An ultra-low power wake-up radio receiver using no oscillators is described. The radio utilizes an envelope detector followed by a baseband amplifier and is fabricated in a 130-nm complementary metal–oxide–semiconductor process. The receiver is preceded by a passive radio-frequency voltage transformer, also providing 50 antenna matching, fabricated as transmission lines on the FR4 chip carrier. A sensitivity of dBm with 200 kb/s on–off keying modulation is measured at a current consumption of 2.3 A from a 1 V supply. No trimming is used. The receiver accepts a dBm continuous wave blocking signal, or modulated blockers 6 dB below the sensitivity limit, with no loss of sensitivity.