L5 System: Role of Computing and Precision Measurements

At the beginning of the Lo project in 1968, the set of computeraided design (CAD) tools and the specialized computer-operated transmission measurement set (COTMS) at the Merrimack Valley location of Bell Laboratories were in an early stage of evolution. The tight system development schedule prevented the thorough, leisurely development of sophisticated programs that could provide the complete analysis and characterization needed for high confidence in design. Rather, a parallel effort was undertaken to augment existing design aids and to develop improved ones. The result was immediate answers generated inefficiently for early designs and a powerful group of programs that 2249 have been "proved in" by use during the later stages of L5 development. These were, however, not completed early enough in the design cycle to allow their full impact to be exerted on the overall design process in the manner that is now possible. The following sections illustrate typical uses of computer programs for seven phases of the design sequence. These include: (i) Small signal ac analysis of circuits having many nodes, including sensitivity and tolerance analyses. (ii) Optimization of element values in a circuit. (iii) Statistical measurements of early production models of repeaters for use in equalizer design. (iv) Nonlinear distortion analysis. (v) Component characterization. (vi) Overall system analysis. (m) Equalizer characterization and alignment during manufacturing. Limitations as well as successes are included to illustrate why and how the evolution of programs took place.