A 0.05 mm², 350 mV, 14 nW Fully-Integrated Temperature Sensor in 180-nm CMOS

In this brief, we present a fully-integrated ring-oscillator based CMOS temperature sensor for Internet-of-Things. Our design relies on a low-complexity PMOS-based sensing circuit to convert temperature into two sub-threshold biasing currents. These are then used to define two oscillation frequencies, whose ratio increases linearly with the temperature. Change in the frequency ratio is finally translated into a digital output code. The proposed sensor was fabricated in 180-nm CMOS technology. When powered at 350 mV, it can achieve an energy/conversion of 0.46 nJ in a conversion time of 33 ms. Moreover, it exhibits a measurement resolution of 0.27°C and a resolution figure-of-merit as low as
$0.034~{\mathrm{ nJ}}^\circ {\mathrm{ C}}^{2}$
.