Hybrid Timestamping Using Crystal and <i>RC</i> Oscillators for Shock-Resistant Precision

Achieving precise timing in miniature systems attached to monarch butterflies is challenging due to the shock sensitivity of crystal oscillators (XOs) and the limited accuracy of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> oscillators. This brief proposes a hybrid timestamping technique that combines both oscillators as timers to deliver shock-resistant, high-accuracy timing. Three algorithms are evaluated to fine-tune a multiplier (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i>), the ratio of the two timers’ speeds, for improved responsiveness and robustness against temperature and voltage variations. The direct ratioing algorithm proves the most effective, determining the correct <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> within a single wake-up cycle and reducing time shift error by 145 times in a 12-h test, compared to using an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> timer alone. This work leverages the existing hardware and introduces new firmware, easily implementable using standard digital circuit design flows, to significantly enhance timing precision and shock resilience in millimeter-scale butterfly tracking systems, making a valuable contribution to the VLSI community.