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Browse Prior Art Database

Simultaneous Bidirectional Baseband Data Transmission

IP.com Disclosure Number: IPCOM000089899D
Original Publication Date: 1968-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

DaCosta, DJ: AUTHOR [+3]

Abstract

The differential amplifier of this circuit cancels out signals being transmitted on line 10 by driver 12 from signals being received on a line by receiver 14. The mixing of these signals by receiver 14 is prevented.

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Simultaneous Bidirectional Baseband Data Transmission

The differential amplifier of this circuit cancels out signals being transmitted on line 10 by driver 12 from signals being received on a line by receiver 14. The mixing of these signals by receiver 14 is prevented.

With no signals present at either the input terminal 16 or 18, transistors T1 and T4 conduct and transistors T2 and T3 are cut off. This is brought about by the offset voltage relative to Vr provided by the source -Ve through resistors R1 and R2. With T2 and T3 cut off, transistors T8 and T9 conduct, biasing transistor T7 on and T6 off. This is because of the offset voltage at the base of transistor T6 provided by diode D1. Thus no signal is supplied at output 20 to the receiver or at output 16 to line 10.

Assume that transmitter 12 starts transmitting. This places a series of negative signals at A Data Input 18 causing T2 and T3 to conduct whenever the input goes negative. The conduction of T2 and T3 causes identical voltage swings at their collectors and therefore at the bases of T6 and T7. As a result, there is no output at B Data output 20 since the differential outputs of T6 and T7 are sensitive only to differences between the voltage at their bases. Thus, output 20 is independent of signals transmitted from terminal 18 to line 10. However, signals coming in on line 10 affect only the base of T7 and not T6. Therefore these inputs are transmitted through to the B Data output 20 since there is a...