# Experimental Clock Calibration\\on a Crystal-Free Mote-on-a-Chip

## TL;DR

This paper demonstrates an experimental approach for calibrating on-chip oscillators in crystal-free radios, enabling stable IEEE802.15.4 communication despite temperature-induced drift, thus reducing size and energy costs.

## Contribution

It introduces novel algorithms for tracking and calibrating on-chip oscillators in crystal-free radios and validates their effectiveness through extensive experiments.

## Key findings

- Successfully maintained +/-40 ppm frequency stability
- Tracked a crystal-based IEEE802.15.4 join proxy
- Operated effectively under rapid temperature changes

## Abstract

The elimination of the off-chip frequency reference, typically a crystal oscillator, would bring important benefits in terms of size, price and energy efficiency to IEEE802.15.4 compliant radios and systems-on-chip. The stability of on-chip oscillators is orders of magnitude worse than that of a crystal. It is known that as the temperature changes, they can drift more than 50 ppm/{\deg}C. This paper presents the result of an extensive experimental study. First, we propose mechanisms for crystal-free radios to be able to track an IEEE802.15.4 join proxy, calibrate the on-chip oscillators and maintain calibration against temperature changes. Then, we implement the resulting algorithms on a crystal-free platform and present the results of an experimental validation. We show that our approach is able to track a crystal-based IEEE802.15.4-compliant join proxy and maintain the requested radio frequency stability of +/-40 ppm, even when subject to temperature variation of 2{\deg}C/min.