A passive subharmonic generation and frequency downconversion method using a memoryless nonlinear circuit coupled to a linear passive resonator is presented. The frequency downconverter can be used to transfer the energy from a high-frequency signal to a lower frequency without requiring any dc power supply. In the synchronous mode, the passive downconverter acts as a self-powered frequency divider. The characteristics of the self-powered frequency downconverter have been studied analytically, and design tradeoffs have been shown for the specific case of a cross-coupled differential pair nonlinearity. As an example, a low-frequency prototype is implemented with discrete components. Analytical results and design procedures are verified in discrete and integrated prototypes.