Browse Prior Art Database

Minimum Overhead for Sparing

IP.com Disclosure Number: IPCOM000107724D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 66K

Publishing Venue

IBM

Related People

Aichelmann Jr, FJ: AUTHOR [+3]

Abstract

A structure is proposed which provides for minimum delay and skew overhead by distributing the delay across the data width rather than limiting the performance by the spare path.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 89% of the total text.

Minimum Overhead for Sparing

       A structure is proposed which provides for minimum delay
and skew overhead by distributing the delay across the data width
rather than limiting the performance by the spare path.

      Memory applications use sparing as a way of enhancing product
reliability by eliminating the effects of large failures (i.e., chip
kills) which would reduce or limit the overall product reliability.

      This method avoids the overhead resulting from the logic
network when full substitution is practiced by using a shifting
structure.  Fig. 1 depicts a simplified example of a spare structure
with full substitution.  Data is written into the memory on the left
("store") and read on the right ("fetch").  The AND/OR (A/OR) network
and logic output gates represent the sparing logic which is
controlled by the personalization and decoder which determines the
sparing substitution.  When a module (chip) has to be replaced, the
personalization register in conjunction with the decoder routes the
data from the faulty chip to the spare chip. This sparing operation
has an additional delay overhead over a non-sparing memory.  During
writing, the data is funneled through the large A/OR network (i.e.,
multiple levels of simple A/OR gates) which adds delay.  Additional
delay is incurred when the data is read out through the loading of
multiple gates.

      Fig. 2 shows a spare structure with data shifting which reduces
this overall time for the spa...