eldo_user

Statistical Experimental Design and Analysis
Selecting the Number of Factors and the Design Matrix
For integrated circuit design, where the designable and noise variables are defined in separate
spaces, consider using a two-stage strategy. This will enable you to identify the critical noise
factors and critical control factor separately. This is particularly useful when some noise factors,
such as environmental noise factors, have large masking effects.
The phase zero of the response surface study will then involve two steps:
• Conduct a screening experiment for noise factors first by not considering the designable
factors. Use EXPERIMENT=SCREENING_NOISE in the .DEX command. The DEX
analysis runs the experiment using x = x 0 , where x 0 is the experiment center in the space
of control variables. This will give the amplitude of the β’s.
• Next conduct a screening experiment for control factors by not considering the noise
factors. Use EXPERIMENT=SCREENING_CTRL in the .DEX command. The
amplitude of the α’s are then analyzed. The DEX analysis runs the experiment using s =
s 0 , where s 0 is the experiment center in the space of noise variables.
Tip
For further details see “.DEX” in the Eldo Reference Manual.
Selecting the Number of Factors and the Design
Matrix
The .DEX command is compatible with the Multiple Run features. The maximum number of
factors N max is 40,000. However, running very large experiments is not recommended. The
range 7 to 150 is considered to be the ideal number of factors.
Tip
See the command description for “.MPRUN” in the Eldo Reference Manual.
The design matrix used to run the experiment enables you to specify either an orthogonal array
at two levels based on Hadamard matrices (DESIGN=ORTHA_2_N or
DESIGN=ORTHA_2_2N) or a full factorial design (DESIGN=FULL_FACT). If N is the
number of factors, the orthogonal arrays, which have an economical run size, will use about N
runs or 2N runs. However, a full factorial design will use 2 N runs.
Figure 12-4 depicts the geometrical differences between a full factorial design and an
orthogonal array based on Hadamard matrices.
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Eldo® User's Manual, 15.3