Abstract: An interface for coupling a modem port with a transmission line includes a hybrid converter having a variable gain amplifier coupling a transmit path of a first differential polarity and a received path of a second differential polarity.

Abstract: The present invention encompasses the reception of a Very High Speed Digital Subscriber Line (VDSL) signal from a twisted wire pair drop cable and an amplification circuit for compensating losses encountered while the signal is traversing the transmission medium. The amplification circuit receives a control signal from a microcontroller for providing selective gain to the signal based on the loop length or the power of the received signal. The amplification circuit incudes at least one resonator circuit which can be selectively switched in and out of the amplification circuit.

Abstract: The S0-interface for ISDN base access connects a four-wire line with a receiver line pair and a transmitter line pair to an ISDN terminal device, subject to potential separation within the interface. Each of the receiver lines has a respective capacitor for potential separation and the transmitter lines have a transformer. An inductance is connected into each receiver line and each transmitter line on the interface side. Preferably, the receiver line pair is connected to a voltage amplifier on the device side. The voltage amplifier has a voltage amplification in the same ratio as the voltage amplification of the transformer in the transmitter line pair.

Abstract: A low noise, low distortion, power efficient DSL/cable line driver has a double Wheatstone impedance bridge network that functions to prevent contamination of DSL signals that are received by and transmitted from the line driver. The line driver employs an external current sensing impedance that can be either purely resistive or complex and that can be selected to accommodate a particular transmission medium. The line driver further employs an internal programmable resistor that can be programmably adjusted to accommodate changes in transmission medium impedance to optimize sidetone rejection.

Abstract: A device comprises a termination impedance circuit, coupled to a communication link. The termination impedance circuit provides a termination impedance of the device, wherein the impedance is selectable. A second device comprises an echo-cancel hybrid circuit, coupled to a communication link, that provides an echo cancel characteristic, wherein the characteristic is selectable.

Abstract: A first device receives and processes signals from a communication link that supports a plurality of signal protocols. The device comprises a converter, coupled to the communication link, that outputs a sampled data stream, and a digital filter that filters the sampled data stream to separate signals associated with different signal protocols. A second device receives a first input sampled data stream representative of a first signal to be transmitted and associated with a first signal protocol and a second input sampled data stream representative of a second signal to be transmitted and associated with a second signal protocol, and combines the data streams into an output data stream which may be coupled to the communication link.

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: Echo cancelling in a communication line system, particularly an ISDN or XDSL system, is performed by means of a tunable hybrid (5) which comprises tunable passive elements and is integrated in the analog part of the front end (3), whereby the values of the tunable passive elements are controlled by digital control means (4), for example a microprocessor.

Abstract: A data access arrangement (DAA) having a transhybrid circuit for separating a transmit signal from a received signal by providing a transmit cancellation signal to the inverting input of a servo-feedback differential amplifier on the receive channel of the DAA. The cancellation signal is provided by a photodiode optically coupleable with a light emitting diode within a optical isolator on the transmission channel of the DAA. The gain of the cancellation signal can be independently controlled.

Abstract: Apparatus for interconnecting the Tip and Ring telephone line interface to subsequent communications equipment or circuits through a differential line bridge circuit that extracts one or more unidirectional paths containing predominantly far-end energy, wherein, near-end speech signals have been canceled. The differential line bridge circuit maintains the longitudinal balance of the telephone line and exhibits improved noise immunity in the recovered far-end signal. It permits all telephone supervisory, alerting and bidirectional communication signals to pass transparently between the telephone line interface and the subsequent communications equipment or circuits. Access to on-hook service signals, such as calling party identification and short text messaging data transmissions, is inherently provided by the line bridge.

Abstract: The present invention provides a switched impedance matching network which may be implemented in a hybrid circuit of a digital subscriber line (DSL) system, or in any other wire-bound communications system for which two-wire-to-four-wire conversion, and vice versa, must be accomplished. In accordance with the preferred embodiment of the present invention, the matching network comprises switchable circuit modules of discrete-valued resistor and capacitor components. Preferably, the circuit modules are assembled into an array of buffered first-order RC circuits. The buffers comprise amplifiers that are switched on or off to control the switching of the circuit modules. The buffer amplifiers also isolate the individual circuit modules from each other and eliminate the need to implement transmission switches between the modules. The switching of the buffer amplifiers clears or blocks the transmission paths between the individual modules, thereby providing the optimum path through the module array.

Abstract: A plurality of stations (S), for instance measuring probes, preferably comprising respective microprocessors (KL), are connected successively to a common two-wire line (SL). Supply voltages and synchronization signals are distributed through this line (SL) from a central unit (CU), and at the same time a full duplex communication between single stations (S) and the central unit (CU) is enabled.

Abstract: A method and device for managing the communication of high speed analog data across a communications line. If the communications line is not authorized for communication of high speed analog data, line conditioning applied (e.g., at a digital line unit or subscriber line interface circuit) to the communications line is varied. The line conditioning may include echo suppression and/or hybrid balancing. If the line conditioning unit is a digital signal processor, the line conditioning is varied by varying coefficients or line types. If the line conditioning unit is a circuit, the line conditioning is varied by varying a control signal to a selection element of the analog circuit.

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The alignment procedure identifies the optimal balance in a rapid manner. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: A current-limiting circuit (110) of a battery-feed circuit (FIG. 1) for a digital telecommunications line (T,R) provides a low start-up current limit (I3) when power is initially applied to the digital line. It automatically and gradually changes (40) to a high current limit (I1) as the load on the line is charged. When the load is fully charged, the circuit provides a low impedance to the line. Upon occurrence of a fault, the circuit switches back to the initial low current-limit state. The circuit comprises a feed transistor (Q1, Q11), a control transistor (Q2, Q12), and a high-impedance resistive circuit (R1-R4, R15). The feed transistor limits (403) current flowing to the R lead of the line to the high limit when the voltage across the feed transistor is low (0-V2) and the feed transistor is saturated.

Abstract: The invention concerns digital processing of analog signals in a telephone set. A signal path runs between a telephone line and the handset of the telephone. A digital signal processor is interconnected within this signal path, together with appropriate analog-to-digital, and digital-to-analog, converters. This approach allows digital processing of the information carried by the signal path. The digital processing facilitates, for example, (1) a high degree of separation of the handset's microphone signal from the received signal, and (2) independent control of volumes of the received signal and sidetone.

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The output is monitored by an AGC circuit which controls the output, and prevents hard clipping. This is particularly important for DTMF receivers. Additionally, the apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The hybrid has capacitors and resistors which can be switched into and out of the circuit by using simple transistor devices. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g., 500, 1500 and 3500 Hz; or 500, 1000, 1500, 2000, 2500, 3000, 3500 Hz).

Abstract: An apparatus connects a data processing system (10) with an analog telephone line and/or an ISDN line. The apparatus modulates and demodulates data from the data processing system (10) to either of the two different telephone protocols without adding unnecessary expense or noise to the system.

Abstract: The present invention provides a two-wire line conditioning apparatus having an improved calibration and cancellation circuit and provides an improved calibration method using a multitone calibration signal. The apparatus automatically adjusts an electronic hybrid as part of a calibration procedure so as to eliminate undesirable echo effects when calls are placed along the line. The results of the balancing procedure are examined, and the values of the resistance and capacitance from the balanced ciruit are compared to determine whether the line is loaded or non-loaded. The electronic hybrid balancing process and echo cancellation circuitry may also be utilized in a circuit for converting four-wire communications systems to two-wire communications systems. The line conditioning device of the present invention utilizes a multitone signal to simulate the voice frequency spectrum between approximately 500 Hz and 3500 Hz to probe the line side with a plurality of tones (e.g.

Abstract: An electronic voice circuit configuration can be connected through a first and a second line terminal to a telephone line. The electronic voice circuit configuration has a calling part, a transmitting device, a receiver device, a symmetrical modulator circuit with voltage stabilization, a symmetrical equipment impedance device with a device for symmetry control and direct-current limiting, and a symmetrical control device.

Abstract: An adaptive handset interface for interfacing a two-wire analog telephone instrument to a telephone set having a base unit connected to a handset via a four-wire handset cable. The interface is suitable for use with a variety of telephone sets produced by different manufacturers despite differences in the signalling between the telephone base and the handset. This is because, upon initiation of a learning technique, the interface automatically adapts to variations in signalling between the telephone base and handset among the different telephone manufacturers. To use the interface, the handset is unplugged from the handset jack of the telephone base and plugged into a handset jack of the interface. In addition, a four-wire cable is plugged into a telephone base jack of the interface and into the handset jack of telephone base. The interface includes a modular jack for coupling the interface device to the two-wire telephone instrument.

Abstract: In a driving stage for driving the two differential amplifier output stages of a subscriber line interface circuit, the driving stage is adapted to generate four driving currents in dependence on, on the one hand, transversal and longitudinal signals incoming to the driving stage and, on the other hand, a reference current, and to supply these driving currents in pairs to the two inputs of the differential amplifier output stages, all four of the driving currents being larger than zero.

Abstract: A transmission apparatus, connected via a hybrid circuit to a line, such as a modulator-demodulator which can perform stable echo cancellation, whether the level of the far-end echo is high or not, provided with a transmission unit which generates a transmission signal to be transmitted to the line via the hybrid circuit, a reception unit which receives the reception signal supplied from the line via the hybrid circuit, and a superimposing means for superimposing the reception signal applied to the hybrid circuit onto the transmission signal. The transmission signal onto which the reception signal is superimposed by the superimposing means is transmitted to the line via the hybrid circuit.

Abstract: A system and method for performing echo cancellation in a communications network including a bi-directional two-wire communication line, and a four-wire communication line having a transmit path and a receive path. The system includes a filter coupled to the receive path for reducing the echo component. The filter uses a number of filter coefficients and selectively employs either a full LMS coefficient calculation technique to compute the filter coefficients during a first period of time to achieve quick convergence, or a sign-sign LMS coefficient calculation technique to compute the filter coefficients during a second period of time to achieve improved stability and convergence. The filter uses a power estimation of the transmit path signal to direct the filter as to which coefficient calculation technique to use.

Abstract: An add-on card and connector including telephone functions is provided. The telephone functions are ones which are unlikely to be eventually performed on a mother board. A connection is provided which is adaptable to either an add-on sound card or eventually a mother board. The interface connection allows the use of the sound board to generate hold music for phone functions, as well as provide text to speech functions. In addition, the sharing of a common microphone and speaker is provided for.

Abstract: A transformerless battery feed circuit for a digital telecommunications line (100) presents a high impedance to digital signals and a low impedance to direct current, and provides a constant-voltage feed with current limiting. The battery feed circuit comprises a pair of transformerless controlled current sources, one for each lead (T,R) of the line, each taking the form of a high-gain transistor (Q1, Q2) having a collector coupled to a source of power (e.g., a battery V1), a base resistively coupled to the power source and capacitively coupled to its corresponding lead, and an emitter coupled to its corresponding lead. The battery feed circuit further comprises a pair of control circuits, one for each current source, each taking the form of a transistor (Q3, Q4) having a collector coupled to the base of the corresponding high-gain transistor, a base resistively coupled to the emitter of the corresponding high-gain transistor and to the power source, and an emitter coupled to the corresponding lead.

Abstract: An adaptive balance filter includes a transmission path, a reception path, and an adaptive filter having a signal output, a coefficient output for outputting filter coefficients, an error signal input, and a signal input coupled to the transmission path. There is a main filter which has a signal output, a signal input coupled to the transmission path, and a coefficient input terminal. There is also a first subtractor which has one input coupled to the reception path, another input coupled to the signal output of the main filter, and an output forming a further course of the reception path. A second subtractor has one input coupled to the reception path, another input coupled to the signal output of the adaptive filter, and an output coupled to the error signal input of the adaptive filter.

Abstract: Large signal swings are obtained for the transmitted signal of a telephone line modem using differential drivers. Compensation for the complex nature of line impedance is provided without affecting the response of the receive circuits. Common-mode noise is effectively cancelled due to a fully balanced topology for the transmit and receive portions of the hybrid circuit.

Abstract: A system and method having automatic selection of impedance values for matching against unknown line impedances. The method stores an expected set of desired return loss measurements at given frequencies and matches the calculated set against the actual measured return losses to arrive at a close approximation of the line impedance. The system is then adjusted based upon this determined close approximation. The starting point for the stored set are standard models established for each network. In situations where the actual varies greatly from the predicted, a different model is selected and the expected scores for that model are used.

Abstract: Isolation and interconnection of a telephone network of tip and ring lines and the analog ports of a modem are achieved with a transhybrid that incorporates optically-coupled isolation stages. Optical isolators directly connect to the tip and ring lines to provide optimal isolation and unidirectional transfer of signals.

Abstract: A data access arrangement (DAA) having a transhybrid circuit for separating a transmit signal from a received signal by providing a transmit cancellation signal to the inverting input of a servo-feedback differential amplifier on the receive channel of the DAA. The cancellation signal is provided by a photodiode optically coupleable with a light emitting diode within a optical isolator on the transmission channel of the DAA. The gain of the cancellation signal can be independently controlled.

Abstract: The balancing bridge circuit is provided between a four-wire circuit and a two-wire circuit, to provide a thin-type balancing bridge circuit having satisfactory transmission characteristics and a MODEM and an exchange and a repeater of a telephone circuit having this balancing bridge circuit built therein. The transmitting terminals of the four-wire circuit and the connection points of the balancing bridge circuit are connected together through the photo-coupler. The receiving terminals of the four-wire circuit and the connection points of the balancing bridge circuit are connected together through the photo-coupler. The terminals of the two-wire circuit are connected to the connection points of the balancing bridge circuit. By the presence of the compact photo-couplers, it is possible to ground the transmitting terminal and the receiving terminal together. Common-mode noise reaching the terminals is not transmitted to the receiving terminals.

Abstract: A method and circuit for loopback testing a telephone subscriber line interface circuit (SLIC) includes current sources connected to each of tip and ring circuits from which switch-hook is detected in the SLIC. A loopback test of the SLIC is conducted when the telephone is on-hook and is successful when the current from the current sources simulates a switch-hook detection, The current sources may also be used during on-hook transmission. A ground key detect circuit in the SLIC may be used to verify a successful loopback test by using current from the current sources in the ground key detect circuit to check for a grounded ring circuit in the SLIC.

Abstract: A processor controlled test set for testing special service circuits of a telecommunication system. A microprocessor controls the overall operation of the test set, while a digital signal processor provides high speed timing signals to the various test circuits for generating the wave forms used in testing, as well as analyzes the test result signals that are converted into digital signals. A calibration of the test generator signals as well as the signal measuring path is carried out prior to the test sequence. The digital signal processor also provides gain control over a talking path to maintain stability thereof. An I/O circuit of the test set provides plural communication paths between remote equipment and the test set to initiate and carry out various tests. Processors in the I/O module are effective to convert the various protocols of the serial data, by way of software, to digital bit streams usable by the test set.

Abstract: An interface scanning circuit includes a current source at the input to a multiplexer. The current source includes a transistor disposed between two resistors, the second one of which limits reverse current. Also provided are an attenuating network including two resistors, and a low pass filter capacitor associated with the attenuating network.

Abstract: A twisted-pair telephone line is connected to a conventional telephone via a low-pass filter and equipment for receiving signals in an upper frequency range, e.g., 25-1000 kHz via a high-pass filter. The low-pass filter is primarily passive (to allow passage of line power, ringing and signalling voltages) but, to improve matching to non-resistive line and telephone impedances, at least the main part of the filter is flanked by impedance convertors in which amplifiers having an appropriate transfer function feed voltages back into the line via transformers through which power, ringing and dialing may pass unimpeded.

Abstract: A method and apparatus for providing a telephone hybrid function is provided. The present invention maximizes dynamic range while providing a receive signal without interference from a transmit signal. The present invention also provides single-ended to differential conversion. The present invention may be practiced with an integrated circuit powered by a telephone line and coupled to the telephone line without the need for a high voltage isolation barrier between the integrated circuit and the telephone line.

Abstract: A signal interface circuit with selectable signal interface parameters for a telephone subscriber line includes an impedance circuit having a selectable impedance value, signal terminals having an associated, definable termination impedance, a transmitter circuit having a definable transmitter transfer function and a receiver circuit having a definable receiver transfer function. The signal terminals connect to an external signal line pair having an associated line impedance for conducting outgoing and incoming signals therefrom and thereto, respectively. The transmitter circuit receives the outgoing signal from the signal terminals and provides a transmit signal in accordance with its transmitter transfer function. The receiver circuit, which includes a differential transconductance amplifier, receives an input signal and the transmit signal and provides the incoming signal to the signal terminals in accordance with its receiver transfer function.

Abstract: A channel unit network having a two-wire port for interconnecting a two-wire, bidirectional signal transmitting means with a four-wire digital transmitting means in a communication system to create a precision bidirectional simulated two-wire cable pair with an extended operation range over a transmission medium includes a signal processing circuit, tip and ring switch mode driver, a negative inductor circuit, a negative capacitor circuit, and a 200 Hz impedance circuit. The negative conductor circuit and the negative capacitor circuit are used to generate respective negative inductance and negative capacitance at 24 Hz in order to maintain loop stability. The 200 Hz impedance circuit is used to generate a positive impedance at a frequency of approximately 200 Hz so as to prevent overloading of external telephone communication testing circuitry.

Abstract: A data access arrangement (DAA) having a transhybrid circuit for separating a transmit signal from a received signal by providing a transmit cancellation signal to the inverting input of a servo-feedback differential amplifier on the receive channel of the DAA. The cancellation signal is provided by a photodiode optically coupleable with a light emitting diode within a optical isolator on the transmission channel of the DAA. The gain of the cancellation signal can be independently controlled.

Abstract: Isolation and interconnection of a telephone network of tip and ring lines and the analog ports of a modem are achieved with a transhybrid that incorporates optically-coupled isolation stages. Optical isolators connect to the tip and ring lines to provide optimal isolation and unidirectional transfer of signals.

Abstract: A system for automatically adjusting the level of a telephone instrument microphone input signal in response to the level of the telephone instrument sidetone signal. The system may provide a test signal to the handset microphone input and receive the sidetone signal that corresponds to the test signal from the handset speaker output. A signal processor may then measure the amount of distortion present in the sidetone. If the amount of distortion is below a predetermined threshold, the level of the test signal is increased by a predetermined increment by adjusting an attenuation or amplification factor, and the amount of distortion in the sidetone is again measured. These steps are repeated until the measured distortion exceeds the threshold. The level of the test signal is then decreased by a predetermined amount. The final test signal thus has a level that maximizes the microphone input signal level with an acceptable minimum of distortion.

Abstract: A communication system including a base station (102) and a handset (104) provides a reduced level of near end reflections which results in a reduced level of sidetone for both near end and far end users. The base station includes an echo canceler (124) that trains on noise generated by the echo canceler (124) during inter digit dialing.

Abstract: A communications station (10) couples a bidirectional input-output signal path (16') to two unidirectional signal paths; a transmit signal path (12') and a receive signal path (14'), using a controllable hybrid (20). A feedback control system in the station minimizes the amount of transmit signal appearing at the receive output port (24) of the hybrid (20). The control system spreads the spectrum of a pilot signal (40) by means of a biphase modulator (46) and a pseudorandom generator (42) to produce a spread-spectrum pilot, which is added, in a summer 30, to the transmit signal. The spread-spectrum pilot signal covers the bandwidth of the information signal, and is reflected in an amount and with a phase which depends upon the relative impedance presented to the hybrid (20) by the bidirectional signal path (16').

Abstract: An echo compensation device, having a digital transverse filter, for an information transmission system is described, as well as a 4/2-wire interface having at least one such device. Accordingly, a scale value device is provided which respectively evaluates the value of the input signal and also the values of the time-delayed signals of the transverse filter and establishes a scale value as a function thereof. Furthermore, a device is provided for scaling all the signal values with the associated scale value before these are weighted with the respectively assigned filter coefficients. After addition of the weighted scaled signal values has been performed, the value of the output signal is descaled with the same scale value with which the signal values had previously been scaled.

Abstract: A hybrid circuit for coupling a modem to an external telephone line substantially compensates for and thereby cancels reflected echo. The hybrid includes a transformer coupled between the telephone line and the modem transceiver, which includes a transmitter and a receiver. A matching resistor connected between the transceiver transmitter and the transformer at a hybrid point presents a matching impedance to the telephone line impedance. A feedback network is implemented between the transceiver receiver and transmitter to feed back sufficient voltage into the receive line to cancel echo produced at the hybrid point.

Abstract: A speaker amplification system incorporates an adaptable notch filter that can dynamically adapt to the frequency of feedback oscillations caused by acoustic feedback frequency in order to remove the feedback oscillation before they are amplified above an audible level. The adaptable notch filter is implemented as an adaptable finite impulse response filter by means of a digital signal processor. The finite impulse response filter also has an adaptable convergence factor which minimizes noise introduced by the filter. A special limiting routine is used to limit the values of the finite impulse response filter coefficients to prevent the filter from "blowing up" due to large input signal disturbances. The speaker amplification system also includes circuitry which provides multiple bands of equalization, with each band being capable of amplification.

Abstract: An interface circuit between a four wire line and a two wire line includes correlator and control circuit means connected for receiving a longitudinal signal (V.sub.1) and a transversal signal (V.sub.t) corresponding to a differential signal received on the terminals of a two wire interface from the two wire line. The correlator and control circuit includes a circuit for creating a correction signals being a measure of the correlation between the longitudinal signal and the transversal signal. The circuit for creating the correction signal is connected for using this correction signal to adaptively control the amplifications in feed back loops so as to minimize the correlation between the longitudinal and transversal signals.

Abstract: An improved solid state isolation device that uses opto-isolators to provide an electrical barrier between a telephone network and user telephone equipment includes a load and current control circuit, and an adjustable termination circuit to eliminate or reduce signal distortion and insensitivity to low signal levels resulting from low loop current, and lack of complex impedance compensation/termination for diverse telephone system parameters. An improved trans-hybrid return loss circuit reduces internal losses; while loop termination losses are reduced by the use of Shottky diodes in the line coupler circuit. A high pass filter improves common mode rejection ratios in the transmit and receive paths, and adjustable compensation is provided to account for manufacturing variances in the opto-isolators. An additional connection is also provided to adapt the opto-isolator circuit for use with 3-wire ring circuitry.