Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Ripple Carry Hardware with One Device Delay per Stage

IP.com Disclosure Number: IPCOM000088099D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Hong, SJ: AUTHOR [+2]

Abstract

By ripple carry, as well as no-carry, we achieve one transistor delay between successively higher carry-bit generation for the ripple-carry address.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 100% of the total text.

Page 1 of 2

Ripple Carry Hardware with One Device Delay per Stage

By ripple carry, as well as no-carry, we achieve one transistor delay between successively higher carry-bit generation for the ripple-carry address.

Consider Addition: A: a(n) a(n - 1)....a(i)....a(2) a(1) B:+b(n) b(n -
1)....b(i)....b(2) b(1) C(n) C(n - 1)....C(i)....C(2) C(1) Carry (C(0) Carry In) S(n)
S(n- 1)....S(i)....S(2) S(1) Sum Let T(i) = a(i) b(i) and G(i) = a(i) b(i) for all i. We
know that: (1) whenever G(i) = 1, C(i) = 1. (2) whenever T(i) = 1, C(i) = 0; and (3) if G(i) = 0 and T(i) = 0 (G(i) T(i) = 1 never occurs), then the carry is 1, if the nearest right side 1 among G(j) or T(j) belonged to G(j) and 0 if the nearest right side i among G(j) or T(j) belonged to T(j).

This suggests that G(j)'s as well as T(j)'s propagate towards the higher digit. The a(i) Not = b(i) positions merely pass on the ripple carries. The implementation of this is shown in the figure. Operation: (1) If G(i) = 0 and T(i) = 0, Q(1) and Q(2) are high impedances, passing on the previous stage values. (2) If T(i) = 1 (or G(i) = 1, but never both 1) the corresponding Q(1) or Q(2) becomes a low impedance, forcing the correct carry values originating from i to the higher digit positions.

1

Page 2 of 2

2

[This page contains 2 pictures or other non-text objects]