Telephonic communications – Subscriber line or transmission line interface – Hybrid circuit
Patent
1990-10-29
1993-12-28
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
Hybrid circuit
379402, 379399, H04B 158, H04B 303
Patent
active
052747042
ABSTRACT:
A telephone line interface circuit includes a transformer provided with first, second and third windings. The first winding is connected across the tip and ring wires of the telephone line and the second winding is connected to the output of an amplifier which has an input connected to a receive line. In a first case where the input to which the receive line is connected is the inverting input, a first resistor is connected in series between the receive line and the inverting input. The third winding is connected in series with a second resistor to form a feedback loop which is connected to the inverting input of the amplifier. The transfer function of the interface circuit is dependent on the ratio of the resistances of the first and second resistors and the turns ratio of the first winding to the third winding but is substantially independent of transformer parasitics. In the case where the receive line is connected to the non-inverting input, the first and second resistors are not required and the transfer function is dependent only on the turns ratio.
REFERENCES:
patent: 2947952 (1960-08-01), Hughes
patent: 4595802 (1986-01-01), Wittman
patent: 4881262 (1989-11-01), Meschkat et al.
Dwyer James L.
Matar Ahmad F.
Northern Telecom Limited
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