Bell Telephone Laboratories

At&t Bell Laboratories

At&t Technologies, Inc.

David C Goldthorp

Milton L Embree

David R Vogelpohl

David M Embree

Howard H Longenecker

John Francis O'Neill

Frank P Tuhy, Jr

An electronic tone ringer provides a distinctive ringing capability through the use of two oscillators which allow selection of four tones and four modulation rates. In determining the type of tone generated, formattable inputs select between frequency shift or amplitude modulation modes or disabling the modulation altogether to generate a single tone. In the frequency shift mode, two fundamental frequencies are generated which are related by a predetermined ratio, the output tone alternating between these two frequencies at one of four selectable modulation rates. In the amplitude modulation mode, a single frequency is switched on and off at the selected modulation rate. All of the tones are produced with a duty cycle appropriate for driving an electromagnetic acoustic transducer.

Electronic tone ringer with distinctive signaling circuitry

An electronic tone ringer responds to ringing signals on a telephone line while being unresponsive to dialing pulses or other signals on the line. Powered directly from the telephone line or alternatively from an external DC supply, the ringer uses a digital integration and detection arrangement for distinguishing between valid and invalid ringing signals. A distinctive ringing capability for the tone ringer is also available through the use of two oscillators which allow selection of four frequencies and four modulation rates.

Electronic tone ringer

In an oscillatory signal generator circuit exceptional frequency stability is insured by the use of interrelated constant current sources (520, 521, 522) that provide an insensitivity to supply voltage variations over a wide range. Two of the current sources determine the duty cycle by controlling the charge and discharge current of a capacitor (C) in the circuit. A third current source determines the voltage swing on the capacitor. By varying the current output from the third current source, the generator circuit provides a variable frequency signal.

Relaxation oscillator with plural constant current sources

An electronic tone ringer responds to ringing signals on a telephone line while being unresponsive to dialing pulses or other signals on the line. Powered directly from the telephone line the ringer uses current sources (223-226) to provide a high impedance to the ringer circuitry and an insensitivity to line voltage variations so that reliable operation of the ringer is maintained on long loops and with multiple ringers terminated on the line. A multitone signal for activating an electroacoustic transducer (300) is provided by frequency modulating a single oscillator (500) within the tone ringer.

A relay driver circuit is disclosed in which a relay coil is operated by enabling the collector-emitter path of a switching transistor. In order to avoid damage to the transistor from voltages induced in the relay coil when the relay is turned off, an isolating semiconductor device is inserted between the transistor and the relay coil. This semiconductor device is operated in synchronism with the driving transistor and thus isolates the driving transistor from transients during the de-energization of the relay.

Relay driver circuit

A line transformer circuit in which the DC component of magnetization produced in the tip and ring windings by the battery supplying loop current to the telephone set microphone may be neutralized by an oppositely-poled, serially-connected balancing winding is disclosed. One end of the balancing winding is connected to the supply battery and is, therefore, at AC ground. The other end is kept at a point of high AC impedance to ground by the collector of a transistor so that audio frequency voltages induced in the balancing winding cannot load the transformer. The AC currents in the tip and ring windings are provided with a virtual ground return path by means of a differential amplifier controlled Darlington pair in circuit between the tip and ring windings and the balancing winding. The AC components of the Darlington pair collector current are bypassed to ground by a shunt capacitor at the junction of the Darlington pair collector terminal and the third winding. The differential amplifier senses voltage changes at the virtual ground so that the Darlington pair is driven to suppress these changes. Advantageously, the differential amplifier may be powered from the voltage drop appearing across the Darlington pair thereby facilitating circuit integration.

Integrable line circuit for use with miniature line transformer

An electronic switch is disclosed comprising a transistor bridge having input and output signaling nodes and bias control nodes. A pair of matched current sources are selectively activated and deactivated in a series arrangement with symmetrical turn-on turn-off circuitry in response to a receipt of instruction signals. The instruction signals control the gating of a constant current to the turn-on/off circuitry for enabling the matched current sources to selectively apply and withdraw matched currents from bias control nodes. Switched turn-off circuitry is employed for reverse biasing the transistor bridge in response to a deactivation of the matched current sources. A pair of voltage reference and antisaturation circuits cooperate with bridge discharge circuits to effect the reverse biasing of the bridge and to discharge rapidly the effective electrical capacitance of that bridge shortly after the receipt of a bridge turn-off instruction.

Bias control circuitry for semiconductor bridge

This specification discloses transistor circuitry suitable for use as a switch or as a floating current driver to control the concurrent operation of a pair of utilization devices. The circuitry comprises an NPN and a PNP output transistor which are substantially simultaneously switchable to ON and OFF states by a bias control means. The output transistors each have a collector connectable to a utilization device and a voltage of a prescribed polarity. Emitters of the output transistors are connected together in a floating voltage arrangement via a resistor. The bias control means comprises a pair of NPN transistors and a diode connected PNP transistor illustrated for switching the NPN output transistor and then the PNP output transistor to ON and OFF states. A logic gate switches a constant current to the bias control transistors for controlling the switching operations.

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Reading, PA, United States of America

David C Goldthorp