Abstract:
A voltage controller increases a DC input voltage in response to a ring instruction received from a processor in a control signal. The increased voltage is converted to an AC ring signal that causes a telephone to ring. The ring signal voltage is generated at a battery high node (“V BH ”) and may be routed to a SLIC before being sent to an on-hook telephone.  
     The voltage at V BH  is kept low during off-hook and other periods when a ring instruction is not present. Thus, voltages internal to an indoor device that houses the controller are kept below a predetermined safe threshold, thereby allowing the periods of high voltage to be deemed as transient. Accordingly, if the device is unearthed, or not grounded to the earth, the device may nevertheless obtain listing by a certifying and testing organization without being subjected to abnormal testing and possible failure thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of priority under 35 U.S.C. 119(e) to the filing date of Everett, U.S. provisional patent application No. 60/342,987 entitled “VBH Switching During Ringing To Eliminate Double Insulation Requirements”, which was filed Dec. 22, 2001, and is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates, generally, to communication networks and, more particularly, providing increased voltage at a telecommunications Subscriber Line Interface Circuit (“SLIC”), during ringing.  
         BACKGROUND  
         [0003]    In a plain old telephone service (“POTS”) system, a telephone is designed to receive a “ring” signal, typically an AC wave at 20 hertz (Hz) of approximately 40 V RMS, when it is supposed to ring. It will be appreciated that other ring voltages are often used that fall within a range equal to or greater than 40 V RMS. The ringing signal is/was traditionally sent along the twisted pair telephone wire that connects an individual telephone to the telephony network. A typical telephone still uses the higher ring signal voltage, even if the telephony communications are transmitted along non-traditional pathways, such as, for example, community antennae television (“CATV”) coaxial cable, optical fiber cable, or any other network technology that transmits communications signals. When one of these technologies is used, a telephone is typically connected to a line card that provides an interface between the telephone and the communications network. Such a line card typically contains subscriber line interface circuitry (“SLIC”) that is designed to translate a signal from the network protocol to the traditional telephony protocol. A node within the line card circuitry may be maintained at a constant 90-95 V level, and when an instruction to ring is received, the 90-95 V source is directed to the telephone in accordance with a predetermined waveform shape. Thus, when a line card receives a signal that instructs it to cause a telephone connected thereto to ring, it generates a ringing signal of about approximately 40 V RMS, or equal to or greater than 40 V RMS as discussed above, having a waveform shape similar to the waveform of a traditional telephony signal.  
           [0004]    A line card may be part of a subscriber&#39;s premise equipment (“SPE”) device inside a consumer&#39;s home. To deliver power to the SPE, a typical household AC power supply may be used that provides AC current in the range of between approximately 105 V and 230 V. In order to facilitate compatibility with different styles of power outlets and powering schemes, the power supply conductor, or cord, may be terminated with a two prong plug that works in either a two prong receptacle or a three prong receptacle.  
           [0005]    Although the use of a two prong plug facilitates compatibility with a wider range of receptacles, a two prong plug does not provide a safety ground path for the device to which it provides power. Thus, the internal circuitry of the device, while being possibly grounded through other means, a coaxial CATV cable, for example, is not safety grounded from the power supply power source. This may cause difficulty in obtaining listing by an independent, product-safety testing and certification organization, such as UNDERWRITERS LABORATORIES, INC.® (“UL®”). Abnormal testing may be required before certification and/or listing of a device that is not safety grounded is granted. This may cause delay in the introducing of a new product that is not safety grounded. In addition to protracted delay for testing, there is the possibility that a device being tested may not meet the certification&#39;s standards, thus delaying further introduction of the device into the stream of commerce until the device can be redesigned and retested. Such delay can be costly at best, and result in the stillbirth of a product at worst in the fast changing realm of modem telephony.  
           [0006]    Current UL® standards specify that continuous internal voltages within an unearthed device not exceed a hazardous voltage level. If a device, such as a cable modem telephony line card, is not safety grounded, it is subjected to abnormal testing that impose “double insulation” requirements, for example, before the device becomes UL® “listed.” However, if a device&#39;s internal voltages that rise above the predetermined safe level, approximately 50-60 volts, for example, are not continuous, but transient in nature, then the device may not be subject to abnormal testing due to internal voltages exceeding the predetermined safe level. Since line cards typically generate a ringing signal voltage of approximately 40 V RMS, or equal to or greater than 40 V, to cause a telephone to ring, an unearthed SPE having a line card that provides a telephone interface may be subjected to abnormal testing, and the aforementioned associated delay, before becoming listed, if an continuous, approximately 90-95 voltage tap, or node, is provided in the circuitry of the line card.  
           [0007]    Thus, there is a need for a method and system that provides a 90-95 V ringing signal that is not continuous, but only high (above the predetermined safe level) during ringing, thereby being deemed transient in nature.  
         SUMMARY  
         [0008]    It is an object to provide a method and system for maintaining telephony line voltages from a SLIC within a line card used in a cable telephony modem system below a predetermined safe level, while providing for increased voltage during ringing. This eliminates the need for meeting double insulation requirements and/or abnormal testing for indoor devices that are not safety grounded. Therefore, such a device can be brought to market rapidly and the design and/or testing costs performed to meet standards in order to obtain listing with a testing and certification organization, UL® for example, are reduced.  
           [0009]    Generally described is an indoor, unearthed cable telephony device comprising an input power source, a control signal source, a voltage converter that operates in response to the control signal source and a node for providing a high battery output from the voltage converter. The control signal is provided from a processor that receives an incoming cable telephony signal to the voltage converter. The processor provides translation between the cable network protocol, typically a digital signal, and the SLIC, which is typically configured to provide and receive analog signals to and from a conventional telephone device. The voltage converter provides an energy signal to the SLIC, while the processor provides an information signal to the SLIC, without passing through the voltage converter. The voltage converter may comprise a fly back transformer, or a boost converter. These are merely examples of the means that may be used, as well as others known in the art, of selectively increasing the voltage to a circuit. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates a system that provides telephony services, as well as television programming, via a CATV network.  
         [0011]    [0011]FIG. 2 illustrates a block diagram of a line card&#39;s components that generate a high voltage signal during ringing.  
         [0012]    [0012]FIG. 3 illustrates a schematic diagram for providing a transient high voltage ringing signal. 
     
    
     DETAILED DESCRIPTION  
       [0013]    As a preliminary matter, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many methods, embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the following description thereof, without departing from the substance or scope of the present invention.  
         [0014]    Accordingly, while the present invention has been described herein in detail in relation to preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purposes of providing a full and enabling disclosure of the invention. The following disclosure is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof. Furthermore, while some aspects of the present invention are described in detail herein, no specific conductor type, integrated circuit, discrete component, connector, enclosure, circuit board arrangement, capacitor or resistor value, or fuse rating, for example, is required to be used in the practicing of the present invention. Indeed, selection of such parts and components would be within the routine functions of a designer skilled in the art.  
         [0015]    Turning now to the figures, FIG. 1 illustrates a system  2  for providing telephony services, as well as television programming, to an end user via a CATV network  4 . A head end  6  acts as a central office for directing signals, including telephony signals, over network  4 . Such signals may be received at subscriber premises equipment (“SPE”) device  8  outside a user&#39;s home or office, for example. SPE  8  may determine how to route the signal based on the information type of signal, e.g., a television signal or a telephony signal. If the information signal contains television content, the signal may routed to television  10  as a standard CATV signal. If, however, the signal contains telephony information, the signal is routed to line card device  12  for further processing.  
         [0016]    As the telephony information may have been transmitted over network  4  as a modulated CATV signal, an internet protocol (“IP”) signal, or preferably as a Data Over Cable Service Interface Specification (“DOCSIS”) signal, the line card translates the incoming signal format to POTS format. As POTS telephone  14  may be designed to ring when a signal having a level of about 40 V RMS, or equal to or greater than 40 V, is impressed into the twisted pair  16  that connects it to line card  12 , the line card must produce this voltage level. Line card  12  uses power and energy from an indoor wall receptacle  18  that supplies standard AC house current at about 120 V. This house current is transmitted from receptacle  18  to line card device  12  via power cord  20 . The household current is typically transformed to DC current at approximately 12-15 V by power supply  21 , which supplies the DC current from its output to line card  12  via DC power cord  22 . It is noted that power cord  20  is terminated with plug  23 , which has only two prongs. A third prong for providing safety ground protection is not provided from plug  23 . This allows compatibility with electrical systems that do not provide a safety ground conductor and that typically provide two-prong receptacles, as Iillustrated by receptacle  24 .  
         [0017]    Although the use of two-prong plug  23  facilitates use with a greater number of electrical system schemes, safety ground functionality is eliminated. This is so even when line card device  12  is used in an electrical system that supports a safety ground circuit, and that provides three-prong receptacles, because there is no third prong on plug  23  to connect the line card device to an existing safety ground circuit. In addition, even if plug  23  and cord  20  provide three conductors, cord  22  may typically contain only two conductors, and thus may not provide a safety ground circuit to line card  12 . Thus, the generation of a 40 V RMS, or equal to or greater than 40 V RMS, signal within line card  12  may prevent the certification of said line card if the 40 V RMS, or equal to or greater than 40 V RMS, ringing signal source is constantly live.  
         [0018]    Turning now to FIG. 2, a block diagram of line card  12  is illustrated. Line card  12  receives power from power cord  22 , which will typically contain two active conductors, a positive and a negative. The positive and the negative conductors carry DC current that has been transformed from AC household current known in the art for house current distribution. The negative conductor may be grounded to the chassis of line card  12 , and the positive lead provides current to voltage controller  26 . Processor  28  interfaces signals between SPE  8  and SLIC  30 . Processor  28  also provides a control signal to voltage controller  26 . It will be appreciated that processor  28  comprises a variety of components, including, for example, a microprocessor, media access control layer circuitry and software, digital-to-analog (“D/A”) and analog-to-digital (“A/D”) circuitry as well as other typical circuitry known in the art of cable telephony. Voltage controller  26  includes means, which will be discussed later, that can increase the 12 V DC signal from power source conductor  22  into the ringing supply voltage of approximately 95 V used by SLIC  30  to generate an approximately 40 V RMS ringing signal, thus causing a telephony device connected to twisted pair  16  to ring.  
         [0019]    When processor  28  receives an information signal, it decodes the received signal, which may be a DOCSIS data signal, and uses D/A converters to convert it to an analog signal. In addition, if the received signal contains an instruction to ring a telephone connected to SLIC  30 , a control signal is sent to voltage controller  26 , thereby causing the means internal to the voltage controller to increase the voltage from the approximately 12-15 V to approximately 90-95 V. This increased voltage signal is produced at VBH node  32 , which is connected to VBH input  34  at SLIC  30 . SLIC  30  impresses the high voltage signal received at VBH node  34  into twisted pair lines  16 , thereby causing a telephone connected thereto to ring. The SLIC  30  detects when a user picks up the handset of the telephone and then disconnects the high voltage signal from the twisted pair cable  16 , thereby allowing an analog information signal received from the processor  28  to pass through the SLIC and on to the handset so that the user may then converse with the calling party.  
         [0020]    Voltage controller  26 , which converts the DC input voltage received from cable  22  into the higher ringing voltage, may comprise a variety of means. Turning now to FIG. 3, the preferred means for converting the DC voltage to the higher AC ringing voltage includes a fly back transformer, a schematic diagram of which is illustrated with reference to circuit  36 , which may be included inside voltage controller  26 , as shown in FIG. 2.  
         [0021]    A fly back transformer  38  is used to store energy received from the supplied voltage V in , and to discharge the stored energy as a higher voltage when the field in transformer&#39;s core  40  collapses. It will be appreciated by those skilled in the art that a flyback transformer is a special type of transformer that does not continuously transform an input voltage into an output voltage in direct proportion to its windings ratio.  
         [0022]    Typically, energy is stored in an air gap in the transformer core. When the field from the primary winding collapses, the stored energy flows within the core, thereby inducing a field, and thus current, into the secondary winding of transformer  38 . Therefore, current does not flow in the secondary when current flows in the primary, but flows as the field in the primary collapses. It will further be appreciated that flyback transformer  38  should be connected according to the dots shown in the figure. This arrangement lends itself for use with providing ringing signaling in telephony devices because telephony devices conventionally use a negative V BH  to ring a telephone ringer.  
         [0023]    In addition to the flyback transformer, various other components are used to provide the functionality of circuit  36 . To provide on/off switching of current through the primary of transformer  38 , transistor  42 , preferably a MOSFET, is used. Transistor  42  receives its gate voltage from an output pin V OUT  of feedback regulator  44 . Feedback regulator  44  may be an off-the-shelf component known in the art, and provides a constant reference voltage at a V REF  pin. The voltage at V OUT  is controlled by a signal received by regulator  44  at a feedback pin (“FB”) and alternates to provide a constantly increasing and collapsing field in the primary of transformer  38 . Resistors  46  and  48  may be used to form a voltage divider that maintains the voltage level at FB in a predetermined range according to the manufacturer&#39;s specifications corresponding to regulator  44 .  
         [0024]    The control signal that provides the ringing instruction is received from the processor shown in FIG. 2 by circuit  36  at port  50 . This ringing control is typically digital signal inasmuch as it is either at zero volts, indicating a no ring state, or at a logical full voltage, typically 3.3 V, indicating ringing state. The control signal passes through biasing resistors  52  and  54  for biasing of feedback transistor  56 . When the control signal is low, transistor  56  is off. Therefore, current does not flow through draw-down resistor  58 , and the voltage applied to operational amplifier (“op amp”) 60 is V REF ×R 62 /(R 62 +R 64 ). The resistance values of resistors  46 ,  48 ,  58 ,  62  and  64 , as well as gain adjusting resistors  66  and  68  are selected such that when the control signal voltage at port  50  is low, the voltage impressed at pin FB of regulator  44  regulates the voltage at V OUT  to maintain the voltage at V BH  less that 60 V. It will be appreciated that the voltage at V BH  is negative according to the phase relationship indication dots at fly back transformer  38 .  
         [0025]    When the control signal voltage at port  50  is high, such as 3.3 V, for example, as discussed above, transistor  56  turns on. This causes the collector of transistor  56  to draw through resistor  58  to ground, such that resistor  58  and resistor  62  are in parallel between the non-inverting input of op amp  60  and ground. Since the resistance of resistor  62  and  58  in parallel is less that the resistance of resistor  62  alone, the voltage at the non-inverting input of op amp  60  drops, and the feedback network comprising resistors  66  and  68  causes the output of op amp  60  to drop proportionally to the drop at the non-inverting input pin.  
         [0026]    In order for the output of the op amp  60  to drop, the voltage at the inverting input drops proportionally thereto. As this inverting input voltage drops, the current through resistor  66  falls according to Ohm&#39;s Law, thereby causing the ringing voltage signal at V BH  to drop. Accordingly, a properly selected resistance value of resistor  66  will cause the ringing signal at VBH to drop to a voltage lower than −60 V (lower because more negative, but having magnitude greater than 60 V), preferably approximately −90 V, when the ringing control signal at port  50  is high. Conversely, the voltage at V BH  will rise above −60 V (the term rise indicates that the sign becomes less negative, although the magnitude is less that 60 V) when the ringing control signal voltage is low.  
         [0027]    These and many other objects and advantages will be readily apparent to one skilled in the art from the foregoing specification when read in conjunction with the appended drawings. It is to be understood that the embodiments herein illustrated are examples only, and that the scope of the invention is to be defined solely by the claims when accorded a full range of equivalents.