Patent ID: 8254562
Filing Date: 2012-08-28
Classification: H04M

Abstract:
1. A port detection and protection circuit, connected between a tip wire, a ring wire and a Subscriber Line Interface Circuit (SLIC), to determine whether an IP phone is connected to a FXS port correctly, wherein the SLIC outputs a SLIC tip signal and a SLIC ring signal, the tip wire and ring wire transmit a tip signal and a ring signal, respectively, and the tip wire and the ring wire are disconnected from the SLIC under normal operation, wherein the port detection and protection circuit comprises: a first voltage detection circuit to detect a voltage difference between the tip signal and the ring signal so as to output a first detection signal according to the determination; a second voltage detection circuit to detect a voltage difference between the tip signal and the ring signal so as to output a second detection signal according to the determination; a ring detection circuit to output a third detection signal according to a voltage difference between the SLIC tip signal and the SLIC ring signal signaling an incoming call; a first logic component to output a first logic signal according to the first detection signal and the third detection signal; a second logic component to output a second logic signal according to the second detection signal and the third detection signal; a switching circuit to switch a loop composed of the tip wire, the ring wire and the SLIC on and/or off based on the first logic signal; a voltage reference circuit to provide a reference voltage to the tip wire and the ring wire and to detect the tip wire and the ring wire by the first and the second voltage detection circuits; and an alarm circuit to issue an alarm according to the second logic signal; wherein each of the first and second voltage detection circuits comprises: