition to voltage supplied from the relay control circuit. Due to this, abnormally high voltage may be applied between the two-wire lines of the telephone set  600 , and a CR circuit serving as the spark killer of the overvoltage suppression circuit which suppresses the generation of the high voltage suppresses the application of the high voltage between the two-wire lines.  
           [0006]    Nevertheless, with the constitution of this conventional case, the spark killer circuit having the same constitution as that of the overvoltage suppression circuit is provided to the subscriber circuit for supplying a ringing signal to each telephone set for every subscriber. Due to this, the exchange of the subscriber circuit storage device accommodating many subscribers disadvantageously pushes up system cost.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    It is, therefore, an object of the present invention to decrease the number of overvoltage suppression circuits of subscriber circuits supplying a ringing signal to telephone sets and to suppress high voltage when the telephone sets are called by means of a subscriber circuit terminating device.  
           [0008]    The present invention is directed to decrease whole system cost between an exchange and subscriber circuits by, when outputting a call signal, synchronizing a method of suppressing overvoltage generated on a subscriber line with a zero crossing point signal indicating a potential VB (V) of a call signal whereby providing a host apparatus of a subscriber circuit terminating the subscriber circuit with a structure of operating a ringing relay as an integrated circuit.  
           [0009]    The present invention is a telephone subscriber call signal control device for calling a telephone set connected to a subscriber circuit by means of a ringing signal when an incoming call is outputted from a subscriber circuit terminating device, characterized in that: the subscriber circuit terminating device comprises: a zero crossing point detection circuit generating a zero crossing point synchronization signal synchronous with a zero potential of the ringing signal, and an order output timing adjustment circuit adjusting output timing of a ringing control order for controlling a ringing relay of the subscriber circuit synchronously with the zero crossing point synchronization signal, and the telephone set is called by the ringing signal through the subscriber circuit synchronously with the zero crossing point synchronization signal in accordance with reception of an order to output a command to turn on the ringing relay from an order output device connected to the subscriber terminating device.  
           [0010]    Further, the present invention is a subscriber circuit terminating device, including a ringing signal transmission device, for supplying a ringing signal to a subscriber circuit, characterized by comprising: a zero crossing point detection circuit generating a zero crossing point synchronization signal synchronous with a zero potential of the ringing signal; an order output timing adjustment circuit adjusting output timing of a ringing control order controlling a ringing relay of the subscriber circuit synchronously with the zero crossing point synchronization signal; and an order development circuit inputting an order reception signal from an order output device and analyzing the order reception signal, and characterized in that a telephone set is called by the ringing signal synchronized with the zero crossing point synchronization signal by the order output timing adjustment circuit in accordance with the order reception signal from the order output device.  
           [0011]    Furthermore, the present invention is characterized in that a control mechanism for controlling a call signal (or a ringing signal) in a subscriber circuit at the zero crossing point of the call signal to prevent the generation of overvoltage on a subscriber line when controlling the call signal is provided in a host apparatus.  
           [0012]    Moreover, the present invention will be described with reference to FIG. 2. A call signal transmitted from a ringing signal transmission device  500  is inputted into a zero crossing point detection circuit  130 . The zero crossing detection circuit  130  detects the potential zero crossing point of the call signal and generates a synchronization signal synchronous with the zero crossing point. This zero crossing synchronization signal is inputted into an order output timing adjustment circuit  110 . The order output timing adjustment circuit  110  synchronizes a ringing order transmitted from an order output device and controlling the ringing relays RL 1  and RL 2  of a subscriber circuit # 0 , with the above-stated zero crossing synchronization signal, and outputs the ringing order to a subscriber circuit. In response to the ringing order outputted at this timing, the subscriber circuit # 0  or the like operates the ringing relays. This operation can prevent the generation of overvoltage on subscriber lines during relay operation.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a block diagram of an order output timing circuit of a conventional subscriber circuit terminating device.  
         [0014]    [0014]FIG. 2 is a block diagram of a subscriber circuit terminating device and peripheral devices of the subscriber circuit terminating device according to the present invention;  
         [0015]    [0015]FIG. 3 is a block diagram of an order output timing circuit of the subscriber circuit terminating device according to the present invention;  
         [0016]    [0016]FIG. 4 is a block diagram of a zero crossing point detection circuit of the subscriber circuit terminating device according to the present invention;  
         [0017]    [0017]FIG. 5 is a timing chart showing an example of the operation of the subscriber circuit terminating device according to the present invention;  
         [0018]    [0018]FIG. 6 is a block diagram of an order output timing circuit of the subscriber circuit terminating device according to the present invention; and  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    The embodiments of the present invention will be described hereinafter in detail with reference to the accompanying drawings.  
         [0020]    [First Embodiment]  
         [0021]    (1) Description of Constitution  
         [0022]    As shown in FIG. 2, a telephone line signal supplied by way of a repeater station or the like reaches an exchange which is a final dependent exchange. The exchange consists of a subscriber circuit terminating device  100  for notifying, in particular, a subscriber of an incoming call, an order output device  400  for issuing an order to notify an incoming call, a ringing signal transmission device  500  outputting a ringing signal and a plurality of subscriber circuits  200 .  
         [0023]    Referring further to FIG. 2, the subscriber circuit terminating device  100  has an order output timing adjustment circuit  110 , an order development circuit  120  and a zero crossing point detection circuit  130 .  
         [0024]    In the order output timing adjustment circuit  110 , a command signal, which is a control order or an order signal, outputted from the order output device  400  to the plural subscriber circuits  200  connected is developed by an order development circuit  120  for analyzing and developing the order signal for every subscriber. A ringing control order signal is extracted from the order signal thus developed and outputted by an order development circuit  120 . The extracted ringing control order signal is synchronized with a ringing signal zero crossing synchronization signal outputted from the zero crossing point detection circuit  130  and outputted to a specific subscriber circuit  200  ordered by the order output device  400 . It is the feature of this embodiment that the zero crossing point detection circuit  130  and the order output timing adjustment circuit are provided in the subscriber circuit terminating device  100 .  
         [0025]    The zero crossing point detection circuit  130  receives a call signal (or a ringing signal) transmitted from the ringing signal generation device  500  and generates a zero crossing synchronization signal indicating the potential VB (V) of the ringing signal. The zero crossing synchronization signal thus generated is outputted to the order output timing adjustment circuit  110  described above. The subscriber circuit # 0  ( 200 ) controls the operation of the relay control circuit  210  to the switch relay RL 1  or RL 2  so as to repeat transmitting a ringing signal from the ringing signal transmission device  300  for, for example, one second and turning on/off the switch relay RL 1  or RL 2  with two second&#39;s null in accordance with a ringing relay control order signal outputted from the order output timing adjustment circuit  110 . As a result of this operation, a call tone bell according to the ringing signal of the subscriber telephone set  600  rings.  
         [0026]    Further, the order output device  400  outputs a command or the like for ordering the output of a ringing voice as the target of this embodiment together with other commands including, for example, a voice level adjustment command used in the subscriber circuit and a balancing network adjustment command from a switching exchange, a line monitoring device or the like which is not shown in FIG. 2.  
         [0027]    It is the order development circuit  120  that distributes various commands from the order output device  400 . The order development circuit  120  outputs the command to output the ringing signal to the relay control circuit  210 , to the order output timing adjustment circuit  110 . Further, the subscriber circuit  200  on/off controls the relays RL 1  and RL 2  using a control signal which timing is adjusted by the order output timing adjustment circuit  110 . Thus, it is possible to prevent high voltage application. At this moment, the control signal of the relay control circuit  210  sets a ringing signal for, for example, one second and null time for, for example, two seconds, and a voltage of -48V on a ringing line side, a voltage of 0V on a chip line side and the ringing signal are supplied from the relay control circuit so as to switch them.  
         [0028]    [0028]FIG. 3 shows a case where the order output timing adjustment circuit  110  is provided while there are two subscribers in the embodiment according to the present invention and is a block diagram showing an example of the constitution of the order output timing adjustment circuit  110 .  
         [0029]    The order output timing adjustment circuit  110  consists of an order drop circuit  111 , an order buffering sections  112  and  113 , order output control circuits  115  and  116  and an order output gate signal generation circuit  114 . The order drop circuit  111  drops only a ringing relay control order signal in a subscriber circuit control order outputted from the order development circuit  120 . The order signal thus dropped is outputted to the order buffering sections  112  and  113 . The order buffering sections  112  and  113  consist of storage means such as FIFO memories, and store and buffer high speed ringing relay control order signals until orders are issued from the order output control circuits  115  and  116 , respectively.  
         [0030]    The order output gate signal generation circuit  114  inputs a zero crossing synchronization signal outputted from the zero crossing point detection circuit  130 , generates a ringing relay control order output signal (or a gate signal) synchronous with this synchronization signal, and outputs the ringing relay control order output signal (or the gate signal) thus generated to the order output control circuits  115  and  116 .  
         [0031]    The order output control circuits  115  and  116  read the ringing relay control orders from the order buffering sections  112  and  113  in response to the gate signal outputted from the order buffering gate signal generation circuit  114 , and output the ringing relay control order thus read to the subscriber circuits # 0200  and#N 200 , respectively.  
         [0032]    [0032]FIG. 4 is a circuit diagram showing an example of the constitution of the zero crossing point detection circuit  130  in this embodiment. The zero crossing point detection circuit  130  inputs a ringing signal, and generates a zero crossing point synchronization signal having a potential of VB (V). In FIG. 4, the zero crossing point detection circuit  130  inputs a ringing signal from the ringing signal transmission device  500 . The ringing signal is inputted into the reversal input terminal of an operational amplifier OP 1  by way of differential circuits C 1 , R 1  and R 2 . A serial circuit consisting of voltage suppression Zener diodes D 1  and D 2  is connected to the reversal input terminal of the operational amplifier OP 1  to suppress an input voltage equal to or higher than a certain voltage level and to prevent the input of over voltage. Further, A resistor R 5 , and potential division circuit resistors R 3  and R 4  between a negative power supply and a ground potential are connected to a feedback circuit from the output of the non-reversal terminal of the operational amplifier OP 1 . Also, the output of the operational amplifier OP 1  is connected to the reversal input terminal of an operational amplifier OP 2 , and potential division circuit resistors R 7  and R 8  between a positive power supply and the ground potential are connected to the non-reversal input terminal of the operational amplifier OP 2 . The operational amplifier OP 2  outputs a zero crossing point synchronization signal through a load resistor R 6  connected to the positive power supply supply.  
         [0033]    (2) Description of Operation  
         [0034]    The operation of this embodiment will be described. First, an operation for generating a zero crossing point synchronization signal will be described with reference to the timing chart of FIG. 5.  
         [0035]    In FIG. 4, the operational amplifier OP 1  into which the ringing signal is inputted, outputs a low level when the ringing signal is higher in voltage than the potential division voltage of the resistors R 3  and R 4 , and outputs a high level when lower than the potential division voltage of the resistors R 3  and R 4 . Next, the operational amplifier OP 2  outputs a low level when the input voltage of the operational amplifier OP 2  is higher than the potential division voltage of the resistors R 7  and R 8 , and outputs a high level when the input voltage is lower than the potential division voltage of the resistors R 7  and R 8 . Therefore, if the potential division voltage of the resistors R 3  and R 4  is a negative voltage close to VB and that of the resistors R 7  and R 8  is a positive voltage close to VB, the zero crossing point detection circuit  130  outputs a zero crossing point synchronization signal shown in FIG. 5( b ). Needless to say, the zero crossing signal detection circuit may be a circuit other than the circuit of FIG. 4.  
         [0036]    The zero crossing point signal thus obtained is generated so as to change from ‘0’to ‘1’ or ‘1’ to ‘0’ at the voltage VB (V) of the ringing signal. The order output gate signal generation circuit  114  detects this change point and generates an order gate output signal.  
         [0037]    On the other hand, the operation of the order output timing adjustment circuit  110  is executed according to a timing chart shown in FIG. 5. In FIG. 5, if a ringing signal (a) at 440 Hz close to a sinusoidal wave is inputted, the zero crossing point detection circuit  130  converts the ringing signal (a) into a pulse signal which repeatedly rises and falls every time the ringing signal (a) becomes a zero level, and outputs the pulse signal. The zero crossing point synchronization signal (b) synchronous with the ringing signal is supplied from the zero crossing point detection circuit  130  to the order output control circuits  115  and  116 .  
         [0038]    At this moment, the zero crossing point synchronization signal (b) is constantly outputted from the zero crossing point detection circuit  130 . As shown in FIG. 5, if a ringing order reception timing signal (c) is received by the order buffering section  112  at the timing of T 1  as shown in FIG. 5, timing for outputting a ringing order signal from the order output gate signal generation circuits  115  and  116  is generated according to the zero crossing point synchronization signal (b) at the timing of T 2  shown in FIG. 5. At the timing of T 2  shown in FIG. 5, the order output control circuit  115  reads a ringing control order signal from the order buffering section  112  and outputs the ringing control order signal thus read to the subscriber circuit # 0  ( 200 ).  
         [0039]    Next, the relay control circuit  210  receives this ringing control order signal when rising as shown in a ringing relay state (d), and actuates the ringing relays RL 1  and RL 2  at the timing of T 2  shown in FIG. 5. By actuating the ringing relays at this timing, it is possible to prevent the telephone set  600  from being influenced by the generation of overvoltage on the subscriber line during the operation of the relays RL 1  and RL 2  and also to prevent the other subscriber circuits from being applied with inductive noise components.  
         [0040]    Furthermore, the ringing signal from the ringing signal transmission circuit  500  on/off controls the switch relay RL 1  of the subscriber circuit  200  for a predetermined time, and the ringing signal is supplied to the switch relay RL 1  until hanging up the receiver of the telephone set or for a predetermined time to thereby stop the switch relay RL 1 .  
         [0041]    [Second Embodiment]  
         [0042]    The second embodiment according to the present invention will be described hereinafter. While the second embodiment is the same in basic constitution as that described above, this embodiment is characterized in that in the order output timing adjustment circuit  110  of FIG. 3 number of order buffering sections  112 ,  113  and that of order output control circuits  115  and  116  are increased according to the number of subscriber circuits  200  accommodated in the exchange and the order output timing adjustment circuit  110  is formed into an integrated circuit, thereby making it possible to further reduce cost. The constitution of the second embodiment is shown in FIG. 6.  
         [0043]    As shown in FIG. 6, the number of two order buffering sections  1121 ,  1131 , and that of order output control circuits  1151  and  1161  are increased according to the number of subscriber circuits accommodated in the exchange and an entire order output timing adjustment circuit is formed into an integrated circuit to thereby make it possible to further reduce cost, compared with the case of two subscribers shown in FIG. 3.  
         [0044]    Here, the order buffering section  112  may be a small capacity recording medium for ordering “turn on the ringing signal of a telephone set #005”. Thus, the order buffering section  112  may be a DRAM or a high speed SRAM. The order output control circuit  115  mainly controls output timing. Therefore, if the switch circuit of the order drop circuit  111 , the order buffering sections  112  and the like and the order output control circuits  115  and the like are constituted out of an LSI circuit, it is possible to contribute to making the entire apparatus small in size and to thereby the improvement of the reliability of the apparatus. Further, a ringing signal transmission device may function as a type of a clock oscillation circuit and output a ringing signal using the oscillation circuit of a CPU mainly controlled by the exchange.  
         [0045]    As stated so far, by providing the subscriber circuit terminating device with the structure of preventing overvoltage on subscriber lines while the ringing relays are operating in subscriber circuits, it is possible to reduce the number of circuits provided for every subscriber circuit so as to prevent overvoltage on the subscriber lines and to reduce a unit price per subscriber line. It is, therefore, possible to considerably reduce the cost of the exchange accommodating many subscriber circuits.