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Slowing the Fall Transition Time of Terminated Emitter Follower Drivers

IP.com Disclosure Number: IPCOM000085456D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 94K

Publishing Venue

IBM

Related People

Davidson, EE: AUTHOR [+4]

Abstract

On many T/2/L logic chips, the chip-to-chip communication is performed by an emitter-follower circuit driving a terminated line. The emitter-follower circuit is driven by two T/2/L circuits in parallel. A basic problem with this arrangement is that the emitter-follower has too fast a fall time which (a) couples noise to adjacent lines when the circuit is switching; and, (b) the receiving circuits on the driven chip do not switch on first incidence because of signal reflections on the line.

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Slowing the Fall Transition Time of Terminated Emitter Follower Drivers

On many T/2/L logic chips, the chip-to-chip communication is performed by an emitter-follower circuit driving a terminated line. The emitter-follower circuit is driven by two T/2/L circuits in parallel. A basic problem with this arrangement is that the emitter-follower has too fast a fall time which (a) couples noise to adjacent lines when the circuit is switching; and, (b) the receiving circuits on the driven chip do not switch on first incidence because of signal reflections on the line.

The fall transition time is slowed by using the Miller effect of a coupling capacitor C deliberately inserted in the T/2/L circuits which drives the emitter- follower.

The circuit and chip implementation is depicted in the drawing where a large PN diode capacitance is realized across the collector-base junction of the output transistor driving the emitter-follower.

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