A boost converter for thermoelectric energy harvesting in 130 nm CMOS achieves energy harvesting from a 10 mV input, which allows wearable body sensors to continue operation with low thermal gradients. The design uses a peak inductor current control scheme and duty cycled, offset compensated comparators to maintain high efficiency across a broad range of input and output voltages. The measured efficiency ranges from 53% at mV to a peak efficiency of 83% at mV. A cold-start circuit starts the operation of the boost converter from 220 mV, and an RF kick-start circuits starts it from 14.5 dBm at 915 MHz RF power.

We present an 802.15.4 compatible transceiver that operates without any off-chip frequency reference. With integrated Cortex-M0, the chip can also transmit BLE beacons with only three external connections (power, ground, and antenna). The RF transmitter operates with >10% system efficiency at -10 dBm output power from a regulated supply. The entire chip, including the microprocessor, can operate below 1 mW peak power when transmitting. The analog receiver power consumption is 1.03 mW from a 1.5V battery.

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We report the first time-synchronized protocol stack running on a crystal-free device. We use an early prototype of the Single-Chip micro Mote, SCμM, a single-chip 2 × 3 mm2 mote-on-a-chip, which features an ARM Cortex-M0 micro-controller and an IEEE802.15.4 radio. This prototype consists of an FPGA version of the micro-controller, connected to the SCμM chip which implements the radio front-end. We port OpenWSN, a reference implementation of a synchronized protocol stack, onto SCμM. The challenge is that SCμM has only on-chip oscillators, with no absolute time reference such as a crystal. We use two calibration steps – receiving packets via the on-chip optical receiver and RF transceiver – to initially calibrate the oscillators on SCμM so that it can send frames to an off-the-shelf IEEE802.15.4 radio. We then use a digital trimming compensation algorithm based on tick skipping to turn a 567 ppm apparent drift into a 10 ppm drift. This allows us to run a full-featured standards-compliant 6TiSCH network between one SCμM and one OpenMote. This is a step towards realizing the smart dust vision of ultra-small and cheap ubiquitous wireless devices.