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Slowing the Rise Time of Unterminated Emitter Follower Drivers

IP.com Disclosure Number: IPCOM000085457D
Original Publication Date: 1976-Apr-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 84K

Publishing Venue

IBM

Related People

Gopalakrishna, YR: AUTHOR [+3]

Abstract

On many T/2/L logic chips, the chip-to-chip communication is performed by an emitter-follower circuit driving an unterminated line. The rise time at the emitter of the emitter-follower is much shorter than the fall time. This causes reflections on the line which force the loads on the line to wait a long time before they can switch.

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Slowing the Rise Time of Unterminated Emitter Follower Drivers

On many T/2/L logic chips, the chip-to-chip communication is performed by an emitter-follower circuit driving an unterminated line. The rise time at the emitter of the emitter-follower is much shorter than the fall time. This causes reflections on the line which force the loads on the line to wait a long time before they can switch.

To increase the rise time, the base of the emitter-follower is loaded by a capacitor C to ground. When the T/2/L circuit driving the emitter-follower turns off, the RC time constant at the base of the emitter-follower causes that point to rise slowly. The emitter of the emitter-follower follows the slower rise time at its base.

The circuit and chip implementation is depicted in the drawing.

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