| 摘要 |
A ground key detector for a subscriber line interface circuit (SLIC) uses information from the tip and ring voltage sensing resistor RS1 and RS2 to determine whether the ring side of the telephone line has been grounded, as when a ground key or fault occurs. The voltage difference between a tip voltage and ground is converted to a DC tip current, and the voltage difference between a ring voltage and a battery voltage is converted to a DC ring current, and the DC ring current is compared to a combination of the DC tip current and a reference current to determine whether the ring side of the telephone system has been grounded. The DC tip and ring currents may also be used to determine whether a fault exists in the tip side of the telephone line, and in the hybrid circuitry of the SLIC.
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