Browse Prior Art Database

Self-Balancing Line Hybrid

IP.com Disclosure Number: IPCOM000061211D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Davis, GT: AUTHOR [+2]

Abstract

A self-balancing technique is described for use in line hybrid circuits for interfacing electronic devices to telephone networks. The technique improves the performance of various devices, such as audio distribution systems and modems, using a single twisted-pair phone line for communications in both directions at once. The operation of this circuit relies on balancing an impedance bridge which uses the impedance of the phone line as one leg of the bridge. The circuit is divided into two portions: the analog portion at the right and the digital portion at the left. Digital samples A of the desired transmit signal are fed into a 90Πshifter 1, such as a Hilbert transformer. The non-shifted data samples and the 90Πshifted data samples are each multiplied by gain factors G1 and G2.

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Self-Balancing Line Hybrid

A self-balancing technique is described for use in line hybrid circuits for interfacing electronic devices to telephone networks. The technique improves the performance of various devices, such as audio distribution systems and modems, using a single twisted-pair phone line for communications in both directions at once. The operation of this circuit relies on balancing an impedance bridge which uses the impedance of the phone line as one leg of the bridge. The circuit is divided into two portions: the analog portion at the right and the digital portion at the left. Digital samples A of the desired transmit signal are fed into a 90OE shifter 1, such as a Hilbert transformer. The non-shifted data samples and the 90OE shifted data samples are each multiplied by gain factors G1 and G2. The samples are then added together to form a complex signal and then fed to the digital-to-analog (D/A) converter and filter 2 to the phone line. The gain factors G1 and G2 are adjusted to compensate for actual resistive and reactive components in the line impedance. The resulting signal at the phone line interface B is a non-distorted output similar to that of a perfectly balanced hybrid. A second digital-to-analog (D/A) converter and filter 3 generates an undistorted version of the output signal. A standard duplex circuit 7 is used to compare this undistorted signal with the transmitted signal. Any distortion in the transmitted signal will be cancelled out...