Sneak circuit analysis is a generic term for a group
of analytical techniques employed to methodically identify sneak circuits in
hardware and software systems.
PRINCIPAL SCA TECHNIQUES
Of the currently available sneak circuit analysis procedures, the following
have proved to be particularly useful:
Sneak Path Analysis
Digital Sneak Circuit Analysis
Software Sneak Path
Sneak Path Analysis is a methodical evaluation of all possible electrical
paths in a hardware system. It is used primarily to detect sneak circuits in
power distribution, control, switching, and analog circuits.
As illustrated in Figure 2,
the analysis process consists of three basic steps: 1) Design elements are
converted into appropriate "analogs," i.e., combinations of switches, diodes,
and resistors, which then become data inputs to a set of pathfinding computer
programs; 2) computer runs from these programs identify all possible
continuities for each operating mode of interest; and 3) the program outputs,
in the form of network trees (schematic breakdowns of the electrical network),
are analyzed by use of formal techniques, with the aid of a checklist of
"clues" derived from previous sneak circuit analyses. Some of these clues are
described in Appendix
Digital Sneak Circuit Analysis performed on networks composed of digital
functional modules, in which the elements of interest include logic gates,
registers, flip-flops, and timers. Unlike sneak path analysis, which seeks to
identify undesired paths in hard-wired circuits, digital SCA is concerned
primarily with logic errors and inconsistencies, timing races, improper
operating modes, and unintended switching patterns.
Software Sneak Path Analysis examines computer program logic flows through
an adaptation of the method used in sneak path analysis of hardware systems.
Experience has shown that program flow diagrams containing sneak paths often
exhibit similar characteristics. For example, where network tree patterns
contain branch or jump instructions, crossing of module or function interfaces
as a result of the branch instruction is a common source of sneak
The results of a sneak circuit analysis take three forms:
Sneak Circuit Reports
Design Concern Reports
Sneak Circuit Reports document all sneak circuit conditions identified
during the analysis and provide recommendations for their correction.
Design Concern Reports describe any design situations detected during the
SCA that, while not representing sneak circuit problems, are potential problem
areas in other respects.
Documentation Error Reports identify errors in system documentation
uncovered during the analysis.
Sneak reports are the main products of an analysis since they describe the
sneak circuits and conditions discovered. However, the design concerns and
documentation errors regularly identified during the SCA represent highly
valuable inputs to the process of perfecting the system
Of major interest to program engineering personnel are
the network trees generated during the analysis. These trees constitute a
powerful data base that can be of significant value in conducting engineering,
safety, reliability, and similar analyses. Some of these additional uses of
the data base are discussed in Appendix