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What is SCAT?
SCAT (Sneak Circuit Analysis Tool) is a Windows program used for automatically identifying
potential sneak paths (i.e., paths which inhibit desired functions or cause undesired
outputs) by processing circuit schematics.
SCAT has a modern easy to use GUI that automates both the preparatory work and the
actual analysis that are part of SCA. When user input is required (such as identifying
ports) the GUI clearly prompts and offers automated menus that induce a streamlined
and smooth work experience.
The SCAT Approach to Sneak Circuit Analysis
SCAT differs from conventional SCA (Sneak Circuit Analysis) techniques in that the
latter are based upon the generation (usually automated) and analysis (mostly manual)
of network trees to identify sneak paths. In contrast, SCAT does not require or
even make use of the traditional network trees.
The automated procedure provides the design engineer or reliability analyst with
a simple yet powerful tool for rapidly identifying and correcting sneak paths. The
automated procedure is based on the fact that sneak paths involve circuit components
which can conduct current in either direction depending upon the switching state
of the circuit. SCAT exhaustively searches for these bidirectional branches which
is more readily automated than searching for specific topological circuit patterns,
as done by conventional SCA techniques. Furthermore, the analyst's task is reduced
to evaluating the significance of specific potential sneak paths rather than applying
"clue lists" to circuit patterns for identifying the sneak paths.
A significant issue that arises is the assurance that sneak paths associated with
interconnecting assemblies or subsystem interfaces are not overlooked. This issue
is addressed in two ways. First, the system compels the user to identify each interface
port of a switching circuit in terms of it being a power input. Interfaces to power
and ground are labeled as such regardless of whether they respectively go to power
and ground directly or through switched or un-switched loads, and they are included
within the sneak path search.
SCAT was developed to enable design engineers to perform SCA early in the project
life so that problems can be corrected early and at minimal cost.
Performing a Sneak Circuit Analysis with SCAT
There are three steps in using SCAT: preparation, analysis and evaluation. These
tasks have been automated utilizing a concurrent engineering environment comprising
the EDIF 2.0 netlist file format for schematic capture and the SCAT software.
Preparation
Preparation consists of automated pre-processing of the schematics, netlist generation,
netlist processing, power port selection and optional switch and capacitor modeling.
Analysis
SCAT can perform sneak circuit analysis with a single command. A printable session
log (audit trail) describing all actions taken by the user during the analysis is
stored and can be printed out as analysis documentation. The user can easily change
the input parameters to SCAT and rerun previous analyses. The first step is performing
a sneak circuit analysis which identifies all the source to sink paths and among
them finds all the bi-directional paths. The next analysis is the power-to-power
analysis which finds all the source-to-source and all the sink-to-sink paths which
are, by definition, bi-directional paths.
SCAT TOOL ACTIVATION
Evaluation
Evaluation consists of viewing the asterisked bi-directional paths on the listing
and all the power-to-power (source-to-source and sink-to-sink) paths. Where such
a path is encountered the analyst must decide whether it is
- An intended bi-directional current path
- An unintended bi-directional path through a high resistor that limits the current
to a fraction of the actuation load - or
- A true sneak circuit that must be eliminated.
SCAT SNEAK ANALYSIS PATHS LIST
SCAT POWER-TO-POWER PATHS LIST
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