Telephone isolation device

Details Telephone isolation device Telephone isolation device

1994-05-24

1996-03-19

Hofsass, Jeffery

Telephonic communications

Subscriber line or transmission line interface

Protective circuit

379405, 379413, 379399, 379377, H04M 176

Patent

active

055008950

ABSTRACT:
An isolation circuit for a telephone line interface includes a pair of capacitors that differentially couple analog transmit and receive channels in full duplex communication across an isolation barrier. Each transmit or receive signal is processed to generate respective paired complementary signals. A switching network is clock driven to differentially charge the paired capacitors in incremental fashion with the paired complementary signals. On the opposite side of the barrier, a clock driven switching network receives the differential charges on the paired capacitors, generating paired complementary signals that are processed to form an analog information signal. Clock signals, off-hook and ringing signals are transmitted in similar fashion. The invention can use two pairs of capacitors that differentially couple analog transmit and receive channels in a user device across an isolation barrier to a line pair for full duplex communication. The interface circuit includes first and second oppositely directed capacitor isolation circuits. The first is disposed between the transmit channel and a hybrid circuit; the second is connected between the receive channel and the hybrid. The transmit capacitor isolation circuit has an input located on the user device side of the isolation barrier and an output on the line side of the barrier and generates analog signals corresponding to analog signals at its input. A receive capacitor isolation circuit has an input located on the line side of the barrier and an output on the user side of the barrier and generates analog signals corresponding to analog signals at its input.

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