Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Patent
1984-04-19
1985-11-05
Wong, Peter S.
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
179 18AD, G05F 146
Patent
active
045516707
ABSTRACT:
Disclosed is a line interface circuit (103) having a negative feedback circuit (205) for maintaining the DC voltage on an electrically isolated communications line at a reference level such as ground for private branch exchanges using ground start supervisory signaling. The feedback circuit comprises a low-pass filter (301), a difference amplifier (302), and two voltage-to-current sources (303,304) each having a high output impedance. The low-pass filter passes only the voltage on the line below a predetermined frequency. The difference amplifier subtracts the passed voltage from a ground reference level to form a difference voltage. Depending on the polarity of the difference voltage, the two voltage-to-current sources source and sink current to and from the line to maintain the DC voltage on the line at the reference level. A load resistor (305) also included in the feedback circuit keeps the circuit from oscillating where the phase shift of any signal through the circuit is an integer multiple of 360 degrees. The high output impedance of the two voltage-to-current sources does not effect the impedance balance on the line.
REFERENCES:
patent: 4056689 (1977-11-01), Freimanis
patent: 4056691 (1977-11-01), Freimanis et al.
patent: 4331913 (1982-05-01), Sparber
patent: 4412347 (1983-10-01), Lipcon
patent: 4423292 (1983-12-01), Turek
patent: 4481462 (1984-11-01), deKleijn
patent: 4499532 (1985-02-01), Hudson et al.
R. G. Sparber, "Engineer's Notes", Bell Laboratories, Inc., Doc. No. 55611-830509.01EN, May 9, 1983.
Anders James V.
Anderson Thomas W.
Geiger Daniel D.
Turnpaugh George F.
AT&T Bell Laboratories
Godlewski Richard J.
Jones Judson H.
Wong Peter S.
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