Large-Scale Nonlinear Optimization in Circuit Tuning

Andreas Waechter
IBM T.J. Watson Research Center

Abstract: Circuit tuning is an essential step in the design of digital circuits. The central task is to find optimal sizes of transistors in order to minimize signal delay or area requirement. This problem can be formulated as a large-scale nonlinearly constrained nonlinear optimization problem, where function evaluations are obtained by simulation of gates (small subcircuits). This approach has been implemented in the IBM-internal circuit tuning tool EinsTuner, which has been used for the design of every custom digital circuit designed by IBM for several years. The numerical optimization engine is IPOPT, which follows a primal-dual interior point approach and uses a line search filter method to ensure global convergence. Details on the optimization algorithm and numerical results will be presented.