Figure 6.6: Variation (delay) estimation error vs. the number of measurements.
The third column is the number of independent paths in each basis path. As
mentioned before, two linear equations can be written for each path (rising and
falling transitions). The last column of the table is number of independent linear
equations that provides each basis path set.
Finally, Table 6.4 shows results of variation estimation on 12 benchmark cir-
cuits. After the benchmarks’ name, the first, the second and the third columns
are the number of gates, the number of inputs in the circuit, and the number of
delay measurements, respectively. The fourth column is the ratio of the V∕2-th
singular value to the first singular value in the measurement matrix (N is num-
ber of gates). This column shows how fast singular values decay; or how the
measurement matrix is well conditioned. The fifth column is the estimation sub-
79