Statistical Circuit Design: A Case Study of the Use of Computer Aids in Circuit Design - Pulse Equalizers for the T2 Digital Transmission Line

T o l e r a n c e analysis is t h e most recent d e v e l o p m e n t in a continuing effort to design circuits a n d systems realistically. Realism requires t h a t you model as closely as possible the complex e n v i r o n m e n t in which t h e requisite functions m u s t be accomplished. As computers evolved, it has become economically feasible to t a k e more and more factors into account. T h e objective of this effort is to a n t i c i p a t e potential prob1243 1244 T H E BELL SYSTEM TECHNICAL J O U R N A L , APRIL 1971 lems so t h a t they m a y be eliminated in the design phase rather t h a n unexpectedly to discover them when the unit is put into service. Standard design practice is to progress through several test phases, first using breadboards and prototypes of individual circuits, then using complete systems in the field trials and limited service trials. If computer simulation is also employed during the design process, it is frequently possible to detect design deficiencies at an earlier stage, and the earlier the problem is detected the less expensive is the corrective action. T h e impact t h a t the computer has had on this quest for realism is most readily illustrated with a specific example. T h e design of the pulse equalizers for the T2 digital transmission line evolved during the era discussed in the introduction to this issue. Thus the improvements in computers and computer-aided design techniques made it possible to introduce more and more realism into the design process.