New non-linear optimisation techniques for the design of self-oscillating mixers are presented. The techniques enable fixing the self-oscillation frequency and selecting the optimum self-oscillating amplitude for maximum conversion gain. Using bifurcation-theory concepts, it has been possible to increase the range with self-oscillating-mixer operation. The new techniques have been applied to the design and simulation of a 5.5GHz-0.5GHz down-converter obtaining very good agreement with the experimental results