A 0.008 ${\hbox {mm}}^{2}$ 500 $\mu{\rm W}$ 469 kS/s Frequency-to-Digital Converter Based CMOS Temperature Sensor With Process Variation Compensation

Abstract

This paper presents a temperature sensor based on a frequency-to-digital converter with digitally controlled process compensation. The proposed temperature sensor utilizes ring oscillators to generate a temperature dependent frequency. The adjusted linear frequency difference slope is used to improve the linearity of the temperature sensor and to compensate for process variations. Furthermore, an additional process compensation scheme is proposed to enhance the accuracy under one point calibration. With one point calibration, the resolution of the temperature sensor is 0.18 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C/LSB and the maximum inaccuracy of 20 measured samples is less than ±1.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C over a temperature range of 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C ~ 110 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C. The entire block occupies 0.008 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 65 nm CMOS and consumes 500 μW at a conversion rate of 469 kS/s.