Dynamic Channel Calibration on a Crystal-Free Mote-on-a-Chip

The single chip integration of a wireless sensor node would allow for cheap, low-power, dust-size devices. The key to realizing this vision is to eliminate bulky off-chip frequency references such as crystal oscillators or resonators, and their associated power-hungry circuitry. The immediate challenge of removing off-chip references is that there is no accurate on-chip frequency references, which makes it hard to tune the radio to the right frequency, and to keep an accurate sense of time. This article offers a full solution for crystal-free devices, which includes (1) initiating communication in an IEEE802.15.4 network, (2) synthesizing the 16 communication channels at startup temperature, and (3) continuously applying corrections to the inaccurate timing source to allow keeping frequency synchronization on all communication channels over a 5-55°C temperature range. The proposed methods are accompanied by simulations and an experimental validation on the first fully-functional Single Chip Micro Mote hardware implementation. Our simulations and experimental results validate that the proposed approach achieves radio clock synchronization accuracy close to the 40 ppm limit imposed by the IEEE802.15.4 standard.