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Sensors 2014, 14(9), 17192-17211;

A CMOS Smart Temperature and Humidity Sensor with Combined Readout

Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK
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)
View Full-Text   |   Download PDF [3255 KB, uploaded 16 September 2014]


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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