At&t Bell Laboratories

Lucent Technologies Inc.

At+t Corp.

American Telephone and Telegraph, Co.

At&t Information Systems Inc.

Walter G Kutzavitch

Paul John

Eugene J Rosenthal

David F Jones

John F Bell

Allen J Rooney

Farid Khalili

Francis Xavier McGroary

Chiu L Hui

Vincent A Illuzzi

Thong V Luu

Manhar R Mahida

A current limiting circuit for a power switching transistor, the current limiting circuit incorporating a DC modulator to control the conducting/non-conducting state of the switching transistor, with an input signal generated and supplied to the modulator (and thus controlling a modulator DC bias output signal and therefore the conducting/non-conducting state of the switching transistor) comprised of two components: a first component which controls the modulator state based upon limiting maximum transistor current when a DC supply voltage is at a nominal design value, and a second component which dynamically adjusts the value of the modulator input signal when values of the DC supply voltage are other than the nominal design value.

Control circuit arrangement for limiting output current in power

A distributed processing telephone system for providing 'plug-and-play' capability. In particular, a key telephone system comprises a plurality of telephone sets. Each telephone set is coupled to a least one common communications channel, or telephone line, and includes at least one tunable RF modem. There is no key service unit (KSU). That is, the system is KSU-less. Resources of the telephone system are allocated using a peer-to-peer protocol. For example, as each telephone set is newly added to the system, the new telephone set adaptively determines its own allocation of resources, e.g., intercom numbers, etc. During operation, each telephone set requests the appropriate resources from its peers.

'Plug and play' telephone system

An improved pulse width modulation type switching power supply uses an opto-isolator as an output voltage error amplifier which feeds back an error signal to control pulse width modulation as well as to provide isolation between the primary and secondary voltages of the power supply.

Pulse width modulator for switching power supply

A high efficiency switching power transistor uses the energy in a snubber circuit to drive the gate driver and the pulse-width-modulator (PWM). The snubber consists of a resistor and a capacitor connected in series between the drain and source of a field-effect-transistor (FET). A steering diode is connected from the junction between the capacitor and the resistor to the power supply of the gate driver and PWM. This diode steers current from the snubber and makes it flow into the power supply thereby lowering the power requirements of the power supply. This energy would have been dissipated in the snubber as heat if it were not used this way. Efficiency of the switcher is increased both by lowering heat loss in the snubber and by using recovered snubber energy to lower the power requirements of the power supply of the gate driver and PWM.

Low dissipation snubber for switching power transistor

Apparatus is disclosed for use in a key set interface to overcome the incompatibility between key sets and tip and ring devices. The interface apparatus rejects ringing voltage and tip and ring loop current intended to be supplied on a first pair of conductors, the TR-pair. The interface further includes apparatus adapted for bi-directional communication of supervisory and control signals. In a preferred embodiment of the invention, a second pair of conductors, the service pair, transports bi-directional supervisory and control signals as well as operating power supplied by a key system controller for non-TR devices. Additionally, a transceiver adapted for sending and receiving voiceband information over the first pair of conductors is incorporated into the interface. An advantage of this key set interface is that operation of a key telephone set does not interfere with the operation of a tip and ring device bridged onto the first conductor pair.

Key telephone interface

Apparatus is disclosed for incorporation into a key telephone system control unit, in at least one station port, for operating an at least one key type set and an at least one tip and ring device simultaneously bridged onto the same station port without the use of any special service circuits or adaptors. The ability to signal alerting indepenedntly via ringing signal on a TR-pair, via messages indicating alerting transmitted on a service pair for a key set or via both techniques simultaneously is also disclosed. Further, the alerting ability disclosed in combination with control by a key system controller of the access of a key set to voiceband communications over the TR-pair allows for incorporation of additional features into a key telephone system. These features include the following: ring specific applications relating to an external event; direct transfer of calls to the transferor station port; calling other sets on the same station port; MEWPRIC (Multiple Extension With Personal Ringing on Incoming Calls) operation, i.e., a party line type of operation where the TR device and the key set sharing a single station port of station ports 103 are assigned different endpoint addresses; prevention of 'barge in', i.e., bridging, by a key type set onto a call to a TR device; time phasing of rings to allow for a coverage operation; and fax trouble detection.

Control and interface apparatus for telephone systems

Apparatus for digital amplitude regulation is disclosed, for use as a volume control or the like, utilizing pulse width modulation to control gain through the variation of the incremental resistance of a two terminal non-linear element, the resistance of which varies with current, e.g., a diode or diode like element. A stream of pulses, the duty cycle of which is variable and digitally controlled, is filtered to produce a quasi-continuously variable direct-current (DC) voltage. The DC voltage either directly or by providing a DC current regulates the gain of an amplifier that is amplifying the signal of interest by regulating the transmission characteristics of the diode. For low cost implementation in a system already employing a microprocessor or microcomputer the determinative duty cycle can be derived under software control and supplied as an output from a single latchable output pin. In an exemplary implementation, the incremental resistance of an ordinary silicon diode operated in accordance with the small signal model of a diode. Additionally, the use of an energy storing type filter allows the the continuous stream of variable duty cycle pulses to be momentarily interrupted so that a pin used for supplying the pulses can be used for the performance of additional functions without affecting the perceived volume level.

General purpose low cost digital amplitude regulator

Apparatus for digital amplitude regulation is disclosed, for use as a volume control or the like, utilizing pulse width modulation to control signal transmission through a two terminal non-linear element, the resistance of which varies with current, e.g., a diode or diode like element. A stream of pulses, the duty cycle of which is variable and digitally controlled, is filtered to produce a quasi-continuously variable reference signal. The value of the reference signal regulates gain by controlling the component of the signal of interest that is actually available for amplification. For low cost implementation in a system already employing a microprocessor or microcomputer the determinative duty cycle can be derived under software control and supplied as an output from a single latchable output pin. In an exemplary implementation, a derived DC component of the variable duty cycle pulses controls the DC output voltage from a voltage divider and is used to regulate the magnitude of a series of fixed magnitude pulses. Additionally, the use of an energy storing type filter allows the continuous stream of variable duty cycle pulses to be momentarily interrupted so that a pin used for supplying the pulses can be used for the performance of additional functions without affecting the perceived volume level.

Low cost digital amplitude regulator

A self-oscillating switching regulator includes an inductor which is switched across the input or output depending, respectively, on whether a control voltage does not or does exceed a predetermined threshold. The control voltage is generated from a predetermined sum of the output voltage and a voltage dependent upon the inductor current when the inductor is connected across the input.

Growing community of inventors

Freehold, NJ, United States of America

Walter G Kutzavitch