# Robust Circuit Design Project Example

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Rockwell Collins Inc. Six Sigma project achieved 6-sigma quality in two out of the three circuit responses

## Description

Rockwell Collins Inc. develops communication and aviation electronics solutions for commercial and government customers. To mitigate inherent variation in supplier manufacturing processes and ensure customer satisfaction, a team applied Design for Six Sigma to a new product design.

The DMADV (Define, Measure, Analyze, Design, Verify) project team focused on a key product characteristic – a discrete input circuit – and dramatically improved the manufacturability and reliability of the product. The project achieved 6-sigma quality in two out of the three circuit responses.

Moreover, the circuit is a fundamental function that will be used in many upcoming products, extending the positive impact of the design.

Define
Traditional electrical design methods use a single or small set of nominal values to prove design specification adherence. Such methods do not consider the real world of variation inherent in all supplier manufacturing processes that produce electrical components.

Often, improvement in manufacturing capability can be realized if the effects of this variation on a given product can be quantified and mitigated at the design stage…

Measure
The primary objectives of the Measure phase were to model the circuit in the appropriate electrical simulator, develop and execute virtual DOEs using the simulator to determine the output responses, and derive mathematical equation(s) that describe the circuit’s output responses as a function of the controlling inputs…

Analyze
The circuit uses the popular LM317 linear voltage regulator integrated circuit (reference designators U25 and U27) to provide the two main input voltage supplies, 15V_Dig and 5.65V_Ref.

The behavior of this regulator is given analytically as equations in the manufacturer’s published datasheet (the output voltage adjustment pin current term was included in the analysis but is not shown since its effect was negligible). Those equations were substituted into the regression polynomials and the resulting equations used as…

Design
Looking at the LM317 datasheet revealed that the onboard reference voltage source is specified with a tolerance of plus or minus 1.6 percent over the operating temperature range of the device. This uncertainty is inherent in the component and cannot be mitigated.

Thus, to reduce the output variation of both supplies, we had to try tighter tolerances for the programming resistors…

Verify
Finally, we reran the full Monte Carlo model with the changes brought about by this project to determine the effect on capability of the performance metrics. In all three cases, capability was significantly improved, with 6-sigma quality achieved in two out of the three circuit responses…

AUTHOR
Terry Peres has spent his engineering career in the electronic manufacturing industry and is currently completing Black Belt certification requirements. He is employed as a manufacturing engineer for Rockwell Collins.

Our analysis was formally presented to the design team as a recommended design change aimed at improving the manufacturability and reliability of the product. The design was subsequently modified to incorporate significant changes beyond those recommended, which resulted in meeting or exceeding the predicted improved Cpks.

The positive impact to the design was further strengthened by the fact that there are 12 such circuits in the product under development, and this particular circuit is a fundamental function to be used in many upcoming products.

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