TY - GEN
T1 - A Self-Powered Wireless Gas Sensor Node Based on Photovoltaic Energy Harvesting
AU - Hung, Phan Dang
AU - Park, Yechan
AU - Kweon, Soon Jae
AU - Lee, Taeju
AU - Jeon, Hyuntak
AU - Koh, Seok Tae
AU - Cho, Incheol
AU - Yoon, Jun Bo
AU - Park, Inkyu
AU - Kim, Chul
AU - Ha, Sohmyung
AU - Je, Minkyu
N1 - Funding Information:
The IC has 4 main blocks: power-on reset and ring oscillator (POR & OSC), MPPT, boost converter and LED controller (BOOST & LED CTRL), and GSP (Fig. 4). Once VPV_REF reaches the threshold (= 400mV) of the POR circuit, the OSC is enabled and provides the system clock (CLK). The system supply (VDD) is provided by a capacitor-less LDO. The LDO input is selected between VOUT from the boost converter and VBKUP from the BAT_BKUP depending on the voltage level of VOUT (Fig. 5). The FOCV MPPT circuits for the two PV cells are identical, and their operation is shown in Fig. 6. They are controlled by CLK_SH, which is generated from CLK. During the sample period (M0_REF: off, S_REF: on), VPV_REF rises towards VOC_REF, and its fraction VMPP_REF (= k VOC_REF) is sampled on CH. During the hold period (M0_REF: on, S_REF: off), the sampled VMPP_REF is held on CH while the boost converter harvests the energy. 5 dynamic comparators are used to compare VPV_REF (VPV_GAS) with VMPP_REF (VMPP_GAS) for MPPT, VOUT/3 with VMAX for detecting the fully charged BAT_LOAD, and VPV_REF with VMIN for detecting the low light condition (Fig. 7). The GSP comprises an offset-canceled subtractor used for taking the difference between VMPP_REF and VMPP_GAS, and a 10-bit SAR ADC (Fig. 8(top)). The ADC uses a modified split-capacitor structure to reduce the area [5], and the comparator offset is corrected by self-calibration without external trimming (Fig. 8(bottom)) [6]. Measurement Results The IC has been fabricated in a 180nm CMOS (Fig. 9(right)). The gas sensor consisting of the two PV cells is placed in a gas chamber, and the ambient light inside the chamber is controlled by the LED (Fig. 9(left)). From the real-time gas sensing test, the subtractor output (ΔVOC) and ADC output code are obtained with varying the H2 concentration (Fig. 10(middle) and (right)). The performance of the subtractor and ADC is summarized in Fig. 10(left). Note that the ADC consumes only 204nW and 0.05mm2. The EH circuits using dual-input shared-inductor boost converter achieve a peak end-to-end efficiency of 88% (Fig. 11(left)) and 11% end-to-end efficiency improvement at 2% H2 concentration compared to the single-input converter with two PV cells connected in parallel (Fig. 11(right)). Compared to other designs, this work achieves competitive EH performance while providing embedded gas sensing function (Table I). The GSP circuits consume only a small area (5.6% and 14.5% of the total area for the subtractor and ADC, respectively) and low power (3.2% of total power) (Fig. 12). Acknowledgements: This work was supported by the Ministry of Science and ICT, Korea under the ITRC Program (IITP-2020-0-01778) and the DGIST R&D Program (21-IJRP-01).
Publisher Copyright:
© 2021 JSAP.
PY - 2021/6/13
Y1 - 2021/6/13
N2 - In this work, we present a compact self-powered wireless gas sensor node based on photovoltaic (PV) energy harvesting (EH). Instead of a bulky and power-hungry gas sensor with separate gas signal processing (GSP) circuits, a mm3-sized colorimetric sensor film is integrated with a PV cell, and the GSP function is seamlessly embedded within EH circuits. Also, a dual-input shared-inductor boost converter is used to improve the EH efficiency under gas exposure. Offset cancellation is performed in GSP circuits to provide accurate gas-sensing readout without any external trimming.
AB - In this work, we present a compact self-powered wireless gas sensor node based on photovoltaic (PV) energy harvesting (EH). Instead of a bulky and power-hungry gas sensor with separate gas signal processing (GSP) circuits, a mm3-sized colorimetric sensor film is integrated with a PV cell, and the GSP function is seamlessly embedded within EH circuits. Also, a dual-input shared-inductor boost converter is used to improve the EH efficiency under gas exposure. Offset cancellation is performed in GSP circuits to provide accurate gas-sensing readout without any external trimming.
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U2 - 10.23919/VLSICircuits52068.2021.9492499
DO - 10.23919/VLSICircuits52068.2021.9492499
M3 - Conference contribution
AN - SCOPUS:85111858033
T3 - IEEE Symposium on VLSI Circuits, Digest of Technical Papers
BT - 2021 Symposium on VLSI Circuits, VLSI Circuits 2021
PB - Institute of Electrical and Electronics Engineers Inc.
T2 - 35th Symposium on VLSI Circuits, VLSI Circuits 2021
Y2 - 13 June 2021 through 19 June 2021
ER -