Six Sigma For Electronic Circuits With Multiple Specifications

The design quality calculation for a single electrical circuit can be expanded to include several design targets for the circuit. To obtain a i design for quality assessment of the circuit, it has to be simulated using any of the available software packages such as SPICE for analog or OMNISYS for microwave circuits. The resulting performance characteristics of the circuit simulation have to be matched to the design specifications. The design quality, expressed as Cpk for each of the design key characteristics, has to be accumulated into a composite Cpk according to the methodology presented in Chapter 5.

A detailed example of an electronic analog circuit design is given in | Table 8.15 for a design analysis of a RF amplifier. The data developed for this example are based on a Monte Carlo simulation on the individual components that make up the RF amplifier. The phase specification exhibits a low Cpk value, which in fact is the major contributor to the composite Cpk value. In addition, some of the characteristics have j two-sided specifications, whereas others are one-sided. The composite Cpk is calculated on the basis of two-sided specifications. This could possibly lead to the condition that the composite Cpk implies a better quality indicator than those of the individual characteristic Cpks.

In the example of Table 8.15, both the worst-case Cpk and the composite Cpk are shown. The worst-case Cpk could help in focusing the design team on where to improve the design. The composite Cpk can be reported back up into the total product design, if this circuit is part of a module to be combined with other modules to complete the design of a product or subsystem. Alternately, the composite Cpk could be reported if the circuit represented a complete unit or subsystem function.