Statistical Circuit Design: History and Introduction

1101 During 1968 several versions of a general-purpose, statistical analysis program (TAP) 3 - 4 were written and used effectively for a range of circuits from passive filter designs to highly nonlinear systems. In their original conception, the tolerance analysis procedures were visualized as a final step in the design process. They belonged to the class of computer aids that allows the computer to manipulate an analysis or simulation in a fashion similar to the general-purpose optimization programs. The computer-aided design process was viewed as consisting of the following three steps: (i) Analysis--Components are modeled and the circuit is analyzed. Components and the network topology are changed until the circuit performance approaches the designer's expectations. (ii) Optimization--The designer identifies a desired measure of performance and the analysis is embedded in a general-purpose optimization program. These optimization programs use various strategies to alter the circuit parameters to bring the performance within the desired bounds. (Hi) Tolerance Analysis--Using a similar measure of performance, the optimized model parameters are varied within their anticipated distributions with the appropriate correlation between parameters. The circuit performance is repetitively analyzed with these different parameters until a histogram of the performance measure can be interpreted with confidence. Our experience in the past several years has shown that the use of statistical analysis is not the simple final step in the design process.