Abstract: An electronic telephone set for use with a telephone headset receiver/transmitter apparatus is disclosed. The telephone set is line-powered, and is capable of transmit muting, last number re-dial, and memory dialing. The volume of the received voice signal is controllable by a user, and a visual indication of the volume setting is provided. The receiver and transmitter amplifiers includes circuitry for compensating for the frequency response characteristics of two or more headsets, the compensation circuitry being selectively and automatically engaged by means of a programmable connecting jack. The design of the telephone is such that it consumes very little power, especially during "on-hook" operation. Moreover, an electrical storage device is employed to provide continuous operational power to the dialer circuitry and electronic hook-switch control circuitry, so that the telephone set retains its dialing memory when not in use.

Abstract: A power supply (ringer power supply) for a telephone exchange comprising a first switching circuit for receiving and subjecting direct current to high frequency switching by means of a switching element, a converter transformer connected to the switching circuit, a smoothing circuit connected to the secondary side of the converter transformer, a second switching circuit connected to the output stage of the smoothing circuit and used for switching the input current by means of a transistor bridge of a plurality of transistors for being alternately turned on, a direct-current bypassing diode connected between the input and output terminals of each transistor, a driving circuit for driving each of the transistors in accordance with a predetermined driving signal, and a driving signal generator circuit for generating the driving signal for setting timing to prevent the period during which a transistor is turned on from overlapping the one during which another transistor is subsequently turned on, permitting a red

Abstract: A telephone device, typically a terminal, that receives a.c. communication signals and that sinks d.c. current to provide the off-hook signal is powered from (i) the telephone lines and, if line voltage is less than 7.4 v.d.c., from (ii) a 6 v.d.c. battery. Connection to telephone lines of voltage greater than 7.4 v.d.c. recharges the battery. The terminal further contains a CMOS microprocessor that may be declocked and placed in standby mode to conserve power. When so placed, the microprocessor maintains some of its signal lines at a logic High, 6 v.d.c., condition. In order to both unpower circuits such as a display, a memory, a DTMF dialer, and a modem to which the microprocessor signal lines connect, and to (ii) disrupt current leakage paths from the signal lines to ground through the unpowered circuits, the ground is removed from the circuits. This removal, controlled by a signal from the standby microprocessor, is performed by a transistor switch.

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: An electronic telephone set which includes first and second connection points for a telephone line and a transmission circuit having a send output stage including a first transistor whose first main electrode is coupled to the first connection point by means of a first resistor. The telephone set includes a supply circuit for peripheral circuits. The supply circuit has a first output terminal coupled to the first main electrode of the first transistor and has a second transistor whose first main electrode is coupled to the second connection point and whose second main electrode is coupled to the second output terminal of the supply circuit. This circuit includes an operational amplifier whose output is coupled to the gate electrode of the second transistor. the set also includes a first voltage source connected between the first main electrode of the second transistor and a first input of the operational amplifier.

Abstract: A private branch exchange for use with different types of telephone sets comprises a current detection device such as a photo-coupler for detecting a current flowing through a data line connecting to a multifunction telephone set to discriminate among different types of telephone sets and a current limiting circuit for limiting a current supplied from a power source device through a voice line in accordance with an detected output from said current detection device.

Abstract: An in-line amplifier is readily connectable to a standard telephone so as to allow for user adjustment of the volume presented to the receiver portion 15 of the handset 14. The in-line amplifier draws electrical power from a replaceable battery 18 so as to be easily attached to the telephone base unit 12. The in-line amplifier includes a voltage level detector 20, which operates to determine when the battery voltage level has fallen below the minimum operating voltage of the in-line amplifier. Ordinarily, the audio signal is passed from the telephone base unit 12 through a controllable amplifier 16 to the receiver portion 15 of the handset 14. However, when the voltage level detector 20 determines that the battery voltage level has fallen below the minimum operating voltage level, a signal is delivered to a low voltage bypass 17, providing a direct electrical path around the controllable amplifier 16 so as to couple the audio signal directly from the base unit 12 to the receiver 15.

Abstract: A balanced transmission device having a pair of impedance element mutually of an equal value and connected between a pair of connecting terminals and an earthing point of an apparatus for superposing alternating signals on a direct current source and transmitting them through parallel two-wire cables. A transformer inserted as a high impedance source with respect to the apparatus for superposing and the transmitter, whereby the device can restrain any noise influence to realize smooth superposed transmission, with simpler arrangement but without enlarging it.

Abstract: Telephone network interface apparatus for interconnecting incoming telephone company wiring to subscriber premises wiring including a base including a bottom and an outwardly extending wall circumscribing the bottom, the wall includes opposed first and second wall portions and the bottom and wall provide a compartment divided generally into opposed first and second compartment portions, the first compartment portion is adjacent the first wall portion and the second compartment portion is adjacent the second wall portion, the first compartment portion is for having first terminals mounted therein for connection to the telephone company wiring and the second compartment is for having second terminals mounted therein for connection to the subscriber premises wiring; a telephone company cover mounted pivotally to the second wall portion and for overlying the entire compartment, the telephone company cover includes opposed first and second portions, the first portion is solid and is for overlying and closing the f

Abstract: An interface circuit provides for coupling of communications signals between a conductor of a transmission path, and a key telephone system and provides for protection against electrical energies, as may be associated with transient electrical event occurrences along the transmission path. The interface circuit provides for coupling of some of these transient electrical energies from the transmission path conductor to an earth ground. The interface circuit includes a plurality of electrical components and a plurality of electrical conductors being fixed to either of first and second surfaces of a sheet of electrically insulating material. The electrical conductors are spaced apart from each other by at least a predetermined amount. Some of the electrical conductors connect the electrical components of the interface circuit in a workable arrangement whereby the communications signals may be coupled.

Abstract: An interface (10) is disclosed for coupling a conventional pay station telephone (12) to a telephone switching system (16). The interface (10) provides supervision signal detection functions normally provided by a switching system, and thus can be connected thereto by a less costly business line (28). The interface includes processor controlled tone generators (72, 76) and detectors (73, 74, 81, 106, 108) for detecting tones and voltages transmitted by either the telephone (12) or the switching system (16). The interface (10) further includes a detector (106) and a procedure (FIG. 8) for providing an answer call indication. Coin collection or return is controlled by the interface (10) depending on the status of the call which is also determined by the interface (10). Further, a fail-safe relay will disconnect the phone from the tip and ring lines in the event of station irregularities.

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 permanent connection public telephone appliance is provided for connection to the switched network by a connection unit. It is permanently fed with power romotely by a source of the connection unit connected in parallel across the line of the appliance. The switched network is isolated from the source by capacitors. Line connection to the appliance is provided by a relay of the connection unit.

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 circuit compensating for the attenuation caused on a line by an LS series type notch filter at frequencies less than the filter cut-off frequency, with such filter connected across said line and a reference voltage, includes a first resistor (R) in series on the line, a series circuit comprising a capacitor (C1) and a second resistor (R1) connected across the line and reference voltage, the capacitor being connected on the side of a first terminal of the first resistor, and an amplifier, the input of which is connected to the connection point of a capacitor and second resistor and the output of which is connected to the second terminal of the first resistor, such amplifier having a transconductance at said lower frequencies capable of ensuring the injection of a current equal to the sum of currents deviated by the series circuit and the filter.

Abstract: The invention is directed to a prower-supply transfer apparatus for a telephone wherein the power supply is fed from a telephone line by a power supply transferring circuit when the operation has been decided as a low speed operation by a speed deciding circuit, the power supply is fed from a separate power supply circuit by the power-supply transferring circuit when the operation has been decided as the high speed operation, so that the low-speed operation is performed through the speed control by the speed decision result not only when the processing may be performed even at the low speed operation in the common telephone or the like, but also when the high-speed processing is required in voice recognition or the like.

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 so-called switching voltage regulator for an interface circuit in a telephone subscriber line, being of a type adapted to control the on/off states of an electronic switch, connected to the interface circuit and consisting of first and second transistors interconnected into a Darlington arrangement, comprises an ON-state sensor connected as an input to the collector of the first transistor and an OFF-state sensor connected as an input to the base of the first transistor, and a pair of current extractor devices respectively associated with the related bases of the first and second transistors. Also provided are first and second current sources, each connected to a corresponding current amplifier. The first of the amplifiers powers both current extractor devices. The second amplifier and a third current source are connected to the base of the second transistor.

Abstract: The invention provides a combination in a SLIC for telecommunication applications of ac impedance synthesis, e.g. raising the impedance of battery feed resistances by feedback techniques; in combination with real battery feed resistors and a dc block transformer. A dc blocked transformer is coupled to line current feed resistors and a feedback loop network to synthesize the desired input impedance, such that the feedback network incorporates both positive and negative feedback. A loop stabilizing resistor is used in shunt with the dc blocked transformer secondary to reduce gain peaking and phase shift.

Abstract: A low-powered remote sensor is achieved by capacitively isolating a long duration perpetual timer which is powered by removing inductively coupled AC power from telephone lines or other long lines. Three embodiments are described using this concept. The first embodiment is a remote utility sensor designed to periodically dial and transmit data to a central site via telephone lines and report its functionality on a periodic basis. The second embodiment of the remote utility sensor is used for reporting utility usage for common utilities such as gas meters, water meters, electric meters and water softeners on a periodic basis over telephone lines. The third embodiment is a remote utility sensor which continually records utility usage and can be read by a portable recording device through a remote cabled interface.

Abstract: A telephone power isolation system that will provide fused AC or DC power for multiple individually isolated telephone circuits using a single AC powered inlet and a multiple pair telephone connector for output connections. LED indicators are provided to illuminate and indicate a blown fuse condition that can be remotely observed and immediately identified.

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 telephone station subscriber line interface circuit for connecting a telephone subscriber station to a telecommunications transmission line comprises a loop current sensing circuit for providing an output signal proportionately representative of DC resistance in the telecommunications transmission line. A ring-side driving circuit is coupled to the loop current sensing circuit and is responsive to the output signal for providing an alternating current voltage source and a direct current voltage source to a transmit amplifier in periods of high constant DC resistance in the telecommunications transmission line, the ring-side driving circuit maintaining the output of the alternating current voltage source constant to the transmit amplifier and automatically transferring from a constant direct current voltage source to a constant direct current current source in the event of a decrease in the DC resistance in the telecommunications transmission line sensed by the loop curent sensing circuit.

Abstract: A telephone line circuit transformer couples tip and ring leads of a telephone line to a telephone facility. Tip and ring transformer windings are connected in series with the respective tip and ring leads, tip and rings feed resistors and terminals of a battery power source for supplying energizing current to the telephone line. A capacitor is connected between a junction of the tip winding and the tip feed resistor and a junction of the ring winding and the ring feed resistor. A compensating circuit is connected to drive a compensating winding in current opposing relationship with respect to differential alternating current signals in the tip and ring windings and being within a range of voice frequencies within which an impedance of the capacitor is significantly shunted by the feed resistors.

Abstract: A telephone having a hook switch is coupled to tip and ring conductors for receiving loop current from a central office responsive to an off-hook condition at the hook switch. The electronic circuitry within the telephone for facilitating various functions is powered entirely from the loop current flowing from the central office during the off-hook condition; with loop current being maintained after termination of the off-hook condition in order to perform certain call functions.

Abstract: A subscriber line interface circuit using integrated semiconductor circuit is provided with improved immunity to overvoltage and overcurrent conditions by increasing value of the battery feed resistors in series circuit with the ring and tip lines to increase the impedance encountered by a lightning-induced voltage spike to increase the survivability of the semiconductor circuit components. The battery supply voltage is increased to effect a commensurate increase in loop current, and the loop impedance is re-adjusted by appropriately configured operational amplifiers. A thermally responsive sensor is mounted in a heat-conducting relationship with resistive elements in the subscriber loop with an increase in temperature representing an overcurrent situation, such as power line cross-over, and provides a control signal effective to disconnect the subscriber loop from interface circuit.

Abstract: The invention relates to an apparatus for powering a loudspeaker amplifier (5) in a telephone set fed with a line current (ILO) from a telephone line (3). An incoming speech signal (S) is amplified (8) and sent to a loudspeaker (4) via the amplifier (5), (I6is powered via its feed connections (19, 20) from a reservoir capacitor (6). By the capacitor feed there are avoided variations in the line current (ILO) on amplification of the speech signal (S). The capacitor is recharged with the aid of the speech circuit (13), which has an amplifier means (16, 17) sensing a line voltage (UO) via a voltage sensing circuit (18). The amplifier means (16, 17) steers the line current (ILO) to a constant value responsive to the line voltage (UO) by sending a current ( to the line (3) via a resistor (R1), thus keeping constant a current I4 ) through the resistor (R1), this current being sensed by the amplifier means.

Abstract: A telephone set is fed with line current via a telephone line from final amplifiers. In order to transmit an undistorted speech signal at restricted battery voltage when the line is long, the final amplifiers are controlled in the following manner. A voltage sensing circuit senses a line voltage and controls first and second current-generating circuits which respectively send a first and a second current. A first difference-forming circuit generates a first difference current between a first reference current and the first current. A second difference-forming circuit generates a second difference current between the second current and a second reference current. When the second current is less than the second reference current the second difference current is diverted and assumes a zero value. A third difference current between the first and second difference current is amplified in an amplifier and controls the final amplifiers.

Abstract: A low power consuming signal detection device for attachment to a telephone line. The device has an impedance of at least five megohms across the telephone lines. The device includes a power supply having an input impedance of least five megohms and an amplifier powered by the power supply for amplifying tone interrogation signals present on the telephone line. A phase-locked-loop is responsive to the amplifier signals for determining when the frequency of the amplified signals are within a predefined bandwidth. Phase locking of the phase-locked-loop to the amplified signals is detected by a lock detector when the frequency of the signals falls within a predetermined bandwidth for a predetermined period of time. the lock detection signal is used to place meter reading circuitry in an "off-hook" condition and for effecting the transfer of data from meter data collection apparatus over the telephone line back to a remote location.

Abstract: The present invention describes a low power consumption type subscriber line interface circuit (SLIC). The SLIC described in the present invention includes a first pair of potential detectors each of which detects the potential difference between each corresponding subscriber line and a first predetermined value, a second pair of potential difference detectors each of which detects a potential difference between each corresponding subscriber line and a second predetermined value, a pair of signal adder circuits each of which sums output signals from one of the first potential difference detectors and one of the second potential difference detectors, and a pair of amplifiers each of which amplifies each output signal from each signal summing circuit and returns a direct current to the each of corresponding subscriber lines.

Abstract: A power circuit for supplying power to a device, which is connected in parallel with a telephone to a telephone line to that power is normally supplied to it from the central telephone office, includes batteries and a switching circuit such that the power source for the device is switched to these batteries when a voltage drop in the normal power source is detected.

Abstract: An electronic speech circuit configuration includes first and second line terminals to be connected to a telephone line. An AC circuit portion includes a modulator circuit for generating a line transmission current. A DC circuit portion supplies energy and generates a DC current/voltage characteristic curve. The DC circuit portion includes a reference potential source and a decoupling capacitor. A current sensing resistor is provided. A high-speed control amplifier has a control circuit and controls current through the current sensing resistor. A buffer capacitor is provided. Output terminals are connected to the buffer capacitor for the connection of external components. The DC circuit portion also includes a current toggle circuit connected upstream of the buffer capacitor. The current for feeding the buffer capacitor flows through the current sensing resistor connected to the first line terminal.

Abstract: A telephone circuit, which may be monolithically integrated, for feeding a subscriber's telephone line which is coupled via the circuit to a supply voltage generator. The circuit supplies the line with an impedance having a first predetermined value up to a given value of the line current, beyond which is supplies the line with an impedance of a second value greater than the first. The circuit is electrically equivalent to a voltage generator, identical to the supply voltage generator, having circuit components solely of the resistive type connected in series therewith.

Abstract: A switched mode DC power supply circuit for a telecommunication line, including a switched converter for charging an output capacitor from a DC source. The converter is controlled by a periodic control signal having a variable duty cycle so as to maintain a selected direct voltage level across the output capacitor. However, due to common mode currents on the telecommunications line, the capacitor may become charged above the selected voltage level even when the duty cycle of the control signal is reduced to zero. Such excess charge is returned to the DC source, without heat dissipation, by providing a further switched converter for coupling the capacitor to the DC source and which is controlled by a second periodic control voltage which is activated when the duty cycle of the first control voltage has been reduced to zero.

Abstract: A communication apparatus (e.g., a facsimile apparatus) has a monitor circuit to monitor line release after a line has been captured, a memory for storing information on a line release time when the line release is detected, and a control unit for controlling the apparatus. The control unit receives the time information from the memory at an end of a predetermined operation and can compute the appropriate time charge. A stand-by power source powers various components of the apparatus at certain times when full power is not needed, saving power use.

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: A subscriber line interface circuit receives and twice inverts currents from a 2-wire subscriber line and returns the currents to the subscriber line so longitudinal input impedance is low. Any differential input current in the subscriber lines is bypassed by a capacitor, so differential input impedance is very high. The circuit also sends a signal current from one system having one ground to another system having a different ground through one current path, while sending another current, having a phase opposite and amplitude equal to the signal current, through another path. This effectively isolates the two systems having different grounds.

Abstract: This power supply is intended, more particularly, for powering a user digital terminal from a remote terminal in an integrated service digital telephone network. It comprises a main D.C. electricity power source (10) provided with a protection device (11) causing its output to go to a high impedance state in the absence of a voltage across its terminals, and an auxiliary D.C. electricity power source (20) connected in parallel and in opposition with the main source (10) and provided with a current limiting device (20) which is normally tripped by the additional current which the main source (10) attempts to impose thereon.

Abstract: An arrangement is disclosed for delivering DC power (battery), voice, and ta signals from a telephone controller to a telephone station over first and second wire-pairs. Minimum interference between these signals is achieved when the first wire-pair is used as the voice signal path and the second wire-pair is used as the data signal path. DC power is fed out of the controller and into the center tap of an audio transformer interconnected with the first wire-pair. Ground current is returned to the controller through a balanced resistive circuit interconnected with the second wire-pair.

Abstract: A telephone set comprising an active line voltage stabilizer circuit having two output terminals 10-1 and 10-2 between which it produces a stabilized direct voltage which is independent of the line current. A series arrangement of a capacitor (14) and a resistor (16) is connected between such output terminals, the junction thereof constituting a DC supply terminal for the telephone set. Such arrangement does not alter the a.c. impedance of the stabilizer circuit between the wires, and has a considerably lower d.c. output resistance than supply terminals previously employed.

Abstract: The present invention uses the input resistances of transconductance amplifiers in a SLIC to isolate battery ground overshoots from the rest of the SLIC circuitry. This is accomplished by allowing the voltages within each driving operational amplifier to rise with any overshoot, and is achieved by powering each operational amplifier with battery ground voltage, which overshoots, instead of with low voltage ground (LVG), which remains at ground. When a lightning surge hits, an overshoot at the SLIC output will occur. However, since the supply voltage of the driving operational amplifiers rises with the overshoot, the voltage stress to the SLIC circuit components is greatly reduced. The remaining SLIC circuitry stays at a low potential and is isolated from the overshoot. In accordance with the present invention, ground overshoot voltages are isolated across a few high ohmic valued resistors instead of appearing across active circuit components.

Abstract: A DC control circuit for limiting metallic and longitudinal currents flowing in a balanced telephone line, and maintaining a predetermined DC bias voltage on tip and ring leads of the balanced line. A negative feedback path is established for monitoring voltage on the tip lead, comparing the monitored voltage with a predetermined offset bias voltage and generating a DC signal for application to tip and ring driver circuits for application to the balanced line in response thereto. Longitudinal and metallic currents are detected in a further pair of differential amplifiers for generating further DC signals such that a voltage corresponding to the detected longitudinal current is generated and applied to the tip lead, whereby a first one of the further pair of differential amplifiers adjusts the generated DC bias signal for limiting the longitudinal current flowing in the tip and ring leads.

Abstract: A telephone apparatus powered directly from the telephone lines without external power includes a current converter in which current from a telephone line is limited by a transistor, current-sense resistor, and optical coupler acting together as a constant current device. This limited current is then converted from direct current (d.c.) to alternating current (a.c.) at the primary of a current transformer by power switching transistors driven by a flip-flop which is in turn driven by a free-running constant frequency oscillator. The alternations are symmetrical and their period or timing controlled so the current transformer does not saturate, thus maintaining maximum efficiency of conversion. The transformer outputs, after being rectified and filtered, are isolated from the primary, and provide d.c. current to maintian the charge on a battery across one output and to power telephone circuitry within a telephone device connected to the d.c. outputs.

Abstract: A circuit for remote supply of subscriber line terminals in telecommunication systems, especially suitable for employment in digital telecommunication systems, is described. The circuit comprises a supply circuit (10) at the beginning of the subscriber line (11), which circuit has a negative internal resistance operative when a preassigned supply amperage is exceeded. Between the subscriber line (1) and the terminal, a current converter cirucit (12) is provided, containing an energy reservoir (40) on the primary side and a switch-on circuit (41-44) operating in dependence upon its charge voltage for the switch pulses required for start-up. The operating current for the switch pulses is then delivered by a secondary winding (57) of the converter transmitter (27).

Abstract: A Subscriber Line Interface Circuit (SLIC) having a voltage regulator for application thereto of a DC supply voltage V.sub.B and connected at the output terminals to an audio transmission line to provide a line current I.sub.L and voltage V.sub.L for a given resistance load R.sub.L on the line, is provided with a control circuit which, by picking up appropriate current and voltage values from the interface circuit, outputs a voltage value which is the equal of the difference between an optimum supply voltage V.sub.BF and the supply voltage V.sub.B. The control circuit output is connected to the voltage regulator to minimize the voltage V.sub.BFK applied to the interface circuit as the transmission line resistance load R.sub.L varies, thus minimizing the power dissipated through the interface circuit.

Abstract: A microprocessor controlled integrated alarm and touch tone telephone system which allows the alarm system to be accessed, programmed, and reported upon through a touch tone telephone, either locally or remotely. Under most circumstances, the telephones on the premises can be operated in a normal manner. However, the alarm system selectively monitors the telephone activities for coded touch tone instructions specifically for the alarm system, and responds thereto by issuing synthesized voice reports on the status of the alarm system. A touch tone decoder circuit decodes dialed touch tones, such that the telephone can be utilized similar to a normal keyboard panel to access and control the alarm system. An internal power supply is provided for the telephone for supplying electrical power thereto independently of the outside telephone lines which normally supply power, in the event the outside telephone lines are inoperative.

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 circuit, which may be monolithically integrated, for measuring longitudinal and transverse currents in a two-wire transmission line, includes first and second current mirror circuits of a first type, each having an input branch and first and second output branches. The measuring circuit also includes third, fourth and fifth current mirror circuits, each having an input branch and an output branch, and first and second currents mirror circuits of a second type, each having first and second input branches and first and second output branches. The input branches of the first and second current mirror circuits of the first type and the first input branches of the first and second current mirror circuits of the second type are used as input terminals for coupling to the line.

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.