Northern Telecom Limited

Other

Edward C Carew

Robert S Morley

Roland Thomas Lockhart

Garth Decker Hillman

Attila J Szanto

Sean G Brophy

A circuit to improve noise mitigation and mode switching in telephony, wherein the noise-floor level is continuously estimated by comparing its stored current value to the signal level value and substituting the latter for the former if it is less than the former.

Noise mitigation and mode switching in communications terminals such as

An interface circuit provides for coupling of communications signals between a conductor of a transmission path, and a key telephone system and provides for protection against electrical energies, as may be associated with transient electrical event occurrences along the transmission path. The interface circuit provides for coupling of some of these transient electrical energies from the transmission path conductor to an earth ground. The interface circuit includes a plurality of electrical components and a plurality of electrical conductors being fixed to either of first and second surfaces of a sheet of electrically insulating material. The electrical conductors are spaced apart from each other by at least a predetermined amount. Some of the electrical conductors connect the electrical components of the interface circuit in a workable arrangement whereby the communications signals may be coupled. First and second electrical conductors are connected to the earth ground and the transmission path conductor, and in combination are arranged to provide a coupling path for said some electrical energies. The coupling path comprises first and second terminating edge portions being arranged one within another, about an opening in the insulating sheet material. One of the first and second electrical conductors is connected to a respective one of the first and second edge portions via the opening. The terminating edge portions are spaced apart one from the other by a distance of less than the predetermined amount.

Interface circuit with transient event tolerance

In a telephone installation in which more than one telephone terminal is connected to one pair of conductors--Tip and Ring--a line status apparatus is provided for each telephone terminal, the apparatus sensing a change in line characteristics resulting from an 'off-hook' condition at any telephone and producing an output which is used to provide an indication. Little or no current is drawn from the telephone lines. Typical examples are sensing variations in AC characteristics, as resulting from voice transmission, ringing tones and the like; sensing DC variations, such as voltage drop when a telephone is 'off-hook'. Indication is generally visual.

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Carleton Place, Canada

Edward C Carew