Digital transmission equipment

Digital termination equipment for use in signal transmission over a 2-wire subscriber line through an interface transformer including a winding which has first and second terminals and a center tap, comprising:

• a first impedance means functionally provided between the first terminal of the interface transformer and a first terminal of the 2-wire subscriber line for generating a high impedance which is large enough to block off the transmission of signals to said first terminal of the subscriber line when a current more than a predetermined value flows in said first impedance means;
• a second impedance means functionally provided between the second terminal of the interface transformer and a second terminal of the 2-wire subscriber line for generating a high impedance which is large enough to block transmission of signals to said second terminal of the subscriber line when a current more than a predetermined value flows in said second impedance means;
• a power supply means having first and second terminals, the first terminal being connected to the center tap of the winding of the interface transformer for supplying a voltage to said first and second impedance means through the winding during a local loopback testing;
• a first current path forming means connected to said first impedance means and to the second terminal of the power supply means for forming a current path between the first impedance means and the second terminal of the power supply means when a voltage more than a predetermined value is applied;
• and
• a second current path forming means connected to said second impedance means and to the second terminal of the power supply means for forming a current path between the second impedance means and the second terminal of the power supply means when a voltage more than a predetermined value is applied.

Digital termination equipment for use in signal transmission over a 2-wire subscriber line through an interface transformer, wherein said interface transformer includes first and second windings respectively having first and second terminals, said equipment further comprising:

• a capacitor connected between the both first terminals of said first and second windings;
• a first impedance means functionally provided between the second terminal of the first winding of the interface transformer and a first terminal of the 2-wire subscriber line for generating a high impedance which is large enough to block off the transmission of signals to said first terminal of the subscriber line when a current more than a predetermined value flows in said first impedance means;
• a second impedance means functionally provided between the second terminal of the second winding of the interface transformer and a second terminal of the 2-wire subscriber line for generating a high impedance which is large enough to block off the transmission of signals to said second terminal of the subscriber line when a current more than a predetermined value flows in said second impedance means;
• a power supply means having first and second terminals connected between the both first terminals of the first and second windings and connected in parallel with said capacitor to supply voltage to said first and second impedance means during a local loopback testing;
• and
• a current path forming means connected between said first and second impedance means for forming a current path between the first and second impedance means.