A 0.7 V Relative Temperature Sensor With a Non-Calibrated <formula formulatype="inline"><tex Notation="TeX">$\pm 1~^{\circ}{\rm C}$</tex></formula> 3<formula formulatype="inline"><tex Notation="TeX">$\sigma$</tex></formula> Relative Inaccuracy

Abstract

This paper presents a new low-voltage relative temperature sensor for multi-core digital processor on-chip thermal management in a 180 nm CMOS process. Three types of sensing diodes including Schottky barrier diode (SBD), subthreshold MOSFET diode and dynamic threshold MOSFET (DTMOS) diode have been investigated for low-voltage operation, while traditional parasitic PNP-bipolar junction transistor (BJT) diodes are implemented to provide a performance reference. A matrix of 7 $\times$ 7 small remote sensor nodes is implemented on the chip with a deployment density of 49/0.81 ${\rm mm}^{2}$ and sharing the same bias current generator, control logic, and data converter. The measured minimum supply voltage (not including the clock control block) of the sensor is 0.7 V over $-55~^{\circ}{\rm C}$ to 125 $~^{\circ}{\rm C}$ . The relative sensing inaccuracies $(3\sigma)$ without calibration are less than $\pm 1.5~^{\circ}{\rm C}$ , $\pm 1.2~^{\circ}{\rm C}$ and $\pm 1~^{\circ}{\rm C}$ for the designs based on SBD, subthreshold MOSFET, and DTMOS, respectively. To the best of the authors’ knowledge, this is the first time that non-calibrated relative sensing accuracy is reported for SBD-based and DTMOS-based temperature sensors, and the best reported result for the design based on subthreshold MOSFET. The absolute inaccuracies with calibration-per-chip are also presented. Furthermore, the multi-location thermal monitoring function has been experimentally demonstrated and a 1.8 $^{\circ}{\rm C/mm}$ on-chip temperature gradient was detected.