Patent
1977-05-20
1978-09-12
Claffy, Kathleen H.
179170D, H04B 158
Patent
active
041139968
ABSTRACT:
An active hybrid circuit equipped with a resistor bridge, balance network and transmit and receive amplifiers for 2-wire to 4-wire long haul trunk communication between a telephone central office and a distantly located operator console is disclosed. High impedance current sources having voltage follower operational amplifiers are integrated into the hybrid for reducing hybrid bridge loading on the bidirectional 2-wire path while providing adjustable levels of transmission in all directions. One of the high impedance sources is responsive to signals received from the receive amplifier via a bridge resistor for generating output currents to produce desired levels of the received signal on the 2-wire bidirectional path. A second one of the sources is responsive to signals received from the receive amplifier via another bridge resistor for generating currents within the bridge which are opposite to those of the first source and which cancel the receive signal at the input of the transmit amplifier to preclude undesired circulation of that signal back to the operator console.
REFERENCES:
patent: 2629024 (1953-02-01), Edwards
patent: 3180947 (1965-04-01), Haselton, Jr. et al.
patent: 3529099 (1970-09-01), Ribner
patent: 3700831 (1972-10-01), Aagaard et al.
patent: 3855430 (1974-12-01), Colardelle et al.
patent: 3909559 (1975-09-01), Taylor
patent: 4053722 (1977-10-01), Nahay
Bell Telephone Laboratories Incorporated
Claffy Kathleen H.
Myers Randall P.
Padden Frederick W.
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