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. 2021 Mar 6;21(5):1840.
doi: 10.3390/s21051840.

A Time-Based Electronic Front-End for a Capacitive Particle Matter Detector

Umberto Ferlito  1 , Alfio Dario Grasso  1 , Michele Vaiana  2 , Giuseppe Bruno  2
Affiliations

A Time-Based Electronic Front-End for a Capacitive Particle Matter Detector

Umberto Ferlito et al. Sensors (Basel). .

Abstract

This paper introduces the electronic interface for a capacitive airborne particle matter detector. The proposed circuit relies on two matched ring oscillators and a mixer to detect the frequency difference induced by the deposition of a particle onto an interdigitated capacitor, which constitutes the load of one of the oscillators. The output of the mixer is digitized through a simple counter. In order to compensate the oscillation frequency offset of the two ring oscillators due to process and mismatch variations, a capacitive trimming circuit has been implemented. The sensor is connected to host through an I2C interface for communication and configuration. The sensor has been implemented using a standard 130-nm CMOS technology by STMicroelectronics and occupies 0.12-mm2 die area. Experimental measurements using talcum powder show a sensitivity of 60 kHz/fF and a 3σ resolution equal to 165 aF.

Keywords: capacitive sensor; particulate matter (PM); ring oscillators; smart sensors.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Block diagram of the proposed circuit.
Figure 2
Figure 2
Simplified schematic of the sensing oscillator (reference oscillator has the same topology but with Cs = Cr).
Figure 3
Figure 3
Schematic of the passive mixer and the low-pass filter.
Figure 4
Figure 4
Schematic of the Schmitt trigger.
Figure 5
Figure 5
Simulated signals at the output of the blocks in Figure 1: (a) sensing oscillator; (b) reference oscillator; (c) mixer; (d) low-pass filter, and (e) Schmitt trigger.
Figure 6
Figure 6
Simulated signal frequency versus temperature for ΔCi = 1 fF of reference ring oscillator (RO) and Schmitt trigger.
Figure 7
Figure 7
Monte Carlo simulation results with a frequency variation of 245 kHz (ΔCi = 4.1 fF).
Figure 8
Figure 8
Capacitive trimming circuit schematic.
Figure 9
Figure 9
Frequency variation as a function of the binary word.
Figure 10
Figure 10
Microphotograph of the chip.
Figure 11
Figure 11
Comparison between the micro photographed particle concentration and the simulation: (a) low coverage; (b) medium coverage; (c) high coverage.
Figure 12
Figure 12
Measured signal at the Schmitt trigger output for the three cases in Figure 11: (a) low coverage; (b) medium coverage; (c) high coverage.
Figure 12
Figure 12
Measured signal at the Schmitt trigger output for the three cases in Figure 11: (a) low coverage; (b) medium coverage; (c) high coverage.
Figure 13
Figure 13
Measured Schmitt trigger output signal frequency versus temperature.
Figure 14
Figure 14
Measured Schmitt trigger output signal frequency for different humidity and temperature values.
See this image and copyright information in PMC

References

    1. Carminati M., Pedalà L., Bianchi E., Nason F., Dubini G., Cortelezzi L., Ferrari G., Sampietro M. Capacitive Detection of Micrometric Airborne Particulate Matter for Solid-State Personal Air Quality Monitors. Sens. Actuators A Phys. 2014;219:80–87. doi: 10.1016/j.sna.2014.09.003. - DOI
    1. Carminati M., Ferrari G., Sampietro M. Emerging Miniaturized Technologies for Airborne Particulate Matter Pervasive Monitoring. Measurement. 2017;101:250–256. doi: 10.1016/j.measurement.2015.12.028. - DOI
    1. Ciccarella P., Carminati M., Sampietro M., Ferrari G. 28.7 CMOS Monolithic Airborne-Particulate-Matter Detector Based on 32 Capacitive Sensors with a Resolution of 65zF Rms; Proceedings of the 2016 IEEE International Solid-State Circuits Conference (ISSCC); San Francisco, CA, USA. 5–9 January 2016; pp. 486–488.
    1. Ciccarella P., Carminati M., Sampietro M., Ferrari G. Multichannel 65 ZF Rms Resolution CMOS Monolithic Capacitive Sensor for Counting Single Micrometer-Sized Airborne Particles on Chip. IEEE J. Solid-State Circuits. 2016;51:2545–2553. doi: 10.1109/JSSC.2016.2607338. - DOI
    1. Carminati M., Ciccarella P., Sampietro M., Ferrari G. Single-Chip CMOS Capacitive Sensor for Ubiquitous Dust Detection and Granulometry with Sub-micrometric Resolution. In: Andò B., Baldini F., Di Natale C., Marrazza G., Siciliano P., editors. Sensors. Volume 431. Springer International Publishing; Cham, Switzerland: 2018. pp. 8–18.

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