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Browse Prior Art Database

Bidirectional Line Driver

IP.com Disclosure Number: IPCOM000078474D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Croisier, A: AUTHOR

Abstract

Shown is a line driver and-receiver for full-duplex digital transmission.

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Bidirectional Line Driver

Shown is a line driver and-receiver for full-duplex digital transmission.

The line is driven by floating sources comprising two complementary transistors T1 and T2 bypassed by diodes D1 and D2, respectively. In one data condition, the loop current flows through diodes D1 and D2 generating a 0.6 to
0.8 Volt voltage drop on each side of the line, while in the other condition-it flows through transistors T1 and T2 which have a negligible voltage drop. Thus in either condition, these elements present a low impedance.

The two conditions are controlled by transistors T3 and T4, which supply equal driving currents to T1 and T2. This current value is determined by the voltage applied on the base of T3.

Regulator 1 supplies a constant voltage to the communication set connected to the driver-receiver, while presenting a high impedance across the line.

Four equal resistors R1, R2, R3 and R4 form a summing network which feed comparator 2. By making Z equal to the line impedance Z0, the driver produces no voltage across comparator 2. Thus the balancing out of the local emitted signal only depends upon the matching of impedance Z to Z0. This matching also insures a correct line transmission.

The data to be received from a remote station are superimposed on the direct current flowing through the line and are detected by comparator 2.

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