Patent Publication Number: US-2007121906-A1

Title: Method and apparatus to detect off-hook state of parallel-connected telephone

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority under 35 U.S.C. §119(a) from Korean Patent Application No.10-2005-0093328, filed on Oct. 5, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present general inventive concept relates to a communication terminal device, and more particularly, to a method and apparatus to detect an off-hook state of a parallel-connected telephone by setting an off-hook determination reference voltage to a second off-hook determination reference voltage different from the off-hook determination reference voltage according to a line input voltage that varies according to an environmental condition of a communication terminal device.  
      2. Description of the Related Art  
      In general, a telephone is connected in parallel to a communication terminal device connected to a telephone network. The parallel-connected telephone is called a branch telephone.  FIG. 1  illustrates a connection between a conventional communication terminal device  100  and a telephone  110 . The general communication terminal device  100  and the telephone  110  are connected to a telephone line  120  in parallel.  
      Referring to  FIG. 1 , since a voltage between a tip  120   a  and a ring  120   b  of the telephone line  120  decreases compared to a normal voltage when the telephone  110  connected in parallel to the communication terminal device  100  is off-hooked, the communication terminal device  100  can inform a user whether the telephone  110  is busy by detecting the voltage between the tip  120   a  and the ring  120   b  and displaying a state of the telephone  110  on a display unit of the communication terminal device  100  according to the detected voltage.  
       FIG. 2  illustrates a voltage between both terminals of a telephone line when an off-hook state of a parallel-connected telephone is detected in the conventional communication terminal device of  FIG. 1 .  
      Referring to  FIGS. 1 and 2 , in a normal state where the parallel-connected telephone is not used (an idle mode), a line voltage of the telephone line  120  has a constant value of a first voltage V 1 . When the parallel-connected telephone is off-hooked, the line voltage decreases to a third voltage V 3 . Here, a second voltage V 2  is a reference voltage for determining whether the parallel-connected telephone is off-hooked, and it is determined that the parallel-connected telephone is off-hooked if the line voltage decreases from the first voltage V 1  to a voltage lower than the second voltage V 2 .  
      While the first voltage V 1  of the communication terminal device connected to a general national switch network in the idle mode has a measured valued of 48V, the third voltage V 3 , when the parallel-connected telephone is off-hooked, is relatively and sufficiently low although the third voltage V 3  varies according to a DC loop current value and a resistance value of the parallel-connected telephone. However, the first voltage V 1  in private switch networks is usually set to a lower value than the first voltage V 1  in a general switch network. In addition, in user environments different from each other, since a line having a small diameter is installed from a private switch network to a connection terminal to which the communication terminal device is connected, a voltage directly supplied to the communication terminal device is lower. Thus, when the first voltage V 1  is low, a line voltage of the communication terminal device in the idle mode in which the parallel-connected telephone is not off-hooked is close to the second voltage V 2  or becomes lower than the second voltage V 2 , and thereby the off-hook state of the parallel-connected telephone cannot be normally detected.  
     SUMMARY OF THE INVENTION  
      The present general inventive concept provides a method and apparatus to detect an off-hook state of a parallel-connected telephone by setting an off-hook determination reference voltage differently according to a line voltage of a communication terminal device when a line voltage varies according to a user environment.  
      Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.  
      The foregoing and/or other aspect of the present inventive concept may be achieved by providing a method of detecting an off-hook state of a telephone connected in parallel to a communication terminal device connected to a telephone network, the method comprising detecting a line voltage between both terminals of a line of the telephone network in an operation-ready state in which the communication terminal device is turned on, setting differently according to the line voltage an off-hook determination reference voltage that is used to determine whether the parallel-connected telephone is off-hooked, and repeatedly detecting the line voltage between both terminals of the line and determining whether the parallel-connected telephone is off-hooked by comparing the repeatedly detected line voltage to the set off-hook determination reference voltage.  
      The setting of the off-hook determination reference voltage may comprise determining that the parallel-connected telephone cannot operate if the repeatedly detected line voltage is lower than a first threshold, and displaying an off-hook detection error according to the determination.  
      The setting of the off-hook determination reference voltage may comprise disabling the off-hook detection of the parallel-connected telephone if the repeatedly detected line voltage is equal to or higher than the first threshold and lower than a second threshold.  
      The setting of the off-hook determination reference voltage may comprise storing reference voltages corresponding to line voltages, and setting the off-hook determination reference voltage to one of the stored reference voltages according to the repeatedly detected line voltage.  
      The foregoing and/or other aspect of the present inventive concept may also be achieved by providing an apparatus to detect an off-hook state of a telephone connected in parallel to a communication terminal device connected to a telephone network, the apparatus comprising a line voltage recognition unit to recognize a line voltage detected between both terminals of a line of the telephone network in an operation-ready state in which the communication terminal device is turned on, a reference voltage setting unit to differently set an off-hook determination reference voltage to determine whether the parallel-connected telephone is off-hooked, according to the line voltage, and an off-hook determiner to determine whether the parallel-connected telephone is off-hooked by comparing the line voltage repeatedly detected between both terminals of the line to the set off-hook determination reference voltage.  
      The foregoing and/or other aspect of the present inventive concept may also be achieved by providing a computer readable recording medium containing computer readable codes to perform a method, the method comprising detecting a line voltage between both terminals of a line of a telephone network in an operation-ready state in which a communication terminal device is turned on, setting differently according to the line voltage an off-hook determination reference voltage that is used to determine whether the parallel-connected telephone is off-hooked, and repeatedly detecting the detected line voltage between both terminals of the line and determining whether the parallel-connected telephone is off-hooked by comparing the repeatedly detected line voltage to the off-hook determination reference voltage.  
      The foregoing and/or other aspect of the present inventive concept may also be achieved by providing a communication terminal device connected to a telephone network with a telephone, the communication terminal device comprising a terminal connected to an external telephone network, and a controller to receive a line voltage from the terminal, and to generate an off-hook determination reference voltage according to an initial value of the line voltage such that the controller determines a state of the telephone according to the line voltage and the generated off-hook determination reference voltage.  
      The foregoing and/or other aspect of the present inventive concept may also be achieved by providing a communication terminal device connected to a telephone network with a telephone in parallel, the communication terminal device comprising a terminal to be connected to an external telephone network having an external telephone connected thereto in parallel, and a controller to receive a first line voltage from the terminal, to generate an off-hook determination reference voltage according to the first line voltage, to receive a second line voltage after the generation of the off-hook determination reference voltage, and determines a state of the telephone according to the second line voltage and the generated off-hook determination reference voltage.  
      The foregoing and/or other aspect of the present inventive concept may also be achieved by providing a method of a communication terminal device connected to an external telephone network with an external telephone connected thereto in parallel, the method comprising receiving a first line voltage from the terminal, generating an off-hook determination reference voltage according to the first line voltage, receiving a second line voltage after the generation of the off-hook determination reference voltage, and determining a state of the telephone according to the second line voltage and the generated off-hook determination reference voltage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
       FIG. 1  illustrates a connection between a conventional communication terminal device and a telephone connected to a telephone line in parallel;  
       FIG. 2  illustrates a voltage between both terminals of a line when an off-hook state of a parallel-connected telephone is detected in the conventional communication terminal device;  
       FIG. 3  is a block diagram illustrating a communication terminal device according to an embodiment of the present general inventive concept;  
       FIG. 4  is a block diagram illustrating an apparatus to detect an off-hook state of a parallel-connected telephone according to an embodiment of the present general inventive concept;  
       FIG. 5  is a flowchart illustrating a method of detecting an off-hook state of a parallel-connected telephone according to an embodiment of the present general inventive concept; and  
       FIG. 6  illustrates an off-hook determination reference voltage differently set according to line voltages detected when a parallel-connected telephone is off-hooked, according to an embodiment of the present general inventive concept. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.  
       FIG. 3  is a block diagram illustrating a communication terminal device according to an embodiment of the present general inventive concept.  
      Referring to  FIG. 3 , the communication terminal device, such as a facsimile device, is connected to a telephone network (or a telephone line) and includes a main unit  300 , a data transmitter  310 , a line unit  320 , and a public switched telephone network (PSTN)  370  as the telephone network. It is possible that a telephone is connected to the PSTN  370  in parallel with the communication terminal device.  
      According to the present embodiment, the main unit  300  includes a controller  302 , a memory  304 , a modem unit  306 , and a line interface unit  308 .  
      The line unit  320  includes a line unit processing element  330 , i.e., an integrated circuit, which includes a main interface unit  332 , an analog/digital-digital/analog (A/D-D/A) converter  334 , a level converter  336 , a line voltage detector  338 , an AC signal input unit  340 , a DC current controller  342 , and an AC signal output unit  344 , a PSTN connection unit  350 , and a bridge diode unit  360 .  
      In the communication terminal device illustrated in  FIG. 3 , due to the bridge diode unit  360 , a positive voltage is always supplied to transistors Tr 1  and Tr 2  even if a polarity of a switch connected to the PSTN connection unit  350  is changed. The DC current controller  342  of the line unit processing element  330 , the transistor Tr 1 , and a resistor R 1  allow a constant current to flow to the PSTN  370 . The AC signal output unit  344 , the transistor Tr 2 , and a resistor R 2  amplify an output AC signal and send the amplified output AC signal to the PSTN  370 . A capacitor C 1  removes a DC component from an input AC signal input from the PSTN  370  and transfers the input AC signal without the DC component to the AC signal input unit  340 .  
      The line unit processing element  330  inter-operating with the PSTN connection unit  350  including the transistors Tr 1  and Tr 2 , the resistors R 1 , R 2 , and R 3 , and the capacitor C 1  described above is commonly called a data access arrangement (DAA) element.  
      The data transmitter  310  is located between the main unit  300  and the line unit  320  and transfers a predetermined data signal, a clock signal, etc.  
      The main unit  300  processes a fax signal and a voice signal. The modem unit  306  is connected to the data transmitter  310  through the line interface unit  308  and transmits/receives the fax signal and the voice signal.  
      When the fax signal is transmitted and/or received, an output signal generated by the modem unit  306  is converted to a predetermined digital data by the line interface unit  308  and transmitted to the main interface unit  332  of the line unit processing element  330  through the data transmitter  310 . The digital data is converted to an AC signal by the A/D-D/A converter  334  of the line unit processing element  330  and the converted AC signal is output to a base of the transistor Tr 2  by the AC signal output unit  344 . The transistor Tr 2  includes two terminals connected to the BD  360  and a potential through the resistor R 2 . The transistor Tr 2  amplifies the converted AC signal input through its base and sends the amplified AC signal to the PSTN  370 .  
      The line voltage detector  338  of the line unit processing element  330  detects a line voltage (or analog signal) between both terminals (a tip and a ring) of a line, which is input through the resistor R 3 , and converts the detected analog signal to a digital signal. The digital signal of the detected line voltage is input to the main unit  300  through the data transmitter  310 .  
       FIG. 4  is a block diagram illustrating an apparatus to detect an off-hook state of a parallel-connected telephone according to an embodiment of the present general inventive concept.  
      Referring to  FIGS. 3 and 4 , the off-hook detection apparatus includes an off-hook detector  400  and may include a memory  410 . That is, the off-hook detector  400  is an internal component of the controller  302  of the communication terminal device of  FIG. 3 , and the memory  410  can be an internal component of the controller  302  of the communication terminal device. In this case, the off-hook detector  400  and the memory  410  are constructed in a single chip. It is possible that the memory  410  can be a different component separate from the controller  302 .  
      The off-hook detector  400  includes a line voltage recognition unit  402 , an error processing unit  404 , an off-hook determiner  406 , and a reference voltage setting unit  408 .  
      An input signal IN 1  indicating a value of the line voltage value is detected by the line voltage detector  338  of  FIG. 3  and input to the line voltage recognition unit  402  by passing through the data transmitter  310 , the line interface unit  308 , and the modem unit  306 .  
      The line voltage recognition unit  402  recognizes the line voltage of the communication terminal device from the input signal IN 1 .  
      The line voltage recognition unit  402  determines that the parallel-connected telephone cannot operate if the line voltage is lower than a first threshold. The line voltage is lower than the first threshold when the parallel-connected telephone cannot operate due to a malfunction of the parallel-connected telephone or a defect of the line.  
      When the line voltage recognition unit  402  determines that the parallel-connected telephone cannot operate, the error processing unit  404  informs a user of an off-hook detection error. The off-hook detection error can be variously displayed according to a display unit (not shown) installed in the communication terminal device. For example, to display the off-hook detection error, a light emitted diode (LED) can flicker, or characters can be displayed on a liquid crystal display (LCD). It is possible that a message indicating the off-hook detection error can be printed using a printer, or if the communication terminal device is connected to a host personal computer (PC), a message indicating the off-hook detection error can be displayed on a monitor of the host PC.  
      If the recognized line voltage is equal to or higher than the first threshold and lower than a second threshold, the voltage recognition unit  402  disables the off-hook detection of the off-hook determiner  406 . When the recognized line voltage is equal to or higher than the first threshold and lower than the second threshold, since an operation of the parallel-connected telephone may be unstable according to a circuit characteristic, i.e., a DC resistance value, of the parallel-connected telephone, the off-hook determiner  406  cannot correctly determine whether the parallel-connected telephone is off-hooked.  
      The reference voltage setting unit  408  sets differently according to the line voltage an off-hook determination reference voltage that is used to determine whether the parallel-connected telephone is off-hooked. That is, the reference voltage setting unit  408  sets the off-hook determination reference voltage to a second off-hook determination reference voltage to replace the off-hook determination reference voltage such that the second off-hook determination reference voltage is used to determine whether the parallel-connected telephone is off-hooked. The memory  410  stores reference voltages corresponding to various line voltages, and the reference voltage setting unit  408  sets the off-hook determination reference voltage to a reference voltage stored in the memory  410  according to a detected line voltage.  
      Table 1 illustrates reference voltages according to line voltages.  
                   TABLE 1                       Line voltage   Reference voltage                  higher than 30 V   25 V       25˜30 V   20 V       20˜25 V   18 V       18˜20 V   16 V       15˜18 V   Parallel-connected telephone does not recognize       Lower than 18 V   Error processing                  
 
      Here, 15 V correspond to the first threshold, and 18 V correspond to the second threshold, for example.  
      The off-hook determiner  406  determines whether the parallel-connected telephone is off-hooked by comparing the off-hook determination reference voltage set by the reference voltage setting unit  408  to a line voltage periodically or repeatedly detected between both terminals of the line.  
       FIG. 5  is a flowchart illustrating a method of detecting an off-hook state of a parallel-connected telephone according to an embodiment of the present general inventive concept.  
      Referring to  FIG. 5 , in operation  500 , it is determined whether a communication terminal device is in an operation-ready state after the communication terminal device is turned on, i.e., in an idle mode. If the communication terminal device is in the idle mode, a line voltage between both terminals of a line of a PSTN is detected in operation  510 .  
      In operation  520 , it is determined whether the detected line voltage is 0 V. If the detected line voltage is 0 V, an off-hook detection error is displayed in operation  530 . For example, a line voltage is 0 V when the PSTN is connected to a line code thereof. The display of the off-hook detection error can be performed in various ways as described above.  
      If the detected line voltage is not 0 V, an off-hook determination reference voltage for determining whether the parallel-connected telephone is off-hooked is differently set according to a line voltage in operation  540 . If the detected line voltage is lower than a first threshold, an off-hook detection error can be displayed by determining that the parallel-connected telephone cannot operate. If the detected line voltage is equal to or higher than the first threshold and lower than a second threshold, the off-hook detection of the parallel-connected telephone can be disabled.  
       FIG. 6  illustrates off-hook determination reference voltages differently set according to line voltages in operation  540 . When the line voltage is a first voltage V 1 , the off-hook determination reference voltage is set to a second voltage V 2 , and when the line voltage is a first sub voltage V 1 - 1  lower than the first voltage V 1 , the off-hook determination reference voltage is set to a second sub voltage V 2 - 1  lower than the second voltage V 2  and higher than a third voltage as illustrated in  FIG. 6 .  
      In operation  550 , the line voltage between both terminals of the line is periodically or repeatedly detected, and it is determined whether the parallel-connected telephone is off-hooked by comparing the repeatedly detected line voltage to the off-hook determination reference voltage.  
      The present general inventive concept can also be embodied as computer-readable codes on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording media include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The computer-readable recording medium can also be distributed over network-coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. Also, functional programs, codes, and code segments to accomplish the present general inventive concept can be easily construed by programmers skilled in the art to which the present general inventive concept pertains.  
      As described above, according to embodiments of the present general inventive concept, even if a line voltage varies according to a user environment, the off-hook detection of a parallel-connected telephone can be correctly performed by differently setting an off-hook determination reference voltage according to a line voltage of a communication terminal device.  
      Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.