Abstract: A SLIC includes in separate and distinct contacts for the output of a tip and ring line driver and their feedback resistors to the balancing resistor of the appropriate tip and ring line. Thus, a Kelvin contact arrangement is produced providing a compensation for the contact resistance of a single connection.

Abstract: A subscriber line interface circuit that provides regulated current to telephone subscribers in an improved manner reducing the amount of power required to operate while maintaining a constant current source. The current to the telephone subscribers flows through a switching transistor, an inductive storage element, sensing resistors and a transformer. The desired operating characteristic is obtained by cycling the switching transistor. The switching transistor is cycled on at a preset interval causing the telephone subscriber current to flow from the switching transistor. The switching transistor is cycled off in response to an increase in the telephone subscriber current as sensed by the sensing resistors thereby causing the current to flow from the inductive storage element.

Abstract: The present invention is a transmission system in which there are provided a bridge circuit in which a balanced condition is provided in an entire frequency band usable for a wire transmission line or a portion thereof, and a cancelling circuit in which a simultaneous two-directional communication is enabled by using the same frequency or the frequency adjacent thereto, and there are provided said cancelling circuits at both terminal devices opposite to each other through a transmission line, thereby enabling said simultaneous two-directional communication.

Abstract: A conversion circuit for connecting a two-wire circuit and a four-wire circuit to each other comprises a transformer having a primary side and a secondary side, the primary side being connected to a two-wire circuit having a variable impedance, a first amplifying circuit having a first input terminal connected to the secondary side of the transformer for receiving an audio frequency signal from the two-wire circuit and a second input terminal, the first amplifying circuit having an output terminal connected to a reception-side line of a four-wire circuit, a second amplifying circuit having an input terminal connected to a transmission-side line of the four-wire circuit and an output terminal connected to the secondary side of the transformer for sending out an audio signal on the transmission-side line to the two-wire circuit, a plurality of impedance matching circuits having respective impedances each determined so as to simulate one state of the variable impedance of the two-wire circuit, and a switch for s

Abstract: A sealing current generator for a telephone circuit provides a conventional nominal DC bias current in a telephone loop, and also temporarily provides a higher "zap" current whenever the DC current path is broken and then reapplied to the telephone loop. During the "zap" period, the voltage placed across the telephone loop is progressively increased in a number of predetermined steps if the current actually measured in the telephone loop fails to exceed a minimum value. The voltage is then maintained at its last level for the remainder of the "zap" period, after which the device returns to its base mode of providing a nominal DC bias current to the telephone loop.

Abstract: A hybrid circuit which converts receiving side four-wire signals from a switching network into two-wire signals, supplies the same through line B and line A to a telephone terminal equipment, and converts two-wire signals supplied from the telephone terminal equipment through the line A and the line B to the switching network into transmitting side four-wire signals, including a pair of battery feeding and terminating resistors connected between power sources (GND and V.sub.BB) and the line B and line A and a receiving side mirror circuit and transmitting side mirror circuit both connected between the lines B and A.

Abstract: Central office line interface circuit connecting a private telephone installation to a local central office. The central office line interface circuit includes a twin-loop line current polarity detector including a first optocoupler (57) for signalling polarity reversal, a transmission bridge (22) including a line loopback circuit operating via a second optocoupler (74) and provided with regulator and blocking means; it further comprises simplified tone and charging pulse detectors (24, 18).

Abstract: A circuit for maintaining hybrid cancellation of signals carried by a signal bus of a communication system, in response to variations in the number of hybrid circuits connected to the bus. One or more microprocessor control switches are utilized for selectively connecting one or more balancing load impedances to the bus in response to variations in the number of hybrid circuits connected thereto, such that a constant total load impedance is maintained on the bus. Also, circuitry is associated with each of the hybrid circuits for effecting hybrid cancellation of signals on the bus relative to the constant total load impedance. The circuit is of simple design and construction, occupying every little circuit board area and being of very low cost.

Abstract: Alternating current signals are differentially coupled between a two wire communications line and a telecommunications facility by a line interface circuit. The line interface circuit differentially drives signals destined for the two wire communications line, with a predetermined source impedance, via tip and ring amplifiers and tip and ring feed resistors. An amplifier circuit differentially receives signal voltages being developed by currents traversing the tip and ring feed resistors, and detects signals destined for the telecommunications facility by subtracting a representation of the signals destined for the two wire communications from a representation of the differentially received signals.

Abstract: A control unit of a subscriber line termination module has access via a programmable interface to the transmitting and receiving arms of a time division multiplex line connected to the switching network. At intervals which are long in relation to the pulse frame length, during the course of existing connections, PCM-words which occur N-times on the receiving arm and, in each case following a reflection time, during a plurality of pulse frames, a plurality of PCM-words occurring on the transmitting arm are received, subjected to amplitude evaluation and, if recognized as valid, subjected to cross-correlation. The result of the cross-correlation provides a control value for the dummy impedance.

Abstract: By the use of a feedback arrangement, deleterious circuit effects of an isolation transformer in a terminal device for a telephone line can be eliminated. By this arrangement, a smaller, cheaper transformer may be used. A terminal device employing such arrangement can present a balanced termination to a telephone line, exhibit a known and controlled impedance to that line and provide for signals to be coupled to and from that line.

Abstract: The universal channel unit includes a channel interface circuit that uses a pair of fixed ratio transformers to terminate both two wire and four wire analog transmission facilities on a selectable basis. The universal channel unit also includes a plurality of signalling circuits, each of which is switchably connectable via the channel interface unit to provide a DC signalling interface to match the signalling format required by the associated analog transmission facility. The signalling circuits include: DX, FXO, FXS, and other DC signalling circuits. The AC component of the signals carried by the analog transmission facility is output to an adaptive impedance and balance circuit which functions to closely match the impedance of the analog transmission facility and minimize signal reflections under control of a microprocessor. This impedance and balance network is connected to a PCM interface that includes an adaptive echo canceller circuit as well as equalization and gain control circuits.

Abstract: A telephone line interface circuit includes a transformer with tip and ring windings connected between tip and ring feed resistors and tip and ring leads of a telephone line, for feeding energizing current from a telephone facility to the telephone line. A secondary winding in combination with the tip and ring windings couples a.c. signals between the facility and the telephone line. A capacitance device is connected in combination with the secondary winding to simulate a function of a capacitance device as would normally be connected between the tip and ring windings in prior art circuits. The telephone line interface circuit is particularly useful in association with battery reversal responsive telemetry devices as any tendency for false ringer activation, in a connected telephone set, is reduced.

Abstract: A system for automatically compensating the transmitting (outgoing) signal level by detecting the receiving (incoming) signal level received from a communication channel to MODEM. Said system includes a gain controller for controlling the output gain of the analog signal received from analog signal input terminal in accordance with gain control data, hybrid means for amplifying the output of said gain controller, providing the amplified signal to transmit to a telephone line, and amplifying the analog signal received from the telephone line, receiving level sensing means for providing a plurality of receiving information data, said receiving information data teaching the level of the received signal, and a microprocessor unit for outputting the gain control data to said gain controller in response to the receiving information data and initial gain control data stored therein.

Abstract: A two-wire telephone line interface circuit includs two transformers each having primary and secondary windings. The primary windings, which are divided into equal halves for balance and d.c. feed purposes, are connected in series between the two wires, and the winding resistance together with optional series resistance provide desired d.c. resistance across the line. To this end one or both of these windings may comprise resistance wire. A signal from a receive line is coupled to the two-wire line via an amplifier whose low output impedance terminates the secondary of one of the transformers. Another amplifier couples a signal from the two-wire line and the secondary of the other transformer to a transmit line, and also provides at its input a transhybrid signal cancellation node, a transhybrid signal being coupled thereto via a balance impedance. A feedback path can be provided for increasing the a.c. impedance presented by the interface circuit to the line.

Abstract: A telephone line interface circuit includes a transformer with tip and ring windings connected between tip and ring feed resistors and tip and ring leads of a telephone line for feeding energizing current from telephone facility to the telephone line. A secondary winding in combination with the tip and ring windings couples a.c. signals between the facility. A capacitance is connected in combination with the secondary winding to simulate a function of a capacitance as would normally be connected between the tip and ring windings in prior art circuits, but without the problem of feed resistor interference at lower voice band frequencies. Network and component values are inserted between the secondary winding and an electronic hybrid circuit whereby the line circuit is precisely tailored for anyone of several national telephone line standards.

Abstract: An analog electronic hybrid circuit having a complex internal impedance includes a coupling transformer. The loss resistances of the transformer are used together with a measuring resistor to establish a predetermined complex internal impedance, thereby providing a balancing network. In one embodiment, nonideal characteristics of the transformer (nonlinearities, parasitics) have only very little effect because the transformer is contained in a feedback loop.

Abstract: An electronic hybrid circuit includes a differential amplifier having its non-inverting input coupled via a resistor to a four-wire input port and via a coupling transformer to a two-wire input/output port, its output coupled to a four-wire output port, and its inverting input coupled via a resistor to the input port and also coupled to an impedance network. The impedance network includes an inductive impedance which is coupled either to the amplifier output or to circuit ground, and which may be constituted by a gyrator or other electronic circuit which simulates an inductor.

Abstract: An office line interface circuit includes a DC circuit for extracting a DC signal component from the office line current, an AC circuit for extracting an AC signal component from the office line current to supply the extracted AC signal component to the receiver of a telephone set, an impedance circuit switchably connected to the office line, and a switching circuit for connecting the impedance circuit to the office line when the extracted DC signal component exceeds a predetermined level to maintain at a substantially constant value the impedance of the office line as viewed from the telephone set. With this interface circuit, the sidetone preventing circuit for the telephone system can operate satisfactorily without complicating the construction under any office line condition.

Abstract: A circuit arrangement for a module in the line-connection section of a digital time-multiplex telecommunication network is disclosed. The module contains, among other things, a transverse filter to perform a two-wire/four-wire conversion and is connected through a transformer to the wires of a subscriber line. In order to compensate for phase distortions caused by reflection of signals from the transformer back to the module, the corresponding signals coming from the module are subjected to an equal and opposite phase pre-distortion. This optimizes the hybrid circuit attenuation.

Abstract: The invention relates to an active symmetrical balance hybrid circuit. The hybrid circuit includes an input, an output and an in/output as well an impedance circuit per half section connected to the input and output which is connected between the in/output and one or more virtual ground points. Between a virtual ground point and one of the supply lines a signal transistor is inserted. The hybrid circuit further includes per half section two auxiliary transistors connected between the supply lines and the in/output. The auxiliary transistors multiply by the same factor the current flowing through a signal transistor together with which the auxiliary transistor is incorporated in a current mirror circuit. A signal transistor can be incorporated in a current mirror circuit with one or two auxiliary transistors in the same half section, but also by means of a universal coupling of the two half sections both with an auxiliary transistor in the one and an auxiliary transistor in the other half section.

Abstract: A data station termination circuit for connecting a four-wire, voice frequency transmission facility to either a four-wire or two-wire subscriber station in a telephone communication system for effecting a four-wire or two-wire mode of operation includes a gain/loss network coupled to a receive-in port for receiving incoming voice frequency data signals from a first signal transmission path of the four-wire transmission facility and for amplifying or attenuating the incoming voice frequency data signals. The gain/loss network is formed of a single operational amplifier, a set of binary weighted resistors, and a plurality of single-pole, single-throw slide switches. Other features disclosed include a battery back-up for use during a loopback condition and an optional equalization network for use in a second signal transmission path.

Abstract: The invention relates to an adaptive cancellation bridge circuit (ACB) for use in a single medium full duplex line termination equipment such as modems where signals are transmitted and received simultaneously along a pair of wires, the transmit and receive signal being separated in frequency. The bridge comprises a bridge network including transconductance cells (TC1, TC2 and TC3), to provide resistive, capacitive, and inductive components and these cells are electronically controlled by a current control device CC driven from a received signal (RXS) inphase and quadrature components to adjust the bridge network so that it becomes balanced and cancels a transmit signal (TXB) completely.

Abstract: An adaptive hybrid circuit for use in a digital telephone switching system is disclosed. The hybrid circuit is adaptive in that it provides cancellation of a far end talker power component in an output signal having both far end talker and near end talker power components. The circuit includes first and second transfer filters for matching loaded and non-loaded subscriber loops, respectively, in the telephone system. The circuit generates a filtered signal representing the difference between loaded and non-loaded subscriber impedances in the telephone system and generates an adaptive control signal responsive to the filtered signal and the output signal such that the far end talker power component is cancelled.

Abstract: A signal limiting amplifier includes interstage limiting devices to restrict the range of output voltage signals. The devices are base-emitter circuits of transistors, one of which operates in response to one polarity of signals and has its collector terminal unconnected, and the other of which operates in response to the other polarity of signals and has its collector circuit connected (when limiting) to operate an appropriate utilization circuit. In one embodiment, the limiting amplifier is applied as a common mode feedback amplifier in a telephone line feed circuit, and the limiter signal is used to limit large longitudinal signals on a customer line and to power down the line feed circuit in the event the limited signals persist beyond a certain interval.

Abstract: A subscriber line interface circuit is provided for a telephone system for interconnecting a two-wire telephone channel with a four-wire telephone channel. The circuit includes a pair of power amplifiers employing complementary circuitry and being coupled in complementary fashion to the two-wire channel so as to provide for both DC electrical excitation to the two-wire channel, as well as providing for an impedance match over the voice frequency spectrum, thereby reducing power dissipation while improving the coupling of voice and/or data signals. The presence of any noise on power line is rejected by use of transistor biasing circuits and by use of feedback circuitry. Both resistive and capacitive feedback branches are provided for the impedance matching.

Abstract: An electronic hybrid circuit for coupling a two-wire communication path to a four-wire communication path includes amplifier circuits having a reactive feedback path such that the output impedance of each amplifier is approximately zero ohms at DC and is a predetermined value at audio frequencies. The amplifiers are arranged to provide battery and voice signal injection on the two-wire path. Serially connected diodes provide protection from lightning.