Telephonic communications – Subscriber line or transmission line interface – Protective circuit
Patent
1987-07-27
1989-02-28
Ng, Jin F.
Telephonic communications
Subscriber line or transmission line interface
Protective circuit
379413, 361 56, 361 91, H02H 904
Patent
active
048093246
ABSTRACT:
The present invention uses the input resistances of transconductance amplifiers in a SLIC to isolate battery ground overshoots from the rest of the SLIC circuitry. This is accomplished by allowing the voltages within each driving operational amplifier to rise with any overshoot, and is achieved by powering each operational amplifier with battery ground voltage, which overshoots, instead of with low voltage ground (LVG), which remains at ground. When a lightning surge hits, an overshoot at the SLIC output will occur. However, since the supply voltage of the driving operational amplifiers rises with the overshoot, the voltage stress to the SLIC circuit components is greatly reduced. The remaining SLIC circuitry stays at a low potential and is isolated from the overshoot. In accordance with the present invention, ground overshoot voltages are isolated across a few high ohmic valued resistors instead of appearing across active circuit components. The present invention is not limited only to the transconductance driven type of SLIC which is described herein by way of example only, but also is applicable to any SLIC circuit by powering the output stage with a battery ground voltage and providing resistive isolation to the rest of the circuitry.
REFERENCES:
patent: 4158109 (1979-06-01), Dijkmans et al.
patent: 4161633 (1979-07-01), Treiber
patent: 4170740 (1979-10-01), Pernyeszi
patent: 4254305 (1981-03-01), Treiber
patent: 4282555 (1981-08-01), Svedberg
patent: 4398143 (1983-08-01), Bonis
patent: 4567331 (1986-01-01), Martin
patent: 4612417 (1986-09-01), Toumani
Publication from IEEE Journal of Solid State Circuits, vol. SC-16, No. 4, Aug. 1981, pp. 261-265.
Morris Jeffrey P.
Ng Jin F.
Siemens Transmission Systems, Inc.
Vaas Randall S.
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