Abstract: A subscriber's telephone system is presented that includes at least one driver circuit connected to Tip and Ring terminals. An additional network is connected between an output of the driver circuit and the Ring terminal. This additional network includes a suitably dimensioned capacitor and a diode limiter connected in parallel with each other to minimize the overall voltage while maintaining a desired battery mean value.

Abstract: A line interface for combining a broad-band XDSL signal and a voice-band telephone signal in a copper duplex cable, where the voice-band signal, over and above the voice signal, carries a DC feed for the user telephone and, during the call phase, also a ring signal. The XDSL signal and the voice signal are coupled to at least one primary winding of a line transformer of which the secondary winding pilots the telephone duplex cable. The secondary winding is not DC-coupled with the duplex cable and the ring and feed signals are injected into the duplex cable by a circuit realized in high-voltage technology and arranged in parallel with the secondary winding. A further inductive winding performs the function of compensating the flow variations induced in the core of the line transformer during the call phase.

Abstract: The invention relates to a MOS transistors substitutive circuit having a transformer/data interface function, in particular for ISDN networks, comprising first (11a) and second (11b) power supply/transmitter blocks, the first power supply/transmitter block (11a) being connected between a voltage reference (V) and a first data interface (RX), and the second power supply/transmitter block (11b) being connected between a ground potential reference (GND) and a second data interface (TX), both power supply/transmitter blocks being connected to a supply voltage reference (VDD). The MOS transistors substitutive circuit according to the invention comprises first (12) and second (12′) MOS transistor pairs connected to the voltage reference (V), the MOS transistors being diode configured and held in their saturation range, so as to have a high A.C. impedance and virtually zero D.C. impedance, thereby minimizing power dissipation through the substitutive circuit.

Abstract: A method of measuring under running conditions operation parameters of an interface circuit and a telephone subscriber line connected to it, said interface circuit comprising a first integrated circuit operating on a high voltage with outputs connected to the line and second outputs on which transverse and longitudinal current values of the line are respectively present in normal operation, and a second integrated circuit operating on a low voltage between the first circuit and a telephone exchange, comprises the steps of: switching the outputs across an impedance of a predetermined value, and measuring through the first circuit the values of the currents present on the second outputs; switching said outputs back to across the line leads, and measuring through the first circuit the values of the transverse and longitudinal line current values; performing, for each measurement through the second circuit, a digital encoding of the measured values and transmitting such encoded values to the telephone exchange.

Abstract: An operational amplifier, of a type which comprises a differential cell transconductor input stage (2) incorporating a current mirror (5) provided with a pair of degenerative resistors (R9,R10) and a gain stage (7), driven directly by a transistor (Q12) of said mirror (5), has each degenerative resistor (R9,R10) formed within an epitaxial well wherewith a parasitic diode (D1,D2) is associated. Each diode (D1,D2) is connected in parallel with its corresponding resistor (R9,R10) to prevent the transistor (Q12) which drives the gain stage (7) from becoming saturated.

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: A monolithically integratable current adding circuit includes a current mirror circuit, the input port of which forms a first input terminal of an adding circuit and the output port of which is connected, via two series connected resistors, to a voltage reference. The point of connection between these series connected resistors forms a second input terminal of the adding circuit. The adding circuit also includes a voltage to current converter which has a first and second input terminal connected respectively to the output port of the current mirror circuit and to the voltage reference and which has an output terminal which forms the output terminal of the adding circuit.

Abstract: A telephone circuit which may be monolithically integrated, for generating control signals for displaying the telephone charges to a telephone user, is coupled to a AC voltage signal generator having a predetermined amplitude and frequency which are constant over time. The circuit includes a voltage generator for generating voltage signals which are spaced over time and have a trapezoidal pulse waveshape. A multiplier circuit calculates the product of the signals supplied by the two generators and supplies a signal which is sent to the speech circuit of the subscriber's line and is added to the speech (i.e.--conversation) signals. The circuit also includes a circuit for receiving an image signal of the overall signal adapted to the telephone line; a high-pass filter for eliminating the speech signal components from the image signal; a rectifier circuit for rectifying the filtered signal and a comparator for comparing the rectified signal with a reference signal.