Abstract: A system and method are disclosed to implement fault detection in DSL loop extenders. The system of the invention includes a plurality of loop extenders coupled to a local loop, a loop extender (LE) test box coupled to the local loop, and fault detection circuitry coupled to each of the plurality of loop extenders. The LE test box sends a tone pair associated with a loop extender over the local loop, the loop extender associated with the tone pair processes the tone pair to generate a response tone and sends the response tone to the LE test box via the local loop. Then, the LE test box determines functionality of the loop extender based upon the received response tone.

Abstract: The present invention provides a distortion precompensator and method of compensating for distortion in a transmission medium and a transmitter employing the same. In one embodiment, the distortion precompensator includes a controller, associated with a transmitter, that employs a predetermined precompensation signal. The distortion precompensator also includes an injector that injects a predetermined precompensation value as a function of the precompensation signal into a waveform propagating along the transmission medium thereby substantially compensating for distortion associated therewith.

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 digital access arrangement for (i) isolating downstream components from twisted pair copper wire and (ii) separating upstream and downstream communications channels. The line isolation is performed with relatively small, lightweight components, such as an optical isolation unit for example, and can be operated with signals modulated at relatively high frequencies and having relatively high data rates and amplitudes.

Abstract: A method of and apparatus for noise reduction for a transceiver transmitting frames over a transmission medium in a frame-based communications network. A transceiver transmit path and a transceiver receive path is provided. A blocking switch is located in the transceiver transmit path, the blocking switch allowing transmit signal propagation when enabled, while preventing both transmit signal propagation and circuit device noise coupling from the transceiver transmit path to the transceiver receive path when the blocking switch is disabled. The blocking switch is disabled when the transceiver transmit path is not transmitting frames over the frame-based communications network.

Abstract: An integrated line card for providing an analog termination for both POTS and xDSL signals that present the appropriate impedances at xDSL frequencies for the xDSL signals and appropriate impedances at POTS frequencies for POTS signals. The line card comprises a front end for coupling combined POTS and xDSL transceiver circuits to a telephone line at a single termination and an impedance generator responsive to the frequency range of the POTS and the xDSL circuits for generating the appropriate impedances on the line at xDSL frequencies for xDSL signals and the appropriate impedances at POTS frequencies for POTS signals, such that the signals are coupled to the card without the use of a splitter. Preferably, the xDSL circuits and the POTS circuits share a common driver for driving signals onto the loop. An advantage of this arrangement is that the two circuits may be designed together thus ensuring out-of-band noise generated by either source does not interfere with the other.

Abstract: In a telephone network, different telephones are connected to a telephone line in a parallel manner. When two or more of the telephones are in use and conduct electricity, known as an “off-hook” condition, they are oftentimes provided with varying amounts of loop current from the telephone line to drive their telephone circuitry. To balance the respective loop current supplies to the off-hook telephones, at least one inventive balancing network is used and connected to one of the off-hook telephones which has the least operating resistance, with respect to all other off-hook telephones.

Abstract: Disclosed is an apparatus for preventing the loss of a portable telephone using a bluetooth communication and the control method thereof capable of preventing the loss of the portable telephone. According to the control method, the portable telephone periodically measures a power level of a radio frequency received from an earphone when a loss prevention mode is determined, and detects a calling state between the portable telephone and the earphone. The portable telephone transmits a warning signal data to the earphone if the power level of the radio frequency received from the earphone is below a predetermined level in a state that the calling state between the portable telephone and the earphone is detected. The earphone generates a warning sound if the warning sound signal is received from the portable telephone during a bluetooth radio communication with the portable telephone.

Abstract: An ADSL modem provides compensation for a nonlinear telephone impedance by predistorting transmit signals such that the voltage across the nonlinear impedance is correct independent of the impedance. Correcting the voltage across the nonlinear impedance reduces noise in the telephone due to intermodulation products generated in the voice band. The modem comprises a transmitter that includes (a) a signal source providing a source data signal and (b) a predistortion circuit for predistorting the source data signal to provide a modem transmit signal for coupling to a transmission loop having a nonlinear impedance coupled thereto. The modem device further includes a receiver for receiving a modem receive signal from the transmission loop. The source data signal comprises source digital words, each source digital word corresponding to a particular voltage level.

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 digital telephone (60) comprises send equipment (40) and receive equipment (50), coupled via a signal splitter/combiner (61) onto a digital telephone line (62) for communication with a remote party (90). The send equipment (40) comprises an A-law map (12) and a mu-law map (43). Receive equipment (50) comprises an inverse A-law map (14) and an inverse mu-law map (52). Maps (12,43) are selectable by the user (80). Similarly, inverse maps (14,52) are also selectable by the user (80). Receive equipment (50) may further comprise an un-quick-fix module (55) for removing unwanted insertions of quick fixes (25) inserted into the telephone line (62) by international telephone companies. Receive equipment (50) may further comprise a digital signal processor (57), computer (56), a set of pre-stored templates (58) corresponding to possible incoming telephone characteristics, and a caller parameter decipher module (51).

Abstract: A transmission line impedance matching apparatus is disclosed that limits longitudinal signals and matches the longitudinal characteristic impedance between two conductors and comprises a common mode choke and an impedance matching device. The common mode choke, comprising two windings wound in the same direction, acts as a high impedance to longitudinal high frequency signals. As a result of this, standing waves are caused by the metallic signals reflecting off the choke. The impedance matching device, comprising two windings wound in the same direction, provides a good match to the longitudinal characteristic impedance and thus reduces standing longitudinal waves and reflections. The apparatus may include a terminal corrector or a mid-line corrector, or a combination thereof. This invention may allow greater bandwidth to be dedicated to services and allow transmission over longer subscriber loops before the minimum S/N ratio is achieved.

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: A system (130) for providing enhancement to a voice-band signal in a telecommunications network (138) is provided. The present system (130) includes a power averager (18) for determining the average power of the voice-band signal. The present system (130) also includes an equalizer (132) for attenuating a predetermined portion of the voice-band signal and an output scaler (134) for scaling the equalized voice-band signal with a scaling factor. The system (130) of the present invention also includes an automatic gain enhancer (136) for applying an automatic gain factor to the scaled voice-band signal and wherein the automatic gain factor is dependent upon the average power of the input voice-band signal.

Abstract: In a communications system containing signal enhancement circuitry capable of selectively enhancing portions of a plurality of signals carried on a corresponding plurality of channels through the signal enhancement circuitry, a system and method for controlling enhancement on a per call basis. The system includes: (1) command generation circuitry for generating an enhancement command for transmission to the signal enhancement circuitry and (2) command reception circuitry, associated with the signal enhancement circuitry, for receiving the enhancement command from the command generation circuitry and selectively enhancing the portion of the signals on the per call basis according to the enhancement command.

Abstract: A telephone subscriber circuit is coupled via a single galvanic isolation element to provide, from a subscriber apparatus unconnected to the telephone line, on- and off-hook signals to the telephone line and to control transfer of telephonic signals between the subscriber apparatus and the telephone line. The galvanic isolation element is a photocoupler. The subscriber circuit includes a speech circuit coupled to the line through a diode bridge circuit and an electronic switch is connected between the speech circuit and the diode bridge circuit. An input terminal of the speech circuit and a control terminal of the electronic switch are each connected through a voltage-generating circuit and level-translating circuit to an output terminal of the galvanic isolation element.

Abstract: A circuit and method for sensing and compensating for longitudinal (common mode) signals in a subscriber loop of a telephone system. The circuit and method may include a longitudinal amplifier for sensing a difference between a reference voltage, V.sub.BAT /2, and a longitudinal voltage in the subscriber loop, and for providing four currents, two to each of two current amplifiers in the telephone system subscriber line interface circuit (SLIC). The longitudinal amplifier includes two current mirrors, each for providing two currents of the same polarity and of the same magnitude. The magnitude of the difference between the two currents being provided to each of the current amplifiers is proportional to the voltage difference. When compensation of the longitudinal signals has been achieved, the two voltages are the same and the magnitudes of the four currents are the same.

Abstract: An electromagnetic interference by-pass filtering mechanism suppresses RF noise currents conducted over the tip and ring leads of a telephone line-powered telephone instrument. Such RF noise currents may result from amplitude modulated radio broadcast signals emanating in the vicinity of the telephone instrument. The filtering mechanism comprises a conductive material coated on the interior surface of the housing of the telephone instrument, so as to surround the printed circuit board containing the telephone circuitry of the instrument. The conductive material is coupled to earth. First and second capacitors are coupled between the tip and ring leads and the conductive material, and first and second inductors are coupled in series with the tip and ring conductors and connections of the tip and ring conductors to the printed circuit board containing the telephone circuitry.

Abstract: A sign bit integrator and method for generating a signal to correct an offset in a signal processing system that can distort the output from the system. A charge pulse is generated when the sign of a input signal is sampled in order to provide an offset correction signal with a polarity opposite that of offsets in the system. The charge pulse is provided to a pair of transistors whose size ratio sets the magnitude of the charge pulse. The polarity of the charge pulse is set responsive to a sign bit in the input signal. An integrator capacitor provides the offset correction signal to the signal processing system. A third transistor may be switchably substituted for one of the pair of transistors to change the ratio of sizes and thus change the magnitude of the charge pulse to thereby change the speed with which the offset correction is made. The sign bit integrator and method may be used to correct distortion in a voice signal in a telephone system.

Abstract: A monolithically integrated AC coupling circuit is presented for DC uncoupling and AC coupling (typically in telephone applications) to an input signal. The AC coupler includes a high-pass filter having a first pole at a frequency well below a frequency of interest and a zero at zero frequency. The AC coupler also includes a pole/zero doublet between the frequency of the first pole and the frequency of interest. The frequency of the first pole for a specified error is increased by addition of the doublet. Because the frequency of the first pole is increased, the size of the required capacitors is decreased, enabling integration. An implementation of the circuit using switched capacitor techniques is described. An alternative circuit employing a unit gain interface is presented. The alternative circuit reduces the dynamic range and driving voltage requirements of its field-effect transistors.

Abstract: In methods and apparatus for estimating the frequency response of telecommunications channels, signals carried on the channels are divided into pluralities of signal segments of limited duration, unvoiced signal segments are identified, and spectral components of the unvoiced signal segments are measured. The measured spectral components may be integrated over time to derive time-averaged measurements of the spectral components. The time-averaged measurements may be compared to corresponding components of expected unvoiced signal spectra to improve the accuracy of the frequency response estimates. Filters may be inserted in the channels to adjust the frequency responses, the filters having filter characteristics selected in response to the measured spectral components. The methods and apparatus can be used to compensate for poor bass frequency response in voice channels.

Abstract: A multi-variate system having a microprocessor-based telecommunications interface which has a digital adaptive all-pass filter and automatically variable delay distortion equalization circuitry which in combination provide both pre and post delay distortion equalization on the transmit and receive sides of bidirectional data lines (or dedicated telephone lines), which interfaces a conventional 4-wire analog facility and a data station termination at the customer premises equipment. A method of practicing the preferred embodiment of the invention is also disclosed.

Abstract: A circuit for simulating the transmission characteristics of lines carrying digital signals, such as bus lines in ISDN networks. A partial line simulating device is assembled as a standard circuit including three different circuit parts in such a manner that any line design of any line length can be simulated.

Abstract: In a quaded cable, coupling between circuits (side circuit 1, side circuit 2, and phantom circuit) is compensated for at the receiving end of a transmission system. By transmitting known signals from the transmission end separately on each circuit, coupling between circuits is initially estimated by measuring the signals received at the opposite end on each of the circuits. Following startup, during data transmission the received data signals are modified in accordance with this initially determined coupling between circuits to produce estimated transmitted data signals. During data transmission the coupling between circuits is reestimated by storing (303) N data signals received on each circuit and the corresponding N estimated transmitted data signals on each circuit. The coupling between circuits is determined as a function of the covariance of these N received signals on each circuit and the covariance of these N estimated transmitted data signals on each circuit.

Abstract: A telecommunications network (120) is provided with adaptive gain control (AGC) of the voice signals in network (120). Network (120) includes an input (12) for receiving a voice signal, an output (14) for receiving the voice signal, and a coupling between input (12) and output (14) including at least one switch (124) or (126). Network (120) also includes voice enhancer (10) including power averager (18) for measuring and determining the average power of an input signal. Voice enhancer (10) also includes bass band equalizer (16) to attenuate a predetermined portion of the input signal to provide an equalized input signal. From the average power of the input signal is determined a scaling factor from a gain/attenuation look-up table (28). Voice enhancer (10) also includes output scaler (30) coupled to output (14), output scaler (30) scales the equalized input signal with the scaling factor and provides the scaled signal to output (14).

Abstract: A circuit for synthesizing an impedance associated with a telephone subscriber's circuit connected to a two-wire telephone line is described. The circuit of the invention is adapted to synthesize a complex impedance which can function both as a termination impedance and a balance impedance. The termination impedance utilizes a positive feedback loop structure having a loop gain which is at all times less than unity. The circuit that implements both the termination and balance impedances with sidetone suppression is also described. Each of the embodiments is realizable with a single external component consisting of a resistor.

Abstract: A two-wire termination impedance generation circuit of a subscriber circuit including differential amplifiers, which is provided with a network circuit including capacitors and resistors, an input point, and current sources, the capacitor being comprised of series connected first and second capacitors, the resistor being comprised of series connected first and second resistors and having a high band bypass capacitor connected at the intermediate connecting point of the same, and the resistor being comprised of a complex termination resistor forming an internal termination impedance and a series connected complex termination resistor and complex termination capacitor being connected directly to the telephone line as an external termination impedance, wherein the frequency characteristics can be improved in three ways.

Abstract: A method and apparatus for connecting a programmable computing device to a digital telephone via an adapter. The digital telephone includes an option bay connection, having a hierarchical control protocol. The option bay connection makes available several types of information including local analog audio, and analog voice, digital voice, digital data and telephone control streams. The adapter passes the telephony control data to and from a programmable computing device such as a personal computer, enabling an application operating on the computing device to control or monitor the operation of the telephone. The adapter includes a microcontroller and an interface for a serial port and can thus be connected to the serial port of the programmable computing device.

Abstract: A device for reducing or eliminating differential mode cross-talk between data communication channels (CH1 and CH2) in a balanced communication system by coupling one or more auxiliary capacitances (C100) across the transmission lines (A, A, B, and B) between the two channels (CH1 and CH2), thereby augmenting the intrinsic capacitive couplings (CA.sub.AB, C.sub.AB, C.sub.BA, and C.sub.BA) and leakage between the channels in order to net the differential cross talk signal to zero.

Abstract: The quality of voice signals transmitted by a telephone station set, or similar device, are enhanced in accordance with the steps of the instant method before such signals are delivered to a receiving telephone station set by restoring the level of speech energy attenuated by the transmitting set, in which such restoration is performed at a point along a telephone connection between the transmitting and receiving telephone stations, for example, at a point within a telecommunications system which establishes the connection.

Abstract: Filter circuitry for filtering noise from a pair of telephone conductors connected to a modem or a facsimile transmission unit includes a capacitor in series with a fixed resistor. A vaariable resistor is connected in series with the capacitor and the fixed resistor. The capacitor is non-polarized. A switch is connected in series with the filter elements for selectively connecting and disconnecting the filter from the telephone conductors.

Abstract: In a system (20) for transmitting voice and data signals, insulated metallic conductor pairs (44--44) which transmit data signals and insulated metallic conductor pairs (46--46) which are capable of transmitting voice signals are enclosed in a common sheath system of a single cable (40). User pickup of station apparatus (34) during the generation of a ringing voltage on a voice conductor pair causes that pair to become disturbing and to impart impulse noise to a closely coupled data pair. The data pair is designated a disturbed pair and the signals transmitted thereby may be affected adversely. This problem is overcome by providing a circuit (80) comprising in parallel a resistance and an inductance and being in series with the station apparatus. Such an arrangement reduces substantially that frequency content of any disturbing signal which appears on the disturbing pair and which is in the range of the data signal spectrum.

Abstract: An interface circuit interfaces a four wire telephone circuit to a telephone headset. An adjustable receiver portion of the interface circuit receives a line input signal from the four wire circuit and produces a headset input signal limited to a predetermined signal level. An adjustable output portion of the interface circuit accepts a headset output signal and conditions it for use as a line output signal on the four wire circuit. A DC voltage is also supplied to a headset microphone through the output portion of the interface circuit.

Abstract: A life safety system for monitoring a building has a plurality of detectors for detecting alarm conditions located throughout the building, a plurality of speakers located throughout the building, a source of pre-stored voice messages which can be broadcast over the speakers, and a telephone network. The improvement is a voice synthesizer for providing the source of pre-stored voice messages and a constant volume telephone system. The constant volume telephone system has a telephone line and a plurality of telephones which can be connected to the telephone line, and a power supply having an adjustable output voltage which provides the voltage for the telephone line. A sensing and adjusting circuit senses the number of telephones off-hook and causes the power supply to be adjusted in response to the number of telephones off-hook.