Widlar-Widlar voltage-reading temperature sensor

Abstract

The paper presents the design of a CMOS integrated circuit whose output voltage varies linearly with temperature. This sensor is implemented using two classical cross-connected current mirrors. The voltage value is read on the resistor of the lower Widlar mirror. We examined how the output voltage varies with temperature considering the open-output circuit. The sensor's design is made using resistors with negative, null or positive temperature-coefficient values. Circuit performance shall be emphasized when NTC and PTC resistor pairs are used. The maximum slope was computed for the output voltage and the maximum slope condition was estimated too. The circuit was sized to fit a maximum slope, thus resulting in a 6.27% error between the analytical and the simulated slope. The sensor's performance parameters are: the optimized output voltage slope (3.2813mV/°C), the optimized percentage slope (0.1946%/°C), low current consumption (30μA measured at 20°C), VDDmin of 2.8V, and supply regulation of 4289ppm/V at 3.5V. The sensor occupied-on-chip area is also small: 3075μm2. The total percentage variation of the output voltage slope with the manufacturing process is 25.4%, while the total variation of the output voltage with the manufacturing process amounts to 31.1%