Temperature Calibration on a Crystal-Free Mote

Yuan, Titan; Maksimovic, Filip; Burnett, D.; Wheeler, Brad; Lee, Lydia; Pister, Kristofer S. J.

doi:10.1109/wf-iot48130.2020.9221351

Cited by 6 publications

(4 citation statements)

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“…Titan et al [14] present a method to calibrate SCµM for use as an IoT temperature sensor between 0 • C and 100 • C. The method finds a linear relationship between the ambient temperature and the ratio of these two clock frequencies. The proposed method allow SCµM used as an temperature sensor with 2 • C errors.…”

Section: Related Workmentioning

confidence: 99%

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

Chang¹,

Watteyne

Wheeler

et al. 2022

IEEE Internet Things J.

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The single chip micro-mote (SCµM) is a 2×3 mm 2 single-chip crystal-free mote-on-chip. SCµM implements the IEEE802.15.4 and BLE standards and can communicate with offthe-shelf radios compliant to those standards. SCµM exclusively uses on-chip oscillators, including a 2.4 GHz LC oscillator to synthesize the communication frequency, and a 2 MHz RC oscillator to clock the chip rate. The challenge is that the LC oscillator drifts at 2,100 ppm over a temperature range of 45 • C, far from the 40 ppm maximum drift mandated by the IEEE802.15.4 standard. While one-shot calibration is possible, any temperature change causes IEEE802.15.4 communication to fail. This paper describes a continuous calibration approach for SCµM to adapt the tuning of its oscillators as the temperature changes. Experimental results show that it allows SCµM to keep communicating with an IEEE802.15.4 radio even under the extreme condition of using a hair dryer to heat up the chip at 3 • C/min. Under these conditions, the drift of the LC oscillator stays within the ±40 ppm limit over 94% of the time. Similarly, the drift of the 2 MHz RC oscillator stays within ±1,000 ppm limit 99.98% of the time.

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Section: Related Workmentioning

confidence: 99%

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

Chang¹,

Watteyne

Wheeler

et al. 2022

IEEE Internet Things J.

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“…Instead, SCµM features a 2 MHz chipping clock and and a 32 kHz sleep timer. The frequencies of these oscillators vary differently over temperature changes, but by characterizing these variations, SCµM can determine the temperature between 0 °C and 100 °C with an accuracy of 2 °C [11].…”

Section: Tuning F I N E By Estimating Temperaturementioning

confidence: 99%

“…This frequency compensation method requires two calibrations over temperature for every chip: one to find the linear model for the temperature estimate [11] and one to find the linear model for the fine code at the measured temperature (Eq. ( 1)).…”

Section: Tuning F I N E By Estimating Temperaturementioning

confidence: 99%

“…In Section III, we describe how we use a flashing infrared LED and the mote's optical receiver to initialize the tuning parameters at a certain temperature. In Section IV, we apply the technique introduced in [11] to use the behavior of the on-chip oscillators' frequencies over temperature to indirectly measure the temperature. We build an open-loop linear model that uses the temperature estimate to tune the LO frequency.…”

Section: Introductionmentioning

confidence: 99%

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

Yuan

Maksimovic

Wheeler

et al. 2022

2021 51st European Microwave Conference (EuMC)

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Crystal-free radios have the potential to revolutionize the IoT: due to their single-chip nature, they are both very cheap (no external components required) and very small (the size of a grain of rice). The Single-Chip Micro Mote (SCµM) is a 2×3×0.3 mm 3 crystal-free chip that can communicate with off-the-shelf transceivers over Bluetooth Low Energy (BLE) or IEEE 802.15.4. Setting its communication frequency is challenging because the crystal-free chip can rely only on internal oscillating circuits, which are very susceptible to temperature. Without compensation, a SCµM chip can no longer communicate with an off-the-shelf BLE receiver if the temperature changes by more than 1.25 °C. This paper introduces a two-step temperature compensation method, allowing SCµM to successfully send BLE frames over a 20 °C temperature range. After performing initial calibration during optical bootloading, we use an open-loop linear model to estimate the ambient temperature and continuously tune the mote's local oscillator (LO) frequency as the temperature changes. We show how the mote can use the intermediate frequency of 802.15.4 frames it receives from nearby off-the-shelf transceivers as a frequency reference to adjust its LO frequency. This compensation method enables SCµM to operate as a tiny BLE beacon, a BLE temperature sensor (for retail or medical applications), or a 802.15.4-to-BLE translation device.

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