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Sensors 2013, 13(9), 11439-11452; doi:10.3390/s130911439
Article

A Linearization Time-Domain CMOS Smart Temperature Sensor Using a Curvature Compensation Oscillator

*  and
Department of Electronic Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, 811, Taiwan
* Author to whom correspondence should be addressed.
Received: 12 July 2013 / Revised: 7 August 2013 / Accepted: 16 August 2013 / Published: 28 August 2013
(This article belongs to the Section Physical Sensors)
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Abstract

This paper presents an area-efficient time-domain CMOS smart temperature sensor using a curvature compensation oscillator for linearity enhancement with a −40 to 120 °C temperature range operability. The inverter-based smart temperature sensors can substantially reduce the cost and circuit complexity of integrated temperature sensors. However, a large curvature exists on the temperature-to-time transfer curve of the inverter-based delay line and results in poor linearity of the sensor output. For cost reduction and error improvement, a temperature-to-pulse generator composed of a ring oscillator and a time amplifier was used to generate a thermal sensing pulse with a sufficient width proportional to the absolute temperature (PTAT). Then, a simple but effective on-chip curvature compensation oscillator is proposed to simultaneously count and compensate the PTAT pulse with curvature for linearization. With such a simple structure, the proposed sensor possesses an extremely small area of 0.07 mm2 in a TSMC 0.35-mm CMOS 2P4M digital process. By using an oscillator-based scheme design, the proposed sensor achieves a fine resolution of 0.045 °C without significantly increasing the circuit area. With the curvature compensation, the inaccuracy of −1.2 to 0.2 °C is achieved in an operation range of −40 to 120 °C after two-point calibration for 14 packaged chips. The power consumption is measured as 23 mW at a sample rate of 10 samples/s.
Keywords: curvature compensation; smart temperature sensor; oscillator; time-domain; delay line curvature compensation; smart temperature sensor; oscillator; time-domain; delay line
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Chen, C.-C.; Chen, H.-W. A Linearization Time-Domain CMOS Smart Temperature Sensor Using a Curvature Compensation Oscillator. Sensors 2013, 13, 11439-11452.

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