Abstract: Problems arise when using an Integrated Service Digital Network infrastructure (6) for providing Asymmetrical Digital Subscriber Line technology. These problems do not always occur but depend on the distance between the end-user location (12) and the central location (11), and the type of network termination (3), and result in the impossibility for the end-user to make voice calls or to send data. The problems are caused by the Asymmetrical Digital Subscriber Line splitters (4) and (7), which change the transmission characteristics of the Integrated Service Digital Network infrastructure (6) between the end-user location (12) and the central location (11). The transmission characteristics that are changed by the Asymmetrical Digital Subscriber Line splitters (4) and (7) are impedance, propagation time and insertion loss. The deviation is frequency-dependent and falls outside the internationally-defined ranges for these transmission characteristics.

Abstract: An inter-network line level adjustment system includes a switch (SW1) and a processing unit (24) for identifying calls between a remote telephone network and a local telephone network. Echo cancellers (20) and/or speech coders (22) collect line level data associated with the identified calls. The processing unit (24) determines statistical properties of the collected line level data. Finally, the processing unit (24) instructs the echo cancellers (20) and/or speech coders (22) to adjust, based on the determined statistical properties, line levels of future calls between the remote telephone network and the local telephone network to a desired line level.

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: A method and apparatus is provided for performing an active impedance differential current feedback. A signal is received. A current feedback of an output signal in an active feedback synthesis mode is performed based upon the signal. The active current feedback includes using an active feedback network for conditioning an output signal, converting the signal into a differential current signal, and summing at least two components of the differential current signal for performing a differential feedback.

Abstract: An improved line driver and method for increasing the power efficiency, signal accuracy, and stability of a transmit signal on a transmission line are disclosed. The improved line driver uses a negative feedback control loop, thereby enhancing operational stability and suppressing both amplifier imperfections and discrete component manufacturing variances. Furthermore, when the improved line driver output stage is integrated with a hybrid, the composite circuit provides a power efficient full duplex solution for line driver applications. In a preferred embodiment, the improved line driver may comprise an active line termination control loop with current sense feedback, a first amplifier, and a second amplifier. The present invention can also be viewed as providing a method for increasing the stability, power efficiency, and accuracy of a line driver in a duplex transmission system.

Abstract: A circuit arrangement for signaling in telecommunications networks has a first connection and a second connection for a first and a second conductor, respectively, in a transmission line. The first connection is connected to the first input of a rectifier, and the second connection is connected to the second input of said rectifier. The positive output and the negative output of the rectifier are connected to one another via a variable resistance. A third connection for a third conductor in the transmission line can be connected via the series circuit formed by a switch and a first diode to the positive output of the rectifier, and via the series circuit formed by the switch and a second diode to the negative output of the rectifier.

Abstract: A subscriber line driver (SLD) is provided for the continuous and automatic transformation of the characteristics of a communication system signal so that the signal conforms to a power spectral distribution (PSD) standard. The signal is transformed by the SLD which may increase (amplify) portions of the signal to a predefined specification, decrease (attenuate) portions of the signal to a predefined specification, and/or frequency modulate or filter the transmit signal frequencies to fit within the communication channel frequency bandwidth as defined by a predefined frequency band. After modification by the SLD, the transformed communication signal is injected (transmitted) into a communication transmission line. An SLD device can be employed in a variety of communication systems such as a public telephony system, a private branch exchange (PBX), a coaxial cable system, a fiber optic system, a microwave system, a radio communication system or the like.

Abstract: A method and apparatus for coupling an xDSL transceiver with a subscriber line is disclosed. A hybrid circuit is disclosed which exhibits a different relative gain factor for transmitted signals and received signals. The difference in gain factors results in part from a combined balance circuit and transformer which exhibit a different coupling ratio between the primary and secondary coils on the receive path and the transmit path. The hybrid circuit may be used to isolate the receive signal from the transmit signal in the full duplex mode of operation. The gain from the transmit port to the receive port is minimum and most of the energy is transmitted to the subscriber line. In an embodiment of the invention a hybrid circuit for communicating a transmit signal and a receive signal across a subscriber line is disclosed. The hybrid circuit includes: a transformer and a balance circuit.

Abstract: A cable balance network for use in a full-duplex telecommunication system and method for optimizing the transhybrid loss of a full-duplex to half-duplex conversion circuit, said cable balance network comprising: (a) a plurality n of resistors Rn, each of said resistors Rn having a fixed resistance value dependent upon the impedance seen by the full-duplex port, and each of said resistors Rn, having a positive node and a negative node; (b) a plurality n−1 of capacitors Cn−1, each of said capacitors Cn−1 having a fixed capacitance value dependent upon the impedance seen by said full-duplex port, and each of said capacitors Cn−1 having a positive node and a negative node; and (c) a circuit configuration comprising at least two of said resistors R1, and R2 (n≧2) and at least one of said capacitors C1, such that all the negative nodes of each of said resistors Rn are effectively connected together, and such that the capacitor Cn−1is connected between the positive nodes of resistors

Abstract: A bidirectional equalizer arrangement for cancelling the effect of residual capacitance and/or residual resistive loss in a separation filter having a low-pass filter and a high-pass filter. The equalizer comprises a differential amplifier whose input forms the equalizer's connection terminals, and whose output is coupled, via a transformer, to a positive feedback circuit that includes the transformer's secondary winding, a capacitor and a resistor of predetermined values. When the equalizer is operatively coupled to the low-pass filter, the positive feedback circuit produces a feedback current of opposite polarity and equal magnitude to that produced by the residual capacitance and/or the residual resistive loss, thereby substantially cancelling their effect. The equalizer may be advantageously used with an ADSL/POTS separation filter.

Abstract: An apparatus and related method for matching antenna pattern to the mobile phone. The mobile phone includes an antenna, at least one radio frequency (RF) circuit and a diplexer for relaying signals of the RF circuits to the antenna. Each RF circuit has its own matching circuit, such that the antenna performance for receiving and transmitting signals can be independently adjusted without affecting each other.

Abstract: A system for transmitting information at high speed to a subscriber's digital terminal (30). According to the invention, said system comprises at least passive adapter means (10, 10′) between an xDSL link (1) for high speed transmission of information and a mains voltage electricity network (2) having at least said subscriber's digital terminal (30) connected thereto. The invention is applicable to high speed transmission over the terminal portion of a subscriber line.

Abstract: A universal interface adapter circuit interfaces, for example, a wireless communications headset with any type of communications system, including those that require push-to-talk (PTT) signaling. The interface adapter is comprised of several main components, including an RF signaling receiver, a microcontroller and associated circuitry for decoding and processing the received signals, and programmable impedance matching and line interfacing circuitry for interfacing a wireless communications headset system base to a communications system. A signaling transmitter, which is preferably portable (e.g., handheld), is employed by the wireless headset user to send signals to the signaling receiver. In an embodiment of the invention directed specifically to push-to-talk (PTT) signaling, the wireless headset user presses a button on the signaling transmitter when they wish to speak. This sends a signal to the microcontroller which decodes the signal and recognizes the signal as being a PTT request.

Abstract: A telephone line interface circuit is disclosed having intelligent line current control that can adjust to the various requirements of worldwide telephone systems (DC masks), and/or can reduce the power consumed by the interface circuit. A controller reads a voltage value and based on the theoretical model of a telephone line network, and the expected current/voltage characteristic, as dictated by the appropriate DC mask. The controller sets the line current (via an output voltage) to an optimum value and causes the line voltage to adjust so as to comply with the DC mask and/or minimize power dissipation in the circuit.

Abstract: An interface apparatus interposed between a cordless telephone base unit and a personal computer sound card. Such interface emulates a Central Office connection with respect to the telephone and a mic and speaker connection with respect to the computer sound card. The apparatus is suitable for all cordless telephones regardless of frequency allocation standards because the interface occurs at the RJ-11 modular jack of the cordless phone base, normally intended for connection to a CO line. Differences in telephone line regulations that exist among countries are accounted for with no burden of complexity to the user of the present invention. The interface comprises active and passive circuits perform two-wire-to-four-wire conversion and signal conditioning. Local loop current may be obtained from batteries or a suitable AC power adapter.

Abstract: An apparatus and method to implement a highly efficient low power line driver. In a first embodiment, the invention provides a method to increase the power efficiency of a line driver. The method includes supplying a digital signal processor output to a first subtractor; supplying the first subtractor output as an input to a modulator of a line driver; subtracting the line driver output from the digital signal processor output at the first subtractor; filtering the line driver output with a low pass filter; routing the line driver output to an impedance match filter; providing a first analog-to-digital converter and a second subtractor to subtract the line impedance match filter output from the low pass filter output; providing a digital filter and a second analog-to-digital converter; and subtracting the digital filter output from the first analog-to-digital converter output at a third subtractor to output a feedback signal to the digital signal processor.

Abstract: A method and apparatus is provided for impedance matching for a system capable of supporting voice and data bands. The method includes receiving an input signal having a voice and data band, filtering at least a portion of the data band of the input signal to provide a filtered signal, and adjusting the impedance of the system for the voice band in response to the filtered signal to provide an output signal.

Abstract: The present invention provides apparatus and methods for attenuating signals received from a source over a data transmission line, having an unknown resistance, to achieve optimized signals in various data terminal and data communications equipment. In a preferred embodiment, a resistor network is operably coupled between the transmission line and a means for processing the signal, such as a digital processor, an ADC and a DAC. The resistor network comprises a termination resistor that is associated with a termination voltage, a variable resistor and another resistor. During use, a switch is operably positioned between a plurality of switch positions so that two voltage measurements will lead to the determination of the voltage of the source and the termination voltage within the resistor network. Once these voltages are known, the unknown resistance can be estimated.

Abstract: The present invention relates to a filter arrangement (8C) and a method for frequency filtering and impedance conversion. The invention makes it possible to perform frequency filtering and impedance conversion using fewer inductors than what is required using previously known technique for obtaining the corresponding effect. According to an alternative aspect the invention provides more effective frequency filtering and equivalent impedance conversion compared to the prior art when the same number of inductors are used. According to the invention an electromotive force (e′) is generated in at least one filter coil (L1, L4). The electromotive force is adjusted so that the filter arrangement (8C) receives a desired impedance converting effect. A filter arrangement according to the invention, compared to the prior art, in this manner provides a filter integrated with an impedance converter. Compared to the prior art the invention can make a saving of one transformer per impedance converter possible.

Abstract: A line driver for connection to a transmission line having a characteristic impedance. The line driver can be arranged in a voltage-mode or a current-mode configuration. In the voltage-mode configuration, the line driver comprises an amplifier, a transformer, a reference resistor and a feedback circuit. The first winding of the transformer has a first end connected to the output of the amplifier and the second winding is connectable to the transmission line. The reference resistor has an end connected to the second end of the first winding at a junction point and the feedback circuit is connected to the input and output of the amplifier and also to the junction point. The reference resistor has a resistance equal to {fraction (1/k)} times the characteristic impedance of the transmission line. The feedback circuit is arranged to produce a voltage at the output of the amplifier substantially equal to −(K−1) times the voltage at the junction point, for a predetermined value of K.

Abstract: A digital device for controlling the DC line current on a telephone line which includes a digital device that utilizes a digital filter for setting the DC line current. By controlling the DC line current digitally, software can be used to set the DC line current in accordance with predefined characteristics. Predefined characteristics can be set to accommodate varying country specifications instead of using switches to control resistors and capacitors. In addition, changes in a country's requirements can be accomplished through software, instead of changing components or redesigning a circuit board. The device also incorporates a method for maintaining DC current level during changes in digital filter characteristics. The use of software results in increased flexibility by allowing an infinite number of settings via software or software updates, and allowing changes to be made quickly and easily throughout the world.

Abstract: Provided is a circuit for terminating a ring signal of a telephone network. A physical impedance is combined with a synthesized impedance to produce an impedance having a magnitude substantially equal to the ring termination impedance of a telephone network. The synthesized impedance is created by generating a current from a voltage controlled current source. By controlling the magnitude of the generated current, the magnitude of the synthesized impedance is also controlled. Because the specified ring termination impedances are known, a satisfactory impedance can be synthesized which results in the ring signal being properly terminated.

Abstract: Using a telephone line interface circuit with negative feedback, it is possible to control the current through the circuit so that the ratio of the voltage applied across the circuit to the current is the desired value of impedance. Voltage feedback from the line controls the current through the circuit, thereby reflecting a “virtual” impedance to the telephone line. By adequately filtering the voltage feedback, the reflected impedance to the line can be adjusted to any desired impedance function, without using the actual values of the impedance. The circuit is thus ideally suited for applications in which the impedance values need to be varied depending upon the characteristics of the telephone system.

Abstract: A method and apparatus for providing an improved telephone hybrid function is provided. The present invention uses a transformer having an galvanically isolated sense winding to improve hybrid performance. Performance improvements include removing the effects of variations in winding resistance, independently adjusting a pick-off voltage, reducing the effects of transformer leakage inductance, providing DC isolation between circuits and increasing the signal to noise ratio at the receiver.

Abstract: A diversity receiving apparatus for use in an OFDM transmission radio communication/broadcasting system where OFDM signals are received by a plurality of antennas and input into a plurality of receivers. The OFDM received signals are further transformed into frequency spectra. Channel frequency responses are calculated by using OFDM received signal frequency spectra and a reference frequency spectrum generated in a reference spectrum generator. OFDM received signal frequency spectra distortions are compensated by using corresponding channel frequency responses. The transformed OFDM received signal frequency spectra are input into a selector unit as first input signals, while the distortion-compensated OFDM received signal frequency spectra are input into the selector unit as second input signals. The selector unit then selects a second input signal corresponding to a first input signal having maximum amplitude or maximum power.

Abstract: A method and system for providing suppression of near-end speech energy for tone signal detectors. In accordance with the invention a system or device is connected between the tip and ring on a subscriber loop, the subscriber loop being connected to office equipment and that subscriber's station set. The system also includes a receive interface that is connected to either a tone signal detector or a frequency shift keying modulator. The system achieves speech cancellation by forming a Wheatstone bridge with a mirror circuit possessing a scaled image of the loop and office equipment impedance. In one embodiment of the invention the Wheatstone bridge is formed using the combined impedance of the loop and office equipment as the impedance that is to be matched by a set of balanced networks included within the system.

Abstract: An AC impedance matching architecture which provides programmable AC impedance matching in a given range using a digital filter to filter a signal fed back from the impedance matched line to generate an AC impedance emulation control signal. The AC impedance emulation control signal is combined with a transmit signal (if desired) and drives a voltage controlled current source, which is in parallel with a reference impedance. A voltage is developed across the reference impedance to drive, e.g., the telephone line. The reference impedance is chosen based on a desired maximum AC impedance. The gain of the digital filter, a first order sigma delta filter in the disclosed embodiment, is chosen based on the desired value of the AC impedance. The transfer function of the digital filter is derived based on a desired AC impedance.

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: The present invention synthesizes a prescribed impedance. The impedance is synthesized by generating a current having a value substantially equal to a voltage divided by a prescribed impedance. Sensing the line voltage and converting that sensed line voltage to its digital equivalent accomplish this first step. The digital line voltage is processed by a factor related to the prescribed impedance to produce an output voltage that has a value substantially equal to the sensed voltage divided by the prescribed impedance. The output voltage controls a voltage to current converter that generates the appropriate current across the points or terminals where the line voltage was measured. Thus, the prescribed impedance is generated across these points or terminals because the line voltage divided by the generated current is substantially equal to the prescribed impedance.

Abstract: A system for matching impedance in the circuitry of an xDSL communication device to improve noise cancellation resulting from signal leakage between transmit and receive signals. The system for matching impedance includes a transformer configured to couple an impedance, which is substantially equal to a line impedance, to a line coupling transformer, and is applicable to all known hybrid topologies. The transformer is ideally as closely matched to the line coupling transformer as possible. This technique allows greatly improved impedance matching in the hybrid, which directly benefits the performance of xDSL communication devices.

Abstract: Combined plain old telephone system (POTS) and digital subscriber loop (DSL) line card capable of suppressing low frequency transients. The line card includes the following elements. A DSL receive path receives DSL data from a loop. A POTS receive path receives POTS data from the loop. A combined POTS and DSL transmit path transmits POTS and DSL data to the loop. An impedance generator is coupled between the POTS receive path and the combined POTS and DSL transmit path for synthesizing impedance for signals in the combined POTS and DSL transmit path. A low frequency detector selectively applies a high pass filter to an output of the impedance generator for filtering the low frequency transients. Further, a clipped signal detector and a variable pole high pass filter are provided in the POTS receive path. The clipped signal detector in the POTS receive path triggers a switch that discharges stored transient energy in the receive path.

Abstract: A circuit for communicating digital data is disclosed. The circuit can connect with up to 12 digital data lines (L0 through L11) for communication under a T1 or E1 standard. Control processor 36 selects the appropriate communication standard to be used by each framer/line interface processor F0 through F11, and communicates these over control bus 38. Control processor 36 also selects an appropriate line impedance for each line input/output circuit IO0 through IO11, and communicates this information over control bus 38 to control logic 34. Control logic 34 uses control lines 39 to electronically select the impedance for each line input/output circuit IO0 through IO11. Circuit 22 can be easily configured or reconfigured to receive data with different data formats and line impedances. In one preferred embodiment, each framer/line interface processor and line input/output circuit can be independently controlled, such that multiple communication formats can be simultaneously processed by circuit 22.

Abstract: A device for echo attenuation in a digital transmission system comprises an impedance replica of the transmission path. The impedance replica consists of a terminating resistance replica, a transformer replica, and a transmission line replica. The device may further comprise a bridged tap replica. The transformer replica and the bridged tap replica are provided as on-chip components. The main transformer inductance replica and all components of the bridged tap replica are variable and may be set by software control.

Abstract: Multiple digital audio transformer circuits are included in a module for mounting in a chassis. These digital audio transformer circuits are comprised of a front mounted twisted pair digital audio cable connector and a rear mounted coaxial cable connector, with circuitry including baluns electrically linking the front and rear connectors to reduce the impedance of the signal and attenuate the amplitude of the signal voltage. In one embodiment, the module may also include removable attenuation pads accessible through the front face of the module to allow variation of the level of voltage attenuation. The preferred embodiment of the module bi-directional transforms 110 Ohm digital audio signals and 75 Ohm coaxial signals. If transformation of other levels of impedance are desired, modules may also allow for removal and replacement of the baluns. A digital audio transformer system including multi-circuit modules and rack mount equipment chassis is also provided.

Abstract: The invention relates to a circuit arrangement (1) for coupling a communication device (3) having at least one unidirectional transmission channel (4) and at least one unidirectional receive channel (5) to a bidirectional communication device having at least one differential amplifier (Q1, Q2). For optimizing the properties of the coupling by such a circuit arrangement (1) with the simplest possible means, there is proposed to couple the control inputs (C, D) of the differential amplifier (Q1, Q2) to the outputs of a transmission channel (4), its outputs (A, B) to the bidirectional communication device and the negative feedback path of the differential amplifier (Q1, Q2) to an input (E) of a receive channel (5). Its negative feedback path includes a matching impedance (R4, R5, C2) for adjusting a DC voltage/DC current characteristic (6) for the circuit arrangement (1) when connected to the bidirectional communication device.

Abstract: To reduce power losses in a SLIC comprising first and second current amplifiers supplying line current to respective wires of a two-wire transmission line to a load, a line current detector detects line currents below a threshold value. For line currents above the threshold value, the second amplifier is supplied from a first battery with a substantially constant voltage. A voltage regulator is connected with its output terminal to the second amplifier, with its current supply terminal to a second battery of higher absolute voltage than said first battery, and with its input terminal to the detector. In response to line currents below said threshold value, the detector outputs control signals proportional to the detected line currents to control the output terminal of the voltage regulator to supply the second amplifier as well as the load from the second battery.

Abstract: A common mode termination includes a shielded connector, a receive section and a transmit section, each section comprising an isolation transformer, a common mode transformer, a reference autotransformer, and an AC shield return. Each transmit section reference autotransformer and receive section reference autotransformer has a center tap for the application of a bias voltage and a bias voltage return. The bias voltage is fed through a common mode transformer, and the resultant common mode termination reduces the conduction of EMI from the serdes coupled to the common mode termination to cables connected to the connector. This common mode termination also provides a reference termination for the copper twisted pair cable and reduces resonances on the cable. Finally, this termination also provides filtering on the DC power source wires and improves noise immunity from transients coupled onto the twisted pair cable into the system.

Abstract: A splitter separates telephony traffic (POTS) from digital subscriber line (ADSL) traffic occupying a higher frequency band. The splitter comprises a low-pass filter for passing the telephony traffic, the low-pass filter being operable to vary its filtering response between a first low-pass response for use during telephony speech traffic, and a second, more restrictive, low-pass response for use during at least part of the time that telephony signalling traffic is present. During speech traffic a filter is used which provides a good impedance match with a telephony terminal or linecard so as to minimize detrimental effects on sidetone and echo performance which may impair a user's speech quality. The filter response can be varied according to a detected property of the telephony traffic, such as amplitude or rate of change of amplitude of the traffic.

Abstract: A communication system of the present invention utilizes ring detection circuitry on both sides of an isolation barrier. More particularly, the ring detection circuitry may include ring burst circuitry on the phone line side of the isolation barrier and ringer timing circuits on the powered side of the isolation barrier. The digital burst peak signal may be transmitted through the isolation barrier to the ringer timing circuits. By splitting the ring detection circuitry so that the ringer timing circuits are placed on the powered side of the isolation barriers, a significant reduction in the power usage on the phone line side of the barrier related to the ring detection function may occur. The outputs of the ringing timing circuits may be provided to circuits on either side of the isolation barrier. Thus, the ring detection function may be accomplished in a system utilizing an efficient bidirectional capacitive barrier while still minimizing power usage on the line side of the barrier.

Abstract: In a splitterless Digital Subscriber Line (DSL) modem 30, a receiver architecture (100) that permits monitoring of harmonics within the upstream channel of a DSL connection. The receiver (100) can detect the harmonics by monitoring the harmonics in some empty tones or specified tones. A threshold can be set to differ the normal noise power and harmonics power in those empty or specified tones. When a POTS device (10) coupled to same wire line pair (20) as the DSL modem (30) goes off-hook, the DSL modem (30) can switch from the normal state to an off-hook state in which the harmonics are reduced to minimum by transmitting only the upper sub-band tones of the upstream transmission channel at reduced power levels.

Abstract: A method and apparatus is provided for impedance matching for an apparatus capable of supporting voice and data. The method includes receiving an input signal having at least one of a voice component, data component, and DC component, and filtering at least a portion of the data component and DC component of the input signal to provide a filtered signal. The method further includes adjusting an input impedance of the apparatus to a first preselected value for the voice band in response to the filtered signal and adjusting the input impedance of the first apparatus from the first preselected value to a second preselected value. The method includes adjusting at least one of a magnitude and phase of the filtered signal to adjust the input impedance to a third value.

Abstract: Method for measuring a load impedance (ZL) of a load circuit which is connected to an SLIC circuit (6) of an analog terminal connection of a terminal device, having the following steps: specifically a digital toll signal (x1) is generated by means of a Codec circuit (13) connected to the SLIC circuit (6), said toll signal (x1) being converted into an analog toll signal; the analog toll signal is output by the SLIC circuit (6) to the load circuit; an analog voltage which is brought about at the terminal connection (4,5) of the terminal device of the SLIC circuit (6) via the analog toll signal is sensed; the digital toll signal (x1) is filtered by means of an adaptive filter (39) which is provided in the Codec circuit (13) and has adjustable filter coefficients (g1, g2) for generating a filtered digital comparison signal (yv) which is converted into an analog comparison voltage (Uv); the filter coefficients (g1, g2) of the adaptive filter (39) are adjusted until the analog comparison voltage (Uv) and the analog

Abstract: A network interface circuit employing differentially driven capacitive couplings across a high voltage isolation boundary and in which a &Sgr;/&Dgr; CODEC is positioned on the line side of the high voltage interface. In this manner, only four wires cross the high voltage boundary, namely differential pairs for transmit data and receive data. The transfer functions for setting AC and DC parameters, such as impedance matching, are provided by digital filters. Further, with the CODEC on the line side of the high voltage isolation interface, the data which crosses the interface is modulated at the &Sgr;/&Dgr; data rate and, thus, capacitive coupling can be used across the high voltage isolation boundary without the loss of DC data.

Abstract: An interface device for transmitting data for data communication in an analog exclusive line includes a modem unit for modulating data, an impedance matching unit for matching an impedance with the analog exclusive line, an FXS signal unit for recognizing a connection request signal from an FXO interface, a hybrid 2:4 wire conversion unit for converting a four wire interface from the modem unit into a two wire interface for the analog exclusive line, and a main processor. The FXS signal unit uses the analog exclusive line which does not have an exchange, and thus performs the data communication as in the PSTN. The modem unit is informed of the connection request signal from another device by a local ring generating unit.

Abstract: A selectable impedance matching circuit for matching the impedance of a telephone handset adapted for either a carbon microphone input or an electronic microphone input to the impedance of a headset microphone. The selectable impedance matching circuit includes a switch for connecting the headset microphone to the handset microphone input via a full wave bridge circuit, or connecting the headset microphone to the handset microphone input via an isolation transformer and resistor load.

Abstract: A system and method for matching a device to a transmission line are disclosed. A matching circuit having optically coupled devices is biased so that harmonics of a reference signal, such as a dial tone, are eliminated. Suppression of the reference signal harmonics indicates a correct impedance match between the matching circuit and the transmission line. The matching circuit also provides two-wire to four-wire conversion. After the matching circuit's impedance is adjusted, the circuit gain is balanced and the circuit is further biased to eliminate echoes. The impedance matching and circuit biasing operations are controlled by a digital signal processor. Before data or other signals are processed by the digital signal processor, an inverse transfer function is derived for the matching circuit. Received signals are convolved with the inverse transfer function to compensate for matching circuit distortion.

Abstract: A line interface apparatus includes a line coupling transformer having first and second windings, and an impedance matching circuit connected to the first winding. The impedance matching circuit includes a first section characterized by a first impedance, a second section characterized by a second impedance, and a switch circuit, connected to the first and second sections and to the first winding of the line coupling transformer, for switching either the first or the second section in series with the first winding of the line coupling transformer. An echo of a transmitted signal is replicated and subtracted from a composite signal comprising a received signal and the echo of the transmitted signal. The result of the subtraction is compared to a threshold value to indicate whether a loop connected to the second winding of the line coupling transformer has an impedance about equal to a first impedance or about equal to a second impedance.

Abstract: A telecommunications card for use in a telecommunications terminal. The telecommunications card includes at least one programmable channel capable of satisfying different telecommunications standards based on configuration input. The different telecommunications standards, such as impedance, gain, and transhybrid impedance, relate to different countries. The card may include circuit blocks that provide different circuit paths that correspond to different telecommunications standards. The card may include a programmable codec for impedance and/or transhybrid balance.

Abstract: A signal line driving circuit with power control for selectively reducing internal power dissipation when driving an external load. While driving the external load with a constant current the output voltage generated across such load is monitored. If the load impedance decreases sufficiently to cause the output voltage to fall below a predetermined threshold value and, therefore, cause the voltage across the signal line driving circuit to increase, the magnitude of the power supply voltage is automatically reduced, thereby reducing the voltage across the signal line driving circuit. Such a signal line driving circuit is particularly advantageous as a subscriber line interface circuit (SLIC). As the subscriber goes from an on-hook condition to an off-hook condition and if the subscriber loop is sufficiently short (or low in impedance), a lower power supply voltage is used to minimize the power dissipation of the SLIC while still maintaining the required subscriber loop current.

Abstract: Systems and methods are described for subscriber loop range extension using negative-impedance repeaters. A method includes: extracting a signal from a digital subscriber loop; then amplifying the signal utilizing a negative impedance converter; and then inserting the signal back into the digital subscriber loop. An apparatus includes a negative impedance converter; a downstream high-pass filter electrically coupled to both i) a digital subscriber loop and ii) the negative impedance converter; and an upstream high-pass filter electrically coupled to both i) the negative impedance converter and ii) the digital subscriber loop.