The topic of this book is the investigation of fault masking effects in
synchronous and asynchronous logic.A fault is said to be masked if it
affects a circuit but never creates an erroneous state and hence stays
ineffective. In synchronous logicit is known that faults can be masked
on three different levels: (1) Electrical masking: A fault is injected
on the electrical level, but it doesn't affect the logical level. The
current pulse induced is not large enough to change the boolean value.
(2) Logical masking: The fault changes a boolean value but the logical
function which is performed on this signal does not take it into
account. For example if you look at an AND-Gate (2 inputs), a "`false"'
logic 1 only propagates if the other input is also 1. This we call
implicit logical masking. Explicit logical masking is related to
majority voting with replicated functions. (3) Temporal
(latching-window) masking: This level deals with the temporal behavior,
the fault disturbs a signal but it isn't captured. For example a
transient fault between two clock edges in a synchronous circuit has no
effect on the storage element as long as its effect has vanished by the
next clock event