International Telephone and Telegraph Corporation

The Singer Company

Robert Treiber

Daniel J Weaver

John M Cotton

John E Cox

Joseph Pernyeszi

Gerald R Wald

James B McLaughlin

Avner Wolanow

Michael J Piccardo

A recursive automatic equalizer is described for implementing the telephone equalization function at a line circuit which may be multiplexed between a plurality of telephone subscriber sets. A recursive digital filter structure having programmable coefficients minimizes the error between the equalizer input and a reference signal. The recursive filter transfer function is variable via feedback coefficient update, with respect to its input and the reference signal. The recursive filter coefficients are adaptively changed to rapidly converge to a final value based upon a mean square error algorithm. The desired filter transfer function can be achieved with a low number of coefficients, for example, five, rather than the heretofore high number of coefficients required in non-recursive filter structures.

Automatic equalizer for synthesizing recursive filters

A digital telecommunication line circuit implementable on one or more large scale integrated circuit (LSI) chips is described. A simplified integrated hardware structure is provided so as to achieve the combination on an LSI chip of an electronic two-to-four wire hybrid, line impedance matching by automatic digital impedance synthesizing of an output impedance and all digital filtering functions for an all LSI telephone line circuit including automatic equalizing.

All digital LSI line circuit for analog lines

A digital electronic hybrid circuit for a telephone line circuit is described wherein the two-to-four wire conversion function is provided with an improved synthesized automatic impedance match between the telephone subscriber line and the digital central office. More particularly, an impedance at the input to the line circuit is simulated without the use of discrete components and which closely matches the subscriber line impedance. The circuit digitally separates the full duplex signals on a two-wire transmission path to a pair of digital signals.

Digital two-to-four wire converter for full duplex signals

A circuit for automatically digitally synthesizing an output impedance, which may be a matching line terminating impedance, is provided. The means for establishing the desired output impedance characteristic is accomplished using a simplified recursive digital filter arrangement. In addition, means are provided for eliminating the effects of incidental undesirable shunting impedances.

Automatic, digitally synthesized matching line terminating impedance

A uniformly manufacturable solid state modular distributed control for a digitally switched local or central office servicing an expandable number of subscribers is disclosed in which subscriber lines and trunks communicate through a standardized hardware interface to a group switch. The described system provides microprocessor control of each call, with software distributed in accordance with the class of service per line, without the limitations of centralized control systems, but expandable without adverse affect on existing software. Switching control signals are communicated to and from the subscriber subsets to the group switch over the same paths which couple the speech signals thereto, thereby eliminating cumbersome and expensive separate control paths. In accordance with a further aspect of the present invention, subscriber calls are divided into orginating and terminating call halves, under subscriber control and separated by the group switch, thereby eliminating undesired interaction therebetween to provide for simplified software requirements.

Distributed control for digital switching system

The present invention discloses a reduced power dissipation telephone subscriber line feed circuit in which the battery feed current from the central office is determined by the subscriber loop resistance for medium to long loops, and for shorter loops, for which the battery feed current would exceed a given predetermined threshold, the feed current is limited to the threshold value. The invention also relates to compensation for loop and subset attenuation characteristics. During operation in the current limited mode, attenuation is automatically inserted into the signal transmission and receiving paths in order that normal equalizer operation will not be impaired by current limiting of the battery feed current. A multiple telephone subscriber system is disclosed wherein the circuitry used in deriving current limiting control signals is shared in a multiplexed arrangement by a plurality of subscriber lines. Line feed current is limited in discrete steps to a predetermined threshold value in each subscriber loop upon the detection of an OFF HOOK condition when the feed current drawn by the subset exceeds the threshold value. A plurality of discrete signals are derived by sensing the amount by which the line voltages exceeds a predetermined selected reference voltage value. These discrete signals are used to determine both the effective battery voltage which will produce a d.c. feed current corresponding to the limiting value and the amount of attenuation to be added at the central office by the line circuit to compensate for the equalizer effect in the subscriber set which occurs as a result of the current limiting.

Current limited subscriber line feed circuit

A microprocessor controlled subscriber line circuit for interfacing analog telephone lines and trunks to a digital switching system is disclosed. All processing of incoming analog signals is accomplished by the line circuit, including the interface between the line and a digital switching matrix, measuring, monitoring, testing of the signals associated with the speech path. Additionally, the dc signal powering the carbon microphone on the handset is generated as well as ringing and other tones. Equalization and providing the two-wire to four-wire conversion with acceptable echo performance and minimized cross-office transmission loss are also accomplished. Analog-to-digital and digital-to-analog conversions are accomplished under microprocessor control as are the tone and power generation functions in a programmable power supply configuration utilizing pulse duration modulated feedback control in a programmable signal generator. The described subscriber circuit is particularly advantageous in that it is designed to maximize its implementation using solid state circuit techniques including large scale integration as opposed to conventional components and relays.

Subscriber line/trunk circuit

A hand-held data-gathering unit is formed by removably connected control and power modules: The control module contains a keyboard, a display device, a data input probe, and a microprocessor. The power module contains a rechargeable battery with a converter and associated power logic, and a memory system with associated memory control logic. The hand-held unit has a normal low-power standby mode which is maintained during the absence of input data from either the keyboard or the data probe, and an operation mode which is initiated by the arrival of input data. During the operation mode, input data enters the control module and is forwarded to the memory in the power module. As data is gathered during portable operation, the memory may reach capacity or the battery voltage may drop, or both. The power module may be removed from the control module and replaced by a fresh power module with a fully charged battery and an empty memory. The expired power module is inserted into a service module for charging the battery or transmitting the data to a remote terminal, or both. The control module may also be inserted into the sevice module where it is activated by a stationary power supply and interfaced with the memory in the power module for stationary operation. In addition to transmitting the contents of the memory, the service module may receive data from the remote terminal and for storage in the memory. This received data may then be accessed and displayed through the control module.

Portable data-gathering apparatus formed by modular components having

Input and output switching transistors are alternatively activated to form a charging path and a discharging path for an inductor. The inductor periodically charges through the input transistor from an unregulated rechargeable battery, and discharges through the output transistor into an output capacitor. The output voltage taken across the output capacitor is regulated by negative feedback which varies the inductor charging period through the input transistor. The converter regulation is bidirectional. The voltage from the battery is initially greater than the regulated output voltage, but decreases to a value less than the output voltage as the battery discharges. When the battery is fully charged the converter regulates the battery voltage down to the output voltage. As the battery voltage drops through discharge, the converter regulates the lower battery voltage up to the output voltage. When the output voltage is not required by the data gathering apparatus, the output transistor is deactivated terminating the output voltage and establishing a residual standby mode in the power converter.

Efficient bidirectional power converter for portable data gathering

A light pen is scanned across a bar coded label to produce a reflected light signal having a modulated intensity. The average peak-to-peak value of the plus and minus peaks of the return signal is continuously generated to provide a reference for detecting each subsequent positive and negative transistion. The instantaneous average peak-to-peak reference permits the positive transistions to be distinguished from the negative transistions in spite of large deviations in the amplitude modulation and large shifts in the signal to ambient light level ratio of the return signal. Initially the light pen is operated in a low power pulsed mode. The initial transistions in the return signal cause the pen to temporarily illuminate the bar coded label with a continuous light, and activate plus and minus peak detectors.

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Centerport, NY, United States of America

Robert Treiber