The realization of truly ubiquitous wireless sensor networks (WSN) demands ultra-low power wireless communication capability. Because the radio transceiver consumes power whenever it is active, it most efficient to leave the receiver off and wake it up asynchronously only when needed. A dedicated wake-up receiver can continuously monitor the channel, listening for a wake-up signal from other nodes and activating the main receiver upon detection. By maximizing the node sleep time without compromising network latency, the use of a wake-up receiver can improve overall network performance. Wake-up receivers are also applicable in asymmetric links such as "active" RFID, where the tag listens in standby mode until queried by a reader.

In order to be practical, the power consumption of the wake-up receiver must be minimized while still preserving adequate sensitivity to detect the wake-up signal. This thesis explores the specific requirements and challenges for the design of a dedicated wake-up receiver, leading to the design of two prototype receivers implemented in 90 nm CMOS technology and incorporating RF-MEMS resonators. The first prototype combines all required blocks in a low power test system, including a simple RF front-end and mixed-signal baseband. The final wake-up receiver design uses a novel "uncertain-IF" architecture to achieve a sensitivity of -72 dBm at 2 GHz while consuming just 52 uW from a 0.5 V supply. The power consumption is nearly an order-of-magnitude below previously published receiver designs for WSN.