Inter-Cal: Inter-Oscillator Calibration for Crystal-Free Mote-on-Chip

SCµM is a single-chip micro mote with dimensions of 2 ×3 mm
²
, It is equipped with a Cortex-M0 processor, an optical receiver, and a radio compliant with IEEE802.15.4/BLE standards. The device foregoes the use of a crystal by leveraging its internal oscillators to enable 2.4 GHz communication. Due to variations in manufacturing and changes in the environment, SCµM's on-chip oscillators require calibration. Inter-Cal, a calibration method for SCµM, accurately determines the necessary frequencies for both transmission (TX) and reception (RX). Unlike other methods, Inter-Cal can calibrate all of SCµM's internal oscillators, including the 2 MHz RC and LC oscillators in both TX and RX modes, by simply listening for a valid packet. Inter-Cal is a scalable solution characterized by its minimal overhead and low latency. Testing with OpenMote has demonstrated that SCµM can consistently adjust its frequency over time using SCµM. In an evaluation using 1000 packets, 94.3% achieved a frequency accuracy within ±80 ppm for the LC oscillator and 91% were within ±1000 ppm for the 2 MHz RC oscillator.