Abstract: A system for driving a first signal onto a wireline includes a driver and feedback circuitry. The driver drives a deterministic signal onto the wireline with an unknown impedance load. The feedback circuitry measures a quality of the output signal from the wireline and modifies a signal strength of the first signal based on the quality of the output signal. The driver then drives the first signal onto the wireline with the modified signal strength.

Abstract: A signal receiving circuit having an equalizer calibration function. The signal receiving circuit includes a sampling circuit, output driver and clock signal generator. The sampling circuit captures samples of a data signal in response to a sampling clock signal. The output driver outputs an equalizing signal to an input of the sampling circuit in response to a first clock signal. The clock signal generator adjusts a phase of the first clock signal to achieve phase alignment between transitions of the equalizing signal and transitions of the data signal.

Abstract: A system and method in accordance with a non-limiting aspect minimizes echo return loss in a communications system. The dial tone is broken on an analog telephone line connected to a hybrid circuit having selectable impedance configurations and that interfaces a digital communications circuit and the analog telephone line. A white noise signal as a test call is inserted through the hybrid circuit onto the analog telephone line corresponding to a selected impedance configuration. The returned white noise signal is used for measuring the echo return loss. The test call is dropped. This process is repeated at different impedance configurations to obtain echo return loss measurements at each of the impedance configurations. The optimum impedance setting configuration is determined based on the results and applied to the hybrid circuit and typically set during a running telephone configuration.

Abstract: Transmission properties of a telecommunications transmission line may be estimated with improved accuracy by numerical solution for ? of Zin·j?^C=?coth(?). At least one curve is adapted to ? solutions already obtained and a starting point for numerical solution is selected in dependence of the at least one curve and in dependence of an already obtained solution close in frequency. In a first frequency range, starting points for numerical solution may be calculated from a biquadratic equation. In a second frequency range, a line in the complex plane may be adapted to solutions already obtained and new starting points selected in dependence of the line and in dependence of the previous solution. In a third frequency range, two lines in the frequency plane may be adapted to solutions already obtained and new starting points selected in dependence of the lines.

Abstract: An antenna tuner is placed between a Power Amplifier (PA) and an antenna. The antenna tuner includes programmable components that can be tuned in order to effect an impedance translation between the antenna and the PA output. In an embodiment, the antenna tuner is adapted dynamically based on changes in the impedance of the antenna. In another embodiment, the antenna tuner is controlled based on measurement of the voltage reflection coefficient S11.

Abstract: Method, arrangement and devices for calibration of a line driving device, such as a DSLAM, having a line port. The method comprises deriving of a first parameter vector, PVinf, for example Hinf. The parameter vector PVinf is derived by performing, at a first site, an echo measurement on the line driving device while the line port on said line driving device is open. The method further comprises calibrating the line driving device based on the first parameter vector PVinf and a second parameter vector PVref, which second parameter vector is based on information on echo measurements performed on at least one reference line driving device.

Abstract: A method and circuit for matching impedance, wherein, a peripheral impedance detection module detects the user telephone impedance and outputs information about the user telephone impedance; an analog switch handover module provides an impedance matching path between the user telephone impedance and an impedance matching module according to information about the user telephone impedance output by the peripheral impedance detection module; the impedance matching module provides a corresponding impedance to match the user telephone impedance through the impedance matching path provided by the analog switch handover module. The above-mentioned technical scheme realizes the impedance matching when communicating between a wireless access box and telephones with different impedance modes. The matching process is automatic and flexible and does not need the manual configuration, and the realization technology is simple and reliable, and the cost is low.

Abstract: A receiver may be operable to receive a signal. A sequence estimation module of the receiver may generate estimated symbols corresponding to the received signal. The generating of the estimated symbols may use tap information associated with one or both of a pulse shaper via which the signal was transmitted and an input filter of the receiver. The sequence estimation module may generate a reconstructed signal based on the estimated symbols and the tap information. A feed forward equalizer (FFE) of the receiver may adapt a plurality of tap coefficients of the FFE based on the reconstructed signal. The signal may be equalized via the FFE. The adaptation of the tap coefficients of the FFE may be based on a least-mean-square (LMS) process for minimizing a mean square of the error signal. An output signal of the FFE may comprise a power gain compensation.

Abstract: In a line driver/receiver circuit where the line driver is connected with its output terminals to a load for supplying a transmit signal thereto and where the receiver is connected with its input terminals to the load for simultaneously receiving a receive signal therefrom, the transmit signal on the input terminals of the receiver is canceled by connecting the output terminals of the line driver to the load via equal complex sense impedances of an impedance value that is much smaller than the impedance value of the load impedance to match the load impedance, connecting the input terminals of the receiver to the load via equal first resistors and to respective output terminal of the line driver via equal second resistors, and providing transconductance amplifiers to sense the voltage across the sense impedances and supply corresponding currents to respective input terminal of the line driver.

Abstract: A system and method for processing a communication signal from a wireline is provided. The system comprises a coupling unit and signal processing circuitry. The coupling unit comprises a transformer and is configured to receive the communication signal from the wireline. The coupling unit is also configured to generate a first signal based on amplifying or attenuating the communication signal according to a first winding ratio of the transformer and a second signal based on amplifying or attenuating the communication signal according to a second winding ratio of the transformer. The signal processing circuitry is configured to process the first signal and the second signal.

Abstract: A communication terminal devicecapable of being connected with an external telephone and of receiving and transmitting facsimile data from and to a network, includes: an off-hook detector configured to detect an off-hook condition of the external telephone, an semiconductor DAA (Data Access Arrangement) including an impedance switcher configured to switch impedances and a direct-current resistance switcher configured to switch direct-current resistances; an impedance switching controller configured to instruct the impedance switcher to switch the impedances; a direct-current resistance switching controller configured to instruct the direct-current resistance switcher to switch the direct-current resistances, wherein, when the off-hook detector detects the off-hook condition of the external telephone, the impedance switching controller instructs the impedance switcher to switch the impedances and the direct-current resistance switching controller instructs the direct-current resistance switcher to switch the d

Abstract: A system and method in accordance with a non-limiting aspect minimizes echo return loss in a communications system. The dial tone is broken on an analog telephone line connected to a hybrid circuit having selectable impedance configurations and that interfaces a digital communications circuit and the analog telephone line. After the telephone line is quiet, a white noise signal as a test call is inserted through the hybrid circuit onto the analog telephone line corresponding to a selected impedance setting configuration. The returned white noise signal is used for measuring the echo return loss corresponding to the selected impedance setting configuration. The test call is dropped. This process is repeated with multiple test calls each at a selectively different impedance setting configuration to obtain echo return loss measurements at each of the impedance setting configurations. The optimum impedance setting configuration is determined based on the results determined from the different test calls.

Abstract: A hybrid circuit without inductors is provided. Embodiments can be used in high-speed communication devices, including Cable modem and Digital Subscriber Line (DSL) devices. In particular, embodiments can be used in Very High Speed DSL (VDSL) devices. Embodiments provide a cheap and compact solution to the echo rejection problem in high-speed communication devices. Furthermore, embodiments perform at least comparably to conventional solutions with respect to key performance measures.

Abstract: Systems and methods for a line amplifier circuit are disclosed. The line amplifier circuit generally includes a first microphone transmit line, a second microphone transmit line, and a light emitting diode with a controllable variable light output. A photo-resistor cell is coupled across the first microphone transmit line and the second microphone transmit line. The photo-resistor cell is operable to attenuate gain on the first microphone transmit line and the second transmit line responsive to the controllable variable light output from the light-emitting diode.

Abstract: A system and method for processing a communication signal from a wireline is provided. The system comprises a coupling unit and signal processing circuitry. The coupling unit comprises at least one transformer and is configured to receive the communication signal from the wireline. The coupling unit is also configured to generate a first signal based on amplifying the communication signal according to a first winding ratio of the at least one transformer and a second signal based on attenuating the communication signal according to a second winding ratio of the transformer. The signal processing circuitry is configured to process the first signal and the second signal. The wireline is optionally a powerline.

Abstract: A multi-stage differential amplifier and method provides a gain versus frequency warping response characteristic that equalizes a transmission line of a given length to compensate for frequency-dependent attenuation. The warping response characteristic comprises the inverse of the attenuation versus frequency characteristic of the line, and affords a substantially flat system gain response over a predetermined frequency spectrum. The individual amplifier stages employ operational amplifiers, and are designed using SPICE simulations such that the individual responses of the stages are tailored so they combine to provide the required overall warping response to compensate the line.

Abstract: The present invention relates to the field of telephony and specifically to a method for correcting the degradation of telephone signal quality caused by analogue lines. The invention describes managing, via the receiver, a specific correction of telephone signal degradation caused by the length of the analogue line between the parties. Said line length between the receiver and the telephone switchboard to which said receiver is connected is stored in the receiver. Advantageously, the line lengths between the receiver of the called party and the corresponding switchboard are stored, for example in the director of the apparatus. During the call, said line length is taken into account by a specific correction means for said correction inside the receiver.

Abstract: A system includes a plurality of modules which are configured for determining a suitable impedance for a modem. The plurality of modules send signals with a plurality of signal frequencies to a telephone and receive feedback signals from the telephone under each of a plurality of impedances of the modem, compute a total decibel value of the feedbacks under each impedance, and determine a suitable impedance according to a minimum total decibel value from the plurality of total decibel values.

Abstract: A line driver comprises a driving amplifier receiving an input of the line driver, a current sense resistor connected between the driving amplifier output and the line driver output, and a feedback amplifier sensing the voltage across the current sense resistor and providing a corresponding feedback voltage that is proportional to the output current to the driving amplifier, thereby determining an output impedance at the line driver output. Precise output impedance can be realized by using a high precision resistor as the current sense resistor, and using resistive feedback amplifiers with accurate gains as the driving and feedback amplifiers. The resistance of the current sense resistor can be substantially less than the line driver output impedance, and the driving amplifier output voltage swing can be substantially less than twice the line driver output voltage swing.

Abstract: A hook switch turns on a transistor by connecting the positive electrode terminal of a capacitor to a base terminal of a transistor in an off-hook state, causing a speech circuit and telephone lines to be connected. The hook switch turns off the transistor by disconnecting the positive electrode terminal of the capacitor from the base terminal of the transistor in an on-hook state, causing the speech circuit and the telephone lines to be disconnected. A holding circuit holds the voltage at the positive electrode terminal of the capacitor at a substantially fixed value by charging the capacitor with electric power supplied from the telephone lines in an off-hook state.

Abstract: A monitor access is gradually applied an removed from a communications circuit, including a digital subscriber line (DSL), by a gradual monitor access (GMA) technique, in which a variable impedance element is gradually applied to the communications circuit until the monitor can be introduced to the communications circuit without data disruption.

Abstract: Programmable plain old telephone line impedance matching circuits that provide an accurate, integrated programmable termination and source impedance for a telephone line interface circuit (SLIC). The accurate matching of this programmable termination and source impedance with the termination impedance of the 2 Wire connection eliminates signal reflections on this connection and therefore removes the echo, which echo can lead to reduced signal quality in packetized VOIP systems. The programmable integrated impedance matching circuits of this invention use a programmable time continuous amplifier preferably in combination with a double sampling programmable switched capacitor feedback stage (sampling twice per clock cycle by sampling on the positive and negative phases of a non-overlapping clock cycle).

Abstract: The present invention relates to a method for attenuating near-end crosstalk between a remote received signal and a locally transmitted signal in a bidirectional signal transmission wherein said method comprises the step of producing an analog automatic feedback-driven correction loop in order to provide a no-correlation between said transmitted and received signals and to a hybrid circuit for enabling said method.

Abstract: A system and method for measuring a characteristic impedance of a transmission-line comprises transmitting energy to the line, and shortly after measuring the voltage/current involved and thus measuring the equivalent impedance. The measured characteristic impedance may then be used in order to determine the termination value required to minimize reflections. In another embodiment, the proper termination is set or measured by adjusting the termination value to achieve maximum power dissipation in the terminating device. The equivalent characteristic impedance measurement may be used to count the number of metallic conductors connected to a single connection point. This abstract is not intended to limit or construe the scope of the claims.

Abstract: A channel memory length selection method for wireless communication systems is provided. The method comprises estimating an initial channel impulse response (CIR) for the wireless communication system; determining a first refined CIR with a first group of taps and a second refined CIR with a second group of taps based upon the initial CIR, number of the second group of taps being less than number of the first group of taps; and selecting either the number of the first group of taps or the number of the second group of taps as the channel memory length according to an energy concentration criterion in regard to the first refined CIR and the second refined CIR.

Abstract: In a line driver/receiver circuit where the line driver is connected with its output terminals to a load for supplying a transmit signal thereto and where the receiver is connected with its input terminals to the load for simultaneously receiving a receive signal therefrom, the transmit signal on the input terminals of the receiver is canceled by connecting the output terminals of the line driver to the load via equal complex sense impedances of an impedance value that is much smaller than the impedance value of the load impedance to match the load impedance, connecting the input terminals of the receiver to the load via equal first resistors and to respective output terminal of the line driver via equal second resistors, and providing transconductance amplifiers to sense the voltage across the sense impedances and supply corresponding currents to respective input terminal of the line driver.

Abstract: A method for detecting inductive elements in a communication line, including the processes of: inputting a detecting signal to an end of the communication line; sampling the time domain voltage vector of one end of the communication line; generating the amplitude-frequency characteristic curve of the differential input impedance of one end of the communication line according to the time domain voltage vector; determining the number of the inductive elements in the communication line according to the number of the apexes or zeros on the curve. The present invention also discloses a device for detecting inductive elements in a communication line. By the present invention, the automatic detections of the number of inductive elements such as load coils or phone splitters in the communication line are implemented with the exact detection and the high efficiency, thereby lowering the cost of detecting failures of communication line.

Abstract: A system, method and apparatus is described that permits a user to configure or select the manner in which an audio signal transmitted or received over a telephony system, such as a wideband telephony system, is shaped or equalized. An implementation of the present invention allows a user to configure or select equalization control parameters on a call-by-call basis. Furthermore, an implementation of the present invention allows a user to associate equalization control parameters with a party initiating a call and/or a party receiving the call, thereby facilitating automated equalizer adjustment at call connection based on an identification of the calling party and/or the called party.

Abstract: An impedance matcher for matching the impedance of a high bit rate transmission channel of a copper-wired terminal installation comprising a high bit rate x-DSL modem (M) and a jack (P; P1; P2, P3), which automatically matches the impedance of the high bit rate transmission channel according to whether a modem is plugged into the jack of the installation or not. The impedance matcher comprises an adjustment module (10) adapted to insert a terminating impedance into the jack (P; P1, P2, P3) when it is not connected to said high bit rate modem (M), and a coupling module (20) adapted to be combined with said adjustment module (10) when said high bit rate modem (M) is connected to said jack (P; P1, P2, P3) to transform the impedance inserted into said jack to make it transparent to high bit rate transmission of broadband services.

Abstract: The invention concerns a method and a device for automatically adapting the levels of signals exchanged in a telephone network, between a first set and a second set. The method is characterized in that it consists in the following steps: digitizing the signal coming from the transmission line and received by the first set; on the basis of the digital data translating the signals exchanged with the transmission line; estimating the transfer function equal to the ratio of the signal received by the first set over the signal transmitted by the first set; respectively multiplying each of the exchanged signals by an appropriate gain determined on the basis of the estimated value of said transfer function. The invention is particularly applicable to telephones, videophones, fax machines or computers connected to a communication network.

Abstract: The invention provides a transmission apparatus (100) for transmission of electrical signals between a line driver (205), which is connected to a transmission line (201), and a switching center (301), having an analog feedback device (101) for coarse setting of a line voltage level (210) on the transmission line (201), and a digital feedback device (102), which is coupled to the analog feedback device (101) and has a feedback filter device (118), designed such that a filter input signal (404) can be converted to a filter output signal (405) at a rate which is lower than the sampling rate (fa) of an analog/digital converter (104).

Abstract: A method and apparatus is provided for performing an active impedance feedback. A signal is received. An active feedback synthesis is performed based upon the signal. Performing the active feedback synthesis includes using an active feedback network for conditioning an output signal and performing a signal summation of at least two components of the conditioned output signal for feedback.

Abstract: In a bidirectional transmission system including an I/O circuit, an I/O circuit, and a bidirectional transmission path which connects the circuits together, a variable impedance circuit is provided at an input end of the circuit connected to the transmission path. First transmission information (an output signal from the circuit) is sent from the circuit to the circuit via the transmission path as a voltage signal. Second transmission information (an impedance control signal from the variable impedance circuit) is sent from the circuit to the circuit via the transmission path as a voltage signal. The second transmission information is transmitted to the circuit as a change in the voltage signal which corresponds to a change in the circuit impedance Z of the variable impedance circuit.

Abstract: A subscriber line interface circuit apparatus includes an impedance bridge coupled to a subscriber line. A first pair of current drivers is coupled to the impedance bridge for driving a voice signal in a first frequency range onto the subscriber line. A second pair of current drivers is coupled to the impedance bridge for driving a data signal in a second frequency range onto the subscriber line. The impedance bridge couples the second pair of current drivers to the subscriber line across an output impedance of Z1+Z2 within the second frequency range.

Abstract: A method of selecting an optimum impedance for a loop start trunk line, comprising successively applying respective ones of a plurality of impedance settings to the loop start trunk line, for each impedance setting measuring the impulse response of the trans-hybrid echo path by applying audio test signals to obtain a time-domain trans-hybrid transfer function and deriving a frequency-domain spectrum representative of trans-hybrid loss, and then calculating figure of merit of the transfer function based on the power spectrum. Once all impedance settings have been tested, the optimum impedance is selected as the impedance setting associated with the highest calculated figure of merit.

Abstract: A passive echo cancellation circuit for reducing echoes on a subscriber line includes an output driver adapted to drive a downstream signal on the subscriber line. First sensing circuitry is coupled to the output driver and adapted to sense a current on the subscriber line to generate a first voltage. A balancing network is adapted to receive at least a portion of the downstream signal. Second sensing circuitry is adapted to sense a current in the portion of the downstream signal passing through the balancing network to generate a second voltage. An upstream driver is adapted to subtract the second voltage from the first voltage to generate an upstream signal.

Abstract: A line interface performs echo cancellation without the use of a hybrid filter network and includes a transmit path having a line driver, a single matching network terminating the line, and a single transformer. The transformer uses split windings on both the primary side and the secondary (line) side. Each half of the primary side is tapped to obtain a turns ratio of N1:N2, while each half of the secondary side of the transformer has N windings. The single matching impedance is coupled in parallel between the first winding and the second winding on each half of the primary side. Either the voltage across the matching impedance or the voltage across the receive terminals is bootstrapped to the receive signal through multiple negative feedbacks. The transfer function of the line driver is shaped as a first-order high-pass filter (HPF) to reject any out-of-band noise and distortion components.

Abstract: An apparatus for controlling operation of a recording device with a telephone configured for orientation in a first state and a second state includes: (a) an information conveying section for conveying information from the telephone to a recording locus in the recording device; (b) an indicating section for receiving a monitor signal having a first value when the telephone is in the first state and having a second value when the telephone is in the second state; the indicating section employs a single fixed bias to generate a first indicating signal when the telephone is in the first state and to generate a second indicating signal when the telephone is in the second state; and (c) an engaging section; the engaging section responds to the first and second indicating signals to orient the recording device for recording the information or for not recording.

Abstract: The present invention relates to a regulator for impedance balancing of first (104) and second wires (106) of a transmission wire pair having respective first and second impedances, the regular comprising: means (108) for determining a first signal (116) being representative of an average of square value of a first current (i1) flowing through the first wire, means (118) for determining a second signal (126) being representative of the average of square value of a second current (i2) flowing through the second wire, means (128, 130) for determining first and second coefficients (k1, k2) on the basis of the first and second signals, first feedback means (132, 134, 136) for regulating the first current on the basis of the first coefficient, second feedback means (138, 140, 142) for regulating the second current on the basis of the second coefficient.

Abstract: Methods for matching adaptive hybrids (15) to lines (16) for making reflectograms of the lines (16) measure (1) input impedances (Zmeas) of the lines (16), model (2) characteristic impedances of the lines (16) via physical models (Zphymod), estimate (3) parameters of the physical models (Zphymod) via cost functions which depend on the measured input impedances (Zmeas), convert (30) the modelled characteristic impedances into impedance values (13), and set (31) the adaptive hybrids (15) with the impedance values (13). Unwanted near-end reflections are minimised and wanted reflections can be measured. The physical models depend on frequencies s, Bessel functions Ji and parameters ai related to geometrical dimensions A, D and L and material constants ?, ? and ? of the lines (16).

Abstract: An XDSL system comprising a hybrid circuit in operative communication with a transmission line and an XDSL modem associated with a subscriber premises. The hybrid circuit comprises a plurality of selectable impedance circuits having different impedance values. A controller selectively engages each of the impedance circuits in-line with the XDSL modem and the transmission line. The controller records the performance of the modem with each circuit engaged, and selects the desired impedance circuit as a function of the performance characteristics associated with each of the impedance circuits. The impedance circuit which provides the best performance characteristic is selected as the impedance circuit for normal modem operation.

Abstract: A system for determining whether a telephone loop is capable of carrying a Digital Subscriber Line (DSL) signal. A Constant Amplitude Zero Auto Correlation (CAZAC) sequence signal is generated and transmitted through the loop plant to a central office and the received echo signal is processed using second-order statistics. The second-order statistics calculation permits determination of the echo signal amplitude and time between the echo signal and sequence signal. The echo signal amplitude and time may be used to obtain telephone loop characteristics such as loop length.

Abstract: A system for monitoring a plurality of communication circuits includes an impedance element configured to be switchably connected to one of the plurality of communication circuits. The impedance element is configured as a short circuit relative to the one of the plurality of communication circuits. The system includes an AC current mirror in communication with the impedance element. The system includes a monitor access element in communication with the AC current mirror. The system includes a communication circuit monitor configured to be connected to the monitor access element. To monitor the one of the plurality of communication circuits, the impedance element is switchably connected to the one of the plurality of communication circuits, thereby connecting the communication circuit monitor to the one of the plurality of communication circuits with a minimum of disruption to data communication within the one of the plurality of communication circuits.

Abstract: A technique for implementing impedance matching circuits 100 that use the transfer functions of each line impedance model. This technique allows implementation of an impedance match for a diverse number of line impedances reusing the same circuit 100 topology, by simply adjusting coefficients to accommodate different line impedances.

Abstract: A method of and apparatus for optimizing signal transformation from a twisted pair transmission line to a combination transmitter and receiver for a frame-based communications network, the transmitter having a transmit output pair port for transmitting signals onto the frame-based communications network over the twisted pair transmission line, the receiver having a receive input pair port for receiving signals from the frame-based communications network over the twisted pair transmission line. A transformer is coupled between the twisted pair transmission line and each of the transmit output pair port and the receive input pair port. The transformer has a coil across the twisted pair, a transmit coil across the transmit output pair port, and a receive coil across the receive input pair port. A transfer ratio between the transmit coil and the coil across the twisted pair is optimized for transmitting signals.

Abstract: In an electronic inductor circuit, an operational amplifier drives the base of the electronic inductor transistor, and receives negative feedback from the emitter of the transistor. The transistor and operational amplifier combine to form a voltage-controlled, current source (VCCS) with respect to the loop current. A voltage divider connected across the rectified Tip and Ring voltage (or another node of the circuit at an equivalent voltage) provides a DC reference to the positive input of the operational amplifier, so that the line current automatically increases with an increase in line voltage. A capacitor couples the transmit signal driver to the positive input of the operational amplifier. This electronic inductor circuit can be driven using a low voltage supply and provides sufficient linearity for high-speed modem applications.

Abstract: A system and method to reduce echoes in voice communications are described. Input data containing return loss values of a communication trunk within a communications network is received, the return loss values being measured at each frequency of a plurality of frequencies within a predetermined frequency band. An optimum transhybrid balance impedance is calculated from the input data. Finally, the optimum transhybrid balance impedance is transmitted to a user for further processing.

Abstract: This apparatus (1) comprises monitoring means for an environment (2). These means are an integral part of a mobile telephone, for example. Thus, if an event occurs, a telephone communication takes place for another telephone apparatus (5). From the apparatus (5) it becomes possible to listen to what is occurring in the environment (2). According to one embodiment a communication is made periodically and, according to another mode, a communication is made as soon as an excessively intense noise occurs in this environment. Application: monitoring of young children.

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 a desired frequency range due to the customer's terminal equipment from an ADSL a DSL 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.

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.