This paper proposes a novel ultra-low power, tunable, and asynchronous baseband architecture for joint radio frequency (RF) wake-up and charging receivers. The designed system switches between the wake-up and charging operations based on the type of the received RF signal. To our knowledge, the proposed system is the first of a kind that introduces multiple power states to reduce the energy consumption by sequentially activating minimal components required for RF wake-up or charging. The fabricated prototype, using off-the-shelf components, features a sensitivity of -40 dBm, a bit rate of 500 bps, and a current consumption of 225 nA at a bias voltage of 2.6 V in the listening state. Current consumption is estimated at 3.225 μA and 13.725 μA while processing the preamble and bit sequence, respectively. The address detector is powered OFF during charging to reduce the system’s current consumption to 150 nA. Our experimental results show that shutting down the address detector during charging reduces charging time and allows charging from received power levels that are as low as -6 dBm. We demonstrate that, operating the detector with multiple power modes reduces its current consumption and enhances its noise immunity when compared to conventional address detectors with two power modes of operation.