A complete 1.9 GHz receiver, with BAW resonator-referenced input matching network, is designed as a wakeup receiver for wireless sensor networks. The 90 nm CMOS chip includes RF amplifier, PGA, ADC, and reference generation, while consuming 65 μW from a single 0.5 V supply. The input RF bandwidth of the receiver is 7 MHz, while the maximum data rate is 100 kbps. When detecting a 31-bit sequence, the receiver exhibits -56 dBm sensitivity for 90% probability of detection.