Abstract: An information processing apparatus includes a display unit that display's a document in a first display mode by switching a document display mode from a second display mode to the first display mode in a case where the document displayed is a distributed document or a document having been distributed, where the document has not been browsed, and where a browsing time limit set for the document expires within a first predetermined period.

Abstract: Apparatuses and Methods of double talk detection for echo suppression in the power domain are disclosed herein. An example method includes comparing a power echo estimate signal to a microphone power signal, determining if the power echo estimate signal is greater than or less than the microphone power signal by a first threshold, based on the power echo estimate signal being greater than or less than the microphone power signal by the first threshold, disabling adaptation of filter coefficients of an adaptive filter of an echo suppressor, and based on the power echo estimate signal not being greater than or less than the microphone power signal by the first threshold, enabling adaptation of filter coefficients of an adaptive filter of an echo suppressor.

Abstract: An echo path change detector may be used to control the rate of adaptation in an acoustic echo canceller. When echo path change is declared, the rate of adaptation may be increased. However, echo path change should not be declared in the presence of double talk, because rapid adaptation during double talk is undesirable. Accordingly, various features are disclosed for detecting echo path changes while avoiding the declaration of such changes in the presence of double talk.

Abstract: A voltage generation apparatus includes a booster circuit which outputs a direct-current voltage after having performed boosting processing, the voltage value of the direct-current voltage being specified on the basis of a pulse width of a series of pulse signals inputted, a direct-current to alternating-current conversion circuit which generates a ringer voltage to be supplied to a device connectable to a telephone line by converting the direct-current voltage outputted by the booster circuit to an alternating-current voltage, and a control unit which outputs a series of pulse signals to the booster circuit. the series of pulse signals having a feeding-voltage pulse width corresponding to a target voltage value of a feeding, voltage or a ringer-voltage pulse width corresponding to a target voltage value. the feeding-voltage pulse width and the linger-voltage pulse width being pulse widths having been set in a voltage adjustment stage.

Abstract: A method line powering a remote access device or telephone from a centralized location that includes abstraction of the ancillary signaling functions to that central location. A method of receiving a request for a telephone call includes receiving a digital telephony packet and determining a ring signal in response to the received digital telephony packet. The method also includes generating a voltage signal in response to the determined ring signal and communicating the voltage signal over a twisted pair connection to a digital telephone. The communicated voltage signal is operable to power the digital telephone and generate a ring signal at the digital telephone. The digital telephone is operable to generate digital telephony packets representative of voice data.

Abstract: A telephone unit device connectable in series between a telephone set and a wire pair coupled to a telephone service and carrying DC power and an AC telephone signal. The device includes: a first connector connectable to the wire pair; a second connector connectable to the telephone set; means connected between the first and second connectors for passing substantially without change the AC telephone signal between the wire pair and the telephone set; and means connected between the first and second connectors for receiving DC power only from the wire pair and converting the DC power to a level suitable for proper telephone operation of the telephone set connected thereto.

Abstract: Apparatus and methods of remote powering of DSL ADMs are disclosed. In a subscriber communication node, at least communication components that enable the subscriber communication node to communicate with a network switching device, and possibly also subscriber communication components that enable one or more subscriber communication devices to communicate with the network switching device, can be powered either by a local power source or remotely through an electrically conductive twisted wire pair. A network node may derive its own power and also supply power to subscriber communication nodes through twisted wire pairs. A linear or ring topology of subscriber communication nodes can thus be kept operational, and subscriber communications can potentially also be maintained, when a local power source at one or more subscriber nodes becomes unavailable.

Abstract: A method for scheduling ringing signals for a plurality of subscriber lines includes maintaining a schedule of ringing signals for the plurality of subscriber lines. A plurality of ringing counts is determined. Each ringing count specifies a number of subscriber lines ringing at a selected point in the schedule. A ringing request for a particular subscriber line is received. A position in the schedule for the ringing request is identified based on the ringing counts that does not exceed a maximum ringing limit. The ringing request is scheduled in the schedule responsive to identifying the position. A ringing signal is generated for the particular subscriber line in accordance with the schedule.

Abstract: A method for controlling power dissipated in a subscriber line interface circuit includes measuring a power parameter of the subscriber line interface circuit during a ringing cycle, comparing the measured power parameter to a target power parameter and adjusting at least one ringing parameter of a ringing signal generated by the subscriber line interface circuit based on the comparison. A line card includes a subscriber line interface circuit operable to generate a ringing signal, and a subscriber line audio-processing circuit operable to measure a power parameter of the subscriber line interface circuit during a ringing cycle, compare the measured power parameter to a target power parameter, and adjust at least one ringing parameter of the ringing signal based on the comparison.

Abstract: A method for controlling a ringing signal includes generating a ringing signal on a subscriber line, detecting a condition indicative of the subscriber line going off-hook and reducing an amplitude of the ringing signal responsive to detecting the condition. A line card includes a subscriber line interface circuit operable to generate a ringing signal on a subscriber line and a subscriber line audio-processing circuit operable to detect a condition indicative of the subscriber line going off-hook and reducing an amplitude of the ringing signal responsive to detecting the condition.

Abstract: Terminals are connected via cables in a star-shaped fashion with respect to a HUB in a LAN. Each of the cables includes therein signal lines and power feed lines. The HUB includes therein a power feed section. The power feed section and the power feed lines of each cable are connected to measure a value of current which flows in the power feed lines. If it is judged based on the measured current value that the terminal connected to the corresponding cable is a telephone terminal, the power feeding to the corresponding power feed lines is continued. On the other hand, if the terminal is judged to be a terminal other than the telephone terminal, the power feeding is stopped.

Abstract: A first clock signal is generated by a first circuit and a second clock signal is generated by an auxiliary clock circuit. A switch controls whether the first clock signal or the second clock signal is provided to a subscriber line integrated circuit (SLIC). The SLIC is operable to generate a line voltage within predetermined tolerances on a loop line at a customer premises if the SLIC is receiving the first clock signal or the second clock signal. A resync signal is sent to the SLIC to cause it to resync with the first clock signal without going through a reset operation.

Abstract: Apparatus for handling an incoming telephone call including a call processor coupled to a wired or wireless telephone network for receiving an incoming telephone call directed to a called person, a conversation detector for determining whether a conversation is currently taking place between said called person and one or more other persons who are near to said called person, and a call inhibitor for inhibiting the delivery of, delaying or rerouting said incoming call if said conversation detector determines that a conversation is taking place. Each participant in the conversation is provided with a speech detector, and vibrator for producing a tactile alert when incoming calls directed to a participant arrive, and a manually operated control for issuing a veto command that inhibits the delivery of, delays, or reroutes the incoming call so that the conversation is not interrupted.

Abstract: A telephone interface circuit comprising a speech circuit, a control circuit turning on upon receiving a supply of a forward direction trigger current so as to connect first and second telephone lines and the speech circuit, and going off upon receiving a supply of a reverse direction trigger current so as to disconnect the first and second telephone lines and the speech circuit, a capacitor charging and discharging charge supplied from the first telephone line, and a hook switch supplying charge accumulated at the capacitor when off-hook to the control circuit as a forward direction trigger current, and supplying charge discharged from the capacitor when on-hook to the control circuit as a reverse direction trigger current.

Abstract: A method for controlling power dissipated in a subscriber line interface circuit includes measuring a power parameter of the subscriber line interface circuit during a ringing cycle, comparing the measured power parameter to a target power parameter and adjusting at least one ringing parameter of a ringing signal generated by the subscriber line interface circuit based on the comparison. A line card includes a subscriber line interface circuit operable to generate a ringing signal, and a subscriber line audio-processing circuit operable to measure a power parameter of the subscriber line interface circuit during a ringing cycle, compare the measured power parameter to a target power parameter, and adjust at least one ringing parameter of the ringing signal based on the comparison.

Abstract: A telephone interface circuit comprises a first transistor for controlling opening and closing between a speech circuit and subscriber lines, a second transistor for controlling the first transistor to turn on and off, a positive feedback circuit connecting a collector terminal of the first transistor and a base terminal of the second transistor, an overcurrent detection circuit detecting overcurrent applied to the subscriber lines, and a breaker circuit for turning off the first transistor by lowering the base potential of the second transistor to a low potential when overcurrent is detected at the overcurrent detection circuit. Here, the base terminal of the first transistor and a collector terminal of the second transistor are connected. Further, when off-hook, the base potential of the second transistor is controlled in such a manner as to become a high potential by a microcomputer.

Abstract: A method and apparatus is provided for ring-trip detection in a line card having an analog-to-digital converter for processing voice signals. The method includes receiving a ringing control signal, transmitting a ringing signal to a subscriber line in response to the ringing control signal, and receiving a portion of the ringing signal from the subscriber line. The method includes converting the portion of the ringing signal to a digital signal using the analog-to-digital converter, and providing a ring-trip indication in response to the digital signal. The apparatus includes first circuitry capable of processing a voice signal, the circuitry including a analog-to-digital converter for processing the voice signal. The apparatus includes a ringing generator, second circuitry, and ring-trip detection logic. The generator is capable providing a ringing signal to a subscriber line in response to receiving a ringing control signal.

Abstract: An apparatus and method for enabling Cisco legacy power to support IEEE 802.3af standard power. A network power system capable of delivering data terminal equipment power via a media dependent interface (MDI) includes power source equipment according to a first power via MDI scheme such as Cisco legacy power and at least one powered device according to a second power via MDI scheme such as IEEE standard power. A power compatibility module is inserted between the power source equipment and the powered device to enable the power source equipment to appear according to the first power via MDI scheme and the powered device to appear according the second power via MDI scheme. In one embodiment, the module includes switches, a DC/DC converter, an IEEE power source equipment circuit, and an isolator. The module may optionally include a user signaling device for communicating operating conditions of the module to a user.

Abstract: A subscriber line interface circuit apparatus includes tip/ring sense circuitry generating a tip sense signal and a ring sense signal from three sensed currents, wherein the tip sense signal and the ring sense signal correspond to subscriber loop tip and ring currents, respectively. In one embodiment, the tip/ring sense circuitry includes a current mirror generating first and second mirrored sense currents from a first sense current proportional to a battery feed node voltage of a subscriber loop. Current differencing circuitry provides the tip sense signal from a difference between the first mirrored sense current and a second sense current associated with a tip line of the subscriber loop. The current differencing circuitry provides the ring sense signal from a difference between the second mirrored sense current and a third sense current associated with a ring line of the subscriber loop.

Abstract: A method and apparatus is provided for DC feed control for a line card. The method includes determining if the line card is operating in a current limit region of a DC feed curve and synthesizing a curve in the current limit region. The method further includes determining a loop voltage based on the synthesized curve, and applying the loop voltage to the subscriber line. The apparatus includes logic capable of determining if the line card is operating in a current limit region of a DC feed curve and capable of determining a loop voltage based on a synthesized curve in the current limit region. The apparatus further includes circuitry for applying the loop voltage to the subscriber line.

Abstract: A path change is detected by multiplying the energy of a signal on the output of a summation circuit in one channel of a telephone by a constant to produce a product. The product is compared with the energy of a signal on the input of the summation circuit. A path change is indicated when the energy of the product exceeds the energy of a signal on the input of the summation circuit. The comparison is made in successive frames of an audio signal and a path change is indicated when the energy of a signal on the input of the summation circuit is exceeded in two or more successive frames.

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 (“VBH”) and may be routed to a SLIC before being sent to an on-hook telephone. The voltage at VBH 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.

Abstract: A power system apparatus replaces outdated and presently unobtainable power systems originally deployed in a variety of RT communication cabinets, incorporating a plug-in programmable control module used to generate alarms in response to the detection of specified events and providing direct plug compatibility to those RT cabinet systems through the use of unique wiring harnesses. Support for advanced broadband and high speed communication circuits, neither originally envisioned nor designed into the original communication RT system, is now provided.

Abstract: A method includes the step of providing subscriber loop pull-down circuitry operating in a first voltage domain. The subscriber loop pull-down circuitry decreases at least one of a tip and a ring line current in response to a corresponding pull-down control signal. The method further includes the step of providing control circuitry operating in a second voltage domain, wherein the first and second voltage domains are substantially distinct. The control circuitry varies the pull-down control signal to decrease a selected one of the tip and ring line currents in response to a sensed current corresponding to an associated one of a tip pull-down current and a ring pull-down current. A subscriber line interface circuit apparatus includes pull-down circuitry operating in a first voltage domain. The pull-down circuitry varies line currents of the tip and ring lines in response to a pull-down control signal provided by control circuitry operating in a second voltage domain.

Abstract: In one embodiment, the present invention includes an apparatus having a first pair of low voltage operational amplifiers to generate an output representative of an absolute value difference of first and second line voltages of a subscriber loop, and a third low voltage operational amplifier having an input coupled to the output of the first pair of low voltage operational amplifiers to filter the output and to provide a switch control signal for a switching regulator that provides a voltage used to generate the first and second line voltages. The apparatus may include additional circuits such as a limit circuit to limit the input to the third low voltage operational amplifier and one or more speedup circuits to reduce a filter time constant of the third low voltage operational amplifier during a ringing mode of the subscriber loop.

Abstract: In one embodiment, the present invention includes a device having a low voltage SLIC to perform SLIC functions at a low voltage and to provide metallic and longitudinal currents to a high voltage SLIC. The low voltage SLIC may be designed based on an operational amplifier cell architecture, and the high voltage SLIC may receive the metallic and longitudinal currents and generate first and second amplified output currents therefrom.

Abstract: According to one embodiment, a terminal apparatus includes a telephony application function which converts a first voice signal input from a voice input unit into a second voice signal to be transmitted on a first communication line by a converter, and converts the second voice signal received from the first communication line into the first voice signal by the converter, a connector which connects a second communication line to transmit the first voice signal, and a processor which treats the first voice signal input from the voice input unit to selectively derived to the converter or the second communication line in response to a use request for a line, and treats the first voice signal output from the converter or the second communication line.

Abstract: A method and apparatus is provided for implementing an unbalanced subscriber line interface circuit with built-in ring circuit. A signal to be conditioned is received. An unbalanced output buffering function is performed upon the signal to be conditioned using an unbalanced buffering circuit. Performing the unbalanced output buffering function includes switching between a plurality of power supplies to maintain a predetermined maximum voltage across a plurality of devices relating to the unbalanced buffering circuit.

Abstract: A mode-dependent, battery-coupling switch for a subscriber line interface circuit (SLIC) selectively adjusts its current requirements to provide optimal current handling capability irrespective of the mode of operation of the SLIC. Where current demands of the SLIC are relatively minimal (e.g., on-hook idle mode), the bias is set at a relatively small, default value. During high current demand, such as ringing and off-hook signaling, the bias is set at a relatively large value, to maintain a low voltage drop across the battery-coupling switch.

Abstract: The present invention relates to a ring voltage generation circuit for generating a ring voltage (VTR) between a TIP lead (9) and a RING lead (10) with minimized power loss for electronic subscriber circuits, comprising: a) an amplifier circuit (2) which receives an input voltage (VI) for amplifying the input voltage (VI) to provide the ring voltage (VTR); b) an absolute value generator (3) which receives the input voltage (VI), measures an absolute value (|VI|) of the input voltage (VI) and outputs the measured absolute value (|VI|) of the input voltage (VI); c) a DC/DC converter (4) which receives the measured absolute value (|VI|) of the input voltage (VI) and converts the measured absolute value (|VI|) of the input voltage (VI) into a supply voltage (VSUPPLY) for the amplifier circuit (2); and d) a common mode feedback device (5) which receives the supply voltage (VSUPPLY), a TIP potential (VT) of the TIP lead (9) and a RING potential (VR) of the RING lead (10) and which generates thereof a control volt

Abstract: Crescendo telephone ringers and methods of providing a crescendo telephone ring signal. The crescendo telephone ringer provides a gradual increase in audible ringing volume as a sequence of incoming electrical ring signals is detected. According to one embodiment, upon receipt of an incoming call, a first audible ring signal corresponding to a first detected electrical ring signal is set to a minimum volume. Subsequent audible ring signals corresponding to subsequent detected electrical ring signals are set to increasing volume levels, and finally to a maximum ringer volume.

Abstract: Terminals are connected via cables in a star-shaped fashion with respect to a HUB in a LAN. Each of the cables includes therein signal lines and power feed lines. The HUB includes therein a power feed section. The power feed section and the power feed lines of each cable are connected to measure a value of current which flows in the power feed lines. If it is judged based on the measured current value that the terminal connected to the corresponding cable is a telephone terminal, the power feeding to the corresponding power feed lines is continued. On the other hand, if the terminal is judged to be a terminal other than the telephone terminal, the power feeding is stopped.

Abstract: A method and apparatus is provided. The method includes transmitting a signal having an AC component to a subscriber line and receiving at least a portion of the transmitted signal from the subscriber line. The method includes determining at least a portion of a period of the AC component of the received signal, and performing a function of a line card in response to determining at least the portion of the period of the AC component. The apparatus includes circuitry that is capable of transmitting a signal having at least one of an AC component and a DC component to a subscriber line, and receiving at least a portion of the transmitted signal from the subscriber line. The apparatus includes a filter and computation logic. The filter is capable of filtering the DC component from the received signal. The computation logic is capable of determining a value proportional to a power of the AC component of the received signal over at least a portion of a period of the AC component.

Abstract: A telephone line interface and associated circuitry that may be implemented to simultaneously couple DC loop voltage, ring bursts, and caller-ID data to the phone line side of a DAA circuit through a single two wire resistively coupled interface. The interface and circuitry may be implemented to combine processing of the DC loop voltage and ring bursts into a single circuit, with processing of caller-ID data being performed separately.

Abstract: In a telecommunications system, a switching device selectively applies one of two different voltage supplies to a common node. A first of the voltage supplies is coupled to the common node by a first switch and a second of the voltage supplies is coupled to the common node by a second switch. The switching device includes the following elements. A difference detector detects a difference between the first and second voltage supplies. A control circuit selectively enables one of the first and second switches and disables the other of the first and second switches, for switching between the first and second voltage supplies in response to the difference detector. The control circuit performs the switching between the first and second voltage supplies when the detected difference falls below a predetermined threshold.

Abstract: A system and a method selectively switch between two different voltage supplies supplying a common node. A first of the voltage supplies is coupled to the common node by a first switch and a second of the voltage supplies is coupled to the common node by a second switch. The switching device comprises: a feedback network comprising a high-pass filter for filtering a signal at the common node and outputting the filtered signal as a feedback signal; a timing controller coupled to at least one of the first and second voltages supplies for determining when to switch between said first and second power supplies; a ring switch controller for applying a first control signal to the first switch for selectively enabling and disabling the first switch in response to the timing controller and the feedback signal; and a battery switch controller for applying a second control signal to the second switch for selective enabling and disabling the second switch in response to the timing controller and the feedback signal.

Abstract: The present invention relates to a possibility to localize a telecommunications terminal over a local area network. More specifically, the invention provides a method for associating a port number of a powering equipment to which will be connected a telecommunications terminal with some identification characteristics of said telecommunications terminal. Furthermore, it provides a telecommunications terminal to be connected to a local area network while being localized when remotely powered. It provides also a supervisor engine like a server connected to a local area network and collecting identification characteristics of a telecommunications terminal for its localization over said local area network.

Abstract: Method and apparatus for transmitting a transmission signal via a two-core line, in particular a telephone line, in which case, with the aid of corresponding transmission devices (2, 3), two partial signals are generated and are transmitted via a respective core (A, B) of the line and the transmission signal is formed by the alternating-current difference between the two partial signals. In order to suppress common-mode components in the partial signals, a calibration is carried out in such a way that the transmission devices (2, 3) output essentially the same output level.

Abstract: A line interface capable of connecting to a variety of transport mediums, each having a different impedance. The line interface comprises a programmable resistor. The programmable resistor along with an external resistor provide a range of resistor values which are used to substantially match the impedance requirements of the various transport mediums.

Abstract: A digital direct access arrangement (DAA) circuitry may be used to terminate the telephone connections at the user's end to provide a communication path for signals to and from the phone lines. Briefly described, a means for providing a proper hookswitch transition for a variety of international phone standards is provided. The invention may also be utilized with means for transmitting and receiving a signal across a capacitive isolation barrier. More particularly, a DAA circuitry may be utilized which satisfies many or all hookswitch transition standards without the use of additional discrete devices. The hookswitch transition standards may be satisfied by ramping down the current flowing through the hookswitch prior to transitioning the hookswitch state. In this manner the hookswitch current change as a function of time (di/dt) may be decreased. Thus, the current through the hookswitch may be actively controlled prior to switching the hookswitch from an off-hook condition to an on-hook condition.

Abstract: A telephone system includes a controllable ringing generator for generating a ringing signal and an interface for providing a ringing voltage derived from that signal on the transmission line. The controllable ringing generator includes a control device for controlling the ringing voltage in response to the ringing current.

Abstract: The ring relay control unit of an FXS includes a main control unit for controlling relay interrupt command; a relay control device for generating a relay control signal in accordance with a relay interrupt command transferred from the main control unit, an SLIC for interfacing a call signal to a subscriber's phone, a ring signal generator for generating a ring signal transferred to the subscriber's phone, and transferring a synchronous signal, which generates a relay control signal, to the relay control device, and a relay for selectively transferring the call signal and the ring signal to the subscriber's phone from the SLIC and the ring signal generator.

Abstract: The invention creates a method for adjusting a ringing signal current in a subscriber line (106), a ringing signal generator (114) which generates the ringing signal being connected with one end of the subscriber line (106) and at least one subscriber (102) being connected to another end of the subscriber line (106), comprising the steps of detecting a ringing signal current of the ringing signal; of comparing the detected ringing signal current with a predetermined current value; and when the detected ringing signal current is greater than the predetermined current value, reducing a ringing signal voltage of the ringing signal in such a manner that the ringing signal current is equal to the predetermined current value, the ringing signal voltage being dropped across the subscriber line (106) and a load of at least one subscriber (102). The invention also creates a circuit arrangement for carrying out the method.

Abstract: A communication system is provided which draws virtually no loop current during a ringing burst and only draws on-hook loop current during the caller ID field. More particularly, ringer burst circuitry may be powered from the user powered circuitry by the transmission of power across the isolation barrier rather than being powered from the phone line. Thus, loop current need not be drawn from the TIP/RING lines during ringer bursts. The isolation barrier may be a capacitive isolation barrier which allows bidirectional communication and extraction of power from signals transmitted across the barrier.

Abstract: In a method and a device for controlling the magnitude of the generated ring signal in a the Subscriber Line Interface Circuit (SLIC) the voltage of the A and B lines to the subscriber from the SLIC is compared to a reference voltage. The device is arranged to control the magnitude of the generated ring signal voltage in response to the outcome of the comparison. In particular, the device is arranged to control the ring signal voltage so that the ring signal voltage is reduced if the voltage on the A or B line exceeds the reference voltage. Also, the reference voltage is preferably chosen so that there is no risk for saturation of the final stages. The reference voltage is preferably selected to have a value being related to the value of the negative supply voltage.

Abstract: Method and apparatus for generating a bandlimited square waveform for use as a ringing voltage in a telephone network is described. One embodiment comprises a method of generating a ringing voltage signal for transmission to a telephone device. The method comprises calculating a truncated Fourier series representation of a square wave using only low order harmonic frequencies thereof; determining a sampling rate; generating digital sample data using the truncated Fourier series representation and the sampling rate; and converting the digital sample data to an analog signal.

Abstract: A cordless telephone-to-sound card interface adapter provides a connection between any standard cordless telephone system and a sound card of a computer for PC-to-PC or PC-to-telephone voice communications over the Internet. The interface adapter includes a hybrid transformer circuit for interfacing a two-wire circuit of the cordless telephone and a four-wire circuit of the computer sound card. This hybrid transformer circuit cancels out the voice echo that would otherwise exist due to mismatched impedances between the two media and/or from leakage of the signal being transmitted and received on the same pair of telephone lines. A Universal Serial Bus (USB) plug may be provided to receive a bias voltage from the PC for biasing circuits of the cordless telephone system through the interface adapter. Advantageously, the preferred interface adapter utilizes 100% passive components for a low-cost yet effective means to provide mobility for an end user during voice communications over the Internet.

Abstract: The telephone line coupler circuit has a single transmit opto-coupler whose output includes a DC bias component connected to a gate of a line seize switch for connecting a DC line seize load across the ring and tip contacts of the telephone line. The line seize switch is saturated by the transmit opto-coupler bias output and the AC component of the transmit opto-coupler output is sent over the telephone lines. The receive opto-coupler is used both for receiving communications signal and for detecting the ring signal. The band pass filter connected to the output of the receive opto-coupler may be switched to pass a ring signal frequency band or a communications frequency band. The circuit operates using two opto-coupler devices while conventional circuits require four opto-coupler devices.

Abstract: The telephone line coupler circuit has a single transmit opto-coupler whose output includes a DC bias component connected to a gate of a line seize switch for connecting a DC line seize load across the ring and tip contacts of the telephone line. The line seize switch is saturated by the transmit opto-coupler bias output and the AC component of the transmit opto-coupler output is sent over the telephone lines. The receive opto-coupler is used both for receiving communications signal and for detecting the ring signal. The band pass filter connected to the output of the receive opto-coupler may be switched to pass a ring signal frequency band or a communications frequency band. The circuit operates using two opto-coupler devices while conventional circuits require four opto-coupler devices.

Abstract: An impedance blocking filter circuit is provided for use in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit. The filter circuit includes first, second, and third inductors connected in series between a first input terminal and a first common point. A first resistor has its one end connected also to the first common point and its other end connected to a first output terminal. Fourth, fifth and sixth inductors are connected in series between a second input terminal and a second common point. A second resistor has its one end also connected to the second common point and its other end connected to a second output terminal. A capacitor has its ends connected across the first and second common points.