Resistance forward telephone line feed circuit
AssigneeReltec Corporation
InventorWilliam I. H. Chen
Life of this patent
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Abstract
A line feed circuit employing a low-inductance transformer, and providing a major portion of the terminating impedance as line feed resistors connected between a telephone line and the transformer primary. A low impedance output amplifier drives a low resistance transformer secondary, thus reducing the need for large transformer inductances. By connecting the line feed resistors between the transformer and the telephone line, high voltage surges are absorbed by the resistors, and thus little is dissipated in the transformer. The transformer can be made physically small, because of the reduced inductance, reduced winding insulation, and reduced power requirements. The resistance forward type of line feed circuit lends itself well to simple implementation with flux cancellation and impedance synthesis circuits.
Claims20
A telephone line feed circuit for use with a telecommunication line, comprising:
- a transformer having a primary and secondary winding wound with low resistance conductors;
- a first discrete resistor connected in series with a tip terminal of the primary winding, and a second discrete resistor connected in series with a ring terminal of the primary winding, a sum of said first and second resistors having a value providing more than about 50% of a termination impedance of the telephone line feed circuit to the telecommunication line while yet maintaining an impedance match between the telecommunications line and the telephone line feed circuit;
- and
- a receive amplifier having a low impedance output connected to the transformer secondary winding for driving the transformer secondary winding directly with substantially no resistance therebetween.
A method of making a multiple telephone line feed circuit for coupling to respective telecommunication lines, comprising the steps of:
- fabricating a plurality of line interface circuits on a single printed circuit board including a line feed transformer in association with each of said line interface circuits;
- fabricating each transformer with a low resistance conductor in a primary and secondary winding, each conductor having two ends;
- connecting an output of each of a plurality of low impedance output amplifiers directly to a respective transformer secondary winding with substantially no resistance therebetween;
- and
- connecting a resistor between each transformer primary conductor end and a respective terminal to which a respective telephone line tip and ring conductor is connectable, said resistors of each primary conductor being selected to represent a majority of an impedance to which the respective telephone line is to be matched.
Dependencies are inferred from the claim text.