We present how microelectromechanical systems (MEMS) with high conversion efficiency and high quality factor (Q) can be leveraged to synthesize extremely low power asynchronous wake-up receivers (WuRx). We utilize MEMS devices to design and demonstrate a resonant micromechanical WuRx capable of detecting OOK modulated radio frequency (RF) signals as tenuous as –80 dBm while consuming just a few 10s of nanoWatts.
We break the fundamental trade-off between sensitivity and power consumption experienced by most wake-up radios by harnessing the unique characteristics of two different MEMS resonant devices. Two MEMS resonator technologies are employed to build the RF front-end of this asynchronous receiver: 1) high-frequency (50-400 MHz) thin film piezoelectric lithium niobate (LN) resonators to perform filtering, voltage amplification and impedance matching; and 2) low-frequency (20-100 kHz) electrostatic resonators (a.k.a. demodulators in this work) to down-convert the RF signal, and apply low-frequency filtering. The demodulator interfaces with a CMOS circuit tightly integrated on the same chip. The CMOS circuit (180 nm from TowerJazz) is used to amplify the output of the low-frequency MEMS demodulator, rectify the signal and trigger a 1 V output whenever the appropriate wake-up signature has been received. The CMOS circuit is the only active component of this system and it is designed to operate in the subthreshold region to minimize power consumption. Because of the multi-frequency and broadband nature of the LN resonant transducers, this wake-up receiver block can be readily modified to accommodate multiple RF channels and receive other RF signatures such as chirp or FSK signals.
We will highlight the record-breaking capabilities of the LN MEMS resonator technology in providing high voltage gains (in excess of 50 V/V) and the high efficiency of narrow gap MEMS demodulators in down-converting RF signals. In our two-chip solution, the MEMS demodulator is tightly integrated with the CMOS circuit on a single chip and can be flip-chipped to the LN devices to form a very compact WuRx that fits within a few mm2. We will review our design considerations in regards to component sizing to assure a robust demonstration of the WuRx. Specifically, we will analyze trade-offs associated with the selection of the RF carrier and modulation frequency in regards to overall power consumption and sensitivity of the WuRx. Finally, we will point out how the developed MEMS technologies could be leveraged for other Internet of Things (IoT) applications that go beyond RF sensing.