Abstract: A low-pass filter is inserted between a two-wire line and a four-wire transmitting line for transmitting a transmission signal supplied from the two-wire line. Input and output signals of the low-pass filter are fedback to a subtracter to provide a subtracted signal which is added to an output signal of a terminal impedance resultant filter. Thus, operation is realized in a stable manner even in a high frequency band, in which an output signal of the low-pass filter is rotated in phase by 180.degree..

Abstract: In an on-hook transmission circuit provided in a subscriber circuit connected between a subscriber terminal and an exchange, a constant-current source unit causes a constant current to flow in first and second wires during a period in which a control signal indicating that on-hook transmission should be turned ON is being received. A loop supervisory unit detects establishment of a loop including the first and second wires and a subscriber terminal connected thereto, and generates a scan signal used for causing the constant-current source means to stop the constant current flowing in the first and second wires after detecting the establishment of the loop.

Abstract: A hybrid circuit includes a two-wire/four-wire conversion unit for forming an interface between a two-wire line and a four-wire line, and a digital balancing unit for canceling a return echo passing through an echo return route including the conversion unit. The digital balancing unit includes first through fourth parts. The first part determines values of elements of a ladder type circuit composed of resistors and capacitors. The ladder type circuit corresponds to an original equivalent circuit having an impedance obtained by viewing the two-wire line from the conversion unit. The second part generates an impedance function of the original equivalent circuit in the form of a z function in accordance with a bilinear transform using an over-sampling frequency. The third part generates filter coefficients of a digital filter by inserting the impedance function into a transfer function of the echo return route.

Abstract: An improved transformer-less electronic isolating transformer is obtained with an output subcircuit that outputs a controlled current rather than voltage. Specifically, the improved hybrid comprises an output drive subcircuit that receives an ac signal and creates a corresponding current that is passed to the line that supports two way communication. The subcircuit not only converts the applied voltage to current but includes means for effecting gain. Signals arriving to the hybrid from the line are applied directly to a near-end echo circuit that is also responsive to the signal applied to the output drive subcircuit. Both the input of the output drive subcircuit and the output of the near-end echo subcircuit are isolated with opto-isolators that employ photodiodes in their photo-voltaic mode.

Abstract: An electric power circuit for telephone set use utilizing a power source drawn from a telephone circuit line. Alternating current components superimposed on a supply voltage, which is taken out by means of a by-pass capacitor, are delivered to a downstream-side of the common-base of an input-side transistor comprised in a current mirror circuit. A constant value of direct-current, which is the same magnitude as a potential difference between the supply voltage and a potential of the common-base of the current mirror circuit, is obtained at the input side transistor by varying the potential of the common base in accordance with fluctuations due to a.c. components superimposed on the supply voltage. An amplified direct-current is output from the output-side transistor capable of producing a magnitude of current in proportion to that of the input-side current.

Abstract: An isolation circuit (20) that is devoid of coupling transformers and yet suitable for use as a telephone line interface. The circuit is characterized by very wide bandwidth, low noise, and high linearity. Opto-isolators couple analog transmit and receive channels in a user device (12) across an isolation barrier (57) to a line pair for full duplex communication on the line pair. The interface circuit, which also includes a hybrid (55), includes first and second oppositely directed linear optocouplers (50,52). The first is disposed between the transmit channel and the hybrid; the second between the receive channel and the hybrid.

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 circuit for the non-linear limiting of the metallic current flowing in telephone line conductors. The circuit senses the metallic current flowing in the conductors. If that current exceeds a predetermined limit, the circuit provides from a controlled and variable voltage source a voltage across the conductors whose amplitude is reduced from the essentially constant amplitude voltage provided across the conductors when the current does not exceed the limit. The reduction in voltage amplitude is sufficient to maintain the metallic current at the limit.

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: An improved ring trip circuit for a subscriber telephone, for detecting an on-hook state or an off-hook state of the telephone. The ring trip circuit can be formed in a small size and can be formed by a LSI. The ring trip circuit includes a voltage detecting circuit (2), for detecting a voltage difference (.DELTA.V) between both ends of a ringer sending resistor, having a first circuit (S1, S2, A1.about.B3) converting the voltage difference to a current difference, and further having a second circuit (F) converting the current difference to a voltage, the voltage difference varying in response to the on-hook state or the off-hook state of the telephone, and a state detecting circuit (3) for detecting the on-hook state or the off-hook state in response to a value of the voltage from the voltage detecting circuit. The voltage detecting circuit is formed by a plurality of current mirror circuits, each of which includes at least two transistors.

Abstract: A channel unit interface circuit for interconnecting a two-wire, bidirectional signal transmitting path and a four-wire signal transmitting path in a communication system includes a tip terminal transconductance amplifier driver, a ring terminal transconductance amplifier driver, a voice sense amplifier, a balance network, A/D signal processing circuit, D/A signal processing circuit, filter network, a voice codec/PCM filter, a channel logic circuit, and a DC-to-DC converter. The tip terminal transconductance driver is formed of a first switching operational amplifier, and the ring terminal transconductance driver is formed of a second switching operational amplifier. Each of the first and second switching operational amplifiers is formed of a low voltage transconductance amplifier, high voltage comparator, a filter network, and a feed forward compensation amplifier.

Abstract: A subscriber line circuit (1) is connected via a subscriber line (3a, 3b) to a telephone set (2). For a raised receiver the subscriber line (3a, 3b) is supplied with a line current (Is) by speech signal amplifiers (4), which are powered from a power source (VBB). The speech signal amplifiers (4) and their power supplying amplifiers (7,9, and 10) have large idling power, apart from the power fed to the subscribe line. To decrease this idling power, the subscriber line circuit (1) has auxiliary amplifiers (5) with low idling power for supplying the subscriber line (3a, 3b) when the receiver is cradled. When a call is in progress and the receiver is lifted, the line current (Is) has a relatively large value, and when the call ceases and the receiver is replaced the line current (Is) decreases. This current decrease is sensed via a resistor (R2) by a loop sensing circuit (13), which sends a signal (S1) to a control circuit (14).

Abstract: A battery feed circuit including a main battery feed part and its peripheral circuits provided in a line circuit of a switching system.

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: A telephone subscriber circuit of a telephone exchange comprising active circuit elements with a capacitively-complex input impednace, wherein the signal which is to be transmitted from the exchange to the subscriber is amplified by two operational amplifiers operating in push-pull and is fed via two coupling arms, formed by a series arrangement of a capacitor and a resistor, into the subscriber loop which is itself supplied with d.c. current via two supply resistors. The subscriber circuit in accordance with the invention serves as a compensation network which directionally isolates the signals of the two speech directions and which includes two arms via which the symmetrical subscriber signal is supplied to a subscriber amplifier. In accordance with the invention the entire complex input impedance is sub-divided into a complex and a real component. The complex component serves as a coupling arm which supplies the LF-signal which is to be transmitted and which blocks the d.c.

Abstract: A compact battery-feed circuit for an exchange, including two feedback circuits provided for two wires, one being a dc feedback circuit for the dc voltage on the two wires, and the other being an ac feedback circuit for the ac voltage signal on the two wires.

Abstract: The subscriber line interface circuit comprises subscriber nodes, reception nodes and transmission nodes, a power feeding unit, adders, impedance elements, an inverting amplifier, and a feedback element. The subscriber nodes are coupled to a subscriber terminal via a subscriber line, and the reception and transmission nodes are coupled to an exchange via a reception line and a transmission line, respectively. The feeding unit supplied a DC current to the terminal and controls the current. The first adder adds the voltage between the subscriber nodes and the voltage from the reception node. The first impedance element has an impedance corresponding to a real-number multiplication of the impedance between the subscriber nodes, and is applied with the output voltage of the first adder. The amplifier is given with the output of the first impedance element.

Abstract: A channel unit interface circuit for interconnecting a two-wire, bidirectional signal transmitting means and a four-wire signal transmitting means in a communication system includes a tip terminal line driver, a ring terminal line driver, a voice sense amplifier, a balance network, A/D signal processing circuit, D/A signal processing circuit, filter network, a voice codec/PCM filter, a channel logic circuit, and a DC-to-DC converter. The channel unit interface circuit is suitable for use with substantially all of the different alarm-signalling techniques utilized by the various alarm companies for connecting their equipment to a channel bank coupled to the four-wire means. The interface circuit simulates a transmission line or cable over carrier in the frequency range of DC to 3.5 KHz with an amplitude variation between +110 to -200 VDC.

Abstract: Telecommunication line circuit including a Herter bridge with a first pair of terminals coupled to a bidirectional 2-wire line, a second pair of terminals coupled to an exchange, and a third pair of terminals where longitudinal currents are eliminated from sensed signals, as well as a ringing generator that may be coupled across the second pair of terminals which is coupled to a receive leg of a 4-wire exchange circuit and, through switching means to a ringing generator while the third pair of terminals is coupled to a transmit leg of the 4-wire exchange circuit.

Abstract: A line interface circuit supplies energizing current for operation of a two wire communication line and couples a.c. signals between the communication line and a telephone facility. Tip and ring rails are resistively connected to the communication line by matched feed resistors in a resistance network also including tip and ring taps. Active impedance circuits in an a.c. signal coupling circuit terminate the tip and ring rails with a predetermined impedance, via the feed resistors, in response to voltages at the tip and ring taps. Active resistance valving circuits in a direct current feed circuit supply the communication line with energizing direct current via the tip and ring rails and feed resistors. The valving circuits may be controlled to limit current for shorter lines and the functions of the a.c. signals coupling circuit may be optimally altered in response thereto.

Abstract: There is disclosed a line circuit for connecting a subscriber set to a switching facility to obtain an impedance match. The subscriber set is connected to first and second subscriber terminals by a two-wire line which presents a complex terminating impedance to said switching facility. A constant current source is connected between the first and second terminals for supplying the subscriber set with a constant direct current. There is a control current source coupled between the first and second terminals for supplying the subscriber set with an alternating current with the control current source having a control input. The first and second terminals are connected to respective first and second inputs of a differential amplifier whose output is coupled to a transmit line. The control input of the control current source is coupled to a receive line.

Abstract: A subscriber line interface circuit comprises a balanced amplifier having positive and negative inputs for amplifying a voltage thereacross to generate a pair of mutually complementary voltages across true and complementary outputs. Four resistors of a first value are respectively connected between a subscriber tip line and the negative input, between a subscriber ring line and the positive input, between the negative input and true output and between the positive input and complementary output. Two resistors of a second value smaller than the impedance of the subscriber loop are respectively connected between the tip line and the complementary output and between the ring line and the true output. A DC feedback circuit is connected to the complementary output to generate a DC feedback signal according to a desired variable DC power feeding characteristic.

Abstract: The interface of the invention comprises a power supply circuit (16) which is a symmetrical amplifier circuit, and a hybrid circuit (29) controlling the power supply circuit in DC and in AC. The hybrid includes a phase shifter circuit (44, 45) simulating long lines.Application: private telephony.

Abstract: This is an improved resistive line battery feed circuit where the improvement consists in establishing a balanced stable power point using an opamp and capacitive input and feeding the AC output to both lines of the tip and ring circuit via opamps and a hybrid for injecting current. In this manner longitudinal balance is maintained. Current is added to the line circuit by a modulated DC current source.

Abstract: A constant current line circuit for connection to balanced tip and ring leads of a telephone line and unbalanced transmit and receive leads of a PABX. A differential amplifier receives and applies incoming audio signals carried by the tip and ring leads to the unbalanced transmit lead, and detects D.C. loop current flowing through the tip and ring leads and generates a D.C. signal in response thereto. A voltage controlled feed current supply, connected in a circuit to the differential amplifier, generates a constant current D.C. voltage to the tip and ring leads in response to receiving the D.C. signal, and an integrator circuit is connected in a feedback path from the output of the differential amplifier to a voltage control input of the supply, for filtering audio signals received by the differential amplifier and regulating the generated D.C. signal to a quiescent value of approximately zero volts. The line circuit provides simultaneous bidirectional signal translation and constant D.C.

Abstract: A circuit arrangement for suppressing interference signals on the receiving arm of a subscriber line circuit is constructed from electronic components and thus comprises no speech transformers. The receiving arm of the subscriber line circuit (SLIC) is connected to a two-pole filter circuit (ZF) which consists of the parallel arrangement of a parallel--and a series--resonance circuit (LP,CP and LS,CS), the resonance frequency of which corresponds to the frequency of the signals which are fed-in for the transmission of charge pulses and which charge pulses can manifest themselves as interference signals when reflected without the provision of the described measures.