Tie/communications, Inc.

Vincent V Korsky

Chansak Laotetpitaks

Raymond T Pajer

Rajmund Krzyszczyk

Jin T Lim

Ronald M Keenan

This invention relates to improved trunk interface circuitry for telephone system common equipment, which is used to connect a local customer system to a central office of the telephone company. The improved trunk interface comprises an active two-terminal current sink for limiting the loop current in a non-linear manner, and means for monitoring the voltage across the trunk line which comprises a voltage-to-pulse width converter. The voltage-to-pulse width converter is designed to operate with a microprocessor which measures the time it takes to linearly discharge a capacitor which has been charged to the line voltage.

Trunk interface circuitry for telephone systems

The present invention is embodied in and carried out by a dual channel transmission system with inherent channel identification and extraction. This system employs a data transmission method which has the inherent characteristic that, when two identical receivers are connected to a single signal driver which is transmitting a data stream containing data for each of the channels including one of these receivers, each identical receiver extracts only the data intended for its channel. This method affords the advantage that the signal driver bandwidth may be reassigned by software control so that, when needed, one receiver may extract both channels.

Dual channel transmission method and apparatus with inherent channel

A method and apparatus for synchronizing a digital data signal from a first location, such as a digital telephone station, and which is transmitted to a second location, such as the station interface of a telephone switching system common equipment input, with a digital data signal at the second location, is disclosed. The method includes transmitting a data signal to the second location from the first location, receiving the data signal at the second location and determining if the data signal is present at a selected time. Digital coded data is sent to the first location from the second location for selecting successive delay times at the first location. When the delayed data signal is present at the second location at the selected time, the optimum value of the delay time is determined at the second location, preferably by averaging the values of the delay times at which the data signal was first detected and last detected at the second location. Digital coded data corresponding to the optimum delay time is then sent to the first location to select the optimum delay time at the first location.

Synchronization method and apparatus for a telephone switching system

A speakerphone control circuit is disclosed. The control circuit includes a first electronic switch coupled between the speakerphone microphone and a hybrid circuit coupled to the telephone line and a second electronic switch coupled between the speakerphone loudspeaker and the hybrid circuit coupled to the telephone line. A first sensing circuit for sensing the microphone signal and a second sensing circuit for sensing the received loudspeaker signal are provided. The outputs of the first and second sensing circuits are multiplexed and digitized and fed to a microprocessor controller. In response to the levels of the multiplexed signal, the microprocessor determines the state of the speakerphone from among four possible states, including a first talk state, low gain talk state, first listen state and low gain listen state. The low gain talk and listen states are provided by gating the respective first and second electronic switches on and off to chop the microphone or speaker signal, respectively, thereby attenuating the signals. This allows substantial minimization of spurious sidetone and echo signals and a lessening of harsh clipping effects. Furthermore, the first talk and listen states preferably are only enterable from each other upon passing through the low gain states.

Speakerphone control circuit having low gain states and method for

An apparatus for indicating to a central service unit of a telephone system having a central service unit coupled to a plurality of station sets whether a particular station set comprises a speakerphone and the type of speakerphone from among two types of speakerphone, is disclosed. The station set includes a microprocessor controller having an input line coupled to a selected one of a low or high logic level. The input line is connected to an electronic switch which receives interrogation signals from the central service unit. Depending on the logic level to which the input line is coupled and the state of the switch, the central service unit can determine whether the station set comprises a speakerphone and the type of speakerphone.

Speakerphone sensing circuit

A station interface for a digital electronic telephone switching system is disclosed. The station interface couples a plurality of digital telephone instruments to a digital data bus having PCM encoded signals representative of analog voice signals time-division multiplexed thereon. The station interface enables two way communication between the telephone instruments and the digital data bus and includes a frame store memory for temporarily storing digital data on the data bus and assigning the digital data to system time slots. The output of the frame store memory is selectively supplied under microprocessor control to a digital audio processor which processes the PCM encoded voice signals from the telephone stations and supplies these signals to the audio processor. The audio processor digitally processes both the selected data from the frame store memory and the data from the telephone stations forwarded by a multiplexer, in respective system time slots, under microprocessor control. The PCM encoded signals are gain modified under the control of the microprocessor by the audio processor. The microprocessor monitors accumulated values of the energy of the voice signals originating at the telephone stations and those being forwarded to the telephone stations to dynamically alter the gain levels of the voice signals. In this way, differences in gain levels between signals originating from different sources, e.g. internal telephone stations or trunk lines, can be compensated. The station interface has particular application in controlling hands-free telephone station operation.

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Shelton, CT, United States of America

Vincent V Korsky