Publication
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Paper

Noise considerations in circuit optimization

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Abstract

Noise can cause digital circuits to switch incorrectly, producing spurious results. It can also have adverse power, timing and reliability effects. Dynamic logic is particularly susceptible to charge-sharing and coupling noise. Thus, the design and optimization of a circuit should take noise considerations into account. Such considerations are typically stated as semi-infinite constraints in the time-domain. Semi-infinite problems are generally harder to solve than standard nonlinear optimization problems. Moreover, the number of noise constraints can potentially be very large. This paper describes a novel and practical method for incorporating realistic noise considerations during automatic circuit optimization by representing semi-infinite constraints as ordinary equality constraints involving time integrals. Using an augmented Lagrangian optimization merit function, the adjoint method is applied to compute all the gradients required for optimization in a single adjoint analysis, no matter how many noise measurements are considered and irrespective of the dimensionality of the problem. Thus, for the first time, a method is described to practically accommodate a large number of noise considerations during circuit optimization. The technique has been applied to optimization using time-domain simulation, but could be applied in the future to optimization on a static-timing basis. Numerical results are presented.