Telephonic communications – Subscriber line or transmission line interface
Patent
1989-08-01
1991-05-28
Dwyer, James L.
Telephonic communications
Subscriber line or transmission line interface
379398, 379345, H04M 908
Patent
active
050201026
ABSTRACT:
A semi-floating AC/DC active termination circuit with current sink. A voice frequency transmission line termination circuit has at least tip and ring terminals and provides an AC termination impedance and a DC termination resistance. The circuit has at least a first resistance element connected between the tip and ring terminate which forms the DC termination resistance. A first resistor/capacitor series circuit, having at least a resistor and capacitor connected in series, is connected between the tip terminals and a first virtual ground terminal, and a second resistor/capacitor series circuit, having at least a resistor and capacitor connected in series, is connected between the ring terminal and a second virtual ground terminal. The first resistance element and the first and second resistor/capacitor series circuits form the AC termination impedance. A first operational amplifier has an output connected to the first virtual ground terminal and a second operational amplifier has an output connected to the second virtual ground terminal. The first and second operational amplifiers provide a virtual ground for voltages and currents appearing at the tip and ring terminals. In a preferred embodiment the first operational amplifier has a negative input operationally connected to a voltage source and has a positive input connected to a signal receiving line. The second operational amplifier has a negative input operationally connected to the signal receiving line and has a positive input connected to a circuit ground.
REFERENCES:
patent: 4037064 (1977-07-01), Nahay
patent: 4283604 (1981-08-01), Chambers, Jr.
patent: 4357494 (1982-11-01), Chambers, Jr.
patent: 4612417 (1986-09-01), Toumani
patent: 4862495 (1989-08-01), Stibila
Dwyer James L.
Hamann H. F.
Patti C. B.
Rockwell International Corporation
Sewell V. L.
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