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 bidirectional amplifier for use in a transmission line, that utilizes a pair of interconnected bridge circuits including isolation transformers and a pair of unidirectional amplifiers. The transmission in each direction uses a single amplifier to amplify the signal for a particular direction of transmission without effecting the other amplifier.

Abstract: An interface circuit for interconnecting an analog telephone device with a digital telephone system includes an independent power supply (58) for driving the loop termination on an analog telephone device (22). An impedance matching circuit (54) and a summing network (42) are utilized to both couple the signal from the analog telephone device (22) to the analog input of a key service unit (10) and match the impedance therebetween. A switch, (46) is provided to disconnect the analog port of a digital telephone device (12) that is compatible with the key service unit (10). When the analog telephone device (22) is in the off-hook mode, a switch control (52) opens the switches (48) and (50) of switch (46). The digital telephone device (12) is under the control of a digital transmission line (20) to maintain an analog interconnection in the key service unit (10). The analog telephone device (22) operates on an independent loop termination with an independent loop current.

Abstract: An integrated circuit for the transmission of telephone signals is designed so as to be inserted in a speech circuit of a subscriber's telephone set and includes a threshold comparator having first and second input terminals coupled to the terminals of a two-wire telephone line and an output terminal connected to a point of the signal path of the circuit. The threshold of this comparator is set such that when the voltage at the terminals of the line drops to a predetermined value, which is not lower than the minimum voltage value required to ensure the correct operation of all the components of the circuit, it generates an output signal used to limit the amplitude of the negative peaks of the waveforms of the transmitted signals.

Abstract: The echo canceller for bidirectional digital transmission systems cancels the echo queues of a desired number N of digital symbols, transmitted on the line in the last N signalling periods. It consists of a part which effects very simply the summation of the last N transmitted symbols, so as to ease the system implementation by an integrated circuit, and of a part which computes the estimated sample of the echo-channel pulse response. The results of the two parts are multiplied by one another and the estimated echo signal is obtained.

Abstract: A telephone set which has a hands-free mode of operation is disclosed. The telephone set includes a telephone circuit connector to a handset and a hands-free circuit connected to a loudspeaker. A hook switch is mechanically operated in accordance with operation of the handset. A semiconductor switch is connected in parallel with the hook switch and is controlled by a control circuit. The telephone circuit or hands-free circuit is selectively connected to a pair of telephone lines through the hook switch or the semiconductor switch.

Abstract: The invention relates to a subscriber telephone set with amplified reception loudspeaker.To avoid distortion of the signals transmitted to this loudspeaker should the power supply of the line be insufficient, it is provided for the amplifier feeding this loudspeaker to have its gain controlled by a signal resulting from the measurement of current passing through a shunt regulator serving for supplying the amplifier.

Abstract: An echo cancelling system incorporated in a conventional echo canceller with additional circuitry to provide tracking and compensation for drifting of any D.C. offset generated.Upon initial energization of the system (i.e. before data signals are processed thereby) an output signal e.sub.1k from an error signal input device represents a D.C. offset value generated by the components of the system.This value is stored in a D.C. offset register, the loading of which is controlled by a load/inhibit signal. Refining of the stored value during data processing is achieved using predetermined increments .DELTA..sub.1 for half-duplex mode and .DELTA..sub.2 (of smaller size) for full-duplex mode.

Abstract: A loudspeaking telephone instrument comprises a transmit path comprising a microphone (1) and comb filter (2); a receive path comprising a comb filter (3), a frequency shifter (4) and a loudspeaker (5); and a hybrid circuit (6). The frequency shifter (4) shifts the frequency of a signal applied to its input by a fixed amount and the comb filters (2,3) are arranged so that the frequency shifted signal falls in their stop bands. This increases the available gain in the loudspeaking telephone instrument before instability occurs. The spacings of the pass and stop bands of the comb filters (2,3) are at a multiple of the frequency by which the frequency shifter shifts that of its input signal.

Abstract: To provide an adequate dc supply to the electronics of a telephone, when on hook or off hook, there is a transistor (T2) with its emitter-collector path in one line wire, and a storage capacitor (Cpsu) across the input to the telephones's circuits. This capacitor is charged up and maintains dc supply when the line voltage (at A) falls below a preset level. The base of this transistor is connected via another transistor (T1) to the other line wire. The speech output (V.sub.IN) is connected via an operational amplifier (A) to the base of the second transistor (T2). Hence the dc supply and the speech output are in parallel.

Abstract: A method for eliminating echos in modems used for full-duplex data communication is disclosed. The technique improves the cancellation of the echos by synthesizing an estimate of the desired signal and subtracting this estimate from the received waveform to improve the estimate of the residual echo. An adaptive filter is used to match the transmitted bit pattern to make an estimate of the frequency offset in the far echo, so that it can be cancelled more accurately.

Abstract: A circuit for switching one of two impedance networks to a line carrying AC signals comprising a unity gain amplifier having differential inputs connected across the first one of the impedance networks, and one of the differential inputs and an output connected across the second one of the impedance networks, and a microprocessor control terminal connected to the other of the differential inputs for applying one of either a high impedance or AC ground thereto. The circuit is small, inexpensive, requires no electromechanical parts, and takes up very little circuit board area.

Abstract: A telephone network interface device adapted to be connected to and in between a telephone subscriber premise wiring and a Telephone Company owned subscriber loop comprising a backwall and a sidewall affixed to the sidewall delimiting a cavity in which there is: first and second sets of terminals connected to the backwall and a device to place the terminals of the first set in removably electrical communication with the second set of terminals, the first set of terminals comprising first and second spaced-apart dielectric blocks, each dielectric block containing a plurality of terminals and a plurality of first slots in a first surface and a second slot in a second surface, each of the first slots in the first dielectric block being in alignment with one of the first slots in the second dielectric block and disposed essentially perpendicular to the base and the second slots are mechanically and slideably fitted over a rib on the base so that the dielectric blocks may be slideably moved towards and away from o

Abstract: A cordless headset includes a headband, a tubular support having one end mounted on the headband, a housing mounted on the other end of the tubular support and having spaced apart opposed walls on the outer surface of which a plurality of telephone operating digits are arranged in a circular pattern for controlling output signals, aligned central apertures formed in the opposed walls of the housing, and a microphone positioned in the housing and aligned with the apertures.

Abstract: An audio bridge for a telephone conference is disclosed. The audio bridge; comprises a channel signal processing unit assigned to at least three channels. Each channel signal processing circuit comprises an echo canceller to cancel an echo signal from the transmitting side fed back to the receiving side, an amplifier and attenuator circuits to adjust levels of an output of the echo canceller and a transmitting signal transmitted through the channel signal processing circuit, an ERL determining circuit to determine an echo cancellation on the basis of the output from the echo canceller and a signal level on the transmitting side, and a gain/loss computing circuit to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition.

Abstract: A subscriber's line closing circuit, in which at least one first photo coupler and at least one second photo coupler connected in parallel but in reverse polarities are inserted in a closing loop so as to detect an incoming call, to form a DC Loop and to sense the direction of a direct current flowing through the closing loop.

Abstract: A current supply circuit for supplying a speech current via subscriber's lines to a telephone set, in which a pair of constant-current circuits, each so constituted as to hold the potential between the base and the emitter of a control transistor therein to be consant, is connected across the subscriber's lines so that the control transistors are connected in series to a DC power source. A constant-voltage circuit is connected across the bases of the control transistors for making the voltage of the base-emitter paths of each of the control transistors to be constant. At least one of the constant-current circuits may be connected across the subscriber's lines via a light emitting diode of a photo coupler.

Abstract: The flow of direct current and/or ringing alternating current in a telephone line subscriber loop is detected by means of current flow detectors. The output signals produced by the current flow detectors are applied to an evaluation circuit, the zero-crossings of the ringing alternating current being used to determine whether a ringing alternating current has been superimposed on the loop direct current.In order to increase the reliability of the evaluation and to detect noise voltages coupled into the subscriber-loop, the durations of positive and negative half-waves of the loop current are measured and the evaluation is effected by comparing the sum and the ratios of the measured values relative to a presettable threshold.

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: The method provides the use, for the determination of the estimation echo-channel pulse response, of digital filtering techniques of the transversal adaptive type, and the subdivision of the pulse-response of the equivalent echo channel into three intervals, the second of which consists of the significant portion of the pulse response and is determined by the iterative search for the value and the position of the coefficient of maximum absolute value; the first interval corresponds to a pure delay and the third corresponds to the contribution given by the lowest frequencies of the base band. To copy the echo-signal, there are only considered the pulse-response coefficients whose indexes are comprised in the second interval, and the samples of the signals to be copied belonging to preceding sampling instants, whose indexes are also comprised in the second interval.