The ever increasing pace of analog IC design demands efficient means of automated design and optimization. Especially important is robust design. Its goal is to produce circuits whose behaviour stays within some predefined range when the manufacturing process variations and envi-ronmental effects remain bounded. Most of the design process is still handled by IC designers manually. We present a simple mathematical formulation of the robust design and optimization problem and its transformation into a constrained optimization problem by means of penalty functions. We illustrate the method on a robust differential amplifier design problem. The resulting circuits show that a computer not only can improve circuits designed by humans, but is also capable of designing a circuit with very little initial knowledge. Optimization runs resulted in circuits with similar or even better performance when compared to humanly designed circuits. The method can take advantage of parallel processing, but is still efficient enough to be run on a single computer.