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

Abstract

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.

Surviving the Hair Dryer: Continuous Calibration of a Crystal-Free Mote-on-Chip

“…Suciu et al [17] provide a calibration technique for SCµM for both transmission and reception. The LC frequency increases in a non-linear manner with the frequency setting.…”

“…The frequency tracking approach proposed in this paper is a comprehensive calibration approach for SCµM to continuously calibrate the on-chip oscillators (2 MHz RC oscillator, 2.4 GHz LC oscillator for transmission and reception). Unlike Suciu et al [17], our approach does not require to model a non-monotonic DAC using a monotonic function. Our approach allows SCµM to keep communicating with off-the-shelf IEEE802.15.4 devices even when temperature changes quickly.…”

“…Our approach allows SCµM to keep communicating with off-the-shelf IEEE802.15.4 devices even when temperature changes quickly. Unlike the approach in Suciu et al [17] which uses linearized settings that vary from chip to chip, our approach function on all chips without needing chip-specific pre-calibration. To deal with the non-linear frequency tuning, we propose a mechanism to constantly "hop" from one setting to another (see Section V-E).…”

QuickCal: Assisted Calibration for Crystal-Free Micromotes

“…During the characterization step, the SCµM chip sweeps though all of the settings of its LC oscillator, and the LC counter, which is detailed in III-A, is used to map these settings against the measured oscillator frequency. The mapping is non-linear, so the authors explore different linearization approaches: recursive least squares (RLS) and moving average (MA) [24]. The results of this characterization (i.e.…”

A Temperature-Compensated BLE Beacon and 802.15.4-to-BLE Translator on a Crystal-Free Mote

“…A growing number of studies focuses on software approaches to compensate for this drift and keep crystal-free motes functional over a wide temperature range. Using SCµM, Suciu et al track the intermediate frequency (IF) of incoming 802.15.4 frames and use a recursive least-squares model to predict the tuning code based on temperature [3], [4]. Elsts et al use a lookup table built from initial calibration and compensation history to calculate the required clock compensation in channel-hopping networks [5].…”