Fault masking probabilities with single and multiple signature analysis

Abstract

We are given a circuit output sequence fed into a d-bit signature analyzer. We investigate the probability that a faulty output sequence is masked, i.e., that its signature and the signature of the correct sequence are the same.

If all possible faulty output sequences are assumed to be equally likely, it is known that the probability comes close to 2^−d. Here we restrict ourselves to faulty output sequences having exactly z faults, z fixed. Small values of z are of practical interest, because they correspond to failures that are hard to detect by most of other circuit testing methods.

Using the theory of error-correcting codes, formulas for the masking probability of such sequences are derived. It is shown that, especially for small z, this probability can be much greater than 2^−d, and that it is not only dependent on the length of the signature analysis register.

The paper is also concerned with multiple signature analysis using more than one signature register.