Telephonic communications – Subscriber line or transmission line interface – Hybrid circuit
Patent
1989-01-19
1991-01-01
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Hybrid circuit
379399, H04M 908, H04B 158
Patent
active
049824260
ABSTRACT:
A two-wire telephone line interface circuit includs two transformers each having primary and secondary windings. The primary windings, which are divided into equal halves for balance and d.c. feed purposes, are connected in series between the two wires, and the winding resistance together with optional series resistance provide desired d.c. resistance across the line. To this end one or both of these windings may comprise resistance wire. A signal from a receive line is coupled to the two-wire line via an amplifier whose low output impedance terminates the secondary of one of the transformers. Another amplifier couples a signal from the two-wire line and the secondary of the other transformer to a transmit line, and also provides at its input a transhybrid signal cancellation node, a transhybrid signal being coupled thereto via a balance impedance. A feedback path can be provided for increasing the a.c. impedance presented by the interface circuit to the line. A four-wire telecommunications line interface circuit using similar transformers is also described.
REFERENCES:
patent: 1564391 (1925-12-01), Wilbur
patent: 3189693 (1965-06-01), Fudaley
patent: 3596011 (1971-07-01), Alexandrovich
patent: 3824344 (1974-07-01), James et al.
patent: 3934099 (1976-01-01), Elder, Jr.
patent: 4595802 (1986-06-01), Wittman
IEEE Standard Dictionary of Electrical and Electronic Terms, 1977, p. 587.
Dwyer James L.
Haley R. John
Northern Telecom Limited
Smith Dallas F.
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