28.2 A 220μW -85dBm Sensitivity BLE-Compliant Wake-up Receiver Achieving -60dB SIR via Single-Die Multi- Channel FBAR-Based Filtering and a 4-Dimentional Wake-Up Signature

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Abstract
Wake-up receivers (WuRXs) offer an attractive low-power means to synchronize low-average-throughput wireless devices without requiring energy-expensive periodic synchronization routines between primary radios. To achieve low-power operation, most prior-art WuRXs tend to utilize custom OOK or FSK modulation schemes that are not compliant with any standards, while also forgoing important capabilities present in more powerful radios, such as the ability to operate in the presence of potentially large interferers or dynamically switch between multiple channels - both of which are very important when operating in congested bands. Since Bluetooth Low Energy (BLE) is one of the most popular standards for lowpower IoT devices, prior work has endeavored to develop BLE-compliant WuRXs that achieve low-power operation through means of back-channel (BC) communication - signals that are generated by a standard-compliant BLE TX, yet encode information in a modality that can be demodulated by low-power means (e.g., direct energy detection [1,2]). Unfortunately, the wideband energy detectors in [1,2] not only directly demodulate interferers with no channel selectivity, they also introduce significant demodulated RF noise, limiting sensitivity to -56.5dBm at 236nW and -58dBm at 164μW, respectively. To impart channel selectivity, a mixer-first architecture was demonstrated in [3], achieving a sensitivity of -80dBm at 230μW, though this does not include the power of a PLL or FLL to stabilize the free-running single-channel VCO. To facilitate stabilized multichannel operation, a 120μW crystal-stabilized FLL-based LO generator was included in [4] with frequency hopping support, for a total WuRX power of 150μW. While selective, the design achieved a sensitivity of only -57.5dBm.