Abstract: The potential impedance mismatch of digital terminal equipment and a line test unit that has been equipped to conform with the Bellcore standard of terminating the line with a 600-900 ohm impedance during data reception is addressed by modifying the craftsman's test unit to include a controllably disabled AC impedance, which is operative to normally bridge the tip and ring leads of the telephone circuit under test with the required (600-900 ohm) impedance during data reception and, under direct control by the craftsman's keypad or software control resident in the test set's microcontroller, to selectively remove the AC matching impedance that would otherwise bridge the line. The AC impedance is comprised of a D.C. blocking capacitor and a resistor coupled in series with a controllable solid state relay which is normally rendered conductive during data reception to bridge the tip and ring leads.

Abstract: The single transformer generally used in a duplex coupler for coupling local telecommunication equipment, such as a modem, to a telephone line may be replaced by a number of transformers or other suitable forms of DC isolation device which then enables each transformer and its associated circuit network to be specifically tailored to optimize the operation of the coupler system. The transmit output path 3 is connected to a transformer 2 having a center-tapped secondary winding 11 which is connected across the communication line 4. A second transformer 5 has its primary winding connected between the center-tap and the line 4, and its secondary winding coupled to the receive input 6. By optimizing each transformer the intermodulation products and other unwanted products are reduced. The coupler system may be miniaturized and the line matching components incorporated in or selected by a specific line cord designed to match the network characteristics.

Abstract: A transformed current sensing relay with reduced AC impedance of the operating coil is accomplished by adding a shorted secondary winding to an otherwise conventional current sensing reed relay. The shorted secondary winding is preferably implemented with a copper tube over the existing coil and inside the magnetic circuit. This transformed current sensing relay is particularly advantageous for the line current sensing function in switched network communications equipment such as high speed modems, where the transformed relay exhibits substantially lower impedance at high frequencies than the conventional current sensing relay. This transformed current sensing relay allows for the elimination of bypass capacitors and results in significant cost and space savings. Moreover, the transformer nature of the transformed current sensing relay allows for the elimination of suppression resistors from the interface resulting in additional cost and space savings.

Abstract: Disclosed is a circuit for providing an appropriate amount of on-hook loss in a digital loop carder transmission system serving telephone customers. The resistance of the customer loop is measured while the customer is off-hook and an amount of loss is added based on that resistance during the off-hook interval. A predetermined constant loss is then added to the appropriate off-hook loss when the equipment returns to on-hook status.

Abstract: A signal separation circuit for separating direct current power on a telephone with a transistor. A CPU, which includes an A/D converter, is connected to detect the emitter-collector voltage of the transistor, and to control the base current of the transistor to maintain the emitter-collector voltage constant.

Abstract: A balancing resistor and thermistor network for telephone circuits, and combination with an external relay, which reliably handles all three levels of adverse conditions, automatically resets under certain conditions, is physically small in size, and is strong. It is a flat ceramic substrate on both surfaces of which are screen-printed thick-film balancing resistor films. Also screen-printed on both surfaces are termination traces having portions so located that when the substrate substantially instantaneously fractures it reliably and substantially instantaneously breaks the circuits through the resistive films, the fracture occurring in response to a sudden high-voltage overload. Accordingly, there is no damage to, or melting or burning of, small wires in the telephone circuits at points near to or remote from the balancing resistor network. A thermistor film is screen-printed directly onto the substrate at a central region where there is no resistive film.

Abstract: A supply circuit for a two-wire telecommunication line includes a voltage adjusting circuit section coupled between one of the wires and a first reference potential point and further includes a current source coupled between the second wire and a second reference potential point. A transistor in the voltage adjusting circuit section has a first main electrode coupled to the first wire, a second main electrode coupled to the first reference potential point, and a control electrode which is coupled to the first wire by way of a capacitor. In order for the supply circuit to meet strict requirements as to symmetry and demodulation, the control electrode is also coupled to the first reference potential point by way of a threshold voltage diode, which may be a zener diode. A voltage control circuit coupled to the threshold voltage diode forms a feedback loop for maintaining the line voltage at a selected value despite the presence of disturbing signals on the line.

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 compensation circuit for adjusting the gain or loss of a four to two wire hybrid circuit in a telephone system automatically, regardless of the length of the telephone line interconnected to the hybrid circuit. The compensation circuit includes a converter, interface, gate array, and controller. The converter, which includes an amplifier with a variable gain, is connected to a digital carrier transmission line. The converter accepts a digital data signal and converts it to an analog intermediate signal. The interface receives the analog intermediate signal and transmits an analog telephone signal, along a customer loop telephone line, to a telephone. The interface also includes a pulse width modulated power converter for which the pulse width varies according to the length of the telephone line between the compensation circuit and the telephone. The gate array senses the pulse width and responsively provides a measured signal to the controller.

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: An autoequalizing hybrid circuit for providing a cancelation path to minimize the two-wire receive path signals that are reflected onto a two-wire transmit path from a subscriber line interface circuit is disclosed. The hybrid circuit includes a variable impedance balance network. A tone generator injects a set of equalization signals into the receive path which are used to control the setting, or equalization, of the balance network. The tone generator also generates a supervisory signal into the receive path used to monitor the performance of the balance network. A detect circuit monitors the level of the reflected equalization sidetone signals and produces balance signals whenever the equalization signals fall to a null level. The detect circuit also monitors the supervisory sidetone signals and produces a recalibration signal whenever an abrupt change in the signals indicates that the balance network is no longer adequately cancelling their reflected signals.

Abstract: Each line wire is separately biassed by DC potentials feeding Inputs of the respective line wire driver amplifiers, the first potential (BA) being nearer ground and the second at an equal distance from the negative supply used to power the amplifiers so as to allow a suitable AC swing for the speech and metering signals also feeding the inputs of the amplifiers. The second potential (BB) is obtained from a DC synthesizing loop voltage and to which is added (OA6) the first potential, both potentials being also combined (OA5) to control a switched mode DC/DC converter delivering the negative power supply. In addition to both potentials being filtered with reference to ground, another measure reducing noise relies on AC signals push-pull outputs driving the amplifier inputs, also in push-pull through four resistances.

Abstract: An arrangement for feeding the subscriber's lines (10) of a public exchange with reduced line current upon the occurrence of a power failure, when the temperature within the public exchange or the temperature of individual components, mounted on circuit boards on which line interface circuits are present, exceeds a predetermined reference value, when the length of a subscriber's line is less than a line length reference value, or when the conversation time on a subscriber's line exceeds a conversation time reference value. All subscriber's lines or individual subscriber's lines only are fed with the reduced line current for a restricted time (FIG. 5B).

Abstract: A two-wire telephone line interface circuit comprises a driver circuit for supplying direct current on the line, a controlled voltage generator, a sensing circuit for monitoring the line current, a control circuit for controlling an output voltage of the voltage generator, and a switching circuit. The control circuit controls the switching circuit to supply, as a supply voltage for the driver circuit, a battery voltage in an on-hook state of the line or the controlled output voltage of the voltage generator in an off-hook state of the line, this output voltage being controlled to provide off-hook current limiting. The control circuit also controls the switching circuit to selectively supply the controlled output voltage of the voltage generator as a signalling voltage to at least one wire of the line for high voltage signalling, e.g. ringing, on the line. Desirable forms of the switching circuit are described.

Abstract: An arrangement for adjusting an adaptive digital balance filter included in a subscriber unit connected to a telephone line includes a selection unit, which can be connected to the subscriber unit either via the exchange or via a separately arranged switch. When the selection unit is connected to the subscriber unit, the balance filter is disconnected from both branches of the subscriber unit. A test signal generator is included in the selector unit for sending a signal on the lines via both branches of the subscriber unit. There is further included a plurality of digital filters wherein the transfer function of any of the filters closely coincides with the transfer function of the filter formed by the line impedance and the portion of the subscriber unit which is connected to the line and to the balance filter.

Abstract: The quality of speech being transmitted in a telecommunication channel is enhanced by adaptively compensating for frequency dependent attenuation in the telecommunication channel. The frequency dependent attenuation in the telecommunication channel is dynamically determined and, then, compensated for by adaptively selecting and inserting an appropriate frequency dependent gain function in the telecommunication channel.

Abstract: A circuit is proposed for adjusting the loss provided to loops in digital loop carrier transmission systems. A constant current is supplied to the loop and the resulting voltage is measured to determine the resistance of the loop. This value is fed to a microprocessor with a look-up table which controls a programmable analog/digital converter. The loss at the output of the converter is a stepwise function based on the resistance of the customer loop.

Abstract: A line unit, used in a line shelf having a line shelf processor and common logic, is provided with an EEPROM device for storing information relative to the line unit. The stored information includes line unit type identification codes, auto provisioning data, gain and equalization adjustment data and signaling translation tables. The data contained within the EEPROM may be utilized by the line shelf processor to provide automatic initialization and provisioning of the line unit when first inserted into the line shelf, and automatic signaling translation so that line unit signaling becomes compatible with a transmission facility connected to the line shelf. The need for factory preset resistors installed in the line unit may be eliminated by storing within the EEPROM a required gain setting.

Abstract: A reciprocal impedance conversion network is disclosed. Such conversion network preferably is used in a reciprocal negative impedance repeater for the nonloaded cable facilities of a telephone system. Two independent voltage sources for generating reciprocal negative impedance are connected between a first port and a second port. The first port is operably connected to the first voltage source such that a series negative impedance appears at that port. This port is specifically connected to the switching equipment of the telephone system. The second port is operably connected to the second voltage source such that a shunt negative impedance appears at that port. The second port is specifically connected to the nonloaded cable facilities of the telephone system. The network further provides a frequency dependent gain circuit which is useful for equalizing the losses along the nonloaded cable facilities.

Abstract: An apparatus for controlling a supply current to a load, such as a telephone subscriber line, generates an output current responsive to the changes in the load according to a predetermined response profile, which is defined by a plurality of parameters and includes a first range extending from a lower load level to higher load level, and a second range extending above the higher load level. A first control circuit generates a first set of parameters establishing the response profile within the first range; a second control circuit generates a second set of parameters establishing the response profile within the second range; and an apportionate feed circuit apportions signals within the apparatus. The first control circuit receives a load indicating current and first reference current, establishes the lower load level, and cooperates with the apportionate feed circuit to impose a first set of the operational parameters in generating an output current within the first range.

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: Measuring the programming resistor in a data jack by placing the resistor in an AC voltage divider circuit via a transformer. An AC voltage (preferably generated by the modem's own transmitter circuitry) is applied to the voltage divider circuit, and an AC voltage measurement (preferably made by the modem's A/D converter) provides the resistance of the programming resistor. Matching the low-pass filter impedance characteristic of a local loop with a network having a matching low-pass filter characteristic, while also compensating the received signal with a compensation network having a high-pass filter characteristic, to reduce the frequency dependent gain effects caused by the matching network and/or the local loop.

Abstract: A speaker telephone comprising a microphone outputting an electrical signal, and a loudspeaker is disclosed. An amplifier has its output coupled to the loudspeaker. This amplifier has non-inverting and inverting inputs. A switch having two positions couples the microphone to the amplifier or couples the tuning signal source to one of the inputs of the amplifier. A tuning signal source and control circuit output a tuning signal. Initiation means initiates a tuning sequence by causing the switch to be in the second position and causing the tuning signal source and control circuit to generate tuning signals. A coupling device is connected to one of the inputs of the amplifier and adopted to be connected to a telephone circuit. A hybrid voltage generator circuit is responsive to the output of the microphone when the switch couples the microphone to the amplifier to generate at its output a cancellation signal which prevents transmitted voice signals from appearing at the loudspeaker.

Abstract: A two-wire/four-wire converter for coupling a two-wire communications path carrying analog transmission and reception signals to a four-wire communications path having a two-wire transmission path carrying digital transmission signals and a two-wire reception path carrying digital reception signals, includes an analog/digital converter having an input coupled to the two-wire communications path and an output coupled to the two-wire reception path. An adder has one input connected to the two-wire reception path and another input connected to the two-wire transmission path. A digital filter with an adjustable communications function generates a predetermined terminating impedance for the two-wire transmission path. The digital filter has an input connected to the output of the adder and an output. A subtractor has one input connected to the output of the digital filter, another input coupled to the output of the analog/digital converter and an output.

Abstract: A circuit supplies a current (I) in which the current variations (I.sub.L) having been equalized according to a given relationship. In order to obtain an equalization characteristic having at least two slopes, the circuit uses the switching of the current sources (xI.sub.o, yI.sub.o and zI.sub.o) by means of switching stages (T.sub.1, T.sub.2, T.sub.14). The output current I passing through the current output stages T.sub.3 and T.sub.4 thus fluctuates between two levels according to the desired equalizing relationship.

Abstract: A key telephone system comprised of a key service unit connected to a plurality of local sets via four-wire conductors for providing full duplex signal communication between the key service unit and sets. Signals are carried by a first pair of each of the conductors for unidirectional transmission of signals from each set to the key service unit, and the remaining pair of conductors carries signals transmitted by the key service unit for reception by one or more of the sets. Four-to-two wire signal conversion and line impedance balancing is effected by one or more trunk circuits of the key service unit in the event one or more of the local sets are connected via the key service unit for communication between the sets and the outside telephone lines.

Abstract: A characteristic of a signal received via a receive line is monitored and used for automatic control of a line buildout circuit in a transmit signal path. The characteristic is conveniently an amplitude level, or differential amplitude levels for different signal bandwidths, of the received signal. The transmit line buildout circuit includes a transversal filter in which multiplier coefficients or delay times are controlled. The arrangement is particularly useful for digital signal interfaces on a digital cross connect.

Abstract: An interface circuit a.c. couples a transmission line and a port of a telecommunications facility. The transmission line may be of any of n characteristic impedances. The interface circuit includes a resistor network having at least 2n+1 resistor elements. The resistor network is connected to ground by at least one of the resistor elements. A switching device includes at least n switching elements being connected between n of the resistor elements and an input of an amplifier. A transformer includes first, second and third windings, the first winding being for connection to the transmission line, the second winding being connected between an output of the amplifier and a junction between the one of the resistor elements and at least another of the resistor elements, and the third winding being connected between ground and a point in the resistance network other than the junction. A resistor connects at least one of the n switching elements and the port of the telecommunication facility.

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 circuit for restoring and converting bipolar customer data signals into a pair of binary signals at a customer data frequency equal to or less than 250 KHz includes a PCM integrated circuit repeater for restoring and converting 1.544 MHz communication signals and transmission lines. Use of the high frequency repeater is enabled by a buffer amplifier connected in series with the input of a repeater amplifier and which has an input connected to a parallel resistance and capacitance network which is connected in series with an ALBO diode of the repeater for automatically inserting loss characteristics in the input signal so that the input signal has characteristics resembling losses of a signal passing through a maximum length transmission line. Fixed equalizer and amplification circuitry restores the original pulse signal magnitude and characteristics.

Abstract: A SLIC includes controlled current circuits (CCCs) which simulate feed resistors for controlling d.c. feed to a two-wire telephone subscriber line which is coupled to two terminals, control being achieved via a feedback loop. A differential amplifier has an inverting input coupled to the tapping point of a potential divider connected between the terminals, and a non-inverting input connected to a reference potential of half of the supply battery voltage. For suppressing longitudinal currents on the line, the amplifier output is connected to each terminal via a d.c. blocking capacitor in series with a resistor, the resistors having closely matched resistances. For maintaining d.c. balance, the output of the amplifier is coupled via a low pass filter to control a current splitter included in the feedback loop, to control the relative proportions of control currents for the CCCs.

Abstract: A power supply circuit for use with telecommunication subscriber lines provides a substantially constant power output over one range of load impedances and a substantially constant voltage output over a range of load impedances greater than a critical impedance. The circuit employs a transformer which includes a sense winding for sensing output voltage across the load. For load impedances below the critical value, the current into the primary of the transformer is controlled by means of a current sensing device sensing the amount of primary current. However, for load impedances greater than the critical impedance the output of the sense winding controls and current to the primary is reduced to avoid the output voltage from rising substantially even in the event of an open circuit load condition. In one embodiment, a supervisory circuit provides a signal indicative of the on-hook and off-hook states of the subscriber line by sensing primary current flow.

Abstract: An improved AC impedance matching arrangement including a first amplifier connected to a subscriber loop through the tip and ring conductors of a subscriber line circuit. The first amplifier is arranged to supply loop current to the subscriber loop through first and second resistors. Each resistor having a set DC value. A second amplifier connected to the tip and ring conductors is arranged to develop and output a signal responsive to AC signals applied to the tip and ring conductors from the subscriber loop. A feedback circuit connected to the second amplifier is arranged to receive the second amplifier output signal and develop and output to the first amplifier an impedance matching signal. The impedance matching signal raises the impedance seen by the tip and ring conductors above the set DC value of the first and second resistors.

Abstract: A wide band high voltage and high power amplifier is particularly useful for telephony applications. The amplifier employs a flyback converter with the capacitor storage element coupled across the line. The subscriber line is characterized in having a definite load impedance which impedance is in parallel with the storage capacitor of the flyback converter. The subscriber lines are monitored by a differential amplifier which provides a single-ended output indicative of the levels across the lines. This output is summed with the input signal to develop an error signal. The input signal to the line circuit is the particular signal of concern such as ringing, the voice signal and so on. The error signal is supplied as one input to a comparator having another input coupled to a triangular reference waveform. The output of the comparator provides a pulse width modulated waveform where the width of the pulses are indicative of the error signal.

Abstract: The invention relates to a supply circuit for a variable load, particularly for a line circuit in telephone systems.Conventional supply circuits, in which each of the two supply-current branches to the line wires contains the collector-emitter path of a transistor in series with an emitter resistor, offer a high AC resistance to voice-frequency voltages and longitudinal noise voltages, so that the bridging loss of the line remains small. To achieve a low AC resistance of the supply circuit to the longitudinal noise voltages, special measures in the control circuits of the transistors, particularly the use of a nonlinear element in the form of a CRD current-limiting diode in parallel with the controlled current path of each of the transistors, are proposed. These measures greatly reduce the amplitude of the longitudinal noise voltages at the inputs of subsequent circuits, which are thus protected.