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Sensors 2014, 14(9), 17192-17211; https://doi.org/10.3390/s140917192

A CMOS Smart Temperature and Humidity Sensor with Combined Readout

1
Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK
2
Department of Medical Physics and Bioengineering, University College London, Malet Place, WC1E 6BT, UK
*
Author to whom correspondence should be addressed.
Received: 15 July 2014 / Revised: 25 August 2014 / Accepted: 3 September 2014 / Published: 16 September 2014
(This article belongs to the Special Issue On-Chip Sensors)
Full-Text   |   PDF [3255 KB, uploaded 16 September 2014]

Abstract

A fully-integrated complementary metal-oxide semiconductor (CMOS) sensor for combined temperature and humidity measurements is presented. The main purpose of the device is to monitor the hermeticity of micro-packages for implanted integrated circuits and to ensure their safe operation by monitoring the operating temperature and humidity on-chip. The smart sensor has two modes of operation, in which either the temperature or humidity is converted into a digital code representing a frequency ratio between two oscillators. This ratio is determined by the ratios of the timing capacitances and bias currents in both oscillators. The reference oscillator is biased by a current whose temperature dependency is complementary to the proportional to absolute temperature (PTAT) current. For the temperature measurement, this results in an exceptional normalized sensitivity of about 0.77%/°C at the accepted expense of reduced linearity. The humidity sensor is a capacitor, whose value varies linearly with relative humidity (RH) with a normalized sensitivity of 0.055%/% RH. For comparison, two versions of the humidity sensor with an area of either 0.2 mm2 or 1.2 mm2 were fabricated in a commercial 0.18 μm CMOS process. The on-chip readout electronics operate from a 5 V power supply and consume a current of approximately 85 µA. View Full-Text
Keywords: capacitive sensor; humidity measurement; microelectronic implants; oscillator; on-chip sensor; temperature sensor capacitive sensor; humidity measurement; microelectronic implants; oscillator; on-chip sensor; temperature sensor
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Eder, C.; Valente, V.; Donaldson, N.; Demosthenous, A. A CMOS Smart Temperature and Humidity Sensor with Combined Readout. Sensors 2014, 14, 17192-17211.

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