Low power wake-up receiver for wireless sensor nodes

Duty cycling is a common method to reduce the energy consumption in wireless sensor nodes. Since all the nodes turn on their radio in a time slot, but only few of them actually exchange messages, energy is wasted. This can be avoided by using a separate wake-up radio. We present a new approach for a wake-up receiver that consumes 2.78 µA of current and integrates a 16 bit address coding for a selective wake-up. We use a low frequency wake-up signal that is modulated on a high frequency carrier in the main radio of the transmitting node. In the receiving node a passive demodulation circuit regains the low frequency signal and feds it to a low power low frequency wakeup IC. Four sample boards were manufactured and measured that operate at 868 MHz in the European ISM band. By using coils with high Q factors in the demodulation circuit we reached a sensitivity of −52 dBm which resulted in a wake-up distance of up to 40 meters at an output power level of +10 dBm in the transmitter. Compared to van der Doorn et. al, “A prototype low-cost wakeup radio for the 868 MHz band” Int. J. Sensor Networks, Vol.5, No.1, 2009, we achieved a 20 times farther wakeup range and a 100 times lower current consumption.