GB1262691A - Data processing system having current drive for transmission line - Google Patents

Abstract

1,262,691. Telegraphy. BURROUGHS CORP. 30 Oct., 1969 [12 Nov., 1968], No. 53164/69. Heading H4P. A high-speed transmission system includes a line connecting one or more receivers to one or more transmitters which have a digitally controlled current source of a high output impedance for applying current pulses to a line. It is stated that the system enables signals to approach the propagation time of the line more closely than systems employing voltage pulses. A line l1, Fig. 1, is terminated in impedances Zt and voltage sources Vte, Vtr and has a plurality of transmitters and receivers connected thereto which are synchronized by a pulse source 14. The period between pulses is equal to twice the propagation time of line. A current source I is connected to the line through a switch 18a controlled by a unit 20 synchronized with the source 14. An opening of switch 18a in unit lk causes current at terminal lk to drop which propagates along the line 12a towards terminal ri. At the same time switch 18a in unit ri is rendered conductive which applies a current pulse from the line, the two current pulses propagating towards each other causing a current change of twice that of one source. The current from terminal ri eventually reaches terminal lk and re-establishes the former level. A particular form of switch unit, Fig. 2, has an output transistor 22 of high output impedance and hence constant current characteristics connected to line 12a and controlled by transistor 24, 25 forming an AND gate, which receives input timing and control signals. An alternative form of transmitter giving negative signals is illustrated in Fig. 3 (not shown). The receiver 16 has an input transistor 82 normally non-conductive controlling differentially connected transistors 86, 88 connected to outputs through transistors 96, 98. On receipt of a negative current pulse transistors 82, 86 are biased conductively and 88 non-conductively hence transistor 96 will give a low output and 98 a high voltage output. It is essential that voltage swings on the line are not limited otherwise advantages of the system are lost. In a preferred arrangement only two transmitters are allowed to apply current to line 12a simultaneously. Multiple transmission lines with transmitters and receivers are envisaged by the Specification.