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Integrated Active Feedback Rise Time Slow-Down Technique

IP.com Disclosure Number: IPCOM000043228D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Cavaliere, JR: AUTHOR [+2]

Abstract

This article describes a very efficient rise time slow-down technique involving the use of active feedback in a modified bootstrap configuration and featuring a minimal increase in delay time, additional components and chip area. A typical push-pull driver circuit, illustrated by Fig. 1, operates with rise and fall times in the order of tr = 135 ps and tf = 224 ps, respectively, with driver delays at 50% signal level of tdp = 234 ps and tdn = 387 ps for positive and negative transitions. Fig. 2 shows only the output section of the driver for the purpose of illustrating the application of the integrated active feedback technique. In the case of a positive transition, as output node 9 is rising, capacitor C914 is feeding signal to the base of amplifier Q14 (transistor) which starts pulling current from node 3.

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Integrated Active Feedback Rise Time Slow-Down Technique

This article describes a very efficient rise time slow-down technique involving the use of active feedback in a modified bootstrap configuration and featuring a minimal increase in delay time, additional components and chip area. A typical push-pull driver circuit, illustrated by Fig. 1, operates with rise and fall times in the order of tr = 135 ps and tf = 224 ps, respectively, with driver delays at 50% signal level of tdp = 234 ps and tdn = 387 ps for positive and negative transitions. Fig. 2 shows only the output section of the driver for the purpose of illustrating the application of the integrated active feedback technique. In the case of a positive transition, as output node 9 is rising, capacitor C914 is feeding signal to the base of amplifier Q14 (transistor) which starts pulling current from node 3. Node 3 will then start slowing down due to the Miller capacitor C314 . Amplifier Q14 is fed by the current source of amplifier Q15 and resistor R18, tied to node 4A in the predriver (thus eliminating the need for a separate voltage reference), and requires very little current. Q14 is only slightly turned on with a gain in the order of K = 1.5. The feedback current starts slowing down the rise time after node 9 has risen by a very slight amount, thereby contributing to a minimal increase in delay. This is accomplished with a small circuit dissipation. For the negative transition case, a Miller capacitor...