Fujitsu Corporation

Kenji Takato

Toshiro Tojo

Yuzo Yamamoto

Kazumi Kinoshita

Kazuyuki Minohara

Yozo Iketani

Kazuhiro Yoshida

Kiyoshi Shibuya

Mitsutoshi Ayano

Atsuo Serikawa

Yoshimi Iijima

Takashi Sato

Kenichi Ogawa

Seiji Miyoshi

Shin-Ichi Itoh

Kiyoshi Kurosaki

Shoji Nojiri

Shin-ichi Ito

Hiroyuki Ujiie

Takeshi Nishioka

Yasuo Miyazaki

Kiyoshi Kasahara

Taichi Kosako

Yoshinobu Imai

In a subscriber circuit implementing the analog system, the 2B1Q system and the ping-pong system, a signal processing unit is divided into a signal output unit for outputting a signal for transmission and a bias unit for providing a voltage, the signal output unit being implemented by an amplifier unit characterized by a low withstand voltage and a broadband characteristic, and the bias unit is implemented by an amplifier unit characterized by a high withstand voltage and a narrowband characteristic.

Subscriber circuit

Disclosed is a method for communication with no power feed in an exchange. (1) A calling subscriber unit transmits a special service code designating the disuse of a direct current loop together with the numeric information on the called subscriber unit to the exchange after formation of a direct current loop. (2) When the special service code is received, an on-hook transmission state in which the transmission and reception of an alternating current signal is possible between the subscriber line interface circuit and the calling subscriber unit even if no direct current loop is formed is established in the subscriber line interface circuit to which the calling subscriber unit which has transmitted the special service code is connected. (3) The calling subscriber unit disconnects the direct current loop, and the exchange maintains the speech path between the calling subscriber unit and the called subscriber unit even after the direct current loop is disconnected. (4) An alternating current signal is transmitted and received between the subscriber line interface circuit and the calling subscriber unit in the state in which no direct current loop is formed.

Method for communication with no power feed and exchange for realizing

Ring trip deciding circuit

A two-wire termination impedance generation circuit of a subscriber circuit including differential amplifiers, which is provided with a network circuit including capacitors and resistors, an input point, and current sources, the capacitor being comprised of series connected first and second capacitors, the resistor being comprised of series connected first and second resistors and having a high band bypass capacitor connected at the intermediate connecting point of the same, and the resistor being comprised of a complex termination resistor forming an internal termination impedance and a series connected complex termination resistor and complex termination capacitor being connected directly to the telephone line as an external termination impedance, wherein the frequency characteristics can be improved in three ways.

Two-wire termination impedance generation circuit of subscriber circuit

A battery feed circuit supplies a feed current to a telephone set via a 2-wire telecommunication line formed of a TIP line and a RING line. The battery feed circuit includes a first voltage detection circuit for detecting a first voltage across the TIP line and a ground line, a second voltage detection circuit for detecting a second voltage across the RING line and a power line connected to a power supply of the battery feed circuit, a current source responsive to a first control signal for respectively generating first and second currents in the TIP and RING lines, the first and second currents being equal in magnitude and opposite in direction, the current source also varying the first and second currents in response to a second control signal so as to be in proportion to a common mode voltage across the TIP and RING lines, a first feedback circuit responsive to the first and second voltages detected by the first and second voltage detection circuits for generating the first control signal, and a second feedback circuit for generating the second control signal by detecting the common mode voltage across the TIP and RING lines.

Battery feed circuit for supplying feed current to telephone set

A ring trip detection circuit detects an OFF-hooked state of a telephone receiver during ringing of a telephone set by detecting a change in a voltage across two terminals of a transmission resistor through which a ringing signal is supplied to the telephone set from a ringing signal source. The ring trip detection circuit includes a voltage dividing circuit coupled to the two terminals of the transmission resistor for dividing voltages at the two terminals and for outputting divided voltages, a pair of transistors having bases for respectively receiving the divided voltages from the voltage dividing circuit, a constant current source, a pair of resistors having first terminals respectively coupled to emitters of the pair of transistors and second terminals coupled in common to the constant current source, where the pair of resistors have the same resistance, and a current mirror circuit coupled to collectors of the pair of transistors for outputting an output current which indicates whether or not the telephone receiver is OFF-hooked.

Ring trip detection circuit

An ISDN interface circuit is provided which is coupled to a terminal device via a transmission line and a reception line, the transmission line being formed of a pair of first and second wires, and the reception line being formed of a pair of third and fourth wires. The ISDN interface circuit includes a first resistor and a second resistor connected in series at a first node and between the first and second wires of the transmission line, and a third resistor and a fourth resistor connected in series at a second node and between the third and fourth wires of the reception line. The ISDN interface circuit also includes a D.C. power source connected to one of the first node, at which the first resistor and the second resistor are mutually connected in series and the second node, at which the third resistor and the fourth resistor are mutually connected in series. One of the first node and the second node, other than the above-mentioned one of the first node and the second node connected to the D.C. power source, is grounded.

ISDN interface circuit and system using the same

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.

Hybrid circuit

Ground fault detector

Ring trip circuit for subscriber telephone

Disclosed is a terminating circuit in a battery feed circuit of an electronic exchange system. The battery feed circuit comprises two transconductance amplifiers connected by a coupling capacitor, for supplying a direct current through a ring terminal and a tip terminal to a load. Each of the transconductance amplifiers comprises an operational amplifier; a resistor connected between the output end of the operational amplifier and the tip terminal or the ring terminal, and an impedance unit connected between the inverting input terminal of the operational amplifier and the output end. The impedance unit has an impedance determined in such a way that the required terminating impedance of the battery feed circuit when viewed from the tip terminal and the ring terminal is formed only by the internal elements including the impedance means and the resistor, whereby an external larger-size capacitance capacitor for matching becomes unnecessary.

Terminating circuit in a battery feed circuit of an electronic exchange

A battery feed circuit including a main battery feed part and its peripheral circuits provided in a line circuit of a switching system. The peripheral circuits include the following: First, a means for forming a low impedance with respect to in-phase signals, simply realized by a capacitor; second, a bias circuit able to suppress the entry of power source noise and easily switch magnitudes of bias voltages and polarities, realized by a bias voltage generating means, a buffer means, and and AC bypass capacitor; third, a battery feed current control circuit able to suppress overflow of battery feed current when the distance to the subscriber is short, which detects an overcurrent component above a predetermined value, and, in accordance with the same, changes the bias voltage; fourth, a battery feed current supervising circuit able to detect current in both the forward and reverse directions, realized by an emitter-follower pair and a voltage/current converting resistor; fifth, a circuit for detecting bidirectional battery feed currents at a high precision, which is formed by forward direction and reverse direction current detection means provided with V.sub.BE cancelling means; and sixth, an overcurrent protection circuit, which changes the voltage applied between the inputs (+,-) of a transconductance amplifier forming the main battery feed part in accordance with an excess voltage.

Battery feed circuit

An operational amplifier for producing an output signal representing the voltage differential between two input signals is powered by first, second and third power sources respectively having high, intermediate and low output voltage levels. A voltage buffer circuit, which is connected to the second power source, interconnects a constant current source, which is connected to the first power source, and an amplifier means, which is connected to the third power source, and separates the constant current source from the third power source. A differential amplifier in the amplifier means responds to the two input signals for producing a voltage differential output signal, and an output circuit connected between the second and third power sources receives the voltage differential output signal of the differential amplifier for producing the voltage differential output signal of the operational amplifier.

Operational amplifier

A protection circuit for a battery feed circuit used in a switching system. The protection circuit is comprised of: a supervising circuit for detecting an abnormal current flowing through a battery feed resistor; and a voltage limiting circuit for clamping a voltage across the battery feed resistor when the abnormal current is detected. Further, a control circuit is employed for stopping an operational amplifier, which is a component of a conventional battery feed circuit, when the abnormal current is detected.

Protection circuit for battery feed circuit

A constant current circuit, including a constant current source which draws a current and a constant current source which sends a current, is connected to a two-wire subscriber line. A ringing signal made up of constant stream of positive and negative current signals is transmitted to the telephone line. The OFF-hook condition of a telephone set is detected by comparing the output voltage of a constant current circuit with a reference voltage for ring trip.

Growing community of inventors

Kawasaki, Japan

Kenji Takato