Browse Prior Art Database

EIA Level Cable Driver

IP.com Disclosure Number: IPCOM000088507D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Myers, AS: AUTHOR

Abstract

When providing EIA (Electronic Industries Association) level control voltages to attached devices from circuits operating at MST-1 (monolithic semiconductor technology) voltage levels, it is sometimes necessary to drive long cables which have a much higher capacitance than the EIA standard cables. Such high capacitance lines will take a large charging current when the voltage level is changed and may overload the driving output circuit. The above circuit will drive such a long line without overloading the drivers.

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EIA Level Cable Driver

When providing EIA (Electronic Industries Association) level control voltages to attached devices from circuits operating at MST-1 (monolithic semiconductor technology) voltage levels, it is sometimes necessary to drive long cables which have a much higher capacitance than the EIA standard cables. Such high capacitance lines will take a large charging current when the voltage level is changed and may overload the driving output circuit. The above circuit will drive such a long line without overloading the drivers.

In the circuit, a logic signal (1 or 0) at MST-1 voltage levels is received at terminal 1 connected to the base of transistor 2 having its collector grounded and its emitter connected through resistor 3 to a negative voltage. Another transistor 4 has its emitter connected to that of transistor 2, its base connected to a reference voltage approximately midway between the logic levels appearing on terminal 1. A resistor 5 from a positive voltage source and an amplifying transistor 6 are connected to the collector of transistor 4. The collector of transistor 6 is connected through resistor 7 to a positive voltage and through resistors 8 and 9 in series to a negative voltage. A pair of transistors 10 and 11 of opposite conductivity type have their emitters grounded, their bases connected to the junction of resistors 8 and 9 and their collectors connected to the positive and negative voltage, respectively, through resistors 12, 13 and 14, 15, respectively.

A pair of driving transistors 16 and 17 have their emitters connected to the positive and negative voltage supplies, respectively, and their bases connected to the junction between the resistors 12, 13 and 14, 15, respectively, connected to the same voltage supply.

Two different drive circuits are shown to drive the EIA output signal line. The first one A comprises two resistors 20 and 21 in series between the collectors of transistors 16 and 17. The EIA output terminal 22 is fed from the junction of resistors 20, 21 through one or more lamp bulbs 23 in parallel. The variable resistance of these bulbs 23 with respect to current flow through them, together with the fixed resistances 20 and 21, will act to limit the average current supplied to terminal 22 to the current which can be safely supplied by transistors 16 and
17. A capa...