Browse Prior Art Database

Critical Path Oscillator

IP.com Disclosure Number: IPCOM000100830D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 77K

Publishing Venue

IBM

Related People

Johnson, CL: AUTHOR [+3]

Abstract

A critical path oscillator allows for measurement of logical critical path structures in very large-scale integrated (VLSI) chips at any level of packaging. The oscillator requires only simple static setup conditions, is extendable from a single circuit to multiple paths, and provides information about hardware performance, process parameter interaction, and process design points.

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Critical Path Oscillator

       A critical path oscillator allows for measurement of
logical critical path structures in very large-scale integrated
(VLSI) chips at any level of packaging.   The oscillator requires
only simple static setup conditions, is extendable from a single
circuit to multiple paths, and provides information about hardware
performance, process parameter interaction, and process design
points.

      It is difficult to measure critical timing paths due to a high
density and complexity of VLSI chips.  There are access problems in
getting to the path and setup condition problems in preconditioning
all of the inputs on the logic blocks in the path.  However, a
duplicate of one or more of the critical paths on the chip serves the
purpose.  The loading conditions on the outputs of all of the logic
blocks are matched, all of the inputs necessary are preconditioned,
and this copy is put in the body of the chip to get as close
as possible to the actual parameter interactions of the critical path
as possible.  See Fig. 1.

      In order to access this path, two problems are overcome.
First, the chip I/O's are at a premium, and few if any are available.
Second, if the paths at various packaging levels are measured, the
input and output loading conditions must be factored into the delays.

      To overcome the loading condition problem, a multiple path
measurement scheme is used.  The path is constructed such that the
critical path is not the only path accessible. Another path in
parallel having all of...