Patent ID: 7907381

Claim:
A protection circuit coupled to a tip lead and a ring lead in a subscriber line interface circuit formed on a silicon substrate, the protection circuit comprising: first and second diodes formed on the silicon substrate and coupled to the tip lead and the ring lead. respectively, the first and second diodes configured to provide a path from the tip lead or the ring lead to ground in response to a positive voltage at the tip lead or the ring lead: a silicon-controlled rectifier formed on the silicon substrate and configured to provide a path from the tip lead to ground via the silicon-controlled rectifier in response to a negative voltage at the tip lead and a path from the ring lead to ground via the silicon-controlled rectifier in response to a negative voltage at the ring lead; and third and fourth diodes formed on the silicon substrate and coupled in series with the first and second diodes and the tip lead and the ring lead, respectively, the third and fourth diodes configured to be coupled to a battery voltage so that the third and fourth diodes are reversed biased during steady-state operation of the subscriber line interface circuit.