This paper presents a passive subharmonic generation and frequency downconversion method using a memoryless nonlinear circuit coupled to a linear passive resonator. 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. As a proof of concept, a low-frequency prototype is implemented with discrete components. Also, an integrated 12 GHz divide-by-2 circuitry has been designed and fabricated in a 0.13µm CMOS technology.