A +0.44°C/−0.4°C Inaccuracy Temperature Sensor With Multi-Threshold MOSFET-Based Sensing Element and CMOS Thyristor-Based VCO

Abstract

A VCO-based(Voltage Controlled Oscillator) temperature sensor with multi-threshold MOSFET based sensing element is proposed. The proposed temperature sensor converts temperature variation into frequency and then into digital readings. In the proposed temperature sensor, the ratio of two reference currents, generated by P-MOSFETs operated in sub-threshold region and with different channel doping concentration, is used to sense the variation of temperature and achieves a $3\sigma $ inaccuracy of ±0.06°C after first-order poly-fit with systematic nonlinearity removal. The ratio of currents is then transformed into difference of the output frequencies of two identical CMOS-thyristor based VCOs, both of which are optimized to alleviate the impact of charge sharing and charge injection on the precision of the temperature sensor. In this way, there is no need for generating an external reference clock. The prototype is fabricated in a 130nm CMOS process and achieves an inaccuracy of +0.44°C/−0.4°C. The proposed sensor achieves a resolution of 0.1°C and a resolution FoM of 0.12nJ $\cdot \text{K}^{2}$ . The prototype occupies an area of 0.07mm2.