US 5,848,127 AGranted

Two-wire channel unit with loopback test capability

AssigneeHubbell Incorporated

InventorsDmitry Levitan, Winston M. Gadsby

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Abstract

A two-wire channel unit or line card for use in a digital loop carrier (DLC) telephone system is disclosed. The channel unit is provided with a loopback test capability by using relays to open-circuit or short-circuit the input terminals of the hybrid circuit that couples the two-wire subscriber line to the separate two-wire transmit and receive paths within the channel unit. When open-circuited or short-circuited in this manner, the hybrid circuit couples voice frequency test signals between the receive and transmit paths of the channel unit, thereby allowing loopback testing to be carried out without providing a dedicated loss/gain circuit in the channel unit. An additional relay may be provided to vary the gain of an amplifier stage in the transmit or receive path of the channel unit during operation in the loopback test mode, in order to control the overall gain of the channel unit during loopback testing.

Claims22

Dependent claims

A two-wire channel unit for use in a digital loop carrier telecommunications system, comprising:

a two-wire subscriber line interface for connecting said channel unit to a two-wire subscriber line;
a common equipment interface for connecting said channel unit to channel bank common equipment in a digital loop carrier channel bank;
a processing circuit connected to said common equipment interface for converting signals from said subscriber line to a format suitable for said channel bank common equipment, and for converting signals from said channel bank common equipment to a format suitable for said subscriber line;
a hybrid circuit having a two-wire transmit/receive port, a two-wire transmit port, and two-wire receive port, said two-wire transmit/receive port being connected to said two-wire subscriber line interface;
a transmit circuit connected between said two-wire transmit port of said hybrid circuit and an input of said processing circuit;
a receive circuit connected between an output of said processing circuit and said two-wire receive port of said hybrid circuit;
and
a loopback circuit for coupling test signals from said receive circuit to said transmit circuit through said hybrid circuit when said channel unit is placed in a loopback test mode;
wherein at least one of said transmit and receive circuits has a variable gain, and wherein said loopback circuit is connected to said at least one of said transmit and receive circuits and is operative to change the gain of said transmit or receive circuit when said channel unit is placed in said loopback test mode.

6 more elements

A two-wire channel unit for use in a digital loop carrier telecommunications system, comprising:

a two-wire subscriber line interface for connecting said channel unit to a two-wire subscriber line;
a common equipment interface for connecting said channel unit to channel bank common equipment in a digital loop carrier channel bank;
a processing circuit connected to said common equipment interface for converting signals from said subscriber line to a format suitable for said channel bank common equipment, and for converting signals from said channel bank common equipment to a format suitable for said subscriber line;
a hybrid circuit having a two-wire transmit/receive port, a two-wire transmit port, and two-wire receive port, said two-wire transmit/receive port being connected to said two-wire subscriber line interface;
a transmit circuit connected between said two-wire transmit port of said hybrid circuit and an input of said processing circuit;
a receive circuit connected between an output of said processing circuit and said two-wire receive port of said hybrid circuit;
and
a loopback circuit for coupling test signals from said receive circuit to said transmit circuit when said channel unit is placed in a loopback test mode;
wherein at least one of said transmit and receive circuits has a variable gain, and wherein said loopback circuit is connected to said at least one of said transmit and receive circuits and is operative to vary the gain of said transmit or receive circuit when said channel unit is placed in said loopback test mode.

6 more elements

Dependencies are inferred from the claim text.