JiffyTune: circuit optimization using time-domain sensitivities. Automating the transistor and wire-sizing process is an important step toward being able to rapidly design high-performance, custom circuits. This paper presents a circuit optimization tool that automates the tuning task by means of state-of-the-art nonlinear optimization. It makes use of a fast circuit simulator and a general-purpose nonlinear optimization package. It includes minimax and power optimization, simultaneous transistor and wire tuning, general choices of objective functions and constraints, and recovery from nonworking circuits. In addition, the tool makes use of designer-friendly interfaces that automate the specification of the optimization task, the running of the optimizer, and the back-annotation of the results of optimization onto the circuit schematic. Particularly for large circuits, gradient computation is usually the bottleneck in the optimization procedure. In addition to traditional adjoint and direct methods, we use a technique called the adjoint Lagrangian method, which computes all the gradients necessary for one iteration of optimization in a single adjoint analysis. This paper describes the algorithms and the environment in which they are used and presents extensive circuit optimization results. A circuit with 6900 transistors, 4128 tunable transistors, and 60 independent parameters was optimized in about 108 min of CPU time on an IBM RISC/System 6000, model 590.